The Annoyance Filter.pdf - Fourmilab

§205 ANNOYANCE-FILTER POP3 PROXY SERVER CLASS DEFINITION 171
205. Read the next request from the client. Requests are always a single line consisting of POP_MAX_MESSAGE
characters or fewer.
〈 Read request from client 205 〉 ≡
if (popProxyTrace ) {
cerr ≪ "POP3:␣Reading␣request␣from␣client." ≪ endl ;
}
clientLength = recv (clientSocket , clientBuffer , POP_MAX_MESSAGE, 0);
if (popProxyTrace ) {
cerr ≪ "POP3:␣Read␣" ≪ clientLength ≪ "␣request␣bytes␣from␣client." ≪ endl ;
}
if (clientLength ≤ 0) {
break;
}
This code is used in section 204.
206. RFC 1939 is silent on the issue, but the POP3 server I tested with seems to silently discard
blank lines without issuing an “−ERR” response. Since this can hang up our proxy cycle, eat blank lines
without passing them on to the server. This shouldn’t happen with a properly operating client, but it’s
all too easy to do when testing with Telnet, and besides, we have to cope with screwball clients which
may do anything.
〈 Check for blank request and discard 206 〉 ≡
if (isspace (clientBuffer [0])) {
continue;
}
This code is used in section 204.
207. Pass on the client request to the server.
〈 Forward request to server 207 〉 ≡
serverLength = send (serverSocket , clientBuffer , clientLength , 0);
if (serverLength ≠ clientLength ) {
perror ("POP3Proxy␣forwarding␣request␣to␣server");
break;
}
This code is used in section 204.