HTTP status codes are a fundamental part of RESTful API design. They are issued by a server in response to a client's request made to the server. These codes help the client understand the result of their request and take appropriate actions. In this section, we will explore the different categories of HTTP status codes and their specific meanings.

HTTP status codes are divided into five categories:

1. 1xx Informational
2. 2xx Success
3. 3xx Redirection
4. 4xx Client Errors
5. 5xx Server Errors

These codes indicate that the request has been received and the process is continuing.

• 100 Continue: The server has received the request headers, and the client should proceed to send the request body.
• 101 Switching Protocols: The requester has asked the server to switch protocols, and the server has agreed to do so.

These codes indicate that the client's request was successfully received, understood, and accepted.

• 200 OK: The request has succeeded. The meaning of the success depends on the HTTP method:
  • GET: The resource has been fetched and is transmitted in the message body.
  • POST: The resource describing the result of the action is transmitted in the message body.
• 201 Created: The request has been fulfilled, resulting in the creation of a new resource.
• 202 Accepted: The request has been accepted for processing, but the processing has not been completed.
• 204 No Content: The server successfully processed the request, but is not returning any content.

These codes indicate that further action needs to be taken by the user agent to fulfill the request.

• 301 Moved Permanently: The resource has been moved to a new URL permanently.
• 302 Found: The resource has been temporarily moved to a different URL.
• 304 Not Modified: The resource has not been modified since the version specified by the request headers.

These codes indicate that the client seems to have made an error.

• 400 Bad Request: The server cannot or will not process the request due to a client error (e.g., malformed request syntax).
• 401 Unauthorized: The request requires user authentication.
• 403 Forbidden: The server understood the request, but refuses to authorize it.
• 404 Not Found: The server cannot find the requested resource.
• 405 Method Not Allowed: The request method is known by the server but is not supported by the target resource.

These codes indicate that the server failed to fulfill a valid request.

• 500 Internal Server Error: The server encountered an unexpected condition that prevented it from fulfilling the request.
• 501 Not Implemented: The server does not support the functionality required to fulfill the request.
• 502 Bad Gateway: The server, while acting as a gateway or proxy, received an invalid response from the upstream server.
• 503 Service Unavailable: The server is currently unable to handle the request due to temporary overloading or maintenance.

Let's look at some practical examples of how HTTP status codes are used in RESTful APIs.

Response:

Response:

Response:

Given the following scenarios, identify the appropriate HTTP status code:

1. A client sends a request to update a resource, but the resource does not exist.
2. A client sends a request to create a new resource, and the server successfully creates it.
3. A client sends a request with invalid syntax.

1. 404 Not Found: The resource does not exist.
2. 201 Created: The resource was successfully created.
3. 400 Bad Request: The request has invalid syntax.

• Using 200 OK for all responses: It's important to use the correct status code to accurately represent the outcome of the request.
• Ignoring 4xx and 5xx codes: Always handle client and server errors appropriately to provide meaningful feedback to the client.
• Not using 201 Created for POST requests: When a new resource is created, always use 201 Created to indicate the successful creation.

Understanding and correctly using HTTP status codes is crucial for designing and developing robust RESTful APIs. These codes provide essential information to clients about the result of their requests and help in debugging and error handling. In the next section, we will explore API versioning and its importance in maintaining backward compatibility.