The HTTP2-Settings header is an essential component of the HTTP/2 protocol, which is the second major version of the HTTP protocol. HTTP/2 aims to improve the performance of web applications by reducing latency, minimizing protocol overhead, and supporting multiplexing and prioritization.
The HTTP2-Settings header is used during the upgrade process from HTTP/1.1 to HTTP/2. It is a base64url-encoded value that carries the settings payload for the HTTP/2 connection. The primary purpose of this header is to convey the sender’s HTTP/2 settings to the recipient, allowing both parties to agree on the parameters for the upgraded connection.
The settings payload consists of a sequence of setting entries, each containing a 16-bit setting identifier and a 32-bit value. The settings identifiers are defined by the HTTP/2 specification and include parameters such as the maximum concurrent streams, initial window size, and header table size.
Request Example
When a client wishes to upgrade an HTTP/1.1 connection to HTTP/2, it sends an HTTP request containing the Upgrade and HTTP2-Settings headers. The Upgrade header indicates the desired protocol, while the HTTP2-Settings header carries the client’s HTTP/2 settings.
GET / HTTP/1.1
Host: example.com
Connection: Upgrade, HTTP2-Settings
Upgrade: h2c
HTTP2-Settings: <base64url-encoded settings payload>In this example, the Upgrade header value is set to h2c, indicating that the client wants to upgrade to HTTP/2 over a cleartext (non-TLS) connection. The HTTP2-Settings header contains the base64url-encoded settings payload.
Response Example
Upon receiving a request containing the Upgrade and HTTP2-Settings headers, the server can choose to accept or reject the upgrade. If the server accepts the upgrade, it responds with a 101 Switching Protocols status code and includes the HTTP2-Settings header with its own settings payload.
HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: h2c
HTTP2-Settings: <base64url-encoded settings payload>In this example, the server has accepted the upgrade to HTTP/2 over a cleartext connection. The HTTP2-Settings header contains the server’s base64url-encoded settings payload.
Summary
The HTTP2-Settings header plays a crucial role in the upgrade process from HTTP/1.1 to HTTP/2. It allows both the client and server to exchange their HTTP/2 settings, enabling a smooth transition to the new protocol.
By understanding the purpose and usage of the HTTP2-Settings header, developers can better leverage the performance benefits of HTTP/2 in their web applications.
