HTTP: Master the Protocol Behind Web Communication

HTTP is the application-layer protocol that enables clients and servers to exchange information on the Web through a request-response model. In this handout, we will analyse the structure of an HTTP request, including methods, targets, headers and optional bodies, and the structure of an HTTP response, including status lines, headers and returned content. We will also study HTTP methods such as GET, POST, PUT, PATCH and DELETE, and learn how HTTP status codes communicate success, redirection, client errors and server errors. Finally, we will examine persistent connections and the role of HTTPS in protecting communication through TLS.

HTTP

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Key points

HTTP (Hypertext Transfer Protocol) = application-layer protocol for exchanging Web resources through a client-server request-response communication model.

HTTP ≠ HTTPS: HTTPS uses TLS to protect communication through encryption and verification of the remote service; default ports → 80 and 443, respectively.

HTTP communication → client sends a request → server processes it → server returns a response → client interprets the result.

HTTP request = message asking a server to perform an operation on a resource; HTTP/1.1 structure → request line, headers, blank line, optional body.

Request line = METHOD TARGET VERSION; the target commonly includes the path and query, while URL fragments are not transmitted to the server.

HTTP methods → GET retrieves, HEAD requests metadata without response content, POST submits data for processing, PUT replaces, PATCH partially modifies, DELETE removes resource associations.

GET is a safe method → requests retrieval without asking the server to modify resource state; secondary activities such as logging remain possible.

Request headers → provide contextual information; Host identifies the destination, User-Agent identifies the client, and Accept indicates preferred response formats.

Accept ≠ Content-Type: Accept expresses which formats the client prefers to receive, while Content-Type describes the format of transmitted content.

Request body = optional data sent to the server, commonly with POST, PUT, or PATCH; its interpretation depends on method semantics and media type.

HTTP response = message communicating the outcome of a request; HTTP/1.1 structure → status line, headers, blank line, optional body.

Status codes → 1xx informational, 2xx successful, 3xx redirection, 4xx client-related problems, 5xx server-related problems; numeric codes take precedence over reason phrases.

Common success and redirection codes → 200 successful, 201 resource created, 204 no content, 301 permanent redirect, 302 temporary redirect, 304 cached response reusable.

Common error codes → 400 invalid request, 401 missing or invalid authentication, 403 forbidden, 404 resource not found, 429 excessive requests.

Server error codes → 500 unexpected server error, 502 invalid upstream response, 503 temporarily unavailable service.

Response headers → Content-Type describes the media format, Content-Length indicates size, Location identifies another URL, and Content-Encoding indicates applied content encoding.

Cache and session management → Cache-Control defines response reuse rules; Set-Cookie instructs the browser to store a cookie under specified conditions.

Response body → carries resources, data, or error information; it may be absent depending on the method, status code, and HTTP rules.

Persistent connections → allow multiple HTTP exchanges without repeatedly establishing connections; loading a Web page can generate separate requests for its resources.

febogamedev | October 13, 2026 | 4:23 pm

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