As libzmq is compiled with optional transports and security mechanisms,
there is no clean way for applications to determine what capabilities
are actually available in a given libzmq instance.
Solution: provide an API specifically for capability reporting. The
zmq_has () method is meant to be open ended. It accepts a string so
that we can add arbitrary capabilities without breaking existing
applications.
zmq.h also defines ZMQ_HAS_CAPABILITIES when this method is provided.
Solution: use same approach as for libsodium/CURVE, i.e. return EINVAL
if the library isn't present when libzmq builds, and the application
still tries to use these options in zmq_getsockopt/setsockopt.
The example is applications passing invalid arguments to a socket option
and then failing to check the return code. The results can be very hard
to diagnose. Here are some threads that show the pain this causes:
* https://github.com/zeromq/zyre/issues/179
* http://lists.zeromq.org/pipermail/zeromq-dev/2014-June/026388.html
One common argument is that a library should never assert, and should
pass errors back to the calling application. The counter argument is
that when an application is broken enough to pass garbage to libzmq,
it cannot be trusted to handle the resulting errors properly. Empirical
evidence from CZMQ, where we systematically assert on bad arguments, is
that this militant approach makes applications more, not less, robust.
I don't see any valid use cases for returning errors on bad arguments,
with one exception: zmq_setsockopt can be used to probe whether libzmq
was e.g. built with CURVE security. I'd argue that it's nasty to use a
side effect like this. If apps need to probe how libzmq was built, this
should be done explicitly, and for ALL build options, not just CURVE.
There are/were no libzmq test cases that check the return code for an
invalid option.
For now I've enabled militant assertions using --with-militant at
configure time. However I'd like to make this the default setting.
Well, not gibberish, but 2^31 on Linux, which is useless. The code
should probably use getrlimit on Linux and other calls depending on
the system. For now I've set the ceiling at 64K.
As mentioned on the mailing list, Windows may return WSAEADDRINUSE when binding
(reconnecting) to a port. Added this to the handled error codes as Pieter
suggested.
The list of error codes is taken from zmq::wsa_error_no(). Most of the
new WSA error codes result in EFAULT, but some return a more specific
value (even EAGAIN).
Fixes#1071
