HTTP Responses

What is an HTTP Response?

An HTTP response is the message sent by a server back to a client (usually a browser or mobile app) after receiving an HTTP request. It includes important information about the result of the request — whether it succeeded, failed, or needs further action.

Understanding HTTP responses is crucial for debugging issues, building reliable APIs, and optimizing web performance.

Structure of an HTTP Response

An HTTP response typically consists of three main parts:

1. Status Line

Indicates the outcome of the request.

Example:

HTTP/1.1 200 OK

• HTTP/1.1: The HTTP version.
• 200: The status code.
• OK: The status message.

2. Headers

Metadata about the response.

Examples:

Content-Type: application/json
Content-Length: 512
Cache-Control: no-cache

Headers provide information like content type, cache policies, server info, cookies, and more.

3. Body

The actual data returned from the server.

Example (JSON response):

{
  "id": 1,
  "name": "Jeremy",
  "role": "Developer"
}

The body is optional and depends on the request type and status.

Common HTTP Status Codes

HTTP status codes are grouped into five classes:

1xx: Informational

• 100 Continue – Indicates that the initial part of the request has been received.
• 101 Switching Protocols – The server is switching to a different protocol.
• 102 Processing (WebDAV) – The server has received and is processing the request.
• 103 Early Hints – Preload resources while waiting for the final response.

2xx: Success

• 200 OK – Standard response for a successful HTTP request.
• 201 Created – A resource was successfully created.
• 202 Accepted – The request was accepted but not yet processed.
• 203 Non-Authoritative Information – Metadata returned from a third-party.
• 204 No Content – The request was successful but returns no content.
• 205 Reset Content – Tells the client to reset the document view.
• 206 Partial Content – Partial GET request succeeded.
• 207 Multi-Status (WebDAV) – Multiple status codes returned for multiple operations.

3xx: Redirection

• 300 Multiple Choices – Multiple options for the resource.
• 301 Moved Permanently – This resource has been permanently moved.
• 302 Found – Resource temporarily moved.
• 303 See Other – See another URI with GET.
• 304 Not Modified – Cached version is still valid.
• 305 Use Proxy – Must access through proxy (deprecated).
• 307 Temporary Redirect – Temporarily redirected; method preserved.
• 308 Permanent Redirect – Permanently redirected; method preserved.

4xx: Client Errors

• 400 Bad Request – The request was malformed.
• 401 Unauthorized – Authentication is required.
• 402 Payment Required – Reserved for future use.
• 403 Forbidden – You don’t have permission.
• 404 Not Found – Resource not found.
• 405 Method Not Allowed – HTTP method not allowed.
• 406 Not Acceptable – Cannot respond with acceptable content.
• 407 Proxy Authentication Required – Proxy authentication needed.
• 408 Request Timeout – Client took too long to send request.
• 409 Conflict – Request conflicts with current server state.
• 410 Gone – Resource is permanently gone.
• 411 Length Required – Content-Length header required.
• 412 Precondition Failed – Conditions in headers not met.
• 413 Payload Too Large – Request body too large.
• 414 URI Too Long – URI is too long for the server.
• 415 Unsupported Media Type – Media type not supported.
• 416 Range Not Satisfiable – Requested range not available.
• 417 Expectation Failed – Expect header failed.
• 418 I'm a teapot – April Fools' joke RFC.
• 422 Unprocessable Entity – Syntax is correct, but semantics are wrong.
• 429 Too Many Requests – Rate limiting exceeded.

5xx: Server Errors

• 500 Internal Server Error – A generic server error.
• 501 Not Implemented – Feature not implemented.
• 502 Bad Gateway – Invalid response from upstream server.
• 503 Service Unavailable – Server is down or overloaded.
• 504 Gateway Timeout – Upstream server timeout.
• 505 HTTP Version Not Supported – HTTP version not supported.
• 507 Insufficient Storage – Not enough storage space.
• 508 Loop Detected – Infinite loop detected (WebDAV).
• 510 Not Extended – Further extensions are required.
• 511 Network Authentication Required – Network login required.

What is WebDAV?

WebDAV (Web Distributed Authoring and Versioning) is an extension of the HTTP protocol that allows clients to perform remote web content authoring operations. It enables features like:

• Creating, editing, and deleting files on a remote server
• Managing document properties (like author, creation date)
• Locking resources to prevent overwrites during editing
• Handling collections (e.g., folders and directories)

Many HTTP status codes like 102, 207, 422, 507, and 508 were introduced specifically to support WebDAV operations. It's commonly used in collaborative tools, CMS systems, and networked file management systems.

Example: HTTP Response

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 86
Connection: keep-alive
 
{
  "message": "Welcome back!",
  "user": {
    "id": 42,
    "name": "Jeremy"
  }
}

Why Understanding HTTP Responses Matters

• Debugging: Interpreting status codes helps pinpoint where things go wrong.
• Security: Proper use of 401/403/429 can improve API security.
• Performance: Effective use of 304 or 204 can enhance client efficiency.
• API Design: Clear, consistent responses improve developer experience.

Final Thoughts

HTTP responses are at the heart of every client-server interaction on the web. Whether you're building REST APIs, working with frontends, or debugging network issues, a solid grasp of status codes and response structures will save you time — and many headaches.

Whenever in doubt, remember: what the server says back matters just as much as what the client asks for.