Allow finding docker containers by short name

Allow docker containers to be found by a short prefix name to match
the behavior of the docker daemon. This change now matches the
examples on the API docs.

Return an error if the given short name of a container is not unique.

manager/manager.go

@@ -566,9 +566,24 @@ func (self *manager) getDockerContainer(containerName string) (*containerData, e
 		Namespace: docker.DockerNamespace,
 		Name:      containerName,
 	}]
+
+	// Look for container by short prefix name if no exact match found.
 	if !ok {
-		return nil, fmt.Errorf("unable to find Docker container %q", containerName)
+		for contName, c := range self.containers {
+			if contName.Namespace == docker.DockerNamespace && strings.HasPrefix(contName.Name, containerName) {
+				if cont == nil {
+					cont = c
+				} else {
+					return nil, fmt.Errorf("unable to find container. Container %q is not unique", containerName)
+				}
+			}
+		}
+
+		if cont == nil {
+			return nil, fmt.Errorf("unable to find Docker container %q", containerName)
+		}
 	}
+
 	return cont, nil
 }
 

manager/manager_test.go

@@ -280,7 +280,8 @@ func TestSubcontainersInfo(t *testing.T) {
 
 func TestDockerContainersInfo(t *testing.T) {
 	containers := []string{
-		"/docker/c1",
+		"/docker/c1a",
+		"/docker/c2a",
 	}
 
 	query := &info.ContainerInfoRequest{
@@ -289,13 +290,27 @@ func TestDockerContainersInfo(t *testing.T) {
 
 	m, _, _ := expectManagerWithContainers(containers, query, t)
 
-	result, err := m.DockerContainer("c1", query)
+	result, err := m.DockerContainer("c1a", query)
 	if err != nil {
 		t.Fatalf("expected to succeed: %s", err)
 	}
 	if result.Name != containers[0] {
 		t.Errorf("Unexpected container %q in result. Expected container %q", result.Name, containers[0])
 	}
+
+	result, err = m.DockerContainer("c2", query)
+	if err != nil {
+		t.Fatalf("expected to succeed: %s", err)
+	}
+	if result.Name != containers[1] {
+		t.Errorf("Unexpected container %q in result. Expected container %q", result.Name, containers[1])
+	}
+
+	result, err = m.DockerContainer("c", query)
+	expectedError := "unable to find container. Container \"c\" is not unique"
+	if err == nil {
+		t.Errorf("expected error %q but received %q", expectedError, err)
+	}
 }
 
 func TestNewNilManager(t *testing.T) {