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WebSocket Source: en.wikipedia.org/wiki/WebSocket

WebSocket
The WebSocket logo
International standardRFC 6455
Developed byIETF
IndustryComputer science
Connector typeTCP
Websitehttps://websockets.spec.whatwg.org/

WebSocket is a computer communications protocol, providing a simultaneous two-way communication channel over a single Transmission Control Protocol (TCP) connection. The WebSocket protocol was standardized by the IETF as RFC 6455 in 2011. The current specification allowing web applications to use this protocol is known as WebSockets.[1] It is a living standard maintained by the WHATWG and a successor to The WebSocket API from the W3C.[2]

WebSocket is distinct from HTTP used to serve most webpages. Although they are different, RFC 6455 states that WebSocket "is designed to work over HTTP ports 443 and 80 as well as to support HTTP proxies and intermediaries", thus making it compatible with HTTP. To achieve compatibility, the WebSocket handshake uses the HTTP Upgrade header[3] to change from the HTTP protocol to the WebSocket protocol.

The WebSocket protocol enables full-duplex interaction between a web browser (or other client application) and a web server with lower overhead than half-duplex alternatives such as HTTP polling, facilitating real-time data transfer from and to the server. This is made possible by providing a standardized way for the server to send content to the client without being first requested by the client, and allowing messages to be passed back and forth while keeping the connection open. In this way, a two-way ongoing conversation can take place between the client and the server. The communications are usually done over TCP port number 443 (or 80 in the case of unsecured connections), which is beneficial for environments that block non-web Internet connections using a firewall. Additionally, WebSocket enables streams of messages on top of TCP. TCP alone deals with streams of bytes with no inherent concept of a message. Similar two-way browser–server communications have been achieved in non-standardized ways using stopgap technologies such as Comet or Adobe Flash Player.[4]

Most browsers support the protocol, including Google Chrome, Firefox, Microsoft Edge, Internet Explorer, Safari and Opera.[5]

The WebSocket protocol specification defines ws (WebSocket) and wss (WebSocket Secure) as two new uniform resource identifier (URI) schemes[6] that are used for unencrypted and encrypted connections respectively. Apart from the scheme name and fragment (i.e. # is not supported), the rest of the URI components are defined to use URI generic syntax.[7]

History

[edit]

WebSocket was first referenced as TCPConnection in the HTML5 specification, as a placeholder for a TCP-based socket API.[8] In June 2008, a series of discussions were led by Michael Carter that resulted in the first version of the protocol known as WebSocket.[9] Before WebSocket, port 80 full-duplex communication was attainable using Comet channels; however, Comet implementation is nontrivial, and due to the TCP handshake and HTTP header overhead, it is inefficient for small messages. The WebSocket protocol aims to solve these problems without compromising the security assumptions of the web. The name "WebSocket" was coined by Ian Hickson and Michael Carter shortly thereafter through collaboration on the #whatwg IRC chat room,[10] and subsequently authored for inclusion in the HTML5 specification by Ian Hickson. In December 2009, Google Chrome 4 was the first browser to ship full support for the standard, with WebSocket enabled by default.[11] Development of the WebSocket protocol was subsequently moved from the W3C and WHATWG group to the IETF in February 2010, and authored for two revisions under Ian Hickson.[12]

After the protocol was shipped and enabled by default in multiple browsers, the RFC 6455 was finalized under Ian Fette in December 2011.

RFC 7692 introduced compression extension to WebSocket using the DEFLATE algorithm on a per-message basis.

Web API

[edit]

A web application (e.g. web browser) may use the WebSocket interface to maintain bidirectional communications with a WebSocket server.[13]

Client example

[edit]
<!DOCTYPE html>
<script>
// Connect to server
ws = new WebSocket("wss://game.example.com/scoreboard")

// Define event listeners

ws.onopen = () => {
    console.log("Connection opened")
    ws.send("Hi server, please send me the score of yesterday's game")
}

ws.onmessage = (event) => {
    console.log("Message received", event.data)
    ws.close() // We got the score so we don't need the connection anymore
}

ws.onclose = (event) => {
    console.log("Connection closed", event.code, event.reason, event.wasClean)
}

ws.onerror = () => {
    console.log("Connection closed due to error")
}
</script>

