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Using the readall_poor() function in the chat server
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-Ian! D. Allen - idallen@idallen.ca

The stateful readall() can't be used in the chat server (selectserver.c);
because, that server never forks and all the readall()s run in the same
address space.  All the client inputs would mix together in the single
internal buffer.

The single readall() in your client will work fine; it's only the
selectserver that has the problem (and only with multiple clients).

The kludge fix is to have a stateless readall() named readall_poor()
that you use *only to build your selectserver*.  Replace the calls
to "read" with calls to "readall_poor" in your selectserver.c file.
Don't use the readall() code in the selectserver; use readall_poor().

Here's the most of the code:

// This function is used as a drop-in replacement for read() on a
// socket.  It reads enough bytes to find either a line ending in a
// newline or a full buffer.  The function has no internal state and
// can be used on other descriptors at the same time.  It is extremely
// inefficient, since it calls read() for every character!  It also
// throws away any partial line collected when EOF/error happens.
//
// This function should only be used in the chat server "selectserver".
//
// Author: Ian D. Allen idallen@idallen.ca
    ssize_t
readall_poor(int fd, char *buf, size_t len){
    char *bufp = buf;      // pointer to output buffer buf
    char *end = bufp+len;  // end of output buffer buf
    ssize_t total = 0;      // count of characters copied to buf

    for(;;) {
        if( bufp == end )
            break;                  // output buffer is full; return
        int ret = read(fd,bufp,1);  // read a single char
        if( ret <= 0 ){
            if( ret < 0 )
                perror("readall reading");
            // BAD: this throws away a partially collected line at EOF/error
            total = 0;              // return EOF indication to caller
            break;
        }
        bufp += ret;                // move to next output position
        total += ret;               // count the character written
        if( bufp[-1] == NEWLINE )
            break;                  // return if last char written was \n
    }
    assert(total <= len);           // "man 3 assert"
    assert(bufp <= end);
    return total;
}