ity header using the COPY method. The HTTP response message (see Figure 28.3) has a status line that includes HTTP version, status code, and the status phrase. The HTTP version in the status line and the request line are the same. A three digit code representing the status is the status code and the status code is explained in text form by the status phrase. Information can also be exchanged between the client and the server using head- ers. The client can request the document be sent in a special format or the server can send additional information about the document using headers. One or more header lines make up the header and each header line consist of the header name, a colon, a space, and a header value. A header line belongs to the following four categories: General header: General information about the message are provided by the general header. The general header can be present in both request and response. Web Communication Response message Space Status line Space Status Status code version phrase Headers Space Header name Header value Blank line Body (optional) Figure 28.3 HTTP response message. Request header: The client's configuration and its preferred document format are specified by the request header. The request header is present only in the request message. Response header: The server's configuration and its special information about the request are specified by the response header. The response header is pres- ent only in the response message. Entity header: Information about the document body is provided by the entity header. It is usually present in response messages. Request messages like POST method that has a body can also uses this header. The request messages contain only general header, request header, and entity header and the response messages contain only general header, response header, and entity headers. An important aspect of HTTP interaction is the proxy server. It is a server that keeps the copies of responses to recent requests. When a request is received from the HTTP clien