Interface

[edit]
WebSocket interface specification[14]
Type Name Description
Constructor ws = new WebSocket(url [, protocols ]) Start opening handshake.[15]
  • url: URL. A string containing:
    • Scheme: must be ws, wss, http or https.
    • Host.
    • Optional port: If not specified, 80 is used for ws and http, and 443 for wss and https.
    • Optional path.
    • Optional query.
    • No fragment. There must not be any fragment, otherwise throw SyntaxError.
  • Optional protocols: A string or an array of strings used as the value for the Sec-WebSocket-Protocol HTTP header.
Method ws.send(data) Send message.[16] data must be string, Blob, ArrayBuffer or ArrayBufferView. Throw InvalidStateError if ws.readyState is CONNECTING.

Note:

  • If the data cannot be sent (e.g. because it would need to be buffered but the buffer is full), the connection is closed and onerror is fired.
ws.close([ code ] [, reason ]) Start closing handshake.[17]
  • Optional code: If specified, must be 1000 (Normal closure) or in the range 3000 to 4999 (application-defined), otherwise throw InvalidAccessError. Defaults to 1000.
  • Optional reason: If specified, must be a string whose UTF-8 encoding is up to 123 bytes, otherwise throw SyntaxError. Defaults to an empty string.

Note:

  • If ws.readyState is OPEN or OPENING, set ws.readyState to CLOSING and start the closing handshake.
  • If ws.readyState is CLOSING or CLOSED, do nothing (because the closing handshake has already started).
Event ws.onopen = (event) => {}

ws.addEventListener("open", (event) => {})

Opening handshake succeeded. event type is Event.
ws.onmessage = (event) => {}

ws.addEventListener("message", (event) => {})

Message received.[18] event type is MessageEvent. This event is only fired if ws.readyState is OPEN.
  • event.data contains the data received, of type:
    • String for text.
    • Blob or ArrayBuffer for binary (see ws.binaryType).
  • event.origin is a string containing ws.url but only with the scheme, host and port (if any) URL components.
ws.onclose = (event) => {}

ws.addEventListener("close", (event) => {})

The underlying TCP connection closed. event type is CloseEvent containing:[19][20][21][22]
  • event.code: status code (integer).
  • event.reason: reason for closing (string).
  • event.wasClean: true if the TCP connection was closed after the closing handshake was completed; false otherwise.

Note:

  • If the received Close frame contains a payload, event.code and event.reason get their value from the payload.
  • If the received Close frame contains no payload, event.code is 1005 (No code received) and event.reason is an empty string.
  • If no Close frame was received, event.code is 1006 (Connection closed abnormally) and event.reason is an empty string.
ws.onerror = (event) => {}

ws.addEventListener("error", (event) => {})

Connection closed due to error. event type is Event.
Attribute ws.binaryType (string) Type of event.data in ws.onmessage when a message containing binary data is received. Initially set to "blob" (Blob object). May be changed to "arraybuffer" (ArrayBuffer object).[23]
Read-only attribute ws.url (string) URL given to the WebSocket constructor with the following transformations:
  • If scheme is http or https, change it to ws or wss respectively.
ws.bufferedAmount (unsigned long long) Number of bytes of application data (UTF-8 text and binary data) that have been queued using ws.send() but not yet transmitted to the network. It resets to zero once all queued data has been sent. If the connection closes, this value will only increase, with each call to ws.send(), and never reset to zero.[24]
ws.protocol (string) Protocol accepted by the server, or an empty string if the client did not specify protocols in the WebSocket constructor.
ws.extensions (string) Extensions accepted by the server.
ws.readyState (unsigned short) Connection state. It is one of the constants below. Initially set to CONNECTING.[25]
Constant WebSocket.CONNECTING = 0 Opening handshake is currently in progress. The initial state of the connection.[26][27]
WebSocket.OPEN = 1 Opening handshake succeeded. The client and server may send messages to each other.[28][29]
WebSocket.CLOSING = 2 Closing handshake is currently in progress. Either ws.close() was called or a Close message was received.[30][31]
WebSocket.CLOSED = 3 The underlying TCP connection is closed.[32][19][20]

Protocol

[edit]
A diagram describing a connection using WebSocket

Steps:

  1. Opening handshake: HTTP request and HTTP response.
  2. Frame-based message exchange: application data, ping, pong messages.
  3. Closing handshake: request and response Close messages.

