# `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 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 on all interfaces:

    ?- 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 the `server_open/2-3` predicates, an available port will be selected and unified with the variable.

The `server_open/4` predicate can be used to accept a connection only on the given interface.

### 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(+Host, ?Port, -ServerSocket, +Options)` - Create a server socket on the given interface

- `server_open(?Port, -ServerSocket, +Options)` - Create a server socket on all interfaces

- `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`.