Interview surprise: What are the common HTTP status codes?

HTTP status code is the response status code returned by the server to the client. According to the (HTTP) status code, we can know the specific meaning that the server wants to express to the client. For example, 200 means the request is successful, and 500 means the server program has an error. HTTP status codes can be divided into 5 categories:

• 1XX: message status code.
• 2XX: Success status code.
• 3XX: Redirection status code.
• 4XX: Client error status code.
• 5XX: Server error status code.

These five categories contain many specific status codes.

1XX

Message status code, where:

• 100: Continue. The client should continue with its request.
• 101: Switching Protocols. The server switches protocols based on the client's request. It can only switch to a more advanced protocol, for example, a new version of HTTP.

2XX

Success status code, where:

• 200: OK The request is successful. Usually used for GET and POST requests.
• 201: Created. A new resource was successfully requested and created.
• 202: Accepted. The request has been accepted but not processed.
• 203: Non-Authoritative Information. The request is successful. However, the returned meta information is not on the original server, but a copy.
• 204: No Content. The server successfully processed but did not return any content. If the web page is not updated, it ensures that the browser continues to display the current document.
• 205: Reset Content Reset content. The server process is successful, and the user terminal (for example: browser) should reset the document view. This return code can be used to clear the form fields of the browser.
• 206: Partial Content Partial content. The server successfully processed part of the GET request.

3XX

Redirect status code, where:

• 300: Multiple Choices. The requested resource may include multiple locations, and a list of resource features and addresses may be returned for the user terminal (e.g., browser) to select.
• 301: Moved Permanently. The requested resource has been permanently moved to a new URI. The returned information will include the new URI, and the browser will automatically be directed to the new URI. Any new requests in the future should use the new URI instead.
• 302: Found Temporary move, similar to 301. However, the resource is only temporarily moved. The client should continue to use the original URI.
• 303: See Other View other addresses. Similar to 301. Use GET and POST requests to view.
• 304: Not Modified. The requested resource has not been modified. When the server returns this status code, no resource will be returned. Clients usually cache the resources they have visited, and provide a header information indicating that the client hopes to return only resources modified after the specified date.
• 305: Use Proxy. The requested resource must be accessed through a proxy.
• 306: Unused This is an obsolete HTTP status code.
• 307: Temporary Redirect Temporary redirection. Similar to 302. Use GET request to redirect.

4XX

Client error status code, where:

• 400: Bad Request The client request has a syntax error and the server cannot understand it.
• 401: Unauthorized The request requires user authentication.
• 402: Payment Required Reserved for future use.
• 403: Forbidden The server understands the client's request, but refuses to execute it.
• 404: Not Found The server cannot find the resource (webpage) according to the client's request. With this code, website designers can set up a personalized page that says "The resource you requested cannot be found."
• 405: Method Not Allowed The method in the client request is prohibited.
• 406: Not Acceptable The server cannot complete the request based on the content characteristics of the client request.
• 407: Proxy Authentication Required The request requires proxy authentication, similar to 401, but the requester should use the proxy for authorization.
• 408: Request Time-out The server waited too long for the request sent by the client and timed out.
• 409: Conflict The server may return this code when completing a client's PUT request. A conflict occurred while the server was processing the request.
• 410: Gone The resource requested by the client no longer exists. 410 is different from 404. If the resource previously existed but is now permanently deleted, the 410 code can be used. Website designers can use the 301 code to specify the new location of the resource.
• 411: Length Required The server cannot process the request information sent by the client without Content-Length.
• 412: Precondition Failed The client requested information with a prerequisite error.
• 413: Request Entity Too Large The request entity is too large for the server to process, so the request is rejected. To prevent the client from making continuous requests, the server may close the connection. If the server is temporarily unable to process the request, a Retry-After response message will be included.
• 414: Request-URI Too Large The requested URI is too long (the URI is usually a URL) and the server cannot process it.
• 415: Unsupported Media Type The server cannot process the media format included with the request.
• 416: Requested range not satisfiable The range requested by the client is invalid.
• 417: Expectation Failed The server cannot meet the Expect request header information.

5XX

Server error status code, where:

• 500: Internal Server Error The server has an internal error and cannot complete the request.
• 501: Not Implemented The server does not support the requested function and cannot complete the request.
• 502: Bad Gateway The server, acting as a gateway or proxy, received an invalid response from the remote server while trying to perform a request.
• 503: Service Unavailable The server is temporarily unable to process the client's request due to overload or system maintenance. The length of the delay can be included in the server's Retry-After header information.
• 504: Gateway Time-out The server, acting as a gateway or proxy, did not get the request from the remote server in time.
• 505: HTTP Version not supported The server does not support the requested HTTP protocol version and cannot complete the processing.

Summarize

HTTP status codes are divided into five categories: 1XX: message status code; 2XX: success status code; 3XX: redirection status code; 4XX: client error status code; 5XX: server error status code. Common status codes include: 200: successful request; 301: permanent redirection; 302: temporary redirection; 404: page not found; 405: requested method type not supported; 500: internal server error.