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// Copyright 2013 The Gorilla WebSocket Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package websocket implements the WebSocket protocol defined in RFC 6455.
//
// Overview
//
// The Conn type represents a WebSocket connection. A server application calls
// the Upgrader.Upgrade method from an HTTP request handler to get a *Conn:
//
// var upgrader = websocket.Upgrader{
// ReadBufferSize: 1024,
// WriteBufferSize: 1024,
// }
//
// func handler(w http.ResponseWriter, r *http.Request) {
// conn, err := upgrader.Upgrade(w, r, nil)
// if err != nil {
// log.Println(err)
// return
// }
// ... Use conn to send and receive messages.
// }
//
// Call the connection's WriteMessage and ReadMessage methods to send and
// receive messages as a slice of bytes. This snippet of code shows how to echo
// messages using these methods:
//
// for {
// messageType, p, err := conn.ReadMessage()
// if err != nil {
// log.Println(err)
// return
// }
// if err := conn.WriteMessage(messageType, p); err != nil {
// log.Println(err)
// return
// }
// }
//
// In above snippet of code, p is a []byte and messageType is an int with value
// websocket.BinaryMessage or websocket.TextMessage.
//
// An application can also send and receive messages using the io.WriteCloser
// and io.Reader interfaces. To send a message, call the connection NextWriter
// method to get an io.WriteCloser, write the message to the writer and close
// the writer when done. To receive a message, call the connection NextReader
// method to get an io.Reader and read until io.EOF is returned. This snippet
// shows how to echo messages using the NextWriter and NextReader methods:
//
// for {
// messageType, r, err := conn.NextReader()
// if err != nil {
// return
// }
// w, err := conn.NextWriter(messageType)
// if err != nil {
// return err
// }
// if _, err := io.Copy(w, r); err != nil {
// return err
// }
// if err := w.Close(); err != nil {
// return err
// }
// }
//
// Data Messages
//
// The WebSocket protocol distinguishes between text and binary data messages.
// Text messages are interpreted as UTF-8 encoded text. The interpretation of
// binary messages is left to the application.
//
// This package uses the TextMessage and BinaryMessage integer constants to
// identify the two data message types. The ReadMessage and NextReader methods
// return the type of the received message. The messageType argument to the
// WriteMessage and NextWriter methods specifies the type of a sent message.
//
// It is the application's responsibility to ensure that text messages are
// valid UTF-8 encoded text.
//
// Control Messages
//
// The WebSocket protocol defines three types of control messages: close, ping
// and pong. Call the connection WriteControl, WriteMessage or NextWriter
// methods to send a control message to the peer.
//
// Connections handle received close messages by calling the handler function
// set with the SetCloseHandler method and by returning a *CloseError from the
// NextReader, ReadMessage or the message Read method. The default close
// handler sends a close message to the peer.
//
// Connections handle received ping messages by calling the handler function
// set with the SetPingHandler method. The default ping handler sends a pong
// message to the peer.
//
// Connections handle received pong messages by calling the handler function
// set with the SetPongHandler method. The default pong handler does nothing.
// If an application sends ping messages, then the application should set a
// pong handler to receive the corresponding pong.
//
// The control message handler functions are called from the NextReader,
// ReadMessage and message reader Read methods. The default close and ping
// handlers can block these methods for a short time when the handler writes to
// the connection.
//
// The application must read the connection to process close, ping and pong
// messages sent from the peer. If the application is not otherwise interested
// in messages from the peer, then the application should start a goroutine to
// read and discard messages from the peer. A simple example is:
//
// func readLoop(c *websocket.Conn) {
// for {
// if _, _, err := c.NextReader(); err != nil {
// c.Close()
// break
// }
// }
// }
//
// Concurrency
//
// Connections support one concurrent reader and one concurrent writer.
