Add a new API to `client.observe()` that accepts a callback.

Resolves #108.

Signed-off-by: Tao He <sighingnow@gmail.com>

etcd/Client.hpp

@@ -598,7 +598,16 @@ namespace etcd
      * Observe the leader change.
      *
      * @param name is the names of election to watch.
-     * @param callback is the names of election to watch.
+     *
+     * @returns an observer that holds that action and will cancel the request when being destructed.
+     */
+    std::unique_ptr<Observer> observe(std::string const &name,
+                                      const bool once = false);
+
+    /**
+     * Observe the leader change.
+     *
+     * @param name is the names of election to watch.
      *
      * @returns an observer that holds that action and will cancel the request when being destructed.
      */

etcd/Response.hpp

@@ -41,6 +41,21 @@ namespace etcd
       });
     }
 
+    template <typename T>
+    static pplx::task<etcd::Response> create(std::shared_ptr<T> call,
+                                             std::function<void(Response)> callback)
+    {
+      return pplx::task<etcd::Response>([call, callback]()
+      {
+        call->waitForResponse(callback);
+        auto v3resp = call->ParseResponse();
+
+        auto duration = std::chrono::duration_cast<std::chrono::microseconds>(
+            std::chrono::high_resolution_clock::now() - call->startTimepoint());
+        return etcd::Response(v3resp, duration);
+      });
+    }
+
     template <typename T>
     static pplx::task<etcd::Response> create(std::function<std::shared_ptr<T>()> callfn)
     {

etcd/SyncClient.hpp

@@ -73,6 +73,8 @@ namespace etcd
     Response proclaim(std::string const &name, int64_t lease_id,
                       std::string const &key, int64_t revision, std::string const &value);
     Response leader(std::string const &name);
+    std::unique_ptr<Client::Observer> observe(std::string const &name,
+                                              const bool once = false);
     std::unique_ptr<Client::Observer> observe(std::string const &name,
                                               std::function<void(Response)> callback,
                                               const bool once = false);

src/Client.cpp

@@ -957,7 +957,7 @@ pplx::task<etcd::Response> etcd::Client::leader(std::string const &name) {
 }
 
 std::unique_ptr<etcd::Client::Observer> etcd::Client::observe(
-    std::string const &name, std::function<void(Response)> callback, const bool once) {
+    std::string const &name, const bool once) {
   etcdv3::ActionParameters params;
   params.auth_token.assign(this->auth_token);
   params.name.assign(name);
@@ -969,6 +969,19 @@ std::unique_ptr<etcd::Client::Observer> etcd::Client::observe(
   return observer;
 }
 
+std::unique_ptr<etcd::Client::Observer> etcd::Client::observe(
+    std::string const &name, std::function<void(Response)> callback, const bool once) {
+  etcdv3::ActionParameters params;
+  params.auth_token.assign(this->auth_token);
+  params.name.assign(name);
+  params.election_stub = stubs->electionServiceStub.get();
+  std::shared_ptr<etcdv3::AsyncObserveAction> call(new etcdv3::AsyncObserveAction(params, once));
+  std::unique_ptr<Observer> observer(new Observer());
+  observer->action = call;
+  observer->resp = Response::create(call, callback);
+  return observer;
+}
+
 pplx::task<etcd::Response> etcd::Client::resign(
     std::string const &name, int64_t lease_id, std::string const &key, int64_t revision) {
   etcdv3::ActionParameters params;

src/SyncClient.cpp

@@ -173,7 +173,14 @@ etcd::Response etcd::SyncClient::leader(std::string const &name)
 }
 
 std::unique_ptr<etcd::Client::Observer> etcd::SyncClient::observe(
-    std::string const &name, std::function<void(etcd::Response)> callback,
+    std::string const &name, const bool once)
+{
+  return client.observe(name, once);
+}
+
+std::unique_ptr<etcd::Client::Observer> etcd::SyncClient::observe(
+    std::string const &name,
+    std::function<void(etcd::Response)> callback,
     const bool once)
 {
   return client.observe(name, callback, once);