[zeromq-dev] Unreasonable behavior of a socket when connection can't be established. How to enable the blocking mode on a socket?

[Jim Melton]

They aren’t reported because they aren’t “errors” in ZMQ. Because the connection can happen independently (asynchronously) from the call to to connect, and because a socket may be connected to a variety of endpoints, the TCP conditions you are concerned about are not exposed to you.

You are asking about detecting a condition that does not exist in the ZMQ architecture.

Now, depending on the type of socket and the options set, there might be an error in trying to send to a socket when the other end isn’t present. Or it might not. PUB sockets, for example, need never have a client connected to allow sends to succeed.
--
Jim Melton



> On Sep 27, 2022, at 10:52 PM, Yuri <yuri at rawbw.com> wrote:
> 
> Different philosophy is fine.
> 
> But why doesn't ZMQ report connection errors?
> When 'Connection refused' (ECONNREFUSED),  'Operation timed out' (ETIMEDOUT) or several other relevant error conditions arise they should be reported to the user. Why aren't they reported?
> 
> 
> Yuri
> 
> 
> 
> 
> 
> On 9/27/22 21:37, Jim Melton wrote:
>> That’s not a bug; it’s a feature. From http://api.zeromq.org/2-1%3azmq-connect <http://api.zeromq.org/2-1:zmq-connect>,
>> 
>> The connection will not be performed immediately but as needed by ØMQ. Thus a successful invocation of zmq_connect() does not indicate that a physical connection was or can actually be established.
>> 
>> 
>> ZMQ sockets are not TCP sockets. There is an unfortunate overloading of terms, and what you think you know may not apply to ZMQ. Go back and read https://zguide.zeromq.org/docs/chapter2/#The-Socket-API <https://zguide.zeromq.org/docs/chapter2/#The-Socket-API> where this is described in some detail.
>> --
>> Jim Melton
> 
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