HTTP Headers - Part 4 of Chapter 3 from HTTP: The Definitive Guide (3/6)
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HTTP: The Definitive Guide, Chapter 3: HTTP Messages
Request Headers
Request headers are headers that make sense only in a request message. They give information about who or what is sending the request, where the request originated, or what the preferences and capabilities of the client are. Servers can use the information the request headers give them about the client to try to give the client a better response. Table 3-13 lists the request informational headers.
Table 3-13: Request informational headers
Header | Description |
|---|---|
Client-IP[7] | Provides the IP address of the machine on which the client is running |
From | Provides the email address of the client's user[8] |
Host | Gives the hostname and port of the server to which the request is being sent |
Referer | Provides the URL of the document that contains the current request URI |
UA-Color | Provides information about the color capabilities of the client machine's display |
UA-CPU[9] | Gives the type or manufacturer of the client's CPU |
UA-Disp | Provides information about the client's display (screen) capabilities |
UA-OS | Gives the name and version of operating system running on the client machine |
UA-Pixels | Provides pixel information about the client machine's display |
User-Agent | Tells the server the name of the application making the request |
Accept headers
Accept headers give the client a way to tell servers their preferences and capabilities: what they want, what they can use, and, most importantly, what they don't want. Servers can then use this extra information to make more intelligent decisions about what to send. Accept headers benefit both sides of the connection. Clients get what they want, and servers don't waste their time and bandwidth sending something the client can't use. Table 3-14 lists the various accept headers.
Table 3-14: Accept headers
Header | Description |
|---|---|
Accept | Tells the server what media types are okay to send |
Accept-Charset | Tells the server what charsets are okay to send |
Accept-Encoding | Tells the server what encodings are okay to send |
Accept-Language | Tells the server what languages are okay to send |
TE[10] | Tells the server what extension transfer codings are okay to use |
7. Client-IP and the UA-* headers are not defined in RFC 2616 but are implemented by many HTTP client applications. Back
8. An RFC 822 email address format. Back
9. While implemented by some clients, the UA-* headers can be considered harmful. Content, specifically HTML, should not be targeted at specific client configurations. Back
10. See "Transfer-Encoding Headers" in Chapter 15 for more on the TE header. Back
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Created: February 5, 2003
Revised: February 5, 2003
URL: https://webreference.com/programming/http/chap3/4/3.html
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