HTTP Protocol and Web Architecture Flashcards

Vocabulary flashcards covering core concepts of HTTP protocols, client-server dynamics, request/response structures, methods, status codes, cookies, web caching, and version evolutions.

HTTP

Hypertext Transfer Protocol; the Web's application layer protocol operating on a client-server model.

Statelessness

A core HTTP property where the server maintains no memory of past interactions, treating every request as a brand-new, unrelated event.

Client

An entity (such as a browser or mobile app) that initiates communication by sending an HTTP request containing all needed information.

Server

An entity hosting websites, APIs, or content that waits for incoming HTTP requests, processes them, and returns responses.

Non-persistent HTTP

An HTTP connection mode where a TCP connection is opened, at most one object is sent over the connection, and the TCP connection is then closed.

Persistent HTTP

An HTTP connection mode where a TCP connection remains open after a response, allowing multiple objects to be sent over a single connection.

RTT (Round Trip Time)

The time required for a small packet to travel from a client to a server and back.

Non-persistent HTTP Response Time

Calculated as $2\text{ RTT} + \text{file transmission time}$ per object.

Request Line

The first line of an HTTP request message composed of an HTTP method, URL, and protocol version.

Status Line

The first line of an HTTP response message containing the protocol version, status code, and status phrase.

Request Headers

HTTP headers providing metadata about the request and client, such as User-Agent, Authorization, and Accept.

General Headers

HTTP headers that apply to both request and response messages, such as Date, Cache-Control, and Connection.

Representation Headers

HTTP headers describing the message body, such as Content-Type, Content-Length, and Content-Encoding.

Security Headers

HTTP headers that instruct browser security behaviors, such as Strict-Transport-Security and Content-Security-Policy.

GET

An idempotent HTTP method used strictly to retrieve data without modifying anything on the server.

POST

A non-idempotent HTTP method used to create a new resource on the server.

PUT

An idempotent HTTP method used to replace an existing resource entirely.

PATCH

An HTTP method preferred over PUT for making partial updates to an existing resource.

DELETE

An idempotent HTTP method used to remove a specified resource.

Idempotency

A property of an HTTP method where calling it multiple times produces the exact same result on the server as calling it once.

Same-Origin Policy

A browser security rule restricting pages from requesting resources from a domain different from the one that served the page.

CORS (Cross-Origin Resource Sharing)

A mechanism that allows servers to safely relax the Same-Origin Policy for cross-domain requests.

Preflight Request

An OPTIONS request sent by the browser before complex cross-origin requests to check allowed origins, methods, and headers.

200 OK

A 2xx status code indicating a standard successful HTTP request.

201 Created

A 2xx status code indicating that a request succeeded and a new resource was created.

204 No Content

A 2xx status code indicating a successful request with no response body returned.

301 Moved Permanently

A 3xx redirection status code indicating that the requested resource has been assigned a new permanent URL.

304 Not Modified

A 3xx redirection status code indicating that a cached copy of the resource is still valid.

400 Bad Request

A 4xx client error status code indicating a malformed or invalid request.

401 Unauthorized

A 4xx client error status code indicating missing or invalid authentication credentials.

403 Forbidden

A 4xx client error status code indicating the server refuses to authorize the request.

404 Not Found

A 4xx client error status code indicating the server cannot locate the requested resource.

Cookie

A state management tool using HTTP headers, backend databases, and local files to identify users and retain state across transactions.

Web Cache (Proxy Server)

An intermediary entity that satisfies client HTTP requests using cached copies of objects without involving the origin server.

Conditional GET

An HTTP GET request including an If-modified-since header so the origin server only sends the object if it was modified after the specified date.

Head-of-line (HOL) Blocking

A bottleneck in HTTP/1.1 where small requested objects are delayed waiting behind large objects delivering in FCFS order.

HTTP/2

An HTTP version that divides objects into frames and interleaves them based on client priorities to reduce head-of-line blocking.

HTTP/3

An HTTP version built on QUIC over UDP that provides built-in security and per-object error and congestion control.