.. _library_sockets:

sockets

Portable abstraction over TCP sockets. Provides a high-level API for client and server socket operations that works across all supported backend Prolog systems: ECLiPSe, GNU Prolog, SICStus Prolog, SWI-Prolog, Trealla Prolog, and XVM.

Design rationale

Different Prolog systems provide socket functionality at different abstraction levels. Some backends (notably SICStus Prolog and Trealla Prolog) do not provide low-level socket creation predicates that can be separated from binding or connecting. This library therefore provides a higher-level API with predicates client_open/4-5 and server_open/2-3 that abstracts over these differences.

API documentation

Open the `../../apis/library_index.html#sockets <../../apis/library_index.html#sockets>`__ link in a web browser.

Loading

To load this library, load the loader.lgt file:

::

| ?- logtalk_load(sockets(loader)).

Testing

To test this library predicates, load the tester.lgt file:

::

| ?- logtalk_load(sockets(tester)).

Usage

Creating a client connection ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To connect to a server using default options:

::

?- socket::client_open(localhost, 8080, Input, Output).

The predicates client_open/4-5 and server_accept/4-5 return separate input and output streams. For backends where the same stream is used for bidirectional communication (SICStus Prolog and ECLiPSe), the same stream handle is returned in both arguments. Use socket::close/2 to close both streams when done.

Creating a server ~~~~~~~~~~~~~~~~~

To create a server that accepts connections using default options:

::

?- socket::server_open(8080, ServerSocket), socket::server_accept(ServerSocket, Input, Output, ClientInfo), % ... communicate with client using Input and Output ... socket::close(Input, Output), socket::server_close(ServerSocket).

If the port is passed as a variable to server_open/2-3, an available port will be selected and unified with the variable.

Getting the current host name ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

::

?- socket::current_host(Host).

API Summary

• client_open(+Host, +Port, -InputStream, -OutputStream, +Options) - Connect to a server
• client_open(+Host, +Port, -InputStream, -OutputStream) - Connect to a server using default options
• server_open(?Port, -ServerSocket, +Options) - Create a server socket
• server_open(?Port, -ServerSocket) - Create a server socket using default options
• server_accept(+ServerSocket, -InputStream, -OutputStream, -ClientInfo, +Options)
  • Accept connection
• server_accept(+ServerSocket, -InputStream, -OutputStream, -ClientInfo)
  • Accept connection using default options
• server_close(+ServerSocket) - Close a server socket
• close(+InputStream, +OutputStream) - Close a client or accepted connection
• current_host(-Host) - Get the current machine's hostname

Backend-specific notes

Stream representation

The library provides separate input and output stream arguments in
``client_open/4-5`` and ``server_accept/4-5``. For backends where the
same stream is used for bidirectional communication (ECLiPSe, SICStus
Prolog, and Trealla Prolog), the same stream handle is returned in both
the input and output arguments. For backends that use separate streams
(GNU Prolog and SWI-Prolog), separate stream handles are returned.

Binary and text modes

The library automatically sets streams by default to binary mode (e.g., for sending and receiving raw bytes). An option is supported for opening streams in text mode.

Known issues

Recent versions of macOS seem to disable the mapping of localhost to 127.0.0.1. This issue may prevent some functionality from working. This can be fixed either by editing the /etc/hosts file or by using '127.0.0.1' as the host argument instead of localhost.