1. General Header Fields: headers used by both the request message and the response message
1.Cache-Control control cache
2.Connection connection management, item by item header
3.Upgrade to other agreements
4. Via proxy server information
5.warning error and warning notification
6. Transfor-Encoding The transmission encoding format of the message body
7. List of headers at the end of the Trailer message
8.Pragma message instruction
9.Data Date the message was created
2. Request Header Fields
1. Accept the media types that the client or agent can handle
2. Accept-Encoding priority can be processed encoding format
3. Accept-Language priority natural language
4. Accept-Charset priority can be processed character set
5. If-Match compare entity flag (ETage)
6. if-None-Match compare entity flag (ETage) is opposite to if-Match
7. If-Modified-Since compare resource update time (Last-Modified)
8. if-Unmodified-Since compare resource update time (Last-Modified), opposite to if-Modified-Since
9. If-Ranges resource is not updated, send entity byte request range request
10.Ranges entity byte request range
11.Authorization web authentication information
12.Proxy-Authorization proxy server requires web authentication message
13.Host The server where the resource is requested
14.From user's email address
15.User-Agent client program information
16.Max-ForWards maximum number of hops
17. Priority of TE transmission coding
18.Referer requests the original URL
19.Expect the specific behavior of the server
3. Response Header Fields: Fields used when responding from the server to the client
1. Accept-Ranges can accept byte range
2.Age estimates the elapsed time of resource creation
3.Location URL to redirect the client
4. Vary proxy server cache information
5. ETag can represent a string of unique resources
6. WWW-Authenticate server requires client authentication information
7.Proxy-Authenticate Proxy server requires client authentication information
8.Server server information
9. Retry-After and status code 503 used together in the header field, indicating the time of the next request to the server
4. Entiy Header Fields: Use the header for the entity part of the request message and response message
1.Allow resource can support http request method
2. Content-Language entity resource language
3. Content-Encoding entity encoding format
4. The size of the Content-Length entity (bytes)
5. Content-Type entity media type
6.Content-MD5 summary of the entity message
7. Location instead of yri Content of the resource
8.Ranges The position of the entity body returns Last
9.Modified resource The last modified resource
10.Expires the expired resources of the entity subject