From Wikipedia, the free encyclopedia
HTTP Headers form the core of an HTTP request, and are very important in an HTTP response. They define various characteristics of the data that is requested or the data that has been provided.
This is an incomplete list of some of the HTTP headers defined in RFC 2616 and RFC 2109 for HTTP/1.1
[edit] Requests
| Header |
Description |
Example |
| Accept |
Content-Types that are acceptable |
Accept: text/plain |
| Accept-Charset |
Character sets that are acceptable |
Accept-Charset: iso-8859-5 |
| Accept-Encoding |
Acceptable encodings |
Accept-Encoding: compress, gzip |
| Accept-Language |
Acceptable languages for response |
Accept-Language: da [1] |
| Accept-Ranges |
Allows the server to indicate its acceptance of range requests for a resource |
Accept-Ranges: bytes |
| Authorization |
Authentication credentials for HTTP authentication |
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ== |
| Cache-Control |
Used to specify directives that MUST be obeyed by all caching mechanisms along the request/response chain |
Cache-Control: no-cache |
| Connection |
What type of connection the user-agent would prefer |
Connection: close |
| Cookie |
an HTTP cookie previously sent by the server with Set-Cookie (below) |
Cookie: $Version=1; UserId=JohnDoe |
| Date |
The date and time that the message was sent |
Date: Tue, 15 Nov 1994 08:12:31 GMT |
| Host |
The domain name of the server (for virtual hosting), mandatory since HTTP/1.1 |
Host: en.wikipedia.org |
| If-Modified-Since |
Allows a 304 Not Modified to be returned if content is unchanged |
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
| If-None-Match |
Allows a 304 Not Modified to be returned if content is unchanged, see HTTP_ETag |
If-None-Match: 737060cd8c284d8af7ad3082f209582d |
| User-Agent |
The user agent string of the user agent |
User-Agent: Mozilla/5.0 (Linux; X11; UTF-8) |
[edit] Responses
| Header |
Description |
Example |
| Accept-Ranges |
What partial content range types this server supports |
Accept-Ranges: bytes |
| Age |
The age the object has been in a proxy cache in seconds |
Age: 12 |
| Allow |
Valid actions for a specified resource. To be used for a 405 Method not allowed |
Allow: GET, HEAD |
| Cache-Control |
Tells all caching mechanisms from server to client whether they may cache this object |
Cache-Control: no-cache |
| Content-Encoding |
The type of encoding used on the data |
Content-Encoding: gzip |
| Content-Language |
The language the content is in |
Content-Language: da |
| Content-Length |
The length of the response body in bytes |
Content-Length: 348 |
| Content-Location |
An alternate location for the returned data |
Content-Location: /index.htm |
| Content-Disposition |
An opportunity to raise a "File Download" dialog box for a known MIME type |
Content-Disposition: attachment; filename=fname.ext |
| Content-MD5 |
An MD5 sum of the content of the response |
Content-MD5: 3167b9c13ad2b6d36946493fc47976c8 |
| Content-Range |
Where in a full body message this partial message belongs |
Content-Range: bytes 21010-47021/47022 |
| Content-Type |
The mime type of this content |
Content-Type: text/html; charset=utf-8 |
| Date |
The date and time that the message was sent |
Date: Tue, 15 Nov 1994 08:12:31 GMT |
| ETag |
An identifier for a specific version of a resource, often a Message Digest, see ETag |
ETag: 737060cd8c284d8af7ad3082f209582d |
| Last-Modified |
The last modified date for the requested object |
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT |
| Location |
Used in redirection |
Location: http://www.w3.org/pub/WWW/People.html |
| Server |
A name for the server |
Server: Apache/1.3.27 (Unix) (Red-Hat/Linux) |
| Set-Cookie |
an HTTP cookie |
Set-Cookie: UserID=JohnDoe; Max-Age=3600; Version=1 |
[edit] Effects of selected HTTP headers
[edit] Cache-Control
If the server responds with Cache-Control: no-cache then in particular a web browser must not cache the object. In a web browser one effect of this is that if one returns to a previous web page by clicking on the back button, then, if that page was sent with the Cache-Control: no-cache directive, the browser will request the page again. This introduces latency. Depending on the situation this may or may not be appropriate. During a login session it is likely that caching is undesirable since pages may contain sensitive data. Therefore, by default in PHP, during a session, the Cache-Control header will be set to prevent caching.
[edit] References
- ^ Climb to the Stars (Stephanie Booth) » Browser Language Detection and Redirection
[edit] See also
[edit] External links
