Status Code

• 1××: Indicating an intermediate state of protocol processing
• 2××：Success
• 3××：Redirection
• 4××：Request error
• 5××：Server error

2××

• 200 OK

• 204 No Content: The response has no body.

• 206 Partial Content: The response has partial body.

  Usually, it has Content-Range. For exemple, Content-Range: bytes 0-99/2000. It means get first 100 bytes of 2000 bytes.

3××

• 301 Moved Permanently:

  The source no longer exists. we need to switch to a new URL.

• 302 Found:

  The source exists, but we need to use another URL to visit it.

Both 301 and 302 have Location that indicts the redirect URL.

• 304 Not Modified

  It's not of redirection. It's for caching.

4××

• 400 Bad Request:

  It's the general request error.

• 403 Forbidden:

  The client has no right to visit.

• 404 Not Found:

  The source requested is not found in the server.

• 405 Method Not Allowed: i.e. POST isn't allowed.

• 406 Not Acceptable: The source doesn't meet request.

• 408 Request Timeout

5××

• 500 Internal Server Error:

  It's general server error, similar to 400.

• 501 Not Implemented:

  The service is beening developed.

• 502 Bad Gateway:

  The error code returned by the gateway or proxy.

• 503 Service Unavailable:

  The service is busy, unavailable for now. It has Retry-after.