Module Fd

module Fd: sig .. end

This module implements miscellaneous functions related to UNIX file descriptors. Currently, the functions listed below are implemented.

Fd.send_fd and Fd.recv_fd, which are respectively used to send and receive descriptors. Tipically, this functionality is used to allow a process to perform all the actions needed to acquire a descriptor, which is then sent to another process, which will then handle the data transfer operations on that descriptor.
Fd.fexecve, which is used to execute a program specified via a file descriptor.

exception Fd_error of string

This exception is raised by Fd.send_fd and Fd.recv_fd when an error is encountered. The string contains the error message.

val send_fd : conn:Unix.file_descr -> fd:Unix.file_descr -> unit

This function sends a descriptor over a Unix socket whose peer may be another process. The peer must receive the file descriptor with the function Fd.recv_fd defined in this module.

The descriptor is sent as a sized message, so the user application may use the connection to other communication needs.
Raises Fd_error This exception is raised on error.

conn : The connection through which the descriptor will be sent.

fd : The descriptor to be sent.

val recv_fd : conn:Unix.file_descr -> Unix.file_descr

This function receives a descriptor sent by Fd.send_fd.
Raises Fd_error This exception is raised on error.
Returns The received file descriptor.

conn : The connection through which the descriptor will be received.

val fexecve : fd:Unix.file_descr -> args:string array -> env:string array -> 'a

This function works like Unix.execve, but the program to be executed, its first paramenter, is specified via a file descriptor. As is the case with the Unix.execv* functions, Fd.fexecve never returns. If the call succeeds, the current process is substituted by the new one.
Raises Fd_error This exception is raised on error.

fd : The file descriptor corresponding to the program to be executed.

args : An array of arguments to be passed to the program.

env : The environment to the program.

val read_cred : fd:Unix.file_descr -> int * int * int

This function reads sender credentials from a descriptor. The descriptor must be associated to a UNIX socket. Currently only Linux is supported.
Raises Fd_error This exception is raised on error.
Returns A tuple of integers containing the sender PID, UID and GID.

fd : The file descriptor to read the credentials from.