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Calling setsockopts on unconnected socket #16
Description
As far as I can tell, it isn't possible to set options on a socket without first getting it into the connected state. It would be useful to do this, for example, to set the socket option SO_REUSEADDR before connecting. The problem is that the socket isn't actually created until connection time.
Using setsockopt with inet_stream::getfd works fine after connecting, because the socket file descriptor is then valid.
Am I missing something, or is this not possible?
Activity
dermesser commentedon Apr 23, 2014
It's hardly possible for both the C and the C++ part because TCP client sockets are created and immediately connected after that in create_inet_stream_socket in C/inet/libinetsocket.c (actual socket()/connect() in lines 185+). From the viewpoint of libsocket++, it's an atomic operation.
The only possibility I see at the moment is introducing some more parameters in create_inet_stream_socket which are passed to a setsockopt call. Or, if you want to especially set the SO_REUSEADDR flag, a boolean (in C: int) flag.
thirtythreeforty commentedon Apr 23, 2014
I follow. Shouldn't the socket be created when the object is created (RAII) and then only connected when you call
connect()? (The constructor could of course callconnect()too if appropriate.)I think the more-parameter option is a decent one, but how would you set multiple options in a scalable way? The only possibility I see is accepting a
std::vectorof parameter:value pairs but that doesn't seem very clean in C.dermesser commentedon Apr 23, 2014
It may at first seem as a better alternative to do it the RAII way you mentioned.
But there comes a load of problems with it, the (in my opinion) most important one being the choice of the address family. Usually I would use
LIBSOCKET_BOTHto letgetaddrinfo()choose what address family to use. In that case, I have to create the socket after callinggetaddrinfo(), which is done increate_inet_stream_socket(). But if I want to create the socket first and then connect it, I already have to know the address family. I may do that, libinetsocket has a function for it, but it's still not desirable (I believe).Using an additional parameter
int sockoptsmay work best in that situation. It would be passed tocreate_inet_stream_socketandinet_stream::inet_stream()(and connect() and so on) and take the values defined in<sys/socket.h>.thirtythreeforty commentedon Apr 23, 2014
Gotcha. That makes sense.
If you are going to pass
sockopts, how would you pass multiple options? For example, if I want to set the two optionsSO_REUSEADDRandSO_REUSEPORT, I can't just bitwise-or them together for a single call... They're defined as 2 and 15.dermesser commentedon Apr 23, 2014
Hm... Didn't think of that...
What about implementing
LIBSOCKET_...wrappers that may get bitwise ORed, for example:LIBSOCKET_REUSEADDR == 1,LIBSOCKET_REUSEPORT == 2,LIBSOCKET_DONTROUTE == 4etc. And then converting them back to theSO_...constants.thirtythreeforty commentedon Apr 23, 2014
That would work. There would be a lot of
ifstatements, but welcome to C 😆. Adding an argument is going to break the interface for existing programs, as C doesn't overload. C++ should be fine though.Also, oops, I didn't mean to close this.
dermesser commentedon Apr 23, 2014
cf. https://github.com/dermesser/libsocket/blob/master/C/inet/libinetsocket.c#L572 Maybe a little more compact, and we're fine 👍