Opening handshake

[edit]

The client sends an HTTP request (method GET, version ≥ 1.1) and the server returns an HTTP response with status code 101 (Switching Protocols) on success. HTTP and WebSocket clients can connect to a server using the same port because the handshake is compatible with HTTP. Sending additional HTTP headers (that are not in the table below) is allowed. HTTP headers may be sent in any order. After the Switching Protocols HTTP response, the opening handshake is complete, the HTTP protocol stops being used, and communication switches to a binary frame-based protocol.[33][34]

HTTP headers relevant to the opening handshake
Side
 Header Value Mandatory
Request
 Origin[35] Varies Yes (for browser clients)
Host[36] Varies Yes
Sec-WebSocket-Version[37] 13
Sec-WebSocket-Key[38] base64-encode(16-byte random nonce)
Response
 Sec-WebSocket-Accept[39] base64-encode(sha1(Sec-WebSocket-Key + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"))
Both
 Connection[40][41] Upgrade
Upgrade[42][43] websocket
Sec-WebSocket-Protocol[44] The request may contain a comma-separated list of strings (ordered by preference) indicating application-level protocols (built on top of WebSocket data messages) the client wishes to use. If the client sends this header, the server response must be one of the values from the list. No
Sec-WebSocket-Extensions[45][46][47][48] Used to negotiate protocol-level extensions. The client may request extensions to the WebSocket protocol by including a comma-separated list of extensions (ordered by preference). Each extension may have a parameter (e.g. foo=4). The server may accept some or all extensions requested by the client. This field may appear multiple times in the request (logically equivalent to a single occurrence containing all values) and must not appear more than once in the response.

The following Python code generates a random Sec-WebSocket-Key. 

import os, base64
print(base64.b64encode(os.urandom(16)))

Example request: 

GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Origin: http://example.com
Sec-WebSocket-Protocol: chat, superchat
Sec-WebSocket-Version: 13

Example response: 

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
Sec-WebSocket-Protocol: chat

The following Python code calculates Sec-WebSocket-Accept using Sec-WebSocket-Key from the example above. 

import base64, hashlib
Sec_WebSocket_Key = b"dGhlIHNhbXBsZSBub25jZQ=="
MAGIC = b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
print(base64.b64encode(hashlib.sha1(Sec_WebSocket_Key + MAGIC).digest()))

Sec-WebSocket-Key and Sec-WebSocket-Accept are intended to prevent a caching proxy from re-sending a previous WebSocket conversation,[49] and does not provide any authentication, privacy, or integrity.

Though some servers accept a short Sec-WebSocket-Key, many modern servers will reject the request with error "invalid Sec-WebSocket-Key header".

Frame-based message

[edit]

After the opening handshake, the client and server can, at any time, send data messages (text or binary) and control messages (Close, Ping, Pong) to each other. A message is composed of one frame if not fragmented or at least two frames if fragmented.

Fragmentation splits a message into two or more frames. It enables sending messages with initial data available but complete length unknown. Without fragmentation, the whole message must be sent in one frame, so the complete length is needed before the first byte can be sent, which requires a buffer. It also enables multiplexing several streams simultaneously (e.g. to avoid monopolizing a socket for a single large payload).[50][51]

  • An unfragmented message consists of one frame with FIN = 1 and opcode ≠ 0.
  • A fragmented message consists of one frame with FIN = 0 and opcode ≠ 0, followed by zero or more frames with FIN = 0 and opcode = 0, and terminated by one frame with FIN = 1 and opcode = 0.

