Stats API to retrieve nw stats from libnetwork

- Container networking statistics are no longer
  retrievable from libcontainer after the introduction
  of libnetwork. This change adds the missing code
  for docker daemon to retireve the nw stats from
  Endpoint.

Signed-off-by: Alessandro Boch <aboch@docker.com>

integration-cli/docker_api_stats_test.go

@@ -3,6 +3,8 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"os/exec"
+	"strconv"
 	"strings"
 	"time"
 
@@ -69,3 +71,41 @@ func (s *DockerSuite) TestStoppedContainerStatsGoroutines(c *check.C) {
 		}
 	}
 }
+
+func (s *DockerSuite) TestApiNetworkStats(c *check.C) {
+	// Run container for 30 secs
+	out, _ := dockerCmd(c, "run", "-d", "busybox", "top")
+	id := strings.TrimSpace(out)
+	err := waitRun(id)
+	c.Assert(err, check.IsNil)
+
+	// Retrieve the container address
+	contIP := findContainerIP(c, id)
+	numPings := 10
+
+	// Get the container networking stats before and after pinging the container
+	nwStatsPre := getNetworkStats(c, id)
+	_, err = exec.Command("ping", contIP, "-c", strconv.Itoa(numPings)).Output()
+	c.Assert(err, check.IsNil)
+	nwStatsPost := getNetworkStats(c, id)
+
+	// Verify the stats contain at least the expected number of packets (account for ARP)
+	expRxPkts := 1 + nwStatsPre.RxPackets + uint64(numPings)
+	expTxPkts := 1 + nwStatsPre.TxPackets + uint64(numPings)
+	c.Assert(nwStatsPost.TxPackets >= expTxPkts, check.Equals, true,
+		check.Commentf("Reported less TxPackets than expected. Expected >= %d. Found %d", expTxPkts, nwStatsPost.TxPackets))
+	c.Assert(nwStatsPost.RxPackets >= expRxPkts, check.Equals, true,
+		check.Commentf("Reported less Txbytes than expected. Expected >= %d. Found %d", expRxPkts, nwStatsPost.RxPackets))
+}
+
+func getNetworkStats(c *check.C, id string) types.Network {
+	var st *types.Stats
+
+	_, body, err := sockRequestRaw("GET", fmt.Sprintf("/containers/%s/stats?stream=false", id), nil, "")
+	c.Assert(err, check.IsNil)
+
+	err = json.NewDecoder(body).Decode(&st)
+	c.Assert(err, check.IsNil)
+
+	return st.Network
+}