Ossasepia

October 18, 2018

SMG Comms Chapter 3: Packing Serpent

Filed under: Coding, SMG_Comms — Diana Coman @ 10:12 a.m.

~ This is a work in progress towards an Ada implementation of Eulora's communication protocol. Start with Chapter 1.~

This chapter uses the raw types of the protocol as defined in the previous chapter and adds two methods that are still at layer 0 of the protocol: one method for packing Serpent messages into corresponding Serpent packets and one method for unpacking such Serpent packets to extract their contained Serpent message. It is a single small step forward but the corresponding .vpatch is still quite large as it contains the Serpent code in addition to the packing/unpacking methods. The packing is effectively an encryption with a given Serpent key while the unpacking is the corresponding decryption. Nevertheless, there are a few bits that are specific to this implementation as they reflect the requirements of Eulora's protocol:

  • Packing receives as input a Serpent_Msg and produced as output a Serpent_Pkt. Symmetrically, unpacking receives as input a Serpent_Pkt and produces a Serpent_Msg. Both Serpent_Pkt and Serpent_Msg are arrays of octets but of fixed, pre-defined size: 1472 octets and nothing else.
  • Both packing and unpacking will split their input into blocks of the size that Serpent can handle, encrypt/decrypt them and then glue together the results to produce the output. So there are effectively 921 encrypting / decrypting operations with the same, given Serpent key, for one single pack / unpack call.

I've adapted the Serpent implementation that I previously published as part of EuCrypt, effectively integrating it into SMG Comms and stripping away anything that isn't directly needed by SMG Comms:

  • Serpent is now simply a package like all the others rather than a stand-alone library. While it is true that any changes to the original will have to be manually ported to this one as well, that was always going to be the case anyway. So I don't really see much point in carrying about all the glue and additional files to make a library out of only 2 files. Hence, Serpent in SMG Comms has 2 files and nothing more: serpent.ads and serpent.adb. Short and clear.
  • Since this is production use already, testing parts such as the "Selftest" method don't really have any business in the code itself. I've moved this method where it belongs, namely with the tests for all the code, in the tests directory (test_serpent.ads/.adb)
  • Since Serpent here becomes part of SMG Comms it follows that it should also use the raw types of the protocol - it will anyway be called to use variables of those types rather than anything else. There is no point in forcing back and forth conversions between SMG Comms' "Octets" and Serpent's "Bytes" types that are both arrays of octets anyway. So I've changed the definition of the "Bytes" type in Serpent so that it is here simply a subtype of the "Octets" type. This has the advantage that it allows smooth calls to Serpent from SMG Comms while being a small, easily-reversible change that also maintains otherwise the clarity of Serpent's code as it is. Basically SMG Comms gets to call Serpent without having to do explicit conversions between types that are anyway the same thing and Serpent gets to keep calling arrays of octets Bytes internally as it does in its stand-alone lib version.

In addition to the above, the .vpatch for this chapter also adds tests for the packing/unpacking methods2. I've also made a small change to raw_types.ads so that there is now only one variable for Serpent length: SERPENT_OCTETS. This reflects better the fact that there really is only one length for Serpent and it still allows to keep code clear by having the two array types Serpent_Pkt and Serpent_Msg - they just use the same length. Clarity of code is a tricky choice, what more can I say. Here's the updated code in raw_types:

  -- constants from SMG.COMMS standard specification
    -- size of a serpent-encrypted packet and message, in octets
    -- note that this corresponds to 1472/16 = 92 Serpent blocks
    -- NB: lengths are the same!
  SERPENT_OCTETS : constant Positive := 1472;

    -- size of a RSA-encrypted packet and message in octets and bits
  RSA_PKT_OCTETS     : constant Positive := 1470;
  RSA_MSG_OCTETS     : constant Positive := 234;
  RSA_MSG_BITS       : constant Positive := RSA_MSG_OCTETS * 8; --1872

  -- raw, low-level types
  -- all messages and packets are simply arrays of octets at low level/raw
  type Octets is array( Natural range <> ) of Interfaces.Unsigned_8;

  -- raw representations of basic types (with fixed, well-defined sizes)
  subtype Octets_1 is Octets( 1 .. 1 );
  subtype Octets_2 is Octets( 1 .. 2 );
  subtype Octets_4 is Octets( 1 .. 4 );
  subtype Octets_8 is Octets( 1 .. 8 );

  -- RSA packets and contained raw messages
  subtype RSA_Pkt is Octets( 1 .. RSA_PKT_OCTETS );
  subtype RSA_Msg is Octets( 1 .. RSA_MSG_OCTETS );

  -- Serpent packets and contained raw messages
  -- NB: length is the same but the distinction makes the code clearer
  subtype Serpent_Pkt is Octets( 1 .. SERPENT_OCTETS );
  subtype Serpent_Msg is Octets( 1 .. SERPENT_OCTETS );

And the new code in packing.ads:

  -- Packing/unpacking for Eulora's communication protocol:
  -- Serpent Message to/from Serpent Packet
  -- RSA Message to/from RSA Packet
  -- S.MG, 2018

with Raw_Types;
with Serpent;

package Packing is
  -- no side effects or internal state
  Pragma Pure(Packing);

  -- Packing a Serpent message into Serpent package, using the given key
  function Pack( Msg : in Raw_Types.Serpent_Msg;
                    K   : in Serpent.Key )
                  return Raw_Types.Serpent_Pkt;

  -- Unpacking a Serpent packet into contained message, using the given key
  function Unpack( Pkt : in Raw_Types.Serpent_Pkt;
                    K   : in Serpent.Key)
                  return Raw_Types.Serpent_Msg;

  -- internals of this package, NOT for outside use
private
  -- length of 1 Serpent block
  Block_Len: constant Natural := Serpent.Block'Length;

  -- number of Serpent blocks in one single Serpent message/packet
  S_Blocks : constant Natural := Raw_Types.SERPENT_OCTETS / Block_Len;

end Packing;

The new code in packing.adb:

  -- Packing/unpacking for Eulora's communication protocol:
  -- Serpent Message to/from Serpent Packet
  -- RSA Message to/from RSA Packet
  -- S.MG, 2018

package body Packing is

  -- Packing a Serpent message into Serpent package, using the given key
  function Pack( Msg : in Raw_Types.Serpent_Msg;
                 K   : in Serpent.Key )
               return Raw_Types.Serpent_Pkt is

    -- single Serpent blocks containing plain / encrypted data
    Plain    : Serpent.Block;
    Encr     : Serpent.Block;

    -- Serpent Key Schedule - needed for direct encr/decr calls
    KS       : Serpent.Key_Schedule;

    -- final resulting Serpent package
    Pkt      : Raw_Types.Serpent_Pkt := (others => 0);
  begin
    -- prepare the Serpent key schedule based on given key
    Serpent.Prepare_Key( K, KS );

    -- encrypt message block by block and copy result in packet
    for I in 1 .. S_Blocks loop
      -- get current block to encrypt
      Plain := Msg( Msg'First + (I-1) * Block_Len ..
                    Msg'First +  I    * Block_Len - 1 );
      -- encrypt with Serpent
      Serpent.Encrypt( KS, Plain, Encr );
      -- copy result to output packet
      Pkt( Pkt'First + (I-1) * Block_Len ..
           Pkt'First +  I    * Block_Len - 1 )
         := Encr;
    end loop;

    -- return result
    return Pkt;
  end Pack;

  -- Unpacking a Serpent packet into contained message, using the given key
  function Unpack( Pkt : in Raw_Types.Serpent_Pkt;
                   K   : in Serpent.Key)
                 return Raw_Types.Serpent_Msg is
    -- single Serpent blocks containing plain / encrypted data
    Plain    : Serpent.Block;
    Encr     : Serpent.Block;

    -- Serpent Key Schedule - needed for direct encr/decr calls
    KS       : Serpent.Key_Schedule;

    -- the message extracted from the given packet
    Msg : Raw_Types.Serpent_Msg := (others => 0);
  begin
    -- prepare the Serpent key for use
    Serpent.Prepare_Key( K, KS );

    -- decrypt the Serpent packet block by block
    for I in 1 .. S_Blocks loop
      -- get current block from input and decrypt
      Encr := Pkt( Pkt'First + (I-1) * Block_Len ..
                   Pkt'First +  I    * Block_Len - 1 );
      Serpent.Decrypt( KS, Encr, Plain );

      -- copy result to its correct position in final output
      Msg( Msg'First + (I-1) * Block_Len ..
           Msg'First +  I    * Block_Len - 1 )
         := Plain;
    end loop;

    -- return the result - the message content of given package
    return Msg;
  end Unpack;

end Packing;

The .vpatch and my signature for it are as usual on my Reference Code Shelf as well as linked here for your convenience:


  1. 1472 / 16 = 92 

  2. And needed they were too for they actually caught an error that had survived somehow several re-readings of the code to the point that I was totally surprised when the tests first...failed. Never underestimate your own capacity of introducing idiotic errors in the simplest of things! 

October 16, 2018

SMG Comms Chapter 2: Raw Types

Filed under: Coding, SMG_Comms — Diana Coman @ 11:20 a.m.

~ This is a work in progress towards an Ada implementation of Eulora's communication protocol. Start with Chapter 1.~

My previous Chapter 1 with its assorted warts and lamentations sparked a rather productive discussion in the forum that ended up with a significant revision of the protocol specification. The main change has to do with packet sizes and types: ALL packets will be either 1470 octets long and RSA encrypted OR 1472 octets long and Serpent encrypted. Those sizes are chosen to ensure that there is no fragmenting of UDP frames sent on the wire since such fragmenting increases significantly the chance of packet loss. A test with those UDP packet sizes sent back and forth between UK and UY did not uncover any trouble - if anything, the results were actually better than expected. In any case, increased chances of reliable communications aside, the added benefit of those fixed, unique sizes is a clearer protocol alltogether. So after a bit of digesting the new specification, I can finally say that I have some sort of plan for its implementation rather than grasping at it from any thread that I could perceive at all (as it was pretty much the case in Chapter 1). Specifically, my current implementation plan is made of 3 layers that build on one another and give me a structure to rely on:

  1. Layer 0 - Raw types
  2. Layer 1 - Sender/Receiver
  3. Layer 2 - Data structures

1. Layer 0 - Raw types

The raw types for Eulora's communication protocol are essentially two: octet (the basic unit, effectively 8 bits) and arrays of octets (various fixed sizes matching the basic types in the protocol's specification). However, for the arrays of octets, there is a useful distinction to be made between packets (i.e. the received array of octets of fixed length, either 1470 or 1472 octets) and messages (i.e. the content of a packet). Essentially messages are obtained from packets in Eulora's communication protocol through decryption using either Serpent (for 1472 octets long packets) or RSA (for 1470 octets long packet). Symmetrically, packets are obtained by encrypting messages with either Serpent (for 1472 octets long messages) or RSA (for 234 octets long messages). Consequently, this layer 0 offers the definitions of types that cover the full set of possible messages and packets together with the relevant conversion methods between packets and messages as well as between raw octets and int/unsigned/float data types. Note that a "message" here is simply the decrypted content of a packet, nothing more. The interpretation of the octets in a message and/or their use to fill some data structure that the protocol defines happens at a higher layer, not here.

