FAB-3: Fix Json output for empty network list

The generated pb.PeersMessage struct will be added "omitempty" tag automatically. So when
 marshal an empty PeersMessage, we get a "{}". Add a new tempoprary struct without
"omitempty" to replace PeerMesssage. Now we can get "{"Peer": []}"

Change-Id: I1fc310c951cf4e85a61660f2c45f700136dc5010
Signed-off-by: jiangyaoguo <jiangyaoguo@gmail.com>

bddtests/peer_cli.feature

@@ -16,9 +16,10 @@ Feature: Peer Command Line Interface
     When I execute "peer network list" in container vp0
     Then the command should complete successfully
     And stdout should contain JSON
+    And I should get result with "{"Peers":[]}"
 
     Scenario: List Peers when two are up
     Given we compose "docker-compose-2.yml"
     When I execute "peer network list" in container vp0
     Then the command should complete successfully
-    And stdout should contain JSON with "peers" array of length 1
+    And stdout should contain JSON with "Peers" array of length 1

bddtests/steps/peer_cli_impl.py

@@ -66,6 +66,10 @@ def step_impl(context, stream, attribute, length):
     array = getAttribute(attribute, json)
     assertLength(array, int(length))
 
+@then(u'I should get result with "{expectResult}"')
+def step_impl(context, expectResult):
+    assert context.command["stdout"].strip('\n') == expectResult
+
 def assertIsJson(data):
     assert isJson(data), "Data is not in JSON format"
 
@@ -86,4 +90,4 @@ def getAttribute(attribute, json):
 
 def assertLength(array, length):
     arrayLength = len(array)
-    assert arrayLength == length, "Unexpected array length. Expected {}, got {}".format(length, arrayLength)
+    assert arrayLength == length, "Unexpected array length. Expected {}, got {}".format(length, arrayLength)

peer/network/list.go

@@ -58,7 +58,9 @@ func networkList() (err error) {
 		return
 	}
 
-	jsonOutput, _ := json.Marshal(peers)
+	// The generated pb.PeersMessage struct will be added "omitempty" tag automatically.
+	// But we still want to print it when pb.PeersMessage is empty.
+	jsonOutput, _ := json.Marshal(struct{ Peers []*pb.PeerEndpoint }{append([]*pb.PeerEndpoint{}, peers.GetPeers()...)})
 	fmt.Println(string(jsonOutput))
 	return nil
 }