Summary of Data Exchange and Web APIs

Data Exchange & Web APIs: A Student's Guide to Digital Communication

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Introduction

A Web API (Application Programming Interface) enables communication between a client and a server over a network. It defines a set of rules and interfaces that applications use to exchange data — typically over HTTP(S). This material summarizes the principles of HTTP, REST, alternative architectures (JSON:API, GraphQL), describing APIs using OpenAPI, and related technologies such as AJAX or WebSocket.

Definition: A Web API is a set of specified methods, protocols, and formats that enable client applications to securely and structuredly call functions and share data with a server.

Communication Fundamentals: HTTP and Client-Server Architecture

Client and Server

Client: A web browser, mobile app, bot, IoT device, or any other application that initiates a request.
Server: A web or application server (Apache, Nginx, IIS), typically running on a physical or virtual machine.

HTTP Principles

HTTP is a protocol layered on top of TCP/QUIC, operating at the application layer. It's a request-response protocol, stateless (state is not automatically maintained between requests).
The standard port is 80; for secure HTTPS traffic, we use TLS (port 443).

Definition: Stateless means that the server does not retain information about previous client requests; each request contains everything needed for processing.

HTTP Methods (Most Important)

GET – Reads a resource (without side effects).
POST – Sends data to the server (e.g., creating a resource or submitting a form).
PUT – Creates or replaces a representation of the target resource.
PATCH – Partially updates a resource.
DELETE – Deletes a resource.

Others: HEAD, OPTIONS, CONNECT, TRACE (primarily for diagnostics or specific scenarios).

HTTP Headers and Response Codes

Headers carry metadata (User-Agent, Content-Type, Authorization, Cache-Control, etc.).
Response code groups:
- 1xx informational
- 2xx success (200, 201, 204)
- 3xx redirection (301, 302, 304)
- 4xx client error (400, 401, 403, 404, 405)
- 5xx server error (500, 502, 503)

💡 Did you know?Fun fact: For faster connection establishment and lower latency, modern websites use HTTP/2 or HTTP/3 — HTTP/3 runs over QUIC and significantly improves reconnection speed and multiplexing.

REST (REpresentational State Transfer)

Core Principles

REST is an architectural style that uses HTTP as its transport layer.
Everything is a resource identified by a URI; clients interact with it using a uniform interface (HTTP methods).
Key constraints: stateless, cacheability, uniform interface, layered system.

Definition: A REST API provides access to resources over HTTP, where resources are identified by URIs and operations are performed using standard HTTP methods.

Data Formats

Most commonly, JSON is used; XML was common previously. REST does not restrict the format, but JSON is more modern for the web.

Example REST URLs and Operations

GET https://api.example.com/users/123 — retrieve user with ID 123
POST https://api.example.com/users — create a new user
PUT https://api.example.com/users/123 — replace user 123
PATCH https://api.example.com/users/123 — modify parts of user 123
DELETE https://api.example.com/users/123 — delete user 123

OpenAPI Specification (OAS)

OAS is an API description in JSON or YAML format that allows for generating documentation, client stubs, mock servers, and tests.
Main sections: openapi, info, servers, paths (operations), components (schemas, parameters, securitySchemes).

💡 Did you know?Fun fact: A single OAS file can be used to automatically generate both a client library and interactive documentation (e.g., Swagger UI).

JSON:API and GraphQL — Alternatives to "Pure" REST

JSON:API

A specification that defines a consistent JSON format for REST APIs (media type application/vnd.api+json).
Standardizes the structure of responses, including relationships, meta, and included sections.