2. Layer 1 - Sender/Receiver

Layer 1 is concerned with sending and receiving packets using the types and conversion methods provided by layer 0 together with the UDP lib for actual network communication. So far this seems to me at the moment a very thin layer really since it's little more than a basic receiver and sender: the receiver simply uses UDP lib to endlessly read all incoming packets and store them in a queue for later processing by consumer(s) external to this layer; the sender may have perhaps an input queue from which it keeps reading packets together with their intended destination and then sends them along using the UDP lib. This layer comes right after the raw types because it needs and uses those raw types but at the moment it's unclear to me whether it belongs as part of a protocol implementation since I can see the case for it being left to the user application of the protocol. At any rate, the protocol specification is not really concerned with this part and this description of the sender/receiver is not a given - it may change as required by each application.

4. Layer 2 - Data Structures

This layer is on top of Layer 0 - it provides the data structures for the different types of messages in Eulora's communication protocol. While any message in Eulora's protocol is just an array of octets at layer 0, the information contained in any message has to be structured according to the protocol's rules described in sections 4, 5 and 7 of the specification. This layer provides the definitions of those data structures as well as the conversion methods from messages to data structures and back.

Note that those 3 layers do not include protocol mechanics since those are really part of the server or client applications. Perhaps a demo / test application implementing the specified protocol mechanics would be useful to include as part of this implementation but I'd rather not specify it as such at this point. For now I'm fine with those 3 layers but if you see any holes in them or problems with them, let me know in the comments below!

Implementation

To start it all off, here's the first part of layer 0 - raw types, including the definitions of types and the most basic conversions via Ada.Unchecked_Conversion:

 -- raw types for the communication protocol
 -- these are used throughout at the lowest level of the protocol
 -- essentially they are the units of packets and of messages
 -- SMG.Comms has only 2 types of packets: RSA and Serpent
 -- a message is the decrypted content of a packet
 -- S.MG, 2018

with Interfaces; use Interfaces; -- Unsigned_n and Integer_n
with Ada.Unchecked_Conversion;

package Raw_Types is

  -- constants from SMG.COMMS standard specification
    -- size of a serpent-encrypted packet and message, in octets
    -- note that this corresponds to 1472/16 = 92 Serpent blocks
    -- NB: lengths are the same but the distinction makes the code clearer
  SERPENT_PKT_OCTETS : constant Positive := 1472;
  SERPENT_MSG_OCTETS : constant Positive := SERPENT_PKT_OCTETS;

    -- size of a RSA-encrypted packet and message in octets and bits
  RSA_PKT_OCTETS     : constant Positive := 1470;
  RSA_MSG_OCTETS     : constant Positive := 234;
  RSA_MSG_BITS       : constant Positive := RSA_MSG_OCTETS * 8; --1872

  -- raw, low-level types
  -- all messages and packets are simply arrays of octets at low level/raw
  type Octets is array( Natural range <> ) of Interfaces.Unsigned_8;

  -- raw representations of basic types (with fixed, well-defined sizes)
  subtype Octets_1 is Octets( 1 .. 1 );
  subtype Octets_2 is Octets( 1 .. 2 );
  subtype Octets_4 is Octets( 1 .. 4 );
  subtype Octets_8 is Octets( 1 .. 8 );

  -- RSA packets and contained raw messages
  subtype RSA_Pkt is Octets( 1 .. RSA_PKT_OCTETS );
  subtype RSA_Msg is Octets( 1 .. RSA_MSG_OCTETS );

  -- Serpent packets and contained raw messages
  -- NB: length is the same but the distinction makes the code clearer
  subtype Serpent_Pkt is Octets( 1 .. SERPENT_PKT_OCTETS );
  subtype Serpent_Msg is Octets( 1 .. SERPENT_MSG_OCTETS );

  -- blind, unchecked casts ( memcpy style )
  function Cast is new Ada.Unchecked_Conversion( Integer_8  , Octets_1 );
  function Cast is new Ada.Unchecked_Conversion( Octets_1   , Integer_8 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_8 , Octets_1 );
  function Cast is new Ada.Unchecked_Conversion( Octets_1   , Unsigned_8 );

  function Cast is new Ada.Unchecked_Conversion( Integer_16 , Octets_2 );
  function Cast is new Ada.Unchecked_Conversion( Octets_2   , Integer_16 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_16, Octets_2 );
  function Cast is new Ada.Unchecked_Conversion( Octets_2   , Unsigned_16 );

  function Cast is new Ada.Unchecked_Conversion( Integer_32 , Octets_4 );
  function Cast is new Ada.Unchecked_Conversion( Octets_4   , Integer_32 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_32, Octets_4 );
  function Cast is new Ada.Unchecked_Conversion( Octets_4   , Unsigned_32 );

  -- Gnat's Float has 32 bits but this might be different with other compilers
  function Cast is new Ada.Unchecked_Conversion( Float, Octets_4 );
  function Cast is new Ada.Unchecked_Conversion( Octets_4, Float );

  function Cast is new Ada.Unchecked_Conversion( Integer_64, Octets_8 );
  function Cast is new Ada.Unchecked_Conversion( Octets_8, Integer_64 );
  function Cast is new Ada.Unchecked_Conversion( Unsigned_64, Octets_8 );
  function Cast is new Ada.Unchecked_Conversion( Octets_8, Unsigned_64 );

end Raw_Types;

I packed the above code as a .vpatch on top of the previous genesis .vpatch mainly for keeping my original promise of showing this being built as it is with detours and corrections on the way. Otherwise this could equally well be a genesis in itself given how radically it changes pretty much everything in there. Nevertheless, at least for now - meaning until a final version is achieved and a regrind makes perhaps sense - I'll keep growing the smg_comms tree. I'll link all smg_comms .vpatches and my signatures for them from the Code Shelf page as usual, while linking the current ones here as well:

The next chapter will add to the raw types layer, providing conversions from packets to messages and back. That will bring in parts of EuCrypt of course, namely the Serpent and RSA implementations. For this reason, I aim to do this perhaps in two steps (first Serpent and only then RSA) in order to keep patches as clear and easy to follow as possible. And this is of course a very good opportunity to re-read the EuCrypt implementation, to re-write it on one level or another as I bring it over to SMG_Comms and to see first-hand how it is to use it!

October 13, 2018

Results of Testing UDP - Take 2

Filed under: Coding, UDP — Diana Coman @ 8:32 p.m.

As the first test revealed that most UDP packets make it safely at least when sent 1 second apart, I decided that the next week-long test should run with a substantially smaller delay: 0.01 seconds between each 2 packets. Moreover, I've changed the sender to simply send 10000 packets at each run, alternating between 1472 and 1470 octets in size. The focus on those 2 sizes reflects the fact that ALL packets are either 14721 or 14702 octets long in the newest version of Eulora's communication protocol. Here's the summary of the data I collected:

UY UK
Sent: 21400003 2140000
Received: 2134569 (99.74%) 2139788 (99.99%)
Errors received: 0 0
1470-size sent: 1070000 1070000
1470-size received: 1067322 (99.75%) 1069901 (99.99%)
1472-size sent: 1070000 1070000
1472-size received: 1067247 (99.74%) 1069887 (99.99%)

From the above, it would seem that even 0.01 delay between any two packets being sent is not causing any problem at all - at least not for the sizes considered4. If anything, the % of received packets increased slightly compared to the previous test. Of the packets that made it to the other side, none were mangled, hence no errors received5. Unsurprising perhaps, the 2 octets difference in size between the 2 types of packets does not seem to have the slightest impact on % of packets that make it to the other side - the route itself is likely to be more important in this respect.

The timings remain iffier to investigate as I did not change the tester specifically for this. Applying the same correction as in the previous test (i.e. calculating first the difference between the logged local times and then simply adjusting so that the minimum difference is 0) yields again the same stats on both sides (if slightly different values than during the last test):

Data Min 1st Q Median Mean 3rd Q Max
UK -> UY 0 7 13 13.09 20 27
UY -> UK 0 7 13 13.19 20 27

As before, I would not suggest taking the above timings for anything really. The only thing that can perhaps be said is that packets don't seem to take all that much to arrive at their destination at least on those routes. This is of course no guarantee at all, just a limited observation of this particular data set.


  1. Serpent encrypted packets that are meant for most communications in Eulora. 

  2. RSA encrypted packets that are meant only for new accounts in Eulora. 

  3. I've ran this for almost 9 days so more than the previous 1 week for the first test. 

  4. Arguably larger sizes that would get fragmented on the way might have higher chances of becoming lost. 

  5. There was however one spam packet received by the node in UY from an entirely unrelated IP but I removed that before making the summary above since it has nothing to do with the test itself. Also, the fact that one will receive spam is not exactly news otherwise so there isn't much to say about it at this moment. 

October 10, 2018

EuCrypt Chapter 14: CRC32 Implementation with Lookup Table

Filed under: Coding, EuCrypt — Diana Coman @ 1:51 p.m.

~ This is part of the EuCrypt series. Start with Introducing EuCrypt. ~

The communication protocol for Eulora uses CRC32 as checksum for its packages and so I found myself looking in disbelief at the fact that GNAT imposes the use of Streams for something as simple as calculating the checksum of anything at all, no matter how small no matter what use, no matter what you might need or want or indeed find useful, no matter what. No matter! As usual, the forum quickly pointed me in the right direction - thank you ave1! - namely looking under the hood of course, in this case GNAT's own hood, the Systems.CRC32 package. Still, this package makes a whole dance of eating one single character at a time since it is written precisely to support the stream monstrosity on top rather than to support the user with what they might indeed need. Happily though, CRC32 is a very simple thing and absolutely easy to lift and package into 52 lines of code in the .adb file + 130 in the .ads file so 182 all in total1, comments and two types of input (string or raw array of octets) included. And since a CRC32 implementation is anyway likely to be useful outside of Eulora's communication protocol too, I'm adding it as a .vpatch on the EuCrypt tree where it seems to fit best at the moment. It's a lib on its own as "CRC32" when compiled via its own crc32.gpr or otherwise part of the aggregate EuCrypt project if you'd rather compile all of EuCrypt via its eucrypt.gpr.

My CRC32 lib uses the 0x04C11DB7 generator polynomial and a lookup table with pre-calculated values for faster execution. As Stanislav points out, implementing the actual division and living with the slow-down incurred is not a huge problem but at least for now I did not bother with it. The CRC32 lib provides as output 32 bits of checksum for either a string or an array of octets. At the moment at least I really don't see the need for anything more complicated than this - even the string-input method is more for the convenience of other/later uses than anything else. For my own current work on Eulora's protocol I expect to use CRC32 on arrays of octets directly.

