fragmented-tcp

Implementation of fragmented tcp server and client.

Requirements

Go 1.17+

Usage

make build - Build application (default goal) make test - Run tests

Low level protocol

Each message from and to server consists of 2 parts.

First 2 bytes is a length of packet;
All other bytes is a packet.

Example in hex:

Length (2 bytes)	Content (x bytes)	Decoded
00 02	41 42	AB
00 03	41 42 41	ABA

High level protocol

The protocol which should be used for communication between clients. The protocol contatins always one or several octets of strings separated by space. The first octet of protocol always is type of message on which application can build its behaviour. Responses on each command will be OK or ERROR:

OK <PARAMETER> - means that command evaluated successfully. <PARAMETER> - dynamic parameter depending on kind of command. See each commands for details.

ERROR <REASON> - menas command has failed. <REASON> - what's happened.

PING/PONG message (Keep Alive)

The Server sends broadcast message PING to All clients each minute. The client should answer on PING message by PONG message that means he's online.

HI message.

When Client connects to the server he should send first hi message:

HI <NAME>

HI is a command means authrization message;
<NAME> is the name of the client or client's id. Not possible to use spaces in name.

There are reserved name for the Server broadcasting - SYSTEM. No one can take this name.

The response will be OK <NAME> or ERROR <REASON>.

Incoming messages

Since client is authorized (see Welcome message) he can receive broadcast messages:

MSG <FROM> <TEXT>

MSG is a command means incoming message;
<FROM> is the name of the client who sent the message;
<TEXT> is the text of message.

List of connected clients

Each client can ask the server about clients' names connected to the server.

CLIENTS

The response will include OK message with param contains names of clients connected to the server separated by new line \n character. Example:

Client1
Client2
Client3

Or an ERROR message with reason.

Send a private message.

Each client can send a message to some another client.

MSG <TO> <TEXT>

MSG is a command means sending a message;
<TO> is the name of the client to whom current client send a message;
<TEXT> is the text of message.

The response will be OK <TO> or ERROR <REASON>.

TODO

The max length of packet should be limited to prevent memory leaks;
Configurable timeouts on read packets;
Configurable timeouts on write packets.

timsolov/fragmented-tcp