Fixed handling of WSAEWOULDBLOCK to be generic (#2260)

* Fixed handling of WSAEWOULDBLOCK to be generic

I don't know what was the intention of this early if statement but
now this is properly evaluated in wsa_error_no function if this is
performance issue I suggest moving evaluating this error code to the
beginning of wsa_error_no.

* Fixed handling of WSAEWOULDBLOCK to be generic

Introduced default pointer to const char * and overrides this as NULL
if function is called by zmq::wsa_error()

* Fixed handling of WSAEWOULDBLOCK to be generic

Introduced default pointer to const char * and overrides this as NULL
if function is called by zmq::wsa_error()

src/err.cpp

@@ -92,15 +92,10 @@ void zmq::zmq_abort(const char *errmsg_)
 
 const char *zmq::wsa_error()
 {
-    const int last_error = WSAGetLastError();
-    //  TODO: This is not a generic way to handle this...
-    if (last_error == WSAEWOULDBLOCK)
-        return NULL;
-
-    return wsa_error_no (last_error);
+    return wsa_error_no (WSAGetLastError(), NULL);
 }
 
-const char *zmq::wsa_error_no (int no_)
+const char *zmq::wsa_error_no (int no_, const char * wsae_wouldblock_string)
 {
     //  TODO:  It seems that list of Windows socket errors is longer than this.
     //         Investigate whether there's a way to convert it into the string
@@ -121,7 +116,7 @@ const char *zmq::wsa_error_no (int no_)
         (no_ == WSAEMFILE) ?
             "Too many open files" :
         (no_ == WSAEWOULDBLOCK) ?
-            "Operation would block" :
+            wsae_wouldblock_string :
         (no_ == WSAEINPROGRESS) ?
             "Operation now in progress" :
         (no_ == WSAEALREADY) ?

src/err.hpp

@@ -65,7 +65,7 @@ namespace zmq
 namespace zmq
 {
     const char *wsa_error ();
-    const char *wsa_error_no (int no_);
+    const char *wsa_error_no (int no_, const char * wsae_wouldblock_string = "Operation would block");
     void win_error (char *buffer_, size_t buffer_size_);
     int wsa_error_to_errno (int errcode);
 }