The .vpatch adding CRC32 to EuCrypt and my signature for it are as usual on my Reference Code Shelf with additional links here for your convenience:


  1. Specifically: 52 lines is the count of crc32.adb that does the work. The .ads file brings in another 130 lines that are mostly the lookup table with pre-calculated values. The .gpr file has another 61 lines and the restrict.adc another 80 lines. 

October 4, 2018

Results of Testing UDP - Take 1

Filed under: Coding, UDP — Diana Coman @ 6:09 p.m.

For one full week, between 26 September 2018 and 3 October 2018, my UDP Tester ran on 2 computers, one in the UK and one in Uruguay (UY), sending and receiving UDP messages in both directions. On each side, the receiver ran continuously, logging all UDP messages that it received during the whole interval. By contrast, the sender ran on both sides hourly but at different times so that the communications did not overlap. I don’t expect it would have been any trouble even if they did overlap but this was meant to be a test of UDP under best conditions and for this reason I set the times so that the sender on one end always finished a full run before the one on the other end started. For the same reason, the messages were sent at a rate of at most 1 message per second1.

At each run, the sender sent exactly 2043 UDP messages with lengths between 6 and 2048, each message having a different length. The order of messages was pseudo-random, relying on the Mersenne Twister prng using as seed the local time at the start of the run (in unix format). The sender kept a log of all messages it sent, including destination IP and port, seed used for MT, local time when message was sent and size of message. The receiver also logged basic information about each message: source IP and port, local time and message size as observed by receiver as well as those contained in the message’s own header, number of observed incorrect bits in the message’s payload as well as the expected and actual values of incorrect octets.

A first look at the week-long data yielded a bit of a surprise in that the UY receiver had actually received *more* messages than were sent from the UK! At a closer look, it turned out that 4933 UDP messages arriving at the UY node were actually sent by its own local switch! And moreover, they were all, without exception, recorded as corrupted since neither size nor payload matched the expected values2. At the moment those switch-generated messages are a bit of a mystery - it’s unclear what they are exactly or why and how they appeared. Working hypotheses would be that they are either local dhcp messages (although the port number would be a weird choice for those) or stray frags of bigger UDP messages. My one single attempt to replicate this behaviour while simultaneously capturing everything with tcpdump has so far failed - there were no such unexpected messages at all over several hours of UK sender at work. I might perhaps try again at a later date after I’m done with the more pressing tests that I need for SMG comms or simply process the existing error log and reconstitute the already observed weird messages from there. Anyway, for now I put those anomalous messages to the side and focus instead on the rest of the messages (which were sent as expected either by the node in the UK or by the one in UY). Here’s a summary of the data thus cleaned:

UK node UY node
Total sent: 3459283 3452674
Total received: 3447175 3451836
% received: 99.84%7 99.78%8
Errors received9: 0 0

Arguably the lost messages are of most interest in all the above: can one say perhaps that the largest messages10 get lost more often? Not really or at least not based on this little set of data. Compare the summary stats for three groups of messages: all messages sent from the UK (reflecting as expected the sizes sent and the fact that the same number of messages of each size are sent), all messages lost at UY (i.e. did not make it on the way from UK to UY) and all messages lost at UK (i.e. did not make it on the way from UY to UK):

Data Min 1st Q Median Mean 3rd Q Max
All sent from UK 6 516 1027 1027 1538 2048
Lost at UY (UK->UY) 13 513 1049 1051 1602 2045
Lost at UK (UY->UK) 16 553.5 1072 1061 1576 2047

While the data set of lost messages is quite small (550 messages lost at UK and 745 at UY), note that this is mainly due to the fact that there are relatively few losses overall: less than 0.4% of messages sent got lost on the way. So it would seem that at least under the conditions and on the routes considered11, UDP is not all that unreliable anyway. In any case, those summaries above seem to me remarkably close to one another - meaning that there isn’t any visible evidence that some sizes would get lost more than others, at least not for the set of sizes considered. Arguably sizes of up to 2048 octets of message are quite fine for communications over UDP - or at any rate, just as fine as smaller sizes.

In terms of order of received messages, the UY node received ALL messages precisely in the order in which they were sent but the UK node reported 66 messages in total that arrived out of order. Although this is a tiny number, it is perhaps reasonable to assume that it might increase in worse conditions (e.g. significantly less than 1 second between sending messages).

The actual timings are a bit iffier to investigate since the precision of UDP Tester turns out to be less than what would be needed for such task. Moreover, there is something weird going on with the way I recorded the time because the difference between the two nodes should be of ~34 seconds (UY node local time = UK node local time + 34) but this doesn't quite square with all the data especially at the UY receiver end12. On the more positive side though, at least the measurement bias there is constant for all the data and it doesn't introduce any weird effects so I can still attempt to infer something considering also that observed behaviour suggests that most UDP messages really make it to the other end within 1 second. Consequently, I calculated the delta on both sides as TR - TS at first and then I added (on UK side) respectively subtracted (on UY side) the quantity needed to make the lowest delta 0. So at the UY receiver, delta = TR - TS - 11 while at the UK receiver, delta = TR - TS + 32. With this correction, the summary stats for the delta on both sides turn out to be remarkably similar:

Data Min 1st Q Median Mean 3rd Q Max
Deltas at UK node: 0 5 11 10.60 16 21
Deltas at UY node: 0 5 11 10.62 16 21

Note that I do *not* recommend taking the above delta values for anything really, as the tester's precision in recording time is just not enough for this.

You are of course warmly invited to run your own tests and to play with this dataset in any way you find fit. So here's the data from both nodes, including the additional 4933 messages that the UY node received from its own switch:

  • udp_test_take1_data.zip (~10MB)
  • SHA512SUM: 963b8a1467630eea35532122ab7c2d25cb8741001808841f7cf02b34abb6ad5300adcb1d667dd902b4278dd2b373dc46427b0b0bbc918ee52f326456535a4114 udp_test_take1_data.zip

Have fun!


  1. Specifically: the sender had a delay of 1 second between any two consecutive messages. 

  2. The UDP tester simply fills the message up to any length with values calculated as Pos mod 256 where Pos is the position of the respective octet in the full message. 

  3. This is precisely 345928/2043=169 runs. 

  4. This includes a partial 170th run since I stopped the whole test while the UY sender was running already its 170th run. 

  5. 550 messages lost in total. 

  6. 745 messages lost in total. 

  7. 344717 / 345267 * 100 

  8. 345183 / 345928 * 100 

  9. This refers to messages received but with payloads that don’t match the expected values. 

  10. Note that this test capped the messages at 2048 so “largest” here means strictly < 2049 octets. 

  11. The UK node is a “consumer” node i.e. behind a router and on a residential connection; the UY node is S.MG’s test server with Pizarro. 

  12. Considering TR as TimeReceived and TS as TimeSent, at UY receiver the delta should be calculated as TR - (TS + 34) = TR - TS - 34; however, there are entries with TR-TS as low as 11 so basically it would seem that messages arrived before they were even sent. 

September 27, 2018

Tester for UDP Communications

Filed under: Coding, UDP — Diana Coman @ 8:33 p.m.

This code builds on Stanislav Datskovskiy's minimal UDP lib to provide a convenient way of gathering data to evaluate UDP communications between any desired two nodes. The initial specification was to provide a reliable way to "send a soup of all packets lengths from 1 to 65536 bytes each hour back and forth" but this was refined further down the line1 to reduce the maximum length of the payload to 2048 and to include a Mersenne-Twister (MT) pseudorandom number generator (prng) for scrambling the various message sizes. To accomplish that, there are two main parts that I'm adding to the original UDP library:

  1. The MT lib that is simply an Ada implementation of the MT prng algorithm.
  2. The UDP_Tester package that uses a slightly adapted UDP lib and the MT lib above to provide a UDP sender and a corresponding UDP receiver that implement the testing specification and log the relevant data.

MT lib
The MT lib is a standalone Ada library implementing the well-known Mersenne Twister algorithm for pseudorandom number generation2. I am not aware of any other Ada implementation of MT and since I really don't want to add C code to my plate unless I absolutely have to, I simply ported to Ada the reference C implementation provided by the original authors of MT. As such, there isn't much to discuss about the implementation itself - I'll point however the changes I made with respect to the original implementation, namely:

  • In my Ada version of MT, there is no default seeding of the MT generator. The C version allows the caller to ask the generator for numbers without having seeded it - in this case, the C implementation seeds itself with a magic default value that is hardcoded at the checking spot and then just proceeds as if nothing was wrong. I find this approach abhorent because it effectively hides an error (calling the generator without seeding it first) rather than complaining about it and forcing its correction. Consequently, my MT lib will simply abort if the generator is asked for numbers without having been seeded first.3
  • Because Ada is most pointedly not a sort of C, there was no need for the various types of hacks added to the C version to ensure that it still worked correctly on 64-bit machines and not only on the 32-bit machines for which the code was initially written. In Ada it's enough to specify one's types correctly to be exactly and guaranteed 32-bits and then proceed to work with them as such, regardless of whether the processor running the code has 32-bit or 64-bit or x-bit registers.
  • My MT lib provides just one type of pseudorandom numbers, namely unsigned integers on 32 bits. The original C implementation had several wrappers around this main function to map the 32 bits pseudorandom numbers to the interval (0,1) for instance and similar. All the mappings were trivial and they can be easily done by any caller that requires them - precisely in the way they require them. At this stage at least I don't quite see the need for those as part of MT lib and so I left them out - there is only the core offering of 32 pseudorandom bits as it were and the caller can then use or interpret them as they see fit.
  • To check that my implementation results in precisely the same sequence of numbers as the original C MT, I added an automated test (still in Ada) that uses the reference seed and checks the output of MT lib (number by number) against the reference output from the original C MT, reporting any mismatches.

