Improve the etcd watcher to detect error when the connection lost.

Signed-off-by: Tao He <linzhu.ht@alibaba-inc.com>

etcd/Response.hpp

@@ -51,6 +51,11 @@ namespace etcd
      */
     bool is_ok() const;
 
+    /**
+     * Returns true if the error is a network unavailable error.
+     */
+    bool is_network_unavailable() const;
+
     /**
      * Returns the error code received from the etcd server. In case of success the error code is 0.
      */

etcd/Watcher.hpp

@@ -30,7 +30,27 @@ namespace etcd
             std::function<void(Response)> callback, bool recursive=false);
     Watcher(std::string const & etcd_url, std::string const & key, int fromIndex,
             std::function<void(Response)> callback, bool recursive=false);
+
+    /**
+     * Wait util the task has been stopped, actively or passively, e.g., the watcher
+     * get cancelled or the server closes the connection.
+     *
+     * Returns true if the watcher is been normally cancalled, otherwise false.
+     */
+    bool Wait();
+
+    /**
+     * An async wait, the callback will be called when the task has been stopped.
+     *
+     * The callback parameter would be true if the watch is been normally cancalled.
+     */
+    void Wait(std::function<void(bool)> callback);
+
+    /**
+     * Stop the watching action.
+     */
     void Cancel();
+
     ~Watcher();
 
   protected:

etcd/v3/AsyncWatchAction.hpp

@@ -24,6 +24,7 @@ namespace etcdv3
       void waitForResponse(std::function<void(etcd::Response)> callback); 
       void CancelWatch();
       void WatchReq(std::string const & key);
+      bool Cancelled() const;
     private:
       WatchResponse reply;
       std::unique_ptr<ClientAsyncReaderWriter<WatchRequest,WatchResponse>> stream;   

src/Response.cpp

@@ -72,6 +72,11 @@ bool etcd::Response::is_ok() const
   return error_code() == 0;
 }
 
+bool etcd::Response::is_network_unavailable() const
+{
+  return error_code() == ::grpc::StatusCode::UNAVAILABLE;
+}
+
 etcd::Value const & etcd::Response::value() const
 {
   return _value;

src/Watcher.cpp

@@ -43,10 +43,24 @@ etcd::Watcher::~Watcher()
   currentTask.wait();
 }
 
+bool etcd::Watcher::Wait()
+{
+  currentTask.wait();
+  return call->Cancelled();
+}
+
+void etcd::Watcher::Wait(std::function<void(bool)> callback)
+{
+  currentTask.then([this, callback](pplx::task<void> const & resp_task) {
+    resp_task.wait();
+    callback(this->call->Cancelled());
+  });
+}
+
 void etcd::Watcher::Cancel()
 {
   call->CancelWatch();
-  currentTask.wait();
+  this->Wait();
 }
 
 void etcd::Watcher::doWatch(std::string const & key, std::function<void(Response)> callback)

src/v3/AsyncLockAction.cpp

@@ -20,7 +20,6 @@ etcdv3::AsyncLockResponse etcdv3::AsyncLockAction::ParseResponse()
   
   if(!status.ok())
   {
-    std::cout << "lock error message is: " << status.error_message() << std::endl;
     lock_resp.set_error_code(status.error_code());
     lock_resp.set_error_message(status.error_message());
   }
@@ -49,7 +48,6 @@ etcdv3::AsyncUnlockResponse etcdv3::AsyncUnlockAction::ParseResponse()
   
   if(!status.ok())
   {
-    std::cout << "unlock error message is: " << status.error_message() << std::endl;
     unlock_resp.set_error_code(status.error_code());
     unlock_resp.set_error_message(status.error_message());
   }

src/v3/AsyncWatchAction.cpp

@@ -93,6 +93,10 @@ void etcdv3::AsyncWatchAction::CancelWatch()
   }
 }
 
+bool etcdv3::AsyncWatchAction::Cancelled() const {
+  return isCancelled;
+}
+
 void etcdv3::AsyncWatchAction::waitForResponse(std::function<void(etcd::Response)> callback) 
 {
   void* got_tag;