Frame structure

[edit]
Offset
(in bits) 		Field[52] Size
(in bits) 		Description
0 FIN[53] 1
  • 1 = final frame of a message.
  • 0 = message is fragmented and this is not the final frame.
1 RSV1 1 Undefined. Must be 0 unless defined by an extension. If a non-zero value is received and none of the negotiated extensions defines the meaning of such a non-zero value, the connection must be closed.[54]
2 RSV2 1
3 RSV3 1
4 Opcode 4 See opcodes below.
8 Masked[55] 1
  • 1 = frame is masked (i.e. masking key is present and the payload has been XORed with masking key).
  • 0 = frame is not masked (i.e. masking key is not present).
See client-to-server masking below.
9 Payload length[56] 7, 7+16 or 7+64 Length of the payload (extension data + application data) in bytes.
  • 0–125 = This is the payload length.
  • 126 = The following 16 bits are the payload length.
  • 127 = The following 64 bits (MSB must be 0) are the payload length.
Endianness is big-endian. Signedness is unsigned. The minimum number of bits must be used to encode the length.
Varies Masking key 0 or 32 A client must mask all frames sent to the server. A server must not mask any frames sent to the client.[57] Frame masking applies XOR between the masking key (a four-byte random nonce) and the payload. The following pseudocode describes the algorithm used to both mask and unmask a frame:[58]
for i = 0 to payload_length - 1
    payload[i] = payload[i] xor masking_key[i modulo 4]
Payload Extension data Payload length (in bytes) Undefined. Must be empty unless defined by an extension.
Application data Depends on the opcode

Opcodes

[edit]
Frame type[59] Opcode[60] Related

Web API

Description Purpose
Fragmentable
 Max. payload length
Continuation frame 0 Non-first frame of a fragmented message. Fragmentation ⁠⁠ bytes
Non-control frame Text 1 send(), onmessage UTF-8-encoded text. Application and extension data Yes
Binary 2 Binary data.
3–7 Reserved for further non-control frames. May be defined by an extension.[61]
Control frame[62] Close 8 close(), onclose The WebSocket closing handshake starts upon either sending or receiving a Close frame.[63] It may prevent data loss by complementing the TCP closing handshake.[64] No frame can be sent after a Close frame. If a Close frame is received and no prior Close frame was sent, a Close frame must be sent in response (typically echoing the status code received). The payload is optional, but if present, it must start with a two-byte big-endian unsigned integer status code, optionally followed by a UTF-8-encoded reason message not longer than 123 bytes.[65] Protocol state No 125 bytes
Ping 9 May be used for latency measurement, keepalive and heartbeat. Both sides can initiate a ping (with any payload). Whoever receives it must, as soon as is practical, send back a pong with the same payload. A pong should be ignored if no prior ping was sent.[66][67][68]
Pong 10
11–15 Reserved for further control frames. May be defined by an extension.[61]

Status codes

[edit]
Range[69] Allowed in Close frame Code

[70]

Description
0–999 No Unused
1000–2999 (Protocol) Yes 1000 Normal closure.
1001 Going away (e.g. browser tab closed; server going down).
1002 Protocol error.
1003 Unsupported data (e.g. endpoint only understands text but received binary).
No 1004 Reserved for future usage
1005 No code received.
1006 Connection closed abnormally (i.e. closing handshake did not occur).
Yes 1007 Invalid payload data (e.g. non UTF-8 data in a text message).
1008 Policy violated.
1009 Message too big.
1010 Unsupported extension. The client should write the extensions it expected the server to support in the payload.
1011 Internal server error.
No 1015 TLS handshake failure.
3000–3999 Yes Reserved for libraries, frameworks and applications. Registered directly with IANA.
4000–4999 Private use.

Server implementation example

[edit]

In Python. 

from socket import socket
from base64 import b64encode
from hashlib import sha1
import struct

MAGIC = b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11"

# Create socket and listen (on all network interfaces) at port 80
ws = socket()
ws.bind(("", 80))
ws.listen()
conn, addr = ws.accept()

# Parse request
for line in conn.recv(4096).split(b"\r\n"):
    if line.startswith(b"Sec-WebSocket-Key"):
        Sec_WebSocket_Key = line.split(b":")[1].strip()

# Format response
response = f"""\
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: {b64encode(sha1(Sec_WebSocket_Key + MAGIC).digest()).decode()}

"""

conn.send(response.replace("\n", "\r\n").encode())

while True: # decode messages from the client
    header = conn.recv(2)
    FIN = bool(header[0] & 0x80) # bit 0
    assert FIN == 1, "We only support unfragmented messages"
    opcode = header[0] & 0xf # bits 4-7
    assert opcode == 1 or opcode == 2, "We only support data messages"
    masked = bool(header[1] & 0x80) # bit 8
    assert masked, "The client must mask all frames"
    payload_size = header[1] & 0x7f # bits 9-15
    assert payload_size <= 125, "We only support small messages"
    masking_key = conn.recv(4)
    payload = bytearray(conn.recv(payload_size))
    for i in range(payload_size):
        payload[i] = payload[i] ^ masking_key[i % 4]
    conn.send(struct.pack("BB", 0x80 | opcode, payload_size) + payload) # echo message
    print("Received", "text" if opcode == 1 else "binary", "message", payload)

Browser support

[edit]

A secure version of the WebSocket protocol is implemented in Firefox 6,[71] Safari 6, Google Chrome 14,[72] Opera 12.10 and Internet Explorer 10.[73] A detailed protocol test suite report[74] lists the conformance of those browsers to specific protocol aspects.

