Key Takeaways
REST API is a REST-compliant API that enables effective communication between clients and servers.
Knowledge of HTTP methods, URLs, headers, and request bodies is crucial for building robust REST APIs with secure data exchange.
REST APIs are widely adopted in modern applications, supporting various use cases and integrations, such as B2B data and service exchanges, B2C interactions like providing users access to trading platforms, and internal use cases like connecting systems for improved data accessibility.
Introduction
In today's interconnected world, software systems need to communicate and share data efficiently across diverse platforms and environments.
However, achieving seamless integration between different systems can be challenging due to varying technologies, data formats, and protocols. This is where Application Programming Interfaces (APIs) come in, providing standardized ways for software to interact.
Among the different types of APIs, Representational State Transfer (REST) has become one of the dominant choices due to its simplicity, flexibility, and broad compatibility. This article will explore the REST architecture and break down how a REST API request is composed.
REST Architecture Standards
Representational State Transfer (REST) is a software architectural style that defines a set of rules and conventions for building and interacting with web services. RESTful web services are systems that comply with the principles of REST, where communication typically occurs over HTTP in a one-way style:
Client: Requests to access or manipulate resources.
Server: Responds to client requests by providing access to the requested resources or performing the requested operation.
A REST API is the specific type of API that enables client-server communication and adheres to the principles and conventions of the REST architectural style, which is characterized by the following key principles:
Client-Server Architecture: The client and server are independent entities that interact over a network. The server provides resources, and the client requests them, ensuring a separation of concerns.
Stateless Communication: Each request from a client must contain all the information needed for the server to understand and process the request. The server doesn’t store any context between requests, making each interaction independent.
Cacheability: Responses from the server should indicate whether they are cacheable or not. If a response is cacheable, the client can reuse the response data for identical requests in the future, reducing the need for repeated server interactions.
Layered System: The client may interact with the server indirectly through multiple layers, such as security layers, load balancers, or caches. Each layer serves a specific function and remains unaware of the other layers, enhancing flexibility and scalability.
Uniform Interface: The API must have a common protocol for interacting with resources, typically through a set of standard HTTP methods like GET, POST, PUT, and DELETE.
HTTP is widely adopted due to its simplicity and alignment with REST principles—such as stateless communication, cacheability, and a uniform interface. While it is technically possible to implement REST over other protocols, the use of HTTP provides a straightforward and standardized approach that facilitates building scalable, reliable, and easy-to-maintain web services.
Client Request
Structure
A REST API request using HTTP is built by the following essential components:
1. HTTP Method: Defines the type of operation being performed. Mainly CRUD operations (Create, Read, Update, and Delete), with each corresponding to a specific HTTP method:
GET: Retrieves data from a server without altering it., enabling clients to access the information they need.
POST: Submits data to a server, often resulting in the creation of a resource.
PUT: Replaces an existing resource or creates a new one if it does not exist already. This ensures that data remains current and accurate.
DELETE: Removes the specified resource at URI from the server, effectively managing the life-cycle of data by eliminating what is no longer needed.
While additional HTTP methods such as PATCH, HEAD, OPTIONS, CONNECT, and TRACE exist, GET, POST, PUT, and DELETE are considered the four fundamental ones.
2. Uniform Resource Locator (URL): Specifies the endpoint of the API that the request is targeting. It includes the base URL (host) of the API and the specific path to the resource.
3. Headers: Provides additional information about the request. Common headers include:
Content-Type: Indicates the media type of the resource being sent, such as application/json for JSON data.
Accept: Informs the server about the types of content the client can understand (e.g., application/json).
User-Agent: Contains information about the client software initiating the request, such as the browser or other user agent.
4. Request Body: For methods like POST and PUT, the request body contains the data to be sent to the server. This data is often formatted as JSON or XML, depending on the Content-Type header.
5. Query Parameters: These are parameters included in the URL after a question mark (?). They are used to filter or modify the request, such as using ?sort=asc to sort results in ascending order. Some requests don’t require parameters; this often happens with the GET method.
Example
GET /users?sort=asc HTTP/1.1
Host: api.example.com
Accept: application/json
User-Agent: PostmanRuntime/7.40.0This GET request retrieves a list of users from api.example.com, sorted in ascending order, and expects a JSON response, using the Postman tool.
POST /users HTTP/1.1
Host: api.example.com
Content-Type: application/json
Accept: application/json
User-Agent: PostmanRuntime/7.40.0
{
"name": "John Doe",
"email": "john.doe@example.com"
}This POST request to api.example.com creates a new user with the name "John Doe" and email "john.doe@example.com," sending the request body data in JSON format and expecting a JSON response, using the Postman tool.
Server Response
Structure
A REST API response is the data sent back from the server to the client after a request is made. It typically includes:
1. Status code: Represents the result of a request
1xx (Informational): Request received, continuing process.
2xx (Success): The request was successfully received, understood, and accepted.
3xx (Redirection): Further action must be taken to complete the request.
4xx (Client Error): The request contains bad syntax or cannot be fulfilled.
5xx (Server Error): The server failed to fulfill a valid request.
500 Internal Server Error: The server encountered a condition that prevented it from fulfilling the request.
2. Headers: Provides metadata like content type. Common:
Content-Type: Indicates the media type of the response body (e.g., application/json, text/html).
Content-Length: The size of the response body in bytes.
Cache-Control: Directives for caching mechanisms in both requests and responses.
Date: The date and time at which the message was sent.
3. Body: actual data returned by the API in formats like JSON or XML.
Example
If a client requests user information from an API endpoint (GET /users/123), the response might look like:
HTTP/1.1 200 OK
Content-Type: application/json
{
"id": 123,
"name": "John Doe",
"email": "john.doe@example.com"
}This response includes a status code (200 OK), a content type (application/json), and a JSON body with user details.
Closing Thoughts
REST APIs have become a cornerstone of modern applications, providing one of the most effective ways to enable communication between clients and servers. By understanding and correctly using HTTP methods, URLs, headers, and request bodies, developers can build scalable and secure APIs that ensure robust and efficient data exchange.
As a result, many companies use REST APIs to expose their services to developers, fostering the creation of countless integrations and applications—whether internally, publicly, or with business partners.
Further Reading
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