Something

// Sends a string over a TCP/IP connection to a connection file descriptor
// Usage: dsend(connfd, "Blah blah %s", moreblah);
// Problem: Sometimes messages are sent, but more often than not they never get sent
// if I change buf (in dsend) to buf[2048] and just vsnprintf 2048 size to start, then it works
// however, I want to support an arbitrary length sent to dsend()
// Any ideas appreciated!

ssize_t writen(int fd, const void* vptr, size_t n)
{
	size_t nleft;
	ssize_t nwritten;
	const char* ptr;

	ptr = vptr;
	nleft = n;
	while( nleft > 0 )
	{
		if( (nwritten = write(fd, ptr, nleft)) <= 0 )
		{
			if( errno == EINTR )
			{
				nwritten = 0;	// and call write() again
			}
			else
			{
				return -1;
			}
		}

		nleft -= nwritten;
		ptr += nwritten;
	}

	return n;
}

void dsend(int sockfd, const char *fmt, ...)
{
	va_list args;
	char c, *buf;
	int buf_len;

	if( sockfd >= 0 )
	{
		va_start(args, fmt);
		buf_len = vsnprintf(&c, 1, fmt, args) + 1;
		buf = malloc(buf_len);
		vsnprintf(buf, buf_len, fmt, args);
		va_end(args);

		writen(sockfd, buf, buf_len+1);
		free(buf);
	}
}