The code of MT lib is self-contained with declarations in mt.ads:

 -- Ada implementation of the Mersenne Twister Pseudo-Random number generator
 -- S.MG, 2018

with Interfaces; use Interfaces;

package MT is
  -- Interfaces.Unsigned_32 in GNAT is mod 2**32 and has bitwise shifts defined
  subtype U32 is Interfaces.Unsigned_32;

  -- period parameters
  N          : constant := 624;
  M          : constant := 397;
  MATRIX_MASK: constant U32 := 16#9908_b0df#;
  UPPER_MASK : constant U32 := 16#8000_0000#;
  LOWER_MASK : constant U32 := 16#7fff_ffff#;

  -- array type for storing the state vector of the generator
  type State_Type is Array( 0 .. N-1 ) of U32;

  -- array type for initialization by array - change key len here if needed
  KEY_LEN    : constant := 4;
  type Init_Array_Type is Array( 0 .. KEY_LEN - 1 ) of U32;

  -- exception raised by a call to generator before initializing it
  No_Init_Exception : exception;

  -- initialize the generator with a seed (number)
  procedure Init_Genrand(Seed : in U32);

  -- initialize the generator with array of 8-octets elements
  procedure Init_Genrand(Seed : in Init_Array_Type);

  -- generate the next pseudo-random 32 bits number in the sequence
  function Gen_U32 return U32;

  -- for testing
  function Get_State return State_Type;

  -- internals of the generator, NOT for direct access
private
  -- actual state of the generator
  State      : State_Type;

  -- flag for generator routine
  Mti_Flag : U32 := N + 1;  -- default value -> state(N) is not initialised

end MT;

And implementation in mt.adb:

 -- Ada implementation of the Mersenne Twister Pseudo-Random number generator
 -- S.MG, 2018

package body MT is

  procedure Init_Genrand(Seed : in U32) is
  begin
    State(0) := Seed;
    for I in State'First + 1 .. State'Last loop
      State(I) := U32(1812433253) *
                  ( State(I - 1) xor
                    ( Shift_Right(State(I - 1), 30) )
                  ) + U32(I) ;
    end loop;
    Mti_Flag := N;
  end Init_Genrand;

  procedure Init_Genrand(Seed : in Init_Array_Type) is
    Default_Seed: constant U32 := U32(19650218); -- magic value!
    I, J, K : Integer;
  begin
    Init_Genrand(Default_Seed);
    I := 1;
    J := 0;
    if N > Seed'Length then
      K := N;
    else
      K := Seed'Length;
    end if;

    while K > 0 loop
      State(I) := (State(I) xor
                  ( (State(I-1) xor
                     Shift_Right(State(I-1), 30)
                    ) * U32(1664525)
                  )) + Seed(J) + U32(J);
      I := I + 1;
      J := J + 1;
      if I >= N then
        State(0) := State(N-1);
        I := 1;
      end if;
      if J >= Seed'Length then
        J := 0;
      end if;
      K := K - 1;
    end loop;

    K := N -1;
    while K > 0 loop
      State(I) := (State(I) xor
                  ( (State(I-1) xor
                     Shift_Right(State(I-1), 30)
                    ) * U32(1566083941)
                  )) - U32(I);
      I := I + 1;
      if I >= N then
        State(0) := State(N-1);
        I := 1;
      end if;
      K := K - 1;
    end loop;
    State(0) := 16#8000_0000#; -- MSB is 1 to ensure non-zero initial state
  end Init_Genrand;

  function Gen_U32 return U32 is
    Y     : U32;
    MASK1 : constant U32 := U32(1);
    Mag01 : Array ( 0 .. 1 ) of U32;
  begin
    -- Mag01[x] is x * Matrix_A of the algorithm for x 0 or 1
    Mag01(0) := U32(0);
    Mag01(1) := MATRIX_MASK;

    -- if no numbers available, generate another set of N words
    if Mti_Flag >= N then

      -- check it's not a non-initialised generator
      if Mti_Flag = (N + 1) then
         -- Generator was NOT initialised!
         -- Original C code initialises with default seed 5489
         -- This code will simply raise exception and abort
         raise No_Init_Exception;
      end if;

      for K in 0 .. N - M - 1 loop
        Y := ( State(K)   and UPPER_MASK ) or
             ( State(K+1) and LOWER_MASK );
        State(K) := State(K+M) xor
                      Shift_Right(Y, 1) xor
                        Mag01(Integer(Y and MASK1));
      end loop;
      for K in N-M .. N - 2 loop
        Y := ( State(K)   and UPPER_MASK  ) or
             ( State(K+1) and LOWER_MASK);
        State(K) := State(K + M - N) xor
                      Shift_Right(Y, 1) xor
                        Mag01(Integer(Y and MASK1));
      end loop;
      Y := (State(N-1) and UPPER_MASK ) or
             (State(0) and LOWER_MASK );
      State(N - 1) := State(M-1) xor
                        Shift_Right(Y, 1) xor
                          Mag01(Integer(Y and MASK1));
      Mti_Flag := 0;
    end if;

    -- retrieve next available number
    Y        := State(Integer(Mti_Flag));
    Mti_Flag := Mti_Flag + 1;

    -- tempering
    Y := Y xor Shift_Right(Y, 11);
    Y := Y xor (Shift_Left(Y, 7) and 16#9d2c_5680#);
    Y := Y xor (Shift_Left(Y, 15) and 16#efc6_0000#);
    Y := Y xor Shift_Right(Y, 18);

    -- return tempered number
    return Y;
  end Gen_U32;

  function Get_State return State_Type is
  begin
    return State;
  end Get_State;

end MT;

The test for the above MT lib is in its own testmt/test_mt.adb, including the reference output (that really is the largest part of the whole file):

  --S.MG, 2018

with Ada.Text_IO; use Ada.Text_IO;
with Interfaces; use Interfaces;
with MT;

