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119 lines
5.2 KiB
Groff
119 lines
5.2 KiB
Groff
.\" **************************************************************************
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.\" * _ _ ____ _
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.\" * Project ___| | | | _ \| |
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.\" * / __| | | | |_) | |
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.\" * | (__| |_| | _ <| |___
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.\" * \___|\___/|_| \_\_____|
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.\" *
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.\" * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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.\" *
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.\" * This software is licensed as described in the file COPYING, which
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.\" * you should have received as part of this distribution. The terms
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.\" * are also available at https://curl.se/docs/copyright.html.
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.\" *
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.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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.\" * copies of the Software, and permit persons to whom the Software is
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.\" * furnished to do so, under the terms of the COPYING file.
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.\" *
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.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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.\" * KIND, either express or implied.
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.\" *
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.\" * SPDX-License-Identifier: curl
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.\" *
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.\" **************************************************************************
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.TH libcurl 3 "10 Sep 2018" "libcurl" "libcurl"
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.SH NAME
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libcurl-ws \- WebSocket interface overview
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.SH DESCRIPTION
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The WebSocket interface provides functions for receiving and sending WebSocket
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data.
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.SH INCLUDE
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You still only include <curl/curl.h> in your code.
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.SH SETUP
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WebSocket is also often known as \fIWebSockets\fP, in plural. It is done by
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upgrading a regular HTTP(S) GET request to a WebSocket connection.
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WebSocket is a TCP-like message-based communication protocol done over HTTP,
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specified in RFC 6455.
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To initiate a WebSocket session with libcurl, setup an easy handle to use a
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URL with a "WS://" or "WSS://" scheme. "WS" is for cleartext communication
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over HTTP and "WSS" is for doing WebSocket securely over HTTPS.
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A WebSocket request is done as an HTTP/1 GET request with an "Upgrade
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WebSocket" request header field. When the upgrade is accepted by the server,
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it responds with a 101 Switching and then the client can speak WebSocket with
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the server. The communication can happen in both directions at the same time.
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.SH MESSAGES
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WebSocket communication is message based. That means that both ends send and
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receive entire messages, not streams like TCP. A WebSocket message is sent
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over the wire in one or more frames. Each frame in a message can have a size
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up to 2^63 bytes.
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libcurl delivers WebSocket data as frame fragments. It might send a whole
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frame, but it might also deliver them in pieces depending on size and network
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patterns. It makes sure to provide the API user about the exact specifics
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about the fragment: type, offset, size and how much data there is pending to
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arrive for the same frame.
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A message has an unknown size until the last frame header for the message has
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been received since only frames have set sizes.
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.SH "Raw mode"
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libcurl can be told to speak WebSocket in "raw mode" by setting the
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\fBCURLWS_RAW_MODE\fP bit to the \fICURLOPT_WS_OPTIONS(3)\fP option.
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Raw WebSocket means that libcurl passes on the data from the network without
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parsing it leaving that entirely to the application. This mode assumes that
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the user of this knows WebSocket and can parse and figure out the data all by
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itself.
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This mode is intended for applications that already have a WebSocket
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parser/engine that want to switch over to use libcurl for enabling WebSocket,
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but keep parts of the existing software architecture.
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.SH PING
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WebSocket is designed to allow long-lived sessions and in order to keep the
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connections alive, both ends can send PING messages for the other end to
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respond with a PONG.
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libcurl automatically responds to server PING messages with a PONG. It does
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not send any PING messages automatically.
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.SH MODELS
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Because of the many different ways WebSocket can be used, which is much more
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flexible than limited to plain downloads or uploads, libcurl offers two
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different API models to use it:
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1. Using a write callback with \fICURLOPT_WRITEFUNCTION(3)\fP much like other
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downloads for when the traffic is download oriented.
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2. Using \fICURLOPT_CONNECT_ONLY(3)\fP and use the WebSocket recv/send
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functions.
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.SH "Callback model"
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When a write callback is set and a WebSocket transfer is performed, the
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callback is called to deliver all WebSocket data that arrives.
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The callback can then call \fIcurl_ws_meta(3)\fP to learn about the details of
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the incoming data fragment.
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.SH "CONNECT_ONLY model"
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By setting \fICURLOPT_CONNECT_ONLY(3)\fP to \fB2L\fP, the transfer only
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establishes and setups the WebSocket communication and then returns control
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back to the application.
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Once such a setup has been successfully performed, the application can proceed
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and use \fIcurl_ws_recv(3)\fP and \fIcurl_ws_send(3)\fP freely to exchange
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WebSocket messages with the server.
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.SH AVAILABILITY
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The WebSocket API was introduced as experimental in 7.86.0 and is still
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experimental today.
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It is only built-in if explicitly opted in at build time. We discourage use of
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the WebSocket API in production because of its experimental state. We might
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change API, ABI and behavior before this "goes live".
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.SH "SEE ALSO"
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.BR curl_easy_init (3),
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.BR curl_ws_meta (3),
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.BR curl_ws_recv (3),
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.BR curl_ws_send (3),
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.BR CURLOPT_CONNECT_ONLY (3),
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.BR CURLOPT_WRITEFUNCTION (3),
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.BR CURLOPT_WS_OPTIONS (3)
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