https://github.com/moki/reliable-protocol-pop

P0P reliable protocol, implemented on top of the UDP
https://github.com/moki/reliable-protocol-pop

Last synced: about 2 months ago
JSON representation

P0P reliable protocol, implemented on top of the UDP

• Host: GitHub
• URL: https://github.com/moki/reliable-protocol-pop
• Owner: moki
• Created: 2019-07-01T07:50:53.000Z (almost 6 years ago)
• Default Branch: master
• Last Pushed: 2019-07-21T23:08:40.000Z (almost 6 years ago)
• Last Synced: 2025-02-10T08:46:49.665Z (4 months ago)
• Language: C
• Homepage:
• Size: 1.35 MB
• Stars: 0
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README

Awesome Lists containing this project

README

        
POP Reliable Protocol

Implementation of the reliable protocol on top of the UDP

Thread based implementation:

thread/server

thread/client

to spinup the server:

cd thread/server

make test

to perform multiple clients test:

cd thread/client

bash concurrent-clients-test.sh

both client and server provides classic usage info.

+--Specificationi--+

|     spec.pdf     |

+------------------+

POP Header:

 0		     1			 2		     3

 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|	      Magic		|    Version	|    Command	|

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|			Sequence Number				|

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|			   Session Id				|

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Magic:

0xC461/50273 decimal when taken as unsigned 16-bit(2 byte) int

in network byte order.

Packet whose first 2 bytes do not match magic - discarded.

Version:

8-bit(1 byte) protocol version, the value is 1.

Command:

Specifies message type, 8-bit(1 byte) value.

+------------+-------+------+-------+---------+

| Type	     | HELLO | DATA | ALIVE | GOODBYE |

+------------+-------+------+-------+---------+

| code point | 0     | 1    | 2     | 3       |

+------------+-------+------+-------+---------+

Sequence Number:

In messages sent by the client is 0 initially for the first packet of the

session, 1 for the next packet and so on. Server sequence numbers, simply

count up each time it sends something in any session.

Field size is 32-bit(4 bytes).

Session Id:

Arbitrary 32-bit(4 bytes) int, in network byte order. The client is to choose

its value at random when it starts. Both the client and the server repeat the

session id in all messages that are part of that session.

Multi byte values are sent big-endian, referred to as network byte order.

DATA Command Messages - POP Header is followed by data, data size can be

determined by subtracting POP Header length from the UDP packet length.

UPD packet contains only one POP Message, all POP Messages must in a single

UDP packet.

UDP packet size limit is 65535(2^16 - 1), which includes 8 byte header,

however actual data limit is imposed by IPv4 with its header size 20 bytes,

which gives us 65535(2^16 - 1) - 8 bytes - 20 bytes = 65507.

Therefore maximum data payload for a POP Message can be 65507 - 12 bytes

(POP Header) = 65495.

State Machine Keys:

Transition: 	State:

*---------*	+------------+

|  event  |	| state name |

| ------- |	+------------+

| actions |

*---------*

Server Session State Machine:

 			*---------------------------------*

			| 	       DATA	          |

			| ------------------------------- |

			| ALIVE; Cancel Timer; Set Timer  |

			*---------------------------------*

		       	 |				 |

 *------------------*	 |				 v

 | 	HELLO       |   +---------------------------------+

 | ---------------- |-->| 	     Receive	 	  |

 | HELLO; Set Timer |   +---------------------------------+

 *------------------*    |	  			 |

			 |				 |

		    *---------*			    *---------*

		    | Timeout |			    | GOODBYE |

		    | ------- |			    | ------- |

		    | GOODBYE |			    | GOODBYE |

            	    *---------*			    *---------*

			 |				 |

			 v				 v

		        +---------------------------------+

		        |	       Done	 	  |

		        +---------------------------------+

Set Timer    - sets the sessions expiration timer.

Cancel Timer - cancels sessions ongoing timer.

Timeout	     - session timed out.

Sessions created by the server after receiving HELLO message

with a new session id, if message is of other type

connection terminated.

Upon received DATA, client is made aware that session still up

with an ALIVE message.

Server session keeps track of the client sequence number it expects next.

Arriving Session packet sequence number should be seq(n - 1) + 1,

where n is the packet number.

* Sequence number for the packet is greater than expected one - "lost packet".

* Sequence number for the packet same as for the last one - "duplicate packet"

  and the packet is discarded.

* Sequence number for the packet less than the last one - protocol error,

  and the session is closed.

  (seq.nums. from the past, packets out of order)

Server receiving message, for which there is no transition in its current state

leads to protocol error, and closing of the session.

Client State Machine:

	  |

	  |

*------------------*

|		   |

| ---------------- |

| HELLO; Set Timer |						  *-------------*

*------------------*						  |    stdin    |

	  |							  | ----------- |

       *--*				     *-----------------*  |    DATA     |

       |				     |      stdin      |  *-------------*

       v				     | --------------- |  |             |

+------------+	*--------------*  +-------+  | DATA; Set Timer |  |             v

|            |  |    HELLO     |  |       |--*-----------------*->+-------------+

| Hello Wait |->| ------------ |->| Ready |			  | Ready Timer |

|	     |  | Cancel Timer |  |  	  |<-*-----------------*--+-------------+

*------------*  *--------------*  +-------+  |      ALIVE      |         |

       |			      |      | --------------- |         |

       |			      |	     |   Cancel Timer  |         |

       |			      |	     *-----------------*         |

       *---------*		  *---*		    *--------------------*

		 |		  |		    |

		 |		  |		    |

	*------------------* *----------* *------------------*

	| { Timeout, eof } | |   eof	| | { Timeout, eof } |

	| ---------------- | | -------- | | ---------------- |

	|      GOODBYE	   | | GOODBYE  | |      GOODBYE     |

	*------------------* *----------* *------------------*

		 |		  |		    |

		 |		  *-----*	    |

		 *------------------*   |   *-------*

				    |   |   |

				    |   |   |

				    |   |   |	*---------*

				    |   |   |	| GOODBYE |

				    v   v   v	| ------- |

			*-------*  +---------+  |	  |  +--------+

			| ALIVE |->|	     |--*---------*->|	      |

			| ----- |  | Closing |		     | Closed |

			|       |--|	     |--*---------*->|	      |

			*-------*  +---------+	| Timeout |  +--------+

						| ------- |

						|	  |

						*---------*

Client usually intiates session termination with a GOODBYE message.

However, if client receives a GOODBYE, it believes that the server is gone,

no matter what the client's current state, immediately transitioning to

the Closed State.

Client shutsdown upon eof, "q" from stdin or timeout.

Async event loop implementation:

async/server

async/client