procedure Tests_MT is
  Seeds : MT.Init_Array_Type;
  X     : MT.U32;
  No    : constant Integer := 1000;
  Result: Array(0..No-1) of MT.U32 := (
    1067595299,  955945823,  477289528, 4107218783, 4228976476,
    3344332714, 3355579695,  227628506,  810200273, 2591290167,
    2560260675, 3242736208,  646746669, 1479517882, 4245472273,
    1143372638, 3863670494, 3221021970, 1773610557, 1138697238,
    1421897700, 1269916527, 2859934041, 1764463362, 3874892047,
    3965319921,   72549643, 2383988930, 2600218693, 3237492380,
    2792901476,  725331109,  605841842,  271258942,  715137098,
    3297999536, 1322965544, 4229579109, 1395091102, 3735697720,
    2101727825, 3730287744, 2950434330, 1661921839, 2895579582,
    2370511479, 1004092106, 2247096681, 2111242379, 3237345263,
    4082424759,  219785033, 2454039889, 3709582971,  835606218,
    2411949883, 2735205030,  756421180, 2175209704, 1873865952,
    2762534237, 4161807854, 3351099340,  181129879, 3269891896,
     776029799, 2218161979, 3001745796, 1866825872, 2133627728,
      34862734, 1191934573, 3102311354, 2916517763, 1012402762,
    2184831317, 4257399449, 2899497138, 3818095062, 3030756734,
    1282161629,  420003642, 2326421477, 2741455717, 1278020671,
    3744179621,  271777016, 2626330018, 2560563991, 3055977700,
    4233527566, 1228397661, 3595579322, 1077915006, 2395931898,
    1851927286, 3013683506, 1999971931, 3006888962, 1049781534,
    1488758959, 3491776230,  104418065, 2448267297, 3075614115,
    3872332600,  891912190, 3936547759, 2269180963, 2633455084,
    1047636807, 2604612377, 2709305729, 1952216715,  207593580,
    2849898034,  670771757, 2210471108,  467711165,  263046873,
    3569667915, 1042291111, 3863517079, 1464270005, 2758321352,
    3790799816, 2301278724, 3106281430,    7974801, 2792461636,
     555991332,  621766759, 1322453093,  853629228,  686962251,
    1455120532,  957753161, 1802033300, 1021534190, 3486047311,
    1902128914, 3701138056, 4176424663, 1795608698,  560858864,
    3737752754, 3141170998, 1553553385, 3367807274,  711546358,
    2475125503,  262969859,  251416325, 2980076994, 1806565895,
     969527843, 3529327173, 2736343040, 2987196734, 1649016367,
    2206175811, 3048174801, 3662503553, 3138851612, 2660143804,
    1663017612, 1816683231,  411916003, 3887461314, 2347044079,
    1015311755, 1203592432, 2170947766, 2569420716,  813872093,
    1105387678, 1431142475,  220570551, 4243632715, 4179591855,
    2607469131, 3090613241,  282341803, 1734241730, 1391822177,
    1001254810,  827927915, 1886687171, 3935097347, 2631788714,
    3905163266,  110554195, 2447955646, 3717202975, 3304793075,
    3739614479, 3059127468,  953919171, 2590123714, 1132511021,
    3795593679, 2788030429,  982155079, 3472349556,  859942552,
    2681007391, 2299624053,  647443547,  233600422,  608168955,
    3689327453, 1849778220, 1608438222, 3968158357, 2692977776,
    2851872572,  246750393, 3582818628, 3329652309, 4036366910,
    1012970930,  950780808, 3959768744, 2538550045,  191422718,
    2658142375, 3276369011, 2927737484, 1234200027, 1920815603,
    3536074689, 1535612501, 2184142071, 3276955054,  428488088,
    2378411984, 4059769550, 3913744741, 2732139246,   64369859,
    3755670074,  842839565, 2819894466, 2414718973, 1010060670,
    1839715346, 2410311136,  152774329, 3485009480, 4102101512,
    2852724304,  879944024, 1785007662, 2748284463, 1354768064,
    3267784736, 2269127717, 3001240761, 3179796763,  895723219,
     865924942, 4291570937,   89355264, 1471026971, 4114180745,
    3201939751, 2867476999, 2460866060, 3603874571, 2238880432,
    3308416168, 2072246611, 2755653839, 3773737248, 1709066580,
    4282731467, 2746170170, 2832568330,  433439009, 3175778732,
      26248366, 2551382801,  183214346, 3893339516, 1928168445,
    1337157619, 3429096554, 3275170900, 1782047316, 4264403756,
    1876594403, 4289659572, 3223834894, 1728705513, 4068244734,
    2867840287, 1147798696,  302879820, 1730407747, 1923824407,
    1180597908, 1569786639,  198796327,  560793173, 2107345620,
    2705990316, 3448772106, 3678374155,  758635715,  884524671,
     486356516, 1774865603, 3881226226, 2635213607, 1181121587,
    1508809820, 3178988241, 1594193633, 1235154121,  326117244,
    2304031425,  937054774, 2687415945, 3192389340, 2003740439,
    1823766188, 2759543402,   10067710, 1533252662, 4132494984,
      82378136,  420615890, 3467563163,  541562091, 3535949864,
    2277319197, 3330822853, 3215654174, 4113831979, 4204996991,
    2162248333, 3255093522, 2219088909, 2978279037,  255818579,
    2859348628, 3097280311, 2569721123, 1861951120, 2907080079,
    2719467166,  998319094, 2521935127, 2404125338,  259456032,
    2086860995, 1839848496, 1893547357, 2527997525, 1489393124,
    2860855349,   76448234, 2264934035,  744914583, 2586791259,
    1385380501,   66529922, 1819103258, 1899300332, 2098173828,
    1793831094,  276463159,  360132945, 4178212058,  595015228,
     177071838, 2800080290, 1573557746, 1548998935,  378454223,
    1460534296, 1116274283, 3112385063, 3709761796,  827999348,
    3580042847, 1913901014,  614021289, 4278528023, 1905177404,
      45407939, 3298183234, 1184848810, 3644926330, 3923635459,
    1627046213, 3677876759,  969772772, 1160524753, 1522441192,
     452369933, 1527502551,  832490847, 1003299676, 1071381111,
    2891255476,  973747308, 4086897108, 1847554542, 3895651598,
    2227820339, 1621250941, 2881344691, 3583565821, 3510404498,
     849362119,  862871471,  797858058, 2867774932, 2821282612,
    3272403146, 3997979905,  209178708, 1805135652,    6783381,
    2823361423,  792580494, 4263749770,  776439581, 3798193823,
    2853444094, 2729507474, 1071873341, 1329010206, 1289336450,
    3327680758, 2011491779,   80157208,  922428856, 1158943220,
    1667230961, 2461022820, 2608845159,  387516115, 3345351910,
    1495629111, 4098154157, 3156649613, 3525698599, 4134908037,
     446713264, 2137537399, 3617403512,  813966752, 1157943946,
    3734692965, 1680301658, 3180398473, 3509854711, 2228114612,
    1008102291,  486805123,  863791847, 3189125290, 1050308116,
    3777341526, 4291726501,  844061465, 1347461791, 2826481581,
     745465012, 2055805750, 4260209475, 2386693097, 2980646741,
     447229436, 2077782664, 1232942813, 4023002732, 1399011509,
    3140569849, 2579909222, 3794857471,  900758066, 2887199683,
    1720257997, 3367494931, 2668921229,  955539029, 3818726432,
    1105704962, 3889207255, 2277369307, 2746484505, 1761846513,
    2413916784, 2685127085, 4240257943, 1166726899, 4215215715,
    3082092067, 3960461946, 1663304043, 2087473241, 4162589986,
    2507310778, 1579665506,  767234210,  970676017,  492207530,
    1441679602, 1314785090, 3262202570, 3417091742, 1561989210,
    3011406780, 1146609202, 3262321040, 1374872171, 1634688712,
    1280458888, 2230023982,  419323804, 3262899800,   39783310,
    1641619040, 1700368658, 2207946628, 2571300939, 2424079766,
     780290914, 2715195096, 3390957695,  163151474, 2309534542,
    1860018424,  555755123,  280320104, 1604831083, 2713022383,
    1728987441, 3639955502,  623065489, 3828630947, 4275479050,
    3516347383, 2343951195, 2430677756,  635534992, 3868699749,
     808442435, 3070644069, 4282166003, 2093181383, 2023555632,
    1568662086, 3422372620, 4134522350, 3016979543, 3259320234,
    2888030729, 3185253876, 4258779643, 1267304371, 1022517473,
     815943045,  929020012, 2995251018, 3371283296, 3608029049,
    2018485115,  122123397, 2810669150, 1411365618, 1238391329,
    1186786476, 3155969091, 2242941310, 1765554882,  279121160,
    4279838515, 1641578514, 3796324015,   13351065,  103516986,
    1609694427,  551411743, 2493771609, 1316337047, 3932650856,
    4189700203,  463397996, 2937735066, 1855616529, 2626847990,
      55091862, 3823351211,  753448970, 4045045500, 1274127772,
    1124182256,   92039808, 2126345552,  425973257,  386287896,
    2589870191, 1987762798, 4084826973, 2172456685, 3366583455,
    3602966653, 2378803535, 2901764433, 3716929006, 3710159000,
    2653449155, 3469742630, 3096444476, 3932564653, 2595257433,
     318974657, 3146202484,  853571438,  144400272, 3768408841,
     782634401, 2161109003,  570039522, 1886241521,   14249488,
    2230804228, 1604941699, 3928713335, 3921942509, 2155806892,
     134366254,  430507376, 1924011722,  276713377,  196481886,
    3614810992, 1610021185, 1785757066,  851346168, 3761148643,
    2918835642, 3364422385, 3012284466, 3735958851, 2643153892,
    3778608231, 1164289832,  205853021, 2876112231, 3503398282,
    3078397001, 3472037921, 1748894853, 2740861475,  316056182,
    1660426908,  168885906,  956005527, 3984354789,  566521563,
    1001109523, 1216710575, 2952284757, 3834433081, 3842608301,
    2467352408, 3974441264, 3256601745, 1409353924, 1329904859,
    2307560293, 3125217879, 3622920184, 3832785684, 3882365951,
    2308537115, 2659155028, 1450441945, 3532257603, 3186324194,
    1225603425, 1124246549,  175808705, 3009142319, 2796710159,
    3651990107,  160762750, 1902254979, 1698648476, 1134980669,
     497144426, 3302689335, 4057485630, 3603530763, 4087252587,
     427812652,  286876201,  823134128, 1627554964, 3745564327,
    2589226092, 4202024494,   62878473, 3275585894, 3987124064,
    2791777159, 1916869511, 2585861905, 1375038919, 1403421920,
      60249114, 3811870450, 3021498009, 2612993202,  528933105,
    2757361321, 3341402964, 2621861700,  273128190, 4015252178,
    3094781002, 1621621288, 2337611177, 1796718448, 1258965619,
    4241913140, 2138560392, 3022190223, 4174180924,  450094611,
    3274724580,  617150026, 2704660665, 1469700689, 1341616587,
     356715071, 1188789960, 2278869135, 1766569160, 2795896635,
      57824704, 2893496380, 1235723989, 1630694347, 3927960522,
     428891364, 1814070806, 2287999787, 4125941184, 3968103889,
    3548724050, 1025597707, 1404281500, 2002212197,   92429143,
    2313943944, 2403086080, 3006180634, 3561981764, 1671860914,
    1768520622, 1803542985,  844848113, 3006139921, 1410888995,
    1157749833, 2125704913, 1789979528, 1799263423,  741157179,
    2405862309,  767040434, 2655241390, 3663420179, 2172009096,
    2511931187, 1680542666,  231857466, 1154981000,  157168255,
    1454112128, 3505872099, 1929775046, 2309422350, 2143329496,
    2960716902,  407610648, 2938108129, 2581749599,  538837155,
    2342628867,  430543915,  740188568, 1937713272, 3315215132,
    2085587024, 4030765687,  766054429, 3517641839,  689721775,
    1294158986, 1753287754, 4202601348, 1974852792,   33459103,
    3568087535, 3144677435, 1686130825, 4134943013, 3005738435,
    3599293386,  426570142,  754104406, 3660892564, 1964545167,
     829466833,  821587464, 1746693036, 1006492428, 1595312919,
    1256599985, 1024482560, 1897312280, 2902903201,  691790057,
    1037515867, 3176831208, 1968401055, 2173506824, 1089055278,
    1748401123, 2941380082,  968412354, 1818753861, 2973200866,
    3875951774, 1119354008, 3988604139, 1647155589, 2232450826,
    3486058011, 3655784043, 3759258462,  847163678, 1082052057,
     989516446, 2871541755, 3196311070, 3929963078,  658187585,
    3664944641, 2175149170, 2203709147, 2756014689, 2456473919,
    3890267390, 1293787864, 2830347984, 3059280931, 4158802520,
    1561677400, 2586570938,  783570352, 1355506163,   31495586,
    3789437343, 3340549429, 2092501630,  896419368,  671715824,
    3530450081, 3603554138, 1055991716, 3442308219, 1499434728,
    3130288473, 3639507000,   17769680, 2259741420,  487032199,
    4227143402, 3693771256, 1880482820, 3924810796,  381462353,
    4017855991, 2452034943, 2736680833, 2209866385, 2128986379,
     437874044,  595759426,  641721026, 1636065708, 3899136933,
     629879088, 3591174506,  351984326, 2638783544, 2348444281,
    2341604660, 2123933692,  143443325, 1525942256,  364660499,
     599149312,  939093251, 1523003209,  106601097,  376589484,
    1346282236, 1297387043,  764598052, 3741218111,  933457002,
    1886424424, 3219631016,  525405256, 3014235619,  323149677,
    2038881721, 4100129043, 2851715101, 2984028078, 1888574695,
    2014194741, 3515193880, 4180573530, 3461824363, 2641995497,
    3179230245, 2902294983, 2217320456, 4040852155, 1784656905,
    3311906931,   87498458, 2752971818, 2635474297, 2831215366,
    3682231106, 2920043893, 3772929704, 2816374944,  309949752,
    2383758854,  154870719,  385111597, 1191604312, 1840700563,
     872191186, 2925548701, 1310412747, 2102066999, 1504727249,
    3574298750, 1191230036, 3330575266, 3180292097, 3539347721,
     681369118, 3305125752, 3648233597,  950049240, 4173257693,
    1760124957,  512151405,  681175196,  580563018, 1169662867,
    4015033554, 2687781101,  699691603, 2673494188, 1137221356,
     123599888,  472658308, 1053598179, 1012713758, 3481064843,
    3759461013, 3981457956, 3830587662, 1877191791, 3650996736,
     988064871, 3515461600, 4089077232, 2225147448, 1249609188,
    2643151863, 3896204135, 2416995901, 1397735321, 3460025646);

begin
  Seeds(0) := MT.U32(16#123#);
  Seeds(1) := MT.U32(16#234#);
  Seeds(2) := MT.U32(16#345#);
  Seeds(3) := MT.U32(16#456#);
  MT.Init_Genrand(Seeds);

  Put_Line("Generating numbers...");
  for I in 0 .. No-1 loop
    X := MT.Gen_U32;
    Put(".");
    if X /= Result(I) then
      Put_Line("");
      Put_Line("ERROR at position " & Integer'Image(I) &
               "; expected " & MT.U32'Image(Result(I)) &
               " but result is " & MT.U32'Image(X));
    end if;
  end loop;
  Put_Line("");
end Tests_MT;

UDP_Tester
The UDP_Tester has two main components: the sender and the receiver. For convenience, there are simple wrappers for those components - udp_sender.adb and udp_receiver.adb respectively - so that a build of UDP_Tester will directly provide two executables - sender and receiver. The IP and port numbers are knobs that can be easily changed from those wrappers directly since they are passed as parameters to the UDP_tester methods themselves.
udp_sender.adb:

  -- S.MG, 2018

with UDP_Tester;

procedure UDP_Sender is
  -- Sender and Receiver addresses + ports
  Receiver_IP   : constant String   := "161.0.121.202"; -- smg.test machine
  Receiver_Port : constant          := 7000;

  Sender_Port   : constant          := 5000;

begin

  UDP_Tester.Sender( Receiver_IP, Receiver_Port, Sender_Port) ;

end UDP_Sender;

udp_receiver.adb:

  -- S.MG, 2018

with UDP_Tester;

procedure UDP_Receiver is
  -- Port to listen on
  Receiver_Port : constant          := 7000;
begin

  UDP_Tester.Receiver( Receiver_Port );

end UDP_Receiver;

The UDP_Tester.Receiver method simply runs an endless loop in which it listens for UDP packages on a given port number and logs basic information about each pacakge it receives. The UDP_Tester.Sender method assembles and sends in a pseudorandom order all packages with length between 6 (size of own header) and maximum length. Note that the sender will send each size of package *only once* and it will simply finish once it sent one package of each size. Consequently, for data collection purposes, the sender will have to be started repeatedly from outside - most conveniently through a cron task4. Because the workings of both sender and receiver are quite basic, I won't cover them here in more detail - the code and comments should make it clear enough and if that's not the case, you can always ask your questions here in the comments. However, it's worth noting instead a few important points about the tester as a whole and the changes it imposes on the UDP lib:

  • To enable sending of packets with various sizes, the UDP lib had to be made generic. In Ada, this means that a calling packet can then instantiate the UDP type with its desired parameters (in this case the size of the UDP package). Specifically, from the UDP_Tester.Sender code, this reads:
          declare
            K : constant Positive := Packet_Size;
            -- sender will have *current* size of UDP packet
            package UDP_Sdr is new UDP( Payload_Size => K );
    

    Essentially the sender runs a loop and at each iteration it selects one of the remaining packet sizes, it instantiates UDP_Sdr as a parametrized UDP package and only then proceeds to use it to send the actual data.

