How to use NSOutputStream's write message?

Answer 1

You should be writing the data only after space becomes available in the output stream. When the stream finishes opening, it doesn't always immediately have space available, so writing to it won't work. If you move the write call to the NSStreamEventHasSpaceAvailable handler, it should succeed.

Also, the computer on the other end of the socket has no way of knowing the length of the data you're sending. Unless you're signaling the end-of-data by closing the socket, you should explicitly send the data length along with the data:

case NSStreamEventHasSpaceAvailable:
{
    if(stream == oStream)
    {
        NSData *data = UIImageJPEGRepresentation(drawImage.image, 90);
        // Convert from host to network endianness
        uint32_t length = (uint32_t)htonl([data length]);
        // Don't forget to check the return value of 'write'
        [oStream write:(uint8_t *)&length maxLength:4];
        [oStream write:[data bytes] maxLength:length];
    }
    break;
}

Answer 2

And how do you do if you want to keep the socket open, and then write to it later???