HTTPHeadern

HTTPHeadern are the metadata of an HTTP message. They consist of a series of header fields placed after the request line or status line and before the message body. Each header field is a name-value pair, separated by a colon, and header names are case-insensitive. The header section communicates information about the request or response, the client or server, and how the message should be interpreted or processed.

Headers are categorized as general headers, request headers, response headers, and entity headers. General headers apply to both requests and responses; entity headers describe the payload. Some headers are hop-by-hop and apply only to a single transport segment (for example, Connection and Upgrade), while others are end-to-end and travel with the message. The definitions and recommended usage are specified in standards such as RFC 7230 through RFC 7235.

In HTTP/1.1, the header section is text-based, with lines terminated by CRLF, followed by an empty line that separates headers from the body. In HTTP/2 and HTTP/3, headers are transmitted as name-value pairs within compressed header frames (HPACK for HTTP/2 and QPACK for HTTP/3), and they use pseudo-headers such as :method, :path, :scheme, and :authority.

Common headers include Host, User-Agent, Accept, Accept-Language, Authorization, and Cookie for requests; Content-Type, Content-Length, Cache-Control, ETag, Set-Cookie, and WWW-Authenticate for responses. Headers support caching, content negotiation, authentication, CORS, and telemetry.

Security and privacy considerations include avoiding leakage of sensitive data in headers, preventing header injection, and ensuring transmission over TLS to protect header confidentiality. Proper handling of HTTPHeadern is essential for interoperability and performance.