    Note that this change is *not* required in production - it's simply needed for testing purposes. It's for this reason that it's part of the .vpatch for UDP_Tester rather than a .vpatch in itself on the UDP lib directly.

  • The sender will wait 1 second between any 2 packages it sends. This is mainly because a first version without this delay proved to result in significant packet loss that was clearly due to the burst mode (i.e. more than 2000 packages sent in 1 second) rather than anything else. Since the point of the test was to gather some data on UDP communication in relaxed rather than stress conditions, the delay of 1 second was introduced. However, should you wish to stress-test for any reason, you can easily remove this delay - simply comment out the "delay 1.0" line in the sender and that's all.
  • The UDP_Tester currently logs some information on both sides. Both sender and receiver will first check for a fixed-name file and if it doesn't exist they will create it, writing the header to it as well. After that, all new data will simply be appended to the file. The sender logs the size, local time, destination IP, destination port and seed used for the MT prng - this seed is the local time (unix style) when the sender is started. The receiver logs the size (both as received and as claimed in the packet's own header), the time (local time when sent and local time when received), the source IP, the source port and the number of octets that are different from expected. In addition, the receiver will further log in a separate file the actual octets that are found to contain errors, if any (together with information to easily link them back to the exact package they were part of).
  • There is no attempt to match directlty the times at the sender and at the receiver - any difference between the two local times should be noted when the tests are run and then provided together with the data so that the analysis can be done in a meaningful way. Specifically, the local times used by sender and receiver are simply retrieved with Ada.Calendar.Clock and then converted to unix style by subtracting from them the "epoch" (0 on 1/1/1970).
  • The use of generic packages and of Ada.Calendar in UDP_Tester imposed a relaxation of restrictions upstream i.e. in the UDP and MT libs. Since the relaxation of those restrictions is again (just like the generics change) required for testing *only*, they are simply commented out as part of the changes included in the UDP_Tester .vpatch.

To obtain a working UDP_Tester, simply download the relevant set of .vpatch and .sig files and press with your favourite V5. The patches are available as usual on my Reference Shelf and linked from here as well, for your convenience:

At the moment I am running the above tester in both directions between a node in the UK and one in Uruguay so hopefully I'll soon have some data to look at!


  1. Follow the discussion in the logs as there is no better way to get the details than to actually read through the log. 

  2. M. Matsumoto and T. Nishimura, "Mersenne Twister: A 623-dimensionally equidistributed uniform pseudorandom number generator", ACM Transactions on Modelling and Computer Simulation Vol. 8, No. 1, January, pp.3-30, 1998. 

  3. If one really wants a default value, this could be perhaps added as a constant in the package and then used as such by the caller but I must say that I don't quite see the point of this. 

  4. It is of course possible to change the code so that the sender also runs in a loop and simply wakes up at given intervals and resends packages but I don't quite see any real benefit to doing it this way - on the contrary, I see benefit to *not* doing it this way, since cron tasks are quite perfect for this and even more robust (no idle time and guaranteed recovery even in more extreme cases such as computer reset). 

  5. NB: Using Keccak hashes, as per current republican standard for V-trees. 

September 23, 2018

Dressing Directions of Sorts

Filed under: Lyf, Young, old and oldest — Diana Coman @ 7:40 p.m.

Dressing up and dressing down used to be all nice and fine when such directions were at least clear and firm. But what does one do when up or down are much the same since all the world around is - apparently - flatly equal at all its points anyway? Well, as per adapted nursery rhyme, when they were up they dressed up and they were down they dressed down and when they were neither up nor down, they were... salad dressing.

Salads and directions aside, sartorial choices at 6 years of age can be interesting to watch - perhaps even more so, at a later time when they have been forgotten. And they can certainly swing from velvet and hat and shiny bow tie one day to apron and chef hat the next1:

victor_pizzaiolo
velvet_and_hat2


  1. Since it took me about 20 years to even start taking pictures, I can hope I'll also start using a decent camera sometime within the next 40 years or so. 

September 14, 2018

SMG.Comms Implementation - Chapter 1

Filed under: Coding, SMG_Comms — Diana Coman @ 11:02 a.m.

~ This is a work in progress towards an Ada implementation of the communication protocol discussed on Trilema four months ago. ~

As far as I know, there isn't any more recent discussion of the above specification, nor any other attempt at all at any sort of implementation. Consequently, this is the first ever attempt - a prototype at this stage rather than a reference implementation. Moreover, it's also a sort of double first, since it clearly requires a deeper knowledge of Ada than I ever needed before. My approach to this pile of unknown here is to simply start working on it and expose the path travelled from this very first attempt to the final product, mistakes and detours and pitfalls to come included. You are welcome to follow along, to help if you can, to question if you don't understand, to extract perhaps in doing so some benefit for yourself.

The first decision I had to make before I could even really attempt any sort of prototype implementation at all concerned the library to use for the actual network communication. Since GNAT is the de-facto republican Ada compiler1, the logical decision is to simply use GNAT's own library, GNAT.Sockets and avoid otherwise as much as possible introducing additional, external dependencies - I really can't see any reason to add even more code even indirectly. So then GNAT.Sockets it is and hooray for that - except that there doesn't seem to be much documentation about it other than the comments in g-socket.ads and g-socket.adb! Still, the .ads file has a rather detailed introduction of the package with some commented examples in there so definitely worth reading as a starting point especially since... there isn't any other starting point really.

The g-socket files reveal essentially that any data to be sent or received through GNAT.Sockets will have to be stored at one point or another in an entity of Ada.Streams.Stream_Element_Array type. The examples in the file (and most everything else I could find on the topic) really focus almost exclusively2 on TCP connections - I suspect one "should prefer" TCP over UDP simply like that and we are even past the point of discussing therefore UDP in any scant docs or something. Nevertheless, I don't prefer it: Eulora's protocol is rather specifically designed to be stateless and to keep communications as simple and clear as possible - for as long as UDP is enough for the job, I'd rather use it!

Rummaging a bit in the g-sockets files reveals happily that UDP with GNAT.Sockets is in fact quite straightforward: one simply needs to specify "Socket_Datagram" as mode for the socket when calling Create_Socket and then use directly the Send_Socket( socket, data, last, to_address) and Receive_Socket(socket, data, last, from_address) methods. As one would expect, there is no reliable connection established, no "stream" of send and receive but only sockets that allow independent "send" and "receive" calls - each of those could in principle use a different address even. A quick example - keep reading for a a full, working example - of a server and client working with a UDP socket looks like this:

 -- on server:
     -- create UDP socket
    Create_Socket( Sock, Family_Inet, Socket_Datagram );

    -- set options on UDP socket
    Set_Socket_Option( Sock, Socket_Level, (Reuse_Address, True));

    -- set address and bind
    Address.Addr := Any_Inet_Addr;
    Address.Port := Port_No; -- the port number that server is listening on
    Bind_Socket( Sock, Address );
    Receive_Socket( Sock, Data, Last, From );

 -- on client:
    Address.Port := Port_No; -- server's port number
    Address.Addr := Inet_Addr("127.0.0.1"); -- this should be server's address here!
    Create_Socket(Sock, Family_Inet, Socket_Datagram);

    Send_Socket(Sock, Data, Last, Address);

With the very basics of the sockets part at least in place, the next part to decide on is how to send and receive over those sockets the actual data types defined by the protocol. After reading quite a bit on the Systems Programming (an annex of the Ada standard and therefore compiler-dependent) part of Ada (that is relevant for data representation) and on streams and on representation clauses and pragmas supported by GNAT and records and discriminants for records and everything else from the Ada reference book3 that I thought could help with this, I got to the conclusion that I'll keep it simple and clear especially for now, while I'm just starting to figure it all out! So I'll simply use GNAT's fixed width types defined in the Interfaces package and I'll copy otherwise the raw octets from and to those types using Ada.Unchecked_Conversion that works as far as I understand it precisely as a raw copy from memory. Once the data is simply obtained as a vector of raw octets, I can implement two simple functions to copy them into the Stream_Element_Array structure that can be sent directly through the UDP socket. Moreover, at this stage - and at this stage *only* - I'll worry about potentially different endianness of the local machine and the network: if local environment is little endian, the methods converting to and from network format will simply read the octets in reverse order. The relevant basic types and conversion methods are defined in the smg_comms_types.ads file:

 -- S.MG, 2018
 -- prototype implementation of S.MG communication protocol

with Ada.Streams; use Ada.Streams;
with Interfaces; use Interfaces; -- Integer_n and Unsigned_n
with Ada.Unchecked_Conversion; -- converting int/uint to array of octets

package SMG_comms_types is
  -- basic types with guaranteed lengths
  type Octet_Array is array(Natural range <>) of Unsigned_8;

  subtype Octets_1 is Octet_Array( 1 .. 1 );
  subtype Octets_2 is Octet_Array( 1 .. 2 );
  subtype Octets_4 is Octet_Array( 1 .. 4 );
  subtype Octets_8 is Octet_Array( 1 .. 8 );

  subtype Message is Octet_Array( 1 .. 512 );
  subtype RSAMessage is Octet_Array( 1 .. 245 );

  -- blind, unchecked casts ( memcpy style )
  function Cast is new Ada.Unchecked_Conversion( Integer_8, Octets_1 );
  function Cast is new Ada.Unchecked_Conversion( Octets_1, Integer_8 );
  function Cast is new Ada.Unchecked_Conversion( Integer_16, Octets_2 );
  function Cast is new Ada.Unchecked_Conversion( Octets_2, Integer_16 );

  function Cast is new Ada.Unchecked_Conversion( Integer_32, Octets_4 );
  function Cast is new Ada.Unchecked_Conversion( Octets_4, Integer_32 );

  function Cast is new Ada.Unchecked_Conversion( Integer_64, Octets_8 );
  function Cast is new Ada.Unchecked_Conversion( Octets_8, Integer_64 );

  -- to and from streams for network communications - general
  procedure ToNetworkFormat(
      Item   : in Octet_Array;
      Buffer : out Stream_Element_Array);

  procedure FromNetworkFormat(
      Buffer : in Stream_Element_Array;
      Item   : out Octet_Array);

  -- specific, convenience methods for the basic types
    -- Integer_8
  procedure ToNetworkFormat(
      Item   : in Integer_8;
      Buffer : out Stream_Element_Array);

  procedure FromNetworkFormat(
      Buffer : in Stream_Element_Array;
      Item   : out Integer_8);

end SMG_comms_types;

As you can easily notice, the above does not yet cover fully even the 3.0 "Basic types" part of the protocol specification. It's all right for now though - there is quite enough there for the first basic tests and once those are fine, I'll add gradually the rest of types too. There is little point in spending the time now to implement them all before I even got the chance to change my mind regarding *how* to implement them! So if you have a better implementation solution than the above, speak up in the comments section below and save me some time and a lot of headache! Note however that simplicity, clarity and hard guarantees are rather important here.