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Web API - Overview

Klíčové pojmy: A Web API defines an interface for communication between applications over a network., HTTP is the foundational protocol for Web APIs; it uses methods such as GET, POST, PUT, PATCH, and DELETE., REST utilizes resources identified by URIs and standard HTTP methods., OpenAPI (OAS) describes APIs in JSON/YAML format, enabling the generation of documentation and stubs., JSON is the primary data format for modern REST APIs; XML is typically used in older services., GraphQL allows clients to specify exactly the data they need, reducing the number of requests., WebSocket provides a persistent, bidirectional connection for real-time communication., AJAX (Fetch/XHR) enables asynchronous updates without a page reload., SOAP and XML-RPC are used in enterprise scenarios with rigidly defined contracts., Security: always use HTTPS/TLS, employ OAuth/JWT, and implement rate limiting., HTTP responses include status codes (1xx–5xx) that describe the outcome of a request., Utilize proper documentation and validation (e.g., OAS, schemas) for robust APIs.

## Introduction A Web API (Application Programming Interface) enables communication between a client and a server over a network. It defines a set of rules and interfaces that applications use to exchange data — typically over HTTP(S). This material summarizes the principles of HTTP, REST, alternative architectures (JSON:API, GraphQL), describing APIs using OpenAPI, and related technologies such as AJAX or WebSocket. > Definition: A Web API is a set of specified methods, protocols, and formats that enable client applications to securely and structuredly call functions and share data with a server. ## Communication Fundamentals: HTTP and Client-Server Architecture ### Client and Server - **Client**: A web browser, mobile app, bot, IoT device, or any other application that initiates a request. - **Server**: A web or application server (Apache, Nginx, IIS), typically running on a physical or virtual machine. ### HTTP Principles - HTTP is a protocol layered on top of TCP/QUIC, operating at the application layer. It's a request-response protocol, stateless (state is not automatically maintained between requests). - The standard port is 80; for secure HTTPS traffic, we use TLS (port 443). > Definition: Stateless means that the server does not retain information about previous client requests; each request contains everything needed for processing. ### HTTP Methods (Most Important) - **GET** – Reads a resource (without side effects). - **POST** – Sends data to the server (e.g., creating a resource or submitting a form). - **PUT** – Creates or replaces a representation of the target resource. - **PATCH** – Partially updates a resource. - **DELETE** – Deletes a resource. Others: HEAD, OPTIONS, CONNECT, TRACE (primarily for diagnostics or specific scenarios). ### HTTP Headers and Response Codes - Headers carry metadata (User-Agent, Content-Type, Authorization, Cache-Control, etc.). - Response code groups: - 1xx informational - 2xx success (200, 201, 204) - 3xx redirection (301, 302, 304) - 4xx client error (400, 401, 403, 404, 405) - 5xx server error (500, 502, 503) Fun fact: For faster connection establishment and lower latency, modern websites use HTTP/2 or HTTP/3 — HTTP/3 runs over QUIC and significantly improves reconnection speed and multiplexing. ## REST (REpresentational State Transfer) ### Core Principles - REST is an architectural style that uses HTTP as its transport layer. - Everything is a **resource** identified by a URI; clients interact with it using a uniform interface (HTTP methods). - Key constraints: stateless, cacheability, uniform interface, layered system. > Definition: A REST API provides access to resources over HTTP, where resources are identified by URIs and operations are performed using standard HTTP methods. ### Data Formats - Most commonly, **JSON** is used; **XML** was common previously. REST does not restrict the format, but JSON is more modern for the web. ### Example REST URLs and Operations - GET https://api.example.com/users/123 — retrieve user with ID 123 - POST https://api.example.com/users — create a new user - PUT https://api.example.com/users/123 — replace user 123 - PATCH https://api.example.com/users/123 — modify parts of user 123 - DELETE https://api.example.com/users/123 — delete user 123 ### OpenAPI Specification (OAS) - OAS is an API description in JSON or YAML format that allows for generating documentation, client stubs, mock servers, and tests. - Main sections: openapi, info, servers, paths (operations), components (schemas, parameters, securitySchemes). Fun fact: A single OAS file can be used to automatically generate both a client library and interactive documentation (e.g., Swagger UI). ## JSON:API and GraphQL — Alternatives to "Pure" REST ### JSON:API - A specification that defines a consistent JSON format for REST APIs (media type application/vnd.api+json). - Standardizes the structure of responses, including relationships, meta, and included sections. ###