The server’s response includes the following:
Status code
Response header
Response data
When a client makes a request, one item the server sends back is a status code, which is a three-digit numeric code. There are four categories of status codes:
Status codes in the 100–199 range indicate a provisional response.
Status codes in the 200–299 range indicate a successful transaction.
Status codes in the 300–399 range are returned when the URL can’t be retrieved because the requested document has moved.
Status codes in the 400–499 range indicate the client has an error.
Status codes of 500 and higher indicate that the server can’t perform the request, or an error has occurred.
Status Code contains some common status codes.
Table B–2 Common HTTP status codes
Status code |
Meaning |
---|---|
OK; successful transmission. This is not an error. |
|
302 |
Found. Redirection to a new URL. The original URL has moved. This is not an error; most browsers will get the new page. |
304 |
Use a local copy. If a browser already has a page in its cache, and the page is requested again, some browsers (such as Netscape Navigator) relay to the web server the “last-modified” timestamp on the browser’s cached copy. If the copy on the server is not newer than the browser’s copy, the server returns a 304 code instead of returning the page, reducing unnecessary network traffic. This is not an error. |
401 |
Unauthorized. The user requested a document but didn’t provide a valid username or password. |
403 |
Forbidden. Access to this URL is forbidden. |
404 |
Not found. The document requested isn’t on the server. This code can also be sent if the server has been told to protect the document by telling unauthorized people that it doesn’t exist. |
500 |
Server error. A server-related error occurred. The server administrator should check the server’s error log to see what happened. |
The response header contains information about the server and information about the document that will follow. Common response headers are shown in Response Header.
Table B–3 Common response headers
Response header |
Description |
---|---|
The name and version of the web server. |
|
The current date (in Greenwich Mean Time). |
|
The date when the document was last modified. |
|
The date when the document expires. |
|
The length of the data that follows (in bytes). |
|
The MIME type of the following data. |
|
Used during authentication and includes information that tells the client software what is necessary for authentication (such as username and password). |
The server sends a blank line after the last header field. The server then sends the document data.