An older, less secure version of the protocol was implemented in Opera 11 and Safari 5, as well as the mobile version of Safari in iOS 4.2.[75] The BlackBerry Browser in OS7 implements WebSockets.[76] Because of vulnerabilities, it was disabled in Firefox 4 and 5,[77] and Opera 11.[78] Using browser developer tools, developers can inspect the WebSocket handshake as well as the WebSocket frames.[79]

Protocol
Version
 Draft date Internet Explorer Firefox[80]
(PC) 		Firefox
(Android) 		Chrome
(PC, Mobile) 		Safari
(Mac, iOS) 		Opera
(PC, Mobile) 		Android Browser
hixie-75 February 4, 2010 4 5.0.0
hixie-76
hybi-00 		May 6, 2010
May 23, 2010 		4.0
(disabled) 		6 5.0.1 11.00
(disabled)
hybi-07, v7 April 22, 2011 6[81][a]
hybi-10, v8 July 11, 2011 7[83][a] 7 14[84]
RFC 6455, v13 December, 2011 10[85] 11 11 16[86] 6 12.10[87] 4.4

Server implementations

[edit]
  • Apache HTTP Server has supported WebSockets since July, 2013, implemented in version 2.4.5[90][91]
  • Internet Information Services added support for WebSockets in version 8 which was released with Windows Server 2012.[92]
  • lighttpd has supported WebSockets since 2017, implemented in lighttpd 1.4.46.[93] lighttpd mod_proxy can act as a reverse proxy and load balancer of WebSocket applications. lighttpd mod_wstunnel can act as a WebSocket endpoint to transmit arbitrary data, including in JSON format, to a backend application. lighttpd supports WebSockets over HTTP/2 since 2022, implemented in lighttpd 1.4.65.[94]

ASP.NET Core have support for WebSockets using the app.UseWebSockets(); middleware.[95]

Security considerations

[edit]

Unlike regular cross-domain HTTP requests, WebSocket requests are not restricted by the same-origin policy. Therefore, WebSocket servers must validate the "Origin" header against the expected origins during connection establishment, to avoid cross-site WebSocket hijacking attacks (similar to cross-site request forgery), which might be possible when the connection is authenticated with cookies or HTTP authentication. It is better to use tokens or similar protection mechanisms to authenticate the WebSocket connection when sensitive (private) data is being transferred over the WebSocket.[96] A live example of vulnerability was seen in 2020 in the form of Cable Haunt.

Proxy traversal

[edit]

WebSocket protocol client implementations try to detect whether the user agent is configured to use a proxy when connecting to destination host and port, and if it is, uses HTTP CONNECT method to set up a persistent tunnel.

While the WebSocket protocol itself is unaware of proxy servers and firewalls, it features an HTTP-compatible handshake, thus allowing HTTP servers to share their default HTTP and HTTPS ports (80 and 443 respectively) with a WebSocket gateway or server. The WebSocket protocol defines a ws:// and wss:// prefix to indicate a WebSocket and a WebSocket Secure connection respectively. Both schemes use an HTTP upgrade mechanism to upgrade to the WebSocket protocol. Some proxy servers are transparent and work fine with WebSocket; others will prevent WebSocket from working correctly, causing the connection to fail. In some cases, additional proxy-server configuration may be required, and certain proxy servers may need to be upgraded to support WebSocket.

