HTTPResponse

An HTTP response is the message a server sends to a client in reply to an HTTP request. It is composed of three parts: a status line, a set of headers, and an optional message body. The status line includes the HTTP version, a three-digit status code, and a reason phrase, for example "HTTP/1.1 200 OK".

Status codes indicate the result of the request and are grouped by numerical range: 1xx informational, 2xx success, 3xx redirection, 4xx client error, 5xx server error.

Headers convey metadata about the response or about the body, such as Content-Type (media type), Content-Length (size in bytes), Date, Server, Cache-Control, and Set-Cookie for session data. Some responses may include a body, such as HTML or JSON; others must not (for example, 204 No Content or 304 Not Modified). The presence and length of the body are indicated by Content-Length or Transfer-Encoding (for example, chunked transfer encoding).

Connection management: HTTP/1.1 default is to use persistent connections; the Connection header can request closing. The body may be transferred using chunked encoding when the length is unknown at the start.

In practice, clients process the status line and headers to decide how to handle the body, caching, and redirect behavior. Server implementations and frameworks generate responses based on request handling logic, routing, and content generation.

With HTTP/2 and HTTP/3, responses are multiplexed over a single connection and header compression reduces overhead, but the basic structure remains the status line, headers, and body.