gloo/tcp: better error message on collective mismatch

Differential Revision: D78377800

Pull Request resolved: #456

Author: d4l3k

gloo/transport/tcp/pair.cc

@@ -453,7 +453,10 @@ ssize_t Pair::prepareRead(
     iov.iov_len = op.preamble.length - offset;
 
     // Bytes read must be in bounds for target buffer
-    GLOO_ENFORCE_LE(op.preamble.length, op.nbytes);
+    GLOO_ENFORCE_LE(
+        op.preamble.length,
+        op.nbytes,
+        "Received data size doesn't match expected size. Is there a distributed collective mismatch in your code?");
     return iov.iov_len;
   }