One small point on which I'm already rather undecided is whether to continue implementing the convenience methods for different types so that one can simply call ToNetworkFormat and FromNetworkFormat for anything or to leave only the generic methods at least for basic types. At the moment I incline towards providing all those methods (i.e. adding to the single pairof methods for the Integer_8 type defined above) because more complex types will likely need such methods anyway and moreover, this approach helps to keep all those casts (unchecked_conversion) in one place rather than scattered all through the rest of the code. However, it does add to the LOC count of this package. Anyway, moving further for now, the corresponding .adb file with the implementation of smg_comms_types:

  -- S.MG, 2018
  -- prototype implementation of S.MG communication protocol

with SMG_comms_types; use SMG_comms_types;
with System; use System; -- endianness
with Ada.Exceptions;
with Ada.Streams; use Ada.Streams;

package body SMG_comms_types is

  -- to and from network format (i.e. big endian, stream_element_array)
  procedure ToNetworkFormat(
      Item   : in Octet_Array;
      Buffer : out Stream_Element_Array) is
  begin
    if Item'Length /= Buffer'Length then
      raise Constraint_Error with "Item and Buffer lengths do NOT match!";
    end if;

    if Default_Bit_Order = Low_Order_First then
      for I in 0 .. Item'Length - 1 loop
        Buffer( Buffer'Last - Stream_Element_Offset(I) ) := Stream_Element(Item(Item'First + I));
      end loop;
    else
      for I in 0 .. Item'Length - 1 loop
        Buffer( Buffer'First + Stream_Element_Offset(I) ) := Stream_Element(Item(Item'First + I));
      end loop;
    end if;
  end ToNetworkFormat;

  procedure FromNetworkFormat(
      Buffer : in Stream_Element_Array;
      Item   : out Octet_Array) is
  begin
    if Item'Length /= Buffer'Length then
      raise Constraint_Error with "Buffer and Item length do NOT match!";
    end if;

    if Default_Bit_Order = Low_Order_First then
      for I in 0 .. Buffer'Length - 1 loop
        Item( Item'Last - I ) :=
          Unsigned_8( Buffer( Buffer'First + Stream_Element_Offset( I ) ) );
      end loop;
    else
      for I in 0 .. Buffer'Length - 1 loop
        Item( Item'First + I ) :=
          Unsigned_8( Buffer( Buffer'First + Stream_Element_Offset( I ) ) );
      end loop;
    end if;
  end FromNetworkFormat;

  -- Integer_8
  procedure ToNetworkFormat(
      Item   : in Integer_8;
      Buffer : out Stream_Element_Array) is
  begin
    ToNetworkFormat( Cast( Item ), Buffer );
  end ToNetworkFormat;
  procedure FromNetworkFormat(
      Buffer : in Stream_Element_Array;
      Item   : out Integer_8) is
    octets: Octets_1;
  begin
    FromNetworkFormat(Buffer, octets);
    Item := Cast( octets );
  end FromNetworkFormat;

end SMG_comms_types;

Something that irks me every time I look at the above: those for loops that convert octet by octet to Stream_Element. This is not only ugly but also rather inefficient, especially given that it's potentially the *second* time when those octets are read one by one (the first time being at the conversion from a protocol type - especially one of the more complex types - to an array of octets). However, I have no idea how to do that conversion from array of octets to array of Stream_Element in one single move! Do you know a better way to do this? A direct assign fails because the cast from one type to another would be on the array type rather than individual elements type. And I'm rather reluctant to work directly with Stream_Element as the basic type because this type is implementation dependent and outside my direct control - so I can't actually really know *what* it is.

The above being said regarding Stream_Element, it is important to note that the code above (and almost all the code for a network communication protocol) is anyway, strictly speaking, rather tightly linked to GNAT since it relies on Stream_Element being exactly 8 bits long. And to make this clear, here is the full trail I followed to make sure that I can indeed simply convert an octet (i.e. 8 bits) to a Stream_Element and the other way around while preserving exactly the number of bits specified in the protocol for each type: first, GNAT implements Stream_Element in a-stream.ads as follows:

type Stream_Element is mod 2 ** Standard'Storage_Unit;

Then, the definition of Standard'Storage_Unit for GNAT, which reads that Standard'Storage_Unit always has, according to the GNAT reference manual, the same value as System.Storage_Unit. In turn, System.Storage_Unit is indeed declared in GNAT's system.ads as a constant with value 8, so a Stream_Element in GNAT will indeed have exactly 8 bits:

Storage_Unit : constant := 8;

Moving on, the next step is to write the client-server part even if only a test version for now. Initially I took the easy way out here and simply wrote the separate server and client, each listening/sending one single packet. Running those on different machines worked perfectly fine. This is both fine and needed for a reasonable basic test of the whole thing, sure. However, at the moment as I'm just starting on this I'd rather *not* faff about with 2 machines each and every time I change or add something to this prototype protocol implementation. Moreover, this server/client part is perfect to experiment as well with threads4 in Ada - a topic that I'm still struggling to learn so perfect to practice! Therefore, in the basic test, server and client are implemented as different tasks (Ada's "threads") of the same main program - obviously, it follows that client and server will send data to one another on the same, local machine. This is of course not ideal nor sufficient as test in the long term but it'll do nicely for now and until the basic layer of the protocol at least is more fleshed out. The code in test_comms.adb:

 -- S.MG, 2018
 -- prototype implementation of S.MG communication protocol

with GNAT.Sockets; use GNAT.Sockets;
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Streams; use Ada.Streams;
with Interfaces; use Interfaces;

with SMG_comms_types; use SMG_comms_types;

procedure test_comms is
  Port_No : constant := 2222;

  task type Client is
    entry Send;
  end Client;

  task type Server is
    entry Listen;
    entry Ready;
  end Server;

  task body Client is
    Sock: Socket_Type;
    Address: Sock_Addr_Type;
    Data: Ada.Streams.Stream_Element_Array(1..10) := (others => 42);
    Last: Ada.Streams.Stream_Element_Offset;
    N   : Integer_8 := -36;
  begin
    accept Send; -- task WILL block here until asked to send
    Address.Port := Port_No;
    Address.Addr := Inet_Addr("127.0.0.1");
    Create_Socket(Sock, Family_Inet, Socket_Datagram);

    ToNetworkFormat( N, Data(1..1));
    Send_Socket(Sock, Data, Last, Address);
    Put_Line("Client sent data " & "last: " & Last'Img);
  end Client;

  task body Server is
    Sock: Socket_Type;
    Address, From: Sock_Addr_Type;
    Data: Ada.Streams.Stream_Element_Array(1..512);
    Last: Ada.Streams.Stream_Element_Offset;
    N : Integer_8;
  begin
    accept Listen; -- wait to be started!
    Put_Line("Server started!");
    -- create UDP socket
    Create_Socket( Sock, Family_Inet, Socket_Datagram );

    -- set options on UDP socket
    Set_Socket_Option( Sock, Socket_Level, (Reuse_Address, True));
    Set_Socket_Option( Sock, Socket_Level, (Receive_Timeout, Timeout => 10.0));

    -- set address and bind
    Address.Addr := Any_Inet_Addr;
    Address.Port := Port_No;
    Bind_Socket( Sock, Address );

    accept Ready; -- server IS ready, when here
    -- receive on socket
    begin
      Receive_Socket( Sock, Data, Last, From );
      Put_Line("last: " & Last'Img);
      Put_Line("from: " & Image(From.Addr));
      Put_Line("data is:");
      for I in Data'First .. Last loop
        FromNetworkFormat(Data(I..I), N);
        Put_Line(N'Image);
      end loop;
    exception
      when Socket_Error =>
      Put_Line("Socket error! (timeout?)");
    end;  -- end of receive

  end Server;

  S: Server;
  C: Client;
begin
  S.Listen;
  S.Ready; -- WAIT for server to be ready!
  C.Send;  -- client is started only after server!
end test_comms;

Tasks in Ada can be defined as types as above. This is not mandatory - one can equally well simply define the tasks and they'll run in parallel with the main begin-end block. However, Task types are effectively needed if one wants to be able to explicitly and potentially dynamically create several workers of the same type. Since I'll need this later for sure, I might as well practice it at any occasion, so there they are, the Client Task type and Server Task type. To make sure that the server is ready *before* the client sends anything, I'm using the rendez-vous communication method that Ada provides: each "entry" of a task is basically a rendez-vous point between the task itself that "accepts" that entry at some specified point in its body and a caller task that "calls" that entry from outside. The main body of test_comms illustrates this: S and C start in parallel with the main body of test_comms but they both stop almost immediately as they wait on their first rendez-vous points (accept Listen for the Server type and accept Send for the Client type). The main body first calls S.Listen, effectively releasing the S (Server type) task from its wait. Immediately after that, the S.Ready entry is called so that now the main body is actually waiting for S to get to its "Ready" entry - basically to finish setting up the socket. Once S got to its Ready entry, the main body can go further and the next statement calls C.Send that releases the client for its wait. The client will send therefore its data and promptly finish, while the server (that was running in parallel all this time) will finally receive the data, process it and finish as well. Go ahead, give it ago and let me know if there's anything funny going on!

To compile all the above with one neat gprbuild call, there is of course a .gpr file:

-- S.MG, 2018
 -- prototype implementation of S.MG communication protocol
 -- http://trilema.com/2018/euloras-communication-protocol-restated/

project SMG_comms is
  for Languages use ("Ada");

  for Source_Dirs use ("src");
  for Ignore_Source_Sub_Dirs use (".svn", ".git", "@*");

  for Object_Dir use "obj";
  for Exec_Dir use ".";

  for Main use ("test_comms.adb");

  package Builder is
    for Executable ("test_comms.adb") use "test_comms";
  end Builder;

  package Compiler is
    for Default_Switches ("Ada") use ("-O2");
  end Compiler;

end SMG_comms;

An example of running the test_comms executable produced by gprbuild:

smg_comms$ ./test_comms
Server started!
Client sent data last:  10
last:  10
from: 127.0.0.1
data is:
-36
 42
 42
 42
 42
 42
 42
 42
 42
 42
smg_comms$

On a slightly different note, I had a bit of an internal debate on whether it's appropriate or not to still release this as a V tree given that it's work in progress and absolutely nowhere near a reference object of any sort or even a fully working item. I came to view V however as simply a versioning system rather than a "set in stone only the end products" sort of thing - for that matter what end products anyway, it's at most, in the happiest of situations, seed products rather than end products. So all the above code is the genesis of smg_comms and it's simply a tiny, far from perfect seed that will hopefully grow into something useful while preserving in its v-tree the whole history of that growth:


  1. Due to a large extent to ave1's work on forcing it into some useful shape so that it builds on a sane, musl-based system. 

