常见的请求头信息

CONTENT_LENGTH– The length of the request body (as a string).
CONTENT_TYPE– The MIME type of the request body.
HTTP_ACCEPT– Acceptable content types for the response.
HTTP_ACCEPT_ENCODING– Acceptable encodings for the response.
HTTP_ACCEPT_LANGUAGE– Acceptable languages for the response.
HTTP_HOST– The HTTP Host header sent by the client.
HTTP_REFERER– The referring page, if any.
HTTP_USER_AGENT– The client’s user-agent string.
QUERY_STRING– The query string, as a single (unparsed) string.
REMOTE_ADDR– The IP address of the client.
REMOTE_HOST– The hostname of the client.
REMOTE_USER– The user authenticated by the Web server, if any.
REQUEST_METHOD– A string such as"GET"or"POST".
SERVER_NAME– The hostname of the server.
SERVER_PORT– The port of the server (as a string).