Socket Application Programming Interface (API) implementation in xv6 Operating System of MIT which extends its functionality to support socket programming via localhost networking.

System calls (added):

• listen (localPort)
  This is for a server to listen to a local port for accepting client socket. Returns 0 for success, negative for failure.

• connect (remotePort, hostname)
  This is for a client to connect to remote port and host. Only "localhost" and "127.0.0.1" as host should be supported. Returns the local port number, if connection was successful. Negative values returned indicate failure.

• send (localPort, buffer, length)
  Sends a buffer to remote host connected to given localPort. Returns 0 for success. Negative values for failure. send() blocks, if remote host has not yet read earlier data

• recv (localPort, buffer, length)
  Receives data from remote host connected to given localPort. Returns 0 for success. Negative values for failure. recv() blocks, if no data is available.

• disconnect (localPort)
  Disconnects (and closes) the socket at given port number.

Limitations :

• a server can connect to only one client at a time
• send() or recv() will block the caller process, until the recipients buffer is ready.
• timeout cannot be specified in the listen() or recv() call

Demonstration:

• run this xv6 repo in qemu and a user program will show up in socktest

  make qemu

• in xv6 shell

  ls

  socktest

socktest user program demonstrates a simple client-server interaction where client takes user input from console and server echoes it back to client. If any error occurs corresponding error codes is returned.

Error codes:

E_NOTFOUND -1025
E_ACCESS_DENIED -1026
E_WRONG_STATE -1027
E_FAIL -1028
E_INVALID_ARG -1029
E_CONNECTION_RESET_BY_REMOTE -1030

Parameter issues would return E_INVALID_ARG.
Accessing a socket that is not in the stable then E_NOTFOUND.
Accessing a socket from wrong process then E_ACCESS_DENIED.
Attempts to send or receive, when the socket is not connected, then E_WRONG_STATE.
If no more socket can be opened (limit exceeded) E_FAIL.
If connection is reset during send or receive then E_CONNECTION_RESET_BY_REMOTE

Error codes are defined in "signalcodes.h"

This xv6 networking extension has been performed as an assignment of Operating System Sessional course in Level-3, Term-2 of Department of CSE, BUET.