  2. The Socket_Datagram mode to be set for UDP communications is at least mentioned in the examples although the rest of differences in effectively comunicating something are left to be discovered. 

  3. My Ada reference book is Barnes, John, "Programming in Ada 2012", Cambridge University Press, 2016, ISBN 978-1-107-42481-4. 

  4. On-demand, resilient threads are crucial for Eulora's server and I'm not yet confident at all that I really fully grasp Ada's mechanisms so I'm pushing it to the front, reading on it and otherwise banging my head on it at any and all occasions - how else to figure it out faster? 

September 13, 2018

Atunci ca si acum ca-ntotdeauna

Filed under: Lyf — Diana Coman @ 11:27 a.m.

Pentru ca unele lucruri chiar nu se schimba indiferent cat calatoresti in timp, in spatiu ori in alte dimensiuni de nici nu-s descoperite inca, pun aici cuvintele cele adevarate, sa fie de referinta1 adica sa am unde trimite tinerele sperante pline de... a-vant :

reclama_oua_1944


  1. Autorul original - al reclamei ori al imaginii scanate macar - nu-l stiu si n-am reusit sa-l descopar ca altminteri circula imaginea dar nu zice nimeni nimic ca de unde a luat-o sau a gasit-o sau cum e. Eu de gasit am gasit-o pentru ca am cautat-o anume, dar nu-i in nici un caz feisbuc acum sursa la asa ceva. Daca stiti anume cine a scanat imaginea si unde, ziceti la comentarii aici.  

September 4, 2018

Pura Vida Like No Other

Filed under: Tgdyk tgdyk — Diana Coman @ 9:11 p.m.

Costa Rica is this enchanted land that has it all: balmy1 weather, sunny skies, warm waters, lush hills and heady mountains, cheeky monkeys and cute crabs, the friendliest people you ever saw and a very good dose of pura vida. This pura vida is the locals' own version of happiness, honey and spice and all the things nice and it really looks quite like this:

crocodilii_zambitori

There, have you ever seen that wonder before? The very smiley crocodiles of Costa Rica! And not only very smiley, but very friendly too for they won't eat those fish that swim - happily, pura vida! - around their tails. It's true that the smile is just a way to soak in more sun and it's true that fish are simply not worth the bother for those two very full crocodiles. Nevertheless, just try and convince those fish of such ugly thoughts and that crocodiles aren't really just being friendly and nice and good neighbours and all that - you psycrocopat!

Fish aside, if you look carefully at those tico crocodiles, you might notice also something else: the one on the shore has a rather short tail and the one in the water is missing the front paws entirely, now how could that be, how could such horrible things happen in this land of beauty, calm and sunshine? Well, they didn't happen through malice and ugly intent, no; they happened through... ineptitude, ain't that much better? In short, one crocodile insisted on fighting with those who were better at it and a bit of tail lost here and there did not make it change behaviour for it couldn't possibly change - it just was. The other crocodile kept eating some farmer's cattle and the farmer was very friendly and humane so he didn't kill the crocodile - he just chained it so well and so competently that the chains entirely destroyed its front paws essentially ensuring the crocodile would starve left by itself as it can't really swim properly anymore and it can't really move much on land anymore either. Don't you love those kind hearted people that won't kill an animal even when it's a pest?

Happily though, Costa Rica certainly has much more than crocodiles and it turns out I really actually quite like its birds, from owls and mini-eagles to tiny parrots. For they are not even just any birds really but the most curious and rather intelligent birds - some would literally come to check you out, to see for themselves from up close this weird huge bird that won't fly and is not even coloured properly with some real contrast! And even from a cage2, one toucan bird came to say hi and have an upside down look, perhaps that way it might - who knows! - make head and tail of me:

A very curious Toucan bird saying hi.

When speaking of animals of Costa Rica, one can easily go on for ages. There are also owls of various sorts and macaws and parrots and snakes and monkeys and crabs and iguanas and frogs and many others that I don't even really know the name of. And almost everything is either brightly coloured or otherwise well camouflaged in dull sandy colours. Tiny crabs will vanish in the sand as soon as they realise that you spotted them and small pebbles will suddenly wake up and start moving as soon as you went past them. From the trees above, monkeys will suddenly dart down and grab anything they find - whether they need it or not is something they don't bother asking themselves until after they got it since dropping stuff from high up comes at no cost whatsoever to them. From under the rocks below, iguanas and all sorts of other reptiles will come out in the morning and take their favourite place for soaking sun up. And from all sides, the ocean will brush the shore rather savagely with a strong push of breaking foam and an even stronger suck of waters back, sand and shells and anything else included. It's only in smaller, mini-gulf areas that are protected between rocks where waves are broken way before they make it to the shore so that they end up as tiny, gentle ripples only. A bit like that everywhere - in smaller, protected areas, the ocean may seem more like a little sea and the world may seem more like a fairytale.

But let's come back to the kind, friendly and totally innocent people of Costa Rica for what would the land and all the wondrous nature even be without the people! Ticos are truly friendly beyond anything you've likely ever saw - the whole country really feels more like one big village where one knows if not everyone else then surely someone who knows someone and so on until... one feels and pretty much acts like one knows everyone else. And just like in one big village, nobody bothers with street names or house numbers or indeed addresses of any kind - everyone is expected to also know where everything is or at best ask for ...directions on how to get there! So your address ends up being not a short ugly thing such as street name and house number but a long and rather intricate description of how to get there with approximate 100 metres before this and 1km towards that and past the one but before the other and green gate3 on the left but not first but second! And you'd think given this habit that they would have at least the basic idea to keep gate colours as diverse as possible at least within short distances or if not that then the pride to make each of their houses properly stand out with some crazy, unique and obvious - even monstruous if need be - thing at the gate! No, not the friendly, innocent ticos, why would they do such a thing? So no, not much in terms of specific or unique for houses and no attention whatsoever to street names or numbers even when they exist. For everyone knows where everything is and directions are just as good as addresses, remember?

Weirdly enough, the direction-instead-of-address even works of sorts - it works that is most of the time, for it requires of course a local to know where all sorts of small shops, car dealers and weird deposits actually are. If you are not a local or your driver is not a local4 then you are lost anyway, directions or no directions. And so you... ask of course and you get an answer - there's always an answer - but that doesn't mean it is the *right* answer! For you see, they want to be helpful and they won't let such small things as not being able to help stand in the way of their wish to be helpful!

At times however it's true that their being helpful is helpful indeed - especially at times when one didn't even imagine there would be a need for any sort of help! After witnessing a lot of the local traffic, I'd say I would probably need local help even with that - and in all fairness, I really preferred to rely on local hired help for all the driving. Even so, it took me some time to realise that they really honked their horn every time they came close to a crossing of roads - traffic lights or no traffic lights, it does seem in hindsight that one would do well to announce they are coming since nobody bothers necessarily with street markings, signs or indeed lights of any kind. And then the traffic jams and the unexpected turns or stops or what have you. The pedestrians walking on the motorway, the vehicles of all descriptions and no descriptions. After tico traffic, I surprised myself after landing in London since I spent the time admiring from my taxi the ordered progress of british cars along the roads - even now that I write it, I can't quite believe it but at the time it had a certain attraction given the stark contrast of previous days.

At any rate, in terms of getting one out of the trouble that is purely local, there is indeed nobody better apt than a local to help. Imagine this little wonder of a direct bus going straight from the capital San Jose all the way to Manuel Antonio national park, on the Pacific coast. Everything nice and tidy and even ordered by tico standards with seats numbered and even assigned by those same numbers - I honestly wonder why wouldn't they give the seat the same style as the addresses sort of walk about 5 steps and then 2nd on the right with the pink arm rest or something. So taking the bus from San Jose is basically no trouble at all, there's a bus terminal and a ticket station and the bus even leaves on time, goes as stated, arrives on time! But then, at the other end, in Manuel Antonio, they don't sell tickets *at all* - you need to go instead some 10km away to the little town of Quepos to buy any tickets because.... well, I don't know, apparently nobody thought that someone would actually want to take the bus back, going away from Manuel Antonio! Or perhaps tickets are really too advanced for selling in anything smaller than Quepos and what does it matter that the bus really leaves from somewhere else?

But let not any of those small details of ineptitude spoil anything for you - pura vida, remember? People are happy and friendly and monkeys are noisy and a bit of a pest and overall everything is perfect, especially as long as you don't really try to change it. Oh, and to make that clear, there is of course cultural life too and even one that depicts - rather truthfully I'd say - the local pura vida from at least one angle if a rather... obtuse angle:
costa_rican_gone_with_the_wind

In other rather greedy recollections, there'd be of course the rum, notwithstanding the fact that it's venezuelan, not costa rican at all. But even before that and certainly more local than that, there is the cocoa and therefore the chocolate that is simply delicious. And the coffee that is so good that even I - who don't really drink much coffee otherwise - still drank coffee in Costa Rica at pretty much any opportunity without any regrets or second thoughts. A certain fig cake there is delicious and some cocktails can be enormous. Some of them really are in fact more like semi-liquid icecreams with alcohol poured in - for better or worse. The fish is always good and - if you ask them to leave the darned salt out of it - well cooked almost always. The local fruit is about 10 times better than anything of same sort I ate anywhere else and I say this although I don't really like unfortunately exotic fruit - to give you some idea, the pineapple there is simply too ... sweet for me! I'm weird like that though and other than the fact that I just don't much like those particular fruits there's otherwise nothing to hold against costa rican avocado, pineapple, mango, coconuts and papayas.

Even in spite of all the monkeys and racoons and iguanas and whatever else the jungle harbours, the best part of it all is for me the water, of course. The warm water and the sun and the sand and all that joy that swimming or even simply jumping the waves can bring. Joy I said, not serenity, for the ocean I find doesn't hold much serenity at all, not with those huge waves, not with the rip current, serenity is just not an ocean thing despite the one thousand words all sorts of pictures might still whisper:

The Pacific ocean at Manuel Antonio, Costa Rica.
Manuel Antonio beach, Costa Rica.


  1. The notion is still debated really: what feels balmy for the first days turns out to be rather too hot after a few days and what feels hot away from water seems all of a sudden rather fine next to water so don't take my word for it - use your own thermometer!  

  2. While I saw toucan birds in the wild too, I couldn't quite get a clear picture of one in the wild, sadly. 

  3. Porton Verde - this is now a character in my house, the Porton Verde! 

  4. We had once this taxi driver from the capital who insisted they knew the place when I asked before getting in and then of course, they didn't but they had no problem with it since in their mind I could just act as a GPS, why not? I really don't recall getting that annoyed with a taxi driver in ages and just like last time more than 10 years ago it ended in just asking them to stop exactly there and then taking another taxi, yes, what else. 

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