4xx - Client Errors, 5xx - Server Errors

362 단어·2 분·원문(.md)

Client Errors #

The server cannot fulfill the request due to malformed syntax in the client's request.
The error originates from the client.
Important: Since the client is already sending an incorrect request or data, retrying the exact same request will fail.

400 Bad Request #

The server cannot process the request because the client sent a malformed request.

Errors in request syntax, message, etc.
The client should review or resend the request content.
Example: When request parameters are incorrect or do not match the API specification.

401 Unauthorized #

The client needs authentication for the requested resource.

Not authenticated.
When a 401 error occurs, the response should include the WWW-Authenticate header explaining the authentication method.
Note
- Authentication: Verifying who you are (login).
- Authorization: Granting permissions (e.g., access rights to specific resources like ADMIN privileges; authorization requires authentication).
- Although the error message is 'Unauthorized', it means 'unauthenticated' (the name is a bit misleading).

403 Forbidden #

The server understood the request but refused to authorize it.

Typically occurs when authentication credentials exist, but access permissions are insufficient.
Example: A non-admin user is logged in but tries to access an admin-level resource.

404 Not Found #

The requested resource could not be found.

The requested resource does not exist on the server.
Or, when the client attempts to access a resource for which they lack sufficient permissions, and the server wishes to hide the existence of that resource.

5xx - Server Errors #

An error occurred due to a server issue.
Since the problem is with the server, retrying might succeed (e.g., if the server recovers).

500 Internal Server Error #

An error occurred due to a server issue; if it's ambiguous, it's a 500 error.

An error occurred due to an internal server problem.
If it's ambiguous, it's a 500 error.

503 Service Unavailable #

Service Unavailable.

The server is temporarily unable to handle the request due to temporary overload or scheduled maintenance.
It may also send a Retry-After header field indicating when the service will be restored.

Ideally, 5xx errors should not occur. They indicate genuine server problems (e.g., NullPointerException, database downtime, etc.).