If unencrypted WebSocket traffic flows through an explicit or a transparent proxy server without WebSockets support, the connection will likely fail.[97]

If an encrypted WebSocket connection is used, then the use of Transport Layer Security (TLS) in the WebSocket Secure connection ensures that an HTTP CONNECT command is issued when the browser is configured to use an explicit proxy server. This sets up a tunnel, which provides low-level end-to-end TCP communication through the HTTP proxy, between the WebSocket Secure client and the WebSocket server. In the case of transparent proxy servers, the browser is unaware of the proxy server, so no HTTP CONNECT is sent. However, since the wire traffic is encrypted, intermediate transparent proxy servers may simply allow the encrypted traffic through, so there is a much better chance that the WebSocket connection will succeed if WebSocket Secure is used. Using encryption is not free of resource cost, but often provides the highest success rate, since it would be travelling through a secure tunnel.

A mid-2010 draft (version hixie-76) broke compatibility with reverse proxies and gateways by including eight bytes of key data after the headers, but not advertising that data in a Content-Length: 8 header.[98] This data was not forwarded by all intermediates, which could lead to protocol failure. More recent drafts (e.g., hybi-09[99]) put the key data in a Sec-WebSocket-Key header, solving this problem.

See also

[edit]

Notes

[edit]
  1. ^ a b Gecko-based browsers versions 6–10 implement the WebSocket object as "MozWebSocket",[82] requiring extra code to integrate with existing WebSocket-enabled code.

