WebSocket Headers: A Comprehensive Guide

WebSocket headers are a crucial aspect of establishing a WebSocket connection. They provide essential information about the connection and the client.

The Upgrade header is a required header in WebSocket requests, indicating that the client wants to upgrade the connection to a WebSocket connection. It's typically set to "websocket" or "Upgrade".

The Connection header is also required and must be set to "Upgrade" to establish a WebSocket connection. This header is used to indicate that the connection will be upgraded to a WebSocket connection.

The Origin header is used to identify the origin of the client making the request, and it's required for security reasons. It helps prevent cross-site request forgery (CSRF) attacks.

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The WebSocket handshake is a crucial step in establishing a WebSocket connection. The client initiates the handshake by sending a request that includes the sub-protocol it prefers, as shown in the example where the client prefers "soap" but also supports "wamp".

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To specify the sub-protocol, the client includes the "Sec-WebSocket-Protocol" field in its handshake, which the server must also include in its response for the connection to be established. This field allows the client to request a specific subprotocol from the server.

The subprotocol names don't need to be registered, but using a domain name can help avoid potential clashes with independently defined subprotocols. For instance, if a company like Example Corporation creates a Chat subprotocol, they could name it "chat.example.com" to avoid conflicts.

Subprotocols can be versioned in backwards-incompatible ways by changing the subprotocol name, which would make the old and new subprotocols completely separate to WebSocket clients. This can be seen in the example where a subprotocol name is changed from "bookings.example.net" to "v2.bookings.example.net".

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The WebSocket protocol is a two-part process consisting of a handshake and data transfer.

The handshake from the client follows the Request-Line format, while the leading line from the server follows the Status-Line format, both defined in [RFC2616].

After the leading line in both cases come an unordered set of headers, the meaning of which is specified in Section 5 of this document.

These headers can include cookies required to identify the user, and their format and parsing are as defined in [RFC2616].

The WebSocket protocol uses framing to send data on the wire in the form of frames that have an associated type.

There are six frame types, including types for textual data, binary data, and control frames, which are not intended to carry data for the application but instead for protocol-level signaling.

The "Request-URI" of the GET method [RFC2616] is used to identify the endpoint of the WebSocket connection.

The Sec-WebSocket-Protocol header is used in the WebSocket handshake to confirm the subprotocol of the connection.

This header is sent from the client to the server and back from the server to the client, enabling scripts to both select a subprotocol and be sure that the server agreed to serve that subprotocol.

Data is sent on the wire in the form of frames, which can be fragmented or coalesced by an intermediary, but the WebSocket protocol assumes that many or most applications will provide APIs in terms of sending and receiving messages.

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WebSocket Security is a crucial aspect to consider when working with WebSockets. The protocol uses the origin model to restrict which web pages can contact a WebSocket server, but this model is not useful when a dedicated client connects directly.

A server should not trust any input from a client, as it can be easily manipulated by an attacker. This includes the "Origin" field, which can be sent by a client as an arbitrary string. All input text should be escaped before being passed to a SQL server, lest the server be susceptible to SQL injection.

If a server is faced with data it doesn't understand or that violates safety criteria, it should disconnect immediately. This is always a safe option, as it prevents potential security risks.

The biggest security risk when sending text data using WebSockets is sending data using the wrong encoding. If an attacker can trick the server into sending data encoded as ISO-8859-1 verbatim, rather than encoded as UTF-8, they can inject arbitrary frames into the data stream.

Messages sent from clients are masked on the wire with a 32-bit value to prevent an attacker from controlling the bits on the wire. This helps lessen the probability of an attacker being able to construct a message that can be misinterpreted by a proxy as a non-WebSocket request.

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A WebSocket connection is established when a client sends a WebSocket handshake request to a server, which is a special type of HTTP request.

The request includes a "Connection" header with the value "Upgrade" to indicate the client's intention to upgrade the connection to a WebSocket connection.

The server responds with a 101 Switching Protocols status code and a "Connection" header with the value "Upgrade", confirming the upgrade to a WebSocket connection.

The client and server then establish a persistent, bidirectional communication channel over the WebSocket connection, allowing for efficient and real-time data exchange.

The WebSocket connection remains open until one of the parties closes it, at which point the connection is terminated.

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WebSocket Extensions are used to agree on a set of protocol-level extensions during the connection.

The Sec-WebSocket-Extensions header is used for this purpose, initially sent from the client to the server and then subsequently sent from the server to the client.

This header allows for the negotiation of specific extensions that can enhance the functionality of the WebSocket connection.

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The Sec-WebSocket-Key header is used in the WebSocket handshake to provide part of the information used by the server to prove that it received a valid WebSocket handshake.

This header is sent from the client to the server to help ensure that the server doesn't accept connections from non-WebSocket clients being abused to send data to unsuspecting WebSocket servers.

The Sec-WebSocket-Key header plays a crucial role in preventing non-WebSocket clients from sending data to WebSocket servers.

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The Sec-WebSocket-Extensions header is used in the WebSocket handshake. It's initially sent from the client to the server, and then subsequently sent from the server to the client.

This header is used to agree on a set of protocol-level extensions to use during the connection. This is a crucial step in establishing a WebSocket connection.

The client sends the Sec-WebSocket-Extensions header to the server, and then the server responds with its own set of extensions. This ensures that both parties are on the same page.

By using the Sec-WebSocket-Extensions header, WebSocket connections can be more efficient and secure. This is particularly important for applications that require real-time communication.

The server confirms the connection by sending the Sec-WebSocket-Accept header back to the client. This header is used in the WebSocket handshake to prove that the server received a valid WebSocket handshake.

The Sec-WebSocket-Accept header is sent from the server to the client, confirming that the server is willing to initiate the connection. This is a crucial step in establishing a secure WebSocket connection.

The server generates the Sec-WebSocket-Accept header by taking the client's Sec-WebSocket-Key header and performing a specific hashing operation on it. This ensures that the client and server are communicating securely.

The Sec-WebSocket-Accept header is used to prevent non-WebSocket clients from abusing the connection to send data to unsuspecting WebSocket servers. This helps maintain the integrity of the WebSocket connection.

The Sec-WebSocket-Accept header is sent from the server to the client, confirming that the connection has been successfully established. This is a critical step in ensuring that the WebSocket connection is secure and reliable.

The Sec-WebSocket-Origin header is a crucial part of the WebSocket handshake, sent from the server to the client to confirm the origin of the script that opened the connection.

This header enables user agents to verify that the server is willing to serve the script that opened the connection. The origin model used by Web browsers is also applied to the WebSocket protocol, which restricts which Web pages can contact a WebSocket server.

In order to establish a connection, the client must provide a valid origin string, which the server can then use to confirm the connection. If the server does not receive a valid origin string, it should disconnect the connection.

Servers should be careful not to trust any input from clients, as it can be fake or misleading. This is especially true for servers that process input as part of SQL queries, which should always be escaped before being passed to the SQL server.

By verifying the origin field and only responding with the corresponding Sec-WebSocket-Origin header if it is an accepted origin, servers can ensure a secure connection.

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