Протокол HTTP | Курс "Компьютерные сети"

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The lecture discusses the HTTP protocol, its significance in the World Wide Web system, and the structure of URLs.

Introduction to HTTP Protocol

• Tim Berners-Lee developed the HTTP protocol at CERN in 1989, forming the basis of the World Wide Web.

• HTML markup language, web servers, and browsers were integral components of early web browsing.

• Hypertext is a special type of markup used to define text display; tags like h1 denote headings.

URL Structure and Components

This section delves into how URLs are structured and their components for accessing web pages.

Understanding URLs

• URLs consist of protocols (e.g., http), domain names, server addresses, and specific page paths.

• Web servers operate on port 80 for clients' automatic port generation; communication follows a request-response model.

Evolution of HTTP Protocol

Evolutionary stages and versions of the HTTP protocol are discussed along with packet composition.

HTTP Protocol Evolution

• The official adoption of HTTP 1.0 as a standard in 1996 marked a significant milestone.

• The introduction of HTTP 1.1 brought enhanced features but faced gradual adoption due to browser-server compatibility issues.

HTTP Request Methods

Various request methods within the HTTP protocol are explored for different interactions with web servers.

Request Methods

• Requests include methods like GET (retrieve webpage), POST (send data), HEAD (retrieve headers), PUT (upload resource), DELETE (remove resource).

• Headers such as host specify server domains; message bodies may contain webpage content or parameters for processing.

HTTP Response Codes and Methods

Response codes and methods in handling requests within the HTTP protocol are detailed.

Response Codes & Methods

• Status codes categorize responses into informational messages (1xx), successful actions (2xx), client errors (4xx), server errors (5xx).

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This section discusses different HTTP status codes and their meanings, including 2xx for successful responses, 3xx for redirection, 4xx for client errors, and 5xx for server errors.

HTTP Status Codes

• Status codes starting with 2 indicate successful responses sent to the client.

• Codes beginning with 3 signify redirection; for instance, 301 denotes permanent redirection while 307 indicates temporary redirection.

• Status codes starting with 4 indicate client-side errors like the common error 404 (page not found) or error 403 (forbidden access).

• Codes starting with 5 denote server-side errors such as the internal server error (500).

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This part delves into making requests and receiving responses from a web server using examples of connecting to a web server via TCP protocol.

Making Requests and Receiving Responses

• To connect to a web server like "www.example.ru" on port 80 using TCP protocol manually through clients like Telnet on Linux or PuTTY on Windows.

• After sending a request specifying the method (e.g., GET), desired resource ("casus nadox" page), and protocol version (HTTP/1.1), headers like 'Host' are crucial for the server's response.

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This segment explores the structure of HTTP requests and responses, detailing protocols, headers, content types, and data transmission processes.

Structure of HTTP Requests and Responses

• HTTP requests include protocol versions (e.g., HTTP/1.1), various headers indicating server details and content type (e.g., text/html), character encoding (UTF-8), page length, etc.

• Initially designed as question-answer interactions with methods like GET or POST exchanging data between clients and servers; modern websites are dynamic with programs generating pages dynamically from databases or other servers.

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This part emphasizes the complexity of modern web pages that incorporate dynamic elements such as images, external data sources, client-side scripts, and user session management requirements.

Complexity of Modern Web Pages