Fist of all I believe that you should ALWAYS use the async methods since they are better and your design will only benefit from a reactor pattern approach.
In the bad case that you're in a hurry and you're kind of prototyping, the sync methods can be useful. In this case I do agree with you that without any timeout support, they cannot be used in the real world.
What I did was very simple:
void HttpClientImpl::configureSocketTimeouts(boost::asio::ip::tcp::socket& socket)
{
#if defined OS_WINDOWS
int32_t timeout = 15000;
setsockopt(socket.native(), SOL_SOCKET, SO_RCVTIMEO, (const char*)&timeout, sizeof(timeout));
setsockopt(socket.native(), SOL_SOCKET, SO_SNDTIMEO, (const char*)&timeout, sizeof(timeout));
#else
struct timeval tv;
tv.tv_sec = 15;
tv.tv_usec = 0;
setsockopt(socket.native(), SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
setsockopt(socket.native(), SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
#endif
}
The code above works both on windows and on Linux and on MAC OS, according to the OS_WINDOWS macro.