References

[edit]
  1. ^ "WebSockets Standard". WHATWG WebSockets. Archived from the original on 2023-03-12. Retrieved 2022-05-16.
  2. ^ "The WebSocket API". www.w3.org. Archived from the original on 2022-06-08. Retrieved 2022-05-16.
  3. ^ Ian Fette; Alexey Melnikov (December 2011). "Relationship to TCP and HTTP". RFC 6455 The WebSocket Protocol. IETF. sec. 1.7. doi:10.17487/RFC6455. RFC 6455.
  4. ^ "Adobe Flash Platform – Sockets". help.adobe.com. Archived from the original on 2021-04-18. Retrieved 2021-07-28. TCP connections require a "client" and a "server". Flash Player can create client sockets.
  5. ^ "The WebSocket API (WebSockets)". MDN Web Docs. Mozilla Developer Network. 2023-04-06. Archived from the original on 2021-07-28. Retrieved 2021-07-26.
  6. ^ Graham Klyne, ed. (2011-11-14). "IANA Uniform Resource Identifier (URI) Schemes". Internet Assigned Numbers Authority. Archived from the original on 2013-04-25. Retrieved 2011-12-10.
  7. ^ Ian Fette; Alexey Melnikov (December 2011). "WebSocket URIs". RFC 6455 The WebSocket Protocol. IETF. sec. 3. doi:10.17487/RFC6455. RFC 6455.
  8. ^ "HTML 5". www.w3.org. Archived from the original on 2016-09-16. Retrieved 2016-04-17.
  9. ^ "[whatwg] TCPConnection feedback from Michael Carter on 2008-06-18 (whatwg.org from June 2008)". lists.w3.org. Archived from the original on 2016-04-27. Retrieved 2016-04-17.
  10. ^ "IRC logs: freenode / #whatwg / 20080618". krijnhoetmer.nl. Archived from the original on 2016-08-21. Retrieved 2016-04-18.
  11. ^ "Web Sockets Now Available In Google Chrome". Chromium Blog. Archived from the original on 2021-12-09. Retrieved 2016-04-17.
  12. ^ <ian@hixie.ch>, Ian Hickson (6 May 2010). "The WebSocket protocol". Ietf Datatracker. Archived from the original on 2017-03-17. Retrieved 2016-04-17.
  13. ^ "Introduction". WHATWG WebSockets. sec. 1.
  14. ^ "Interface definition". WHATWG WebSockets. sec. 3.1. Archived from the original on 2023-03-12. Retrieved 2024-04-10.
  15. ^ "new WebSocket(url, protocols)". WHATWG WebSockets. sec. 3.1. Archived from the original on 2023-03-12. Retrieved 2024-04-30.
  16. ^ "send(data)". WHATWG WebSockets. sec. 3.1.
  17. ^ "close(code, reason)". WHATWG WebSockets. sec. 3.1. Archived from the original on 2023-03-12. Retrieved 2024-04-10.
  18. ^ "When a WebSocket message has been received". WHATWG WebSockets. sec. 4.
  19. ^ a b "When the WebSocket connection is closed; substep 3". WHATWG WebSockets. sec. 4. Archived from the original on 2023-03-12. Retrieved 2024-04-13.
  20. ^ a b The WebSocket Connection is Closed. sec. 7.1.4. doi:10.17487/RFC6455. RFC 6455.
  21. ^ The WebSocket Connection Close Code. sec. 7.1.5. doi:10.17487/RFC6455. RFC 6455.
  22. ^ The WebSocket Connection Close Reason. sec. 7.1.6. doi:10.17487/RFC6455. RFC 6455.
  23. ^ "socket.binaryType". WHATWG WebSockets. sec. 3.1.
  24. ^ "socket.bufferedAmount". WHATWG WebSockets. sec. 3.1.
  25. ^ "ready state". WHATWG WebSockets. sec. 3.1.
  26. ^ "CONNECTING". WHATWG WebSockets. sec. 3.1. Archived from the original on 2023-03-12. Retrieved 2024-04-13.
  27. ^ Client Requirements. p. 14. sec. 4.1. doi:10.17487/RFC6455. RFC 6455.
  28. ^ "OPEN". WHATWG WebSockets. sec. 3.1. Archived from the original on 2023-03-12. Retrieved 2024-04-10.
  29. ^ _The WebSocket Connection is Established_. p. 20. doi:10.17487/RFC6455. RFC 6455.
  30. ^ "CLOSING". WHATWG WebSockets. sec. 3.1. Archived from the original on 2023-03-12. Retrieved 2024-04-10.
  31. ^ The WebSocket Closing Handshake is Started. sec. 7.1.3. doi:10.17487/RFC6455. RFC 6455.
  32. ^ "CLOSED". WHATWG WebSockets. sec. 3.1. Archived from the original on 2023-03-12. Retrieved 2024-04-10.
  33. ^ Opening Handshake. sec. 1.3. doi:10.17487/RFC6455. RFC 6455.
  34. ^ Protocol Overview. sec. 1.2. doi:10.17487/RFC6455. RFC 6455.
  35. ^ Client requirement 8. p. 18. doi:10.17487/RFC6455. RFC 6455.
  36. ^ Client requirement 4. p. 17. doi:10.17487/RFC6455. RFC 6455.
  37. ^ Client requirement 9. p. 18. doi:10.17487/RFC6455. RFC 6455.
  38. ^ Client requirement 7. p. 18. doi:10.17487/RFC6455. RFC 6455.
  39. ^ Server step 5.4. p. 24. doi:10.17487/RFC6455. RFC 6455.
  40. ^ Client requirement 6. p. 18. doi:10.17487/RFC6455. RFC 6455.
  41. ^ Server step 5.3. p. 24. doi:10.17487/RFC6455. RFC 6455.
  42. ^ Client requirement 5. p. 17. doi:10.17487/RFC6455. RFC 6455.
  43. ^ Server step 5.2. p. 24. doi:10.17487/RFC6455. RFC 6455.
  44. ^ Client requirement 10. p. 18. doi:10.17487/RFC6455. RFC 6455.
  45. ^ Client requirement 11. p. 19. doi:10.17487/RFC6455. RFC 6455.
  46. ^ Sec-WebSocket-Extensions. sec. 11.3.2. doi:10.17487/RFC6455. RFC 6455.
  47. ^ Extensions. sec. 9. doi:10.17487/RFC6455. RFC 6455.
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  53. ^ FIN. p. 28. doi:10.17487/RFC6455. RFC 6455.
  54. ^ RSV1, RSV2, RSV3. p. 28. doi:10.17487/RFC6455. RFC 6455.
  55. ^ Mask. p. 29. doi:10.17487/RFC6455. RFC 6455.
  56. ^ Payload length. p. 29. doi:10.17487/RFC6455. RFC 6455.
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  59. ^ frame-opcode. p. 31. doi:10.17487/RFC6455. RFC 6455.
  60. ^ Opcode. p. 29. doi:10.17487/RFC6455. RFC 6455.
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  64. ^ Closing Handshake. sec. 1.4. doi:10.17487/RFC6455. RFC 6455.
  65. ^ Close. sec. 5.5.1. doi:10.17487/RFC6455. RFC 6455.
  66. ^ Ping. sec. 5.5.2. doi:10.17487/RFC6455. RFC 6455.
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