fix goroutine leak in compilation

Creating a new docker.Client each time was leaking persistent http
conns.

Change-Id: Ib6302b2bffcb54373b8057ab26974fa1d9c347c8

engine/compilation.go

@@ -69,11 +69,9 @@ func (image *Image) Remove() {
 // Compile sets up a new Container and gets ready to execute the given source code.
 // It's important to Remove the Container to clean up resources.
 func (lang *Language) Compile(timeout int64, source string) (image *Image, result *ExecutionResult, err error) {
-	client, _ := docker.NewClient(endpoint)
-
 	filePath := fmt.Sprintf("/src/%s", lang.Filename)
 
-	container, err := createContainer(client, docker.CreateContainerOptions{
+	container, err := createContainer(lang.client, docker.CreateContainerOptions{
 		Config: &docker.Config{
 			Image:           lang.DockerImage,
 			Cmd:             []string{"--build", filePath},
@@ -87,7 +85,7 @@ func (lang *Language) Compile(timeout int64, source string) (image *Image, resul
 	})
 
 	if err == nil {
-		err = client.UploadToContainer(container.id, docker.UploadToContainerOptions{
+		err = lang.client.UploadToContainer(container.id, docker.UploadToContainerOptions{
 			InputStream: lang.tarSource(source, filePath),
 			Path:        "/",
 		})
@@ -112,12 +110,12 @@ func (lang *Language) Compile(timeout int64, source string) (image *Image, resul
 		image = &Image{
 			ID:     container.id,
 			lang:   lang,
-			client: client,
+			client: lang.client,
 		}
 	}
 
 	if image == nil {
-		client.RemoveContainer(docker.RemoveContainerOptions{ID: container.id, Force: true})
+		lang.client.RemoveContainer(docker.RemoveContainerOptions{ID: container.id, Force: true})
 	}
 
 	return

engine/engine.go

@@ -34,6 +34,11 @@ func New(confPath string, disableApparmor bool) (result *Engine, err error) {
 		return
 	}
 
+	result.client, err = docker.NewClient(endpoint)
+	if err != nil {
+		return
+	}
+
 	for _, config := range configs {
 		var lang *Language
 		lang, err = loadLanguage(config)
@@ -42,14 +47,13 @@ func New(confPath string, disableApparmor bool) (result *Engine, err error) {
 			// fail everything if one language fails to load
 			return
 		}
+		lang.client = result.client
 		if disableApparmor {
 			lang.disableAppArmor()
 		}
 		result.languages = append(result.languages, lang)
 	}
 
-	result.client, err = docker.NewClient(endpoint)
-
 	return
 }
 

engine/language.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"io/ioutil"
 
+	"github.com/fsouza/go-dockerclient"
 	"gopkg.in/yaml.v2"
 )
 
@@ -21,6 +22,7 @@ type Language struct {
 	CompilerProfile string   `yaml:"compiler_profile"`
 	Checks          Checks   `yaml:"tests"`
 	FileExtensions  []string `yaml:"file_extensions"`
+	client          *docker.Client
 }
 
 // RunResult contains the full results for each executed step of a code run.