//
// Applications are responsible for ensuring that no more than one goroutine
// calls the write methods (NextWriter, SetWriteDeadline, WriteMessage,
// WriteJSON, EnableWriteCompression, SetCompressionLevel) concurrently and
// that no more than one goroutine calls the read methods (NextReader,
// SetReadDeadline, ReadMessage, ReadJSON, SetPongHandler, SetPingHandler)
// concurrently.
//
// The Close and WriteControl methods can be called concurrently with all other
// methods.
//
// Origin Considerations
//
// Web browsers allow Javascript applications to open a WebSocket connection to
// any host. It's up to the server to enforce an origin policy using the Origin
// request header sent by the browser.
//
// The Upgrader calls the function specified in the CheckOrigin field to check
// the origin. If the CheckOrigin function returns false, then the Upgrade
// method fails the WebSocket handshake with HTTP status 403.
//
// If the CheckOrigin field is nil, then the Upgrader uses a safe default: fail
// the handshake if the Origin request header is present and the Origin host is
// not equal to the Host request header.
//
// The deprecated package-level Upgrade function does not perform origin
// checking. The application is responsible for checking the Origin header
// before calling the Upgrade function.
//
// Buffers
//
// Connections buffer network input and output to reduce the number
// of system calls when reading or writing messages.
//
// Write buffers are also used for constructing WebSocket frames. See RFC 6455,
// Section 5 for a discussion of message framing. A WebSocket frame header is
// written to the network each time a write buffer is flushed to the network.
// Decreasing the size of the write buffer can increase the amount of framing
// overhead on the connection.
//
// The buffer sizes in bytes are specified by the ReadBufferSize and
// WriteBufferSize fields in the Dialer and Upgrader. The Dialer uses a default
// size of 4096 when a buffer size field is set to zero. The Upgrader reuses
// buffers created by the HTTP server when a buffer size field is set to zero.
// The HTTP server buffers have a size of 4096 at the time of this writing.
//
// The buffer sizes do not limit the size of a message that can be read or
// written by a connection.
//
// Buffers are held for the lifetime of the connection by default. If the
// Dialer or Upgrader WriteBufferPool field is set, then a connection holds the
// write buffer only when writing a message.
//
// Applications should tune the buffer sizes to balance memory use and
// performance. Increasing the buffer size uses more memory, but can reduce the
// number of system calls to read or write the network. In the case of writing,
// increasing the buffer size can reduce the number of frame headers written to
// the network.
//
// Some guidelines for setting buffer parameters are:
//
// Limit the buffer sizes to the maximum expected message size. Buffers larger
// than the largest message do not provide any benefit.
//
// Depending on the distribution of message sizes, setting the buffer size to
// to a value less than the maximum expected message size can greatly reduce
// memory use with a small impact on performance. Here's an example: If 99% of
// the messages are smaller than 256 bytes and the maximum message size is 512
// bytes, then a buffer size of 256 bytes will result in 1.01 more system calls
// than a buffer size of 512 bytes. The memory savings is 50%.
//
// A write buffer pool is useful when the application has a modest number
// writes over a large number of connections. when buffers are pooled, a larger
// buffer size has a reduced impact on total memory use and has the benefit of
// reducing system calls and frame overhead.
//
// Compression EXPERIMENTAL
//
// Per message compression extensions (RFC 7692) are experimentally supported
// by this package in a limited capacity. Setting the EnableCompression option
// to true in Dialer or Upgrader will attempt to negotiate per message deflate
// support.
//
// var upgrader = websocket.Upgrader{
// EnableCompression: true,
// }
//
// If compression was successfully negotiated with the connection's peer, any
// message received in compressed form will be automatically decompressed.
// All Read methods will return uncompressed bytes.
//
// Per message compression of messages written to a connection can be enabled
// or disabled by calling the corresponding Conn method:
//
// conn.EnableWriteCompression(false)
//
// Currently this package does not support compression with "context takeover".
// This means that messages must be compressed and decompressed in isolation,
// without retaining sliding window or dictionary state across messages. For
// more details refer to RFC 7692.
//
// Use of compression is experimental and may result in decreased performance.
package websocket
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