Question

I have a socket that is receiving streaming stock tick data. However, I seem to get a lot of truncated messages, or what appears to be truncated messages. Here is how I am receiving data:

if((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {
    perror("recv()");
    exit(1);
}
else {
    buf[numbytes] = '\0';
    // Process data
}

Can recv() receive just a partial message of what was sent?

My feeling is I might need another loop around the recv() call that receives until a complete message is sent. I know that a libcurl implementation I have (not possible to use libcurl here I would think) has an outer loop:

// Read the response (sum total bytes read in tot_bytes)
for(tot_bytes=0; ; tot_bytes += iolen)
{  
    wait_on_socket(sockfd, 1, 60000L);
    res = curl_easy_recv(curl, buf + tot_bytes, sizeof_buf - tot_bytes, &iolen);

    if(CURLE_OK != res) {
        // printf( "## %d", res );
        break;
    }
}

Do I need an recv() loop similar to the libcurl example (that verifiably works)?

Answer 1

You’re right, you need a loop. recv only retrieves the data that’s currently available; once any data has been read, it doesn’t wait for more to appear before it returns.

The manual page says “The receive calls normally return any data available, up to the requested amount, rather than waiting for receipt of the full amount requested.”