Merge branch 'zj-plain-diffs-by-workhorse' into 'master'

Diffs served by workhorse

First iteration; mainly pushed the branch to trigger a build.

Based on `archive.go` and `blob.go`. 

TODO:
- [x] Add the correct route
- [x] Test locally
- [x] Write tests

See merge request !45

internal/git/diff.go

+package git
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+
+	"gitlab.com/gitlab-org/gitlab-workhorse/internal/helper"
+	"gitlab.com/gitlab-org/gitlab-workhorse/internal/senddata"
+)
+
+type diff struct{ senddata.Prefix }
+type diffParams struct {
+	RepoPath string
+	ShaFrom  string
+	ShaTo    string
+}
+
+var SendDiff = &diff{"git-diff:"}
+
+func (d *diff) Inject(w http.ResponseWriter, r *http.Request, sendData string) {
+	var params diffParams
+	if err := d.Unpack(&params, sendData); err != nil {
+		helper.Fail500(w, fmt.Errorf("SendDiff: unpack sendData: %v", err))
+		return
+	}
+
+	log.Printf("SendDiff: sending diff between %q and %q for %q", params.ShaFrom, params.ShaTo, r.URL.Path)
+
+	gitDiffCmd := gitCommand("", "git", "--git-dir="+params.RepoPath, "diff", params.ShaFrom, params.ShaTo)
+	stdout, err := gitDiffCmd.StdoutPipe()
+	if err != nil {
+		helper.Fail500(w, fmt.Errorf("SendDiff: create stdout pipe: %v", err))
+		return
+	}
+
+	if err := gitDiffCmd.Start(); err != nil {
+		helper.Fail500(w, fmt.Errorf("SendDiff: start %v: %v", gitDiffCmd, err))
+		return
+	}
+	defer helper.CleanUpProcessGroup(gitDiffCmd)
+
+	w.Header().Del("Content-Length")
+	if _, err := io.Copy(w, stdout); err != nil {
+		helper.LogError(fmt.Errorf("SendDiff: copy %v stdout: %v", gitDiffCmd, err))
+		return
+	}
+	if err := gitDiffCmd.Wait(); err != nil {
+		helper.LogError(fmt.Errorf("SendDiff: wait for %v: %v", gