produce more meaningful error messages

arangod/Aql/ClusterBlocks.cpp

@@ -1076,10 +1076,7 @@ static bool throwExceptionAfterBadSyncRequest(ClusterCommResult* res,
                                               bool isShutdown) {
   ENTER_BLOCK
   if (res->status == CL_COMM_TIMEOUT) {
-    std::string errorMessage =
-        std::string("Timeout in communication with shard '") +
-        std::string(res->shardID) + std::string("' on cluster node '") +
-        std::string(res->serverID) + std::string("' failed.");
+    std::string errorMessage = res->stringifyErrorMessage();
 
     // No reply, we give up:
     THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_CLUSTER_TIMEOUT, errorMessage);
@@ -1087,10 +1084,7 @@ static bool throwExceptionAfterBadSyncRequest(ClusterCommResult* res,
 
   if (res->status == CL_COMM_BACKEND_UNAVAILABLE) {
     // there is no result
-    std::string errorMessage = 
-        std::string("Empty result in communication with shard '") +
-        std::string(res->shardID) + std::string("' on cluster node '") +
-        std::string(res->serverID) + std::string("'");
+    std::string errorMessage = res->stringifyErrorMessage(); 
     THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_CLUSTER_CONNECTION_LOST,
                                    errorMessage);
   }

arangod/Aql/ExecutionEngine.cpp

@@ -559,10 +559,7 @@ struct CoordinatorInstanciator : public WalkerWorker<ExecutionNode> {
           error += "\n";
         }
       } else {
-        error += std::string("Communication with shard '") +
-                 std::string(res.shardID) + std::string("' on cluster node '") +
-                 std::string(res.serverID) + std::string("' failed : ") +
-                 res.errorMessage;
+        error += res.stringifyErrorMessage();
       }
     }
 
@@ -963,11 +960,10 @@ ExecutionEngine* ExecutionEngine::instantiateFromPlan(
                                 url, "{\"code\": 0}", headers, 120.0);
             // Ignore result, we need to try to remove all.
             // However, log the incident if we have an errorMessage.
-            if (res->errorMessage.length() > 0) {
+            if (!res->errorMessage.empty()) {
               std::string msg("while trying to unregister query ");
-              msg += queryId + std::string("from shard: ") + shardId +
-                     std::string("communication failed: ") + res->errorMessage;
-              LOG(WARN) << "" << msg;
+              msg += queryId + ": " + res->stringifyErrorMessage();
+              LOG(WARN) << msg;
             }
           } else {
             // Remove query from registry:

arangod/Cluster/ClusterComm.cpp

@@ -115,6 +115,61 @@ void ClusterCommResult::setDestination(std::string const& dest,
     }
   }
 }
+  
+/// @brief stringify the internal error state
+std::string ClusterCommResult::stringifyErrorMessage() const {
+  // append status string
+  std::string result(stringifyStatus(status));
+  
+  if (!serverID.empty()) {
+    result.append(", cluster node: '");
+    result.append(serverID);
+    result.push_back('\'');
+  }
+
+  if (!shardID.empty()) {
+    result.append(", shard: '");
+    result.append(shardID);
+    result.push_back('\'');
+  }
+  
+  if (!endpoint.empty()) {
+    result.append(", endpoint: '");
+    result.append(endpoint);
+    result.push_back('\'');
+  }
+
+  if (!errorMessage.empty()) {
+    result.append(", error: '");
+    result.append(errorMessage);
+    result.push_back('\'');
+  }
+
+  return result;
+}
+  
+/// @brief stringify a cluster comm status
+char const* ClusterCommResult::stringifyStatus(ClusterCommOpStatus status) {
+  switch (status) {
+    case CL_COMM_SUBMITTED:
+      return "submitted";
+    case CL_COMM_SENDING:
+      return "sending";
+    case CL_COMM_SENT:
+      return "sent";
+    case CL_COMM_TIMEOUT:
+      return "timeout";
+    case CL_COMM_RECEIVED:
+      return "received";
+    case CL_COMM_ERROR:
+      return "error";
+    case CL_COMM_DROPPED:
+      return "dropped";
+    case CL_COMM_BACKEND_UNAVAILABLE:
+      return "backend unavailable";
+  }
+  return "unknown";
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief ClusterComm constructor

arangod/Cluster/ClusterComm.h

@@ -212,6 +212,12 @@ struct ClusterCommResult {
   //////////////////////////////////////////////////////////////////////////////
 
   void setDestination(std::string const& dest, bool logConnectionErrors);
+  
+  /// @brief stringify the internal error state
+  std::string stringifyErrorMessage() const;
+
+  /// @brief stringify a cluster comm status
+  static char const* stringifyStatus(ClusterCommOpStatus status);
 };
 
 ////////////////////////////////////////////////////////////////////////////////