Question

I am reading character by character of a socket response in a BufferedReader written from a socket that I am connecting to a SMTP and POP server. But how do I know if I have read until the end of the response to avoid having the read() to hang for reading beyond what the server responded? The following code is how I am reading from the BufferedReader:

boolean endOfResponse = false;
while(!endOfResponse) {
    c = in.read();
    if ((c >= 32 && c < 127) || c == '\t' || c == '\r' || c == '\n') { 
        response.append((char)c);
        //The following check has a problem: If the response has multiple lines, the other lines will not be read.
        if(c == '\n') endOfResponse = true;
    }
}

For instance, in POP, when I do a LIST, the response ends with a .. But in SMTP, when I do a EHLO, it doesn’t give clear indication of when the response has ended.

The use of in.read() == -1, sadly, doesn’t work as it will still attempt to read beyond the responded data and causes the socket to hang.

So, how do I determine the end of a SMTP and POP response? Better still, is it even possible to know before hand how many bytes I should read from the buffer so that I won’t even have to check for end of response?

Answer 1

The 2 protocols are different but both are sending messages that end with a newline. With SMTP, you read 1 line at a time (ending with \n), each line you read should start with 3 numbers, then either a space or a ‘-‘, if it’s a space, then that’s the end of the server’s response, if it’s a ‘-‘ (like 250-VRFY which is what you’d get if you opened up with an EHLO, prompting the server to respond with a list of extended ESMTP commands) then you need to read another line.

With POP3, I believe it depends on the command that you issue. Something like USER or PASS gives you a ‘+’ or ‘-‘ response (followed by a code and some text). A command like LIST gives you a ‘+’ or ‘-‘, and if ‘+’, you get your list of emails, which will end with a single ‘.’ by itself. Each of these responses (as well as each index of an email) will be a line.

You should take a look at RFC 821 for SMTP and RFC 1939 for POP3 to get a detailed description of the protocols