A simple program for sending/receiving files/text on a local network.

Commands:

l/ls/list
p/pub/publish [<TOPIC>]
up/unpublish <TOPIC>
s/sub/subscribe <TOPIC>
us/unsubscribe <TOPIC>
o/path <DOWNLOAD_PATH>
q/quit

Packet formats:

if (MessageType::PUBLISH && (SubMessageType::TEXT || SubMessageType::FILE_PIECE)):
    MessageType (1 byte)
    | Topic Length (1 byte)
    | Topic ("Topic Length" bytes)
    | SubMessageType (1 byte)
    | Port (4 bytes) (that this publisher listens on for TCP connection)
    | Random ID Number (4 bytes) (unique)

if (MessageType::REQUEST):
    MessageType (1 byte)
    | Topic Length (1 byte)
    | Topic ("Topic Length" bytes)
    | ID Number (4 bytes) (corresponding to the id in the PUBLISH message)

if (MessageType::TEXT):
    MessageType (1 byte)
    | Index (4 bytes) (needed when splitting the TEXT into multiple packets)
    | Length (4 bytes)
    | Text ("Length" bytes)

if (MessageType::FILE_INFO):
    MessageType (1 byte)
    | Name Length (4 bytes)
    | Name ("Name Length" bytes)
    | TotalFileLength (8 bytes)
    | HashType (1 byte) (can NOT be HashType::NONE)
    | Hash-digest (of whole file) (x bytes)
    
if (MessageType::FILE_PIECE):
    MessageType (1 byte)
    | Index (4 bytes)
    | Length (4 bytes)
    | PieceContent ("Length" bytes)
    | HashType (1 byte)
    | Hash-digest (of this piece) (x bytes) (can be zero bytes if HashType::NONE)
    
if (MessageType::YES || MessageType::NO || MessageType::DONE):
    MessageType (1 byte)

Communication:

*** FILE COM ***
A                   B
Publish ->          (Subscribe)
(Publish ->)        Subscribe
                    <- Request
File_info ->
                    <- Yes
    File_piece ->
    ...
    Done ->
File_info ->        
                    <- No
...
Done ->

*** TEXT COM ***
A                   B
Publish ->          (Subscribe)
(Publish ->)        Subscribe
                    <- Request
Text ->
...
Done ->

TODO:

• Compression of files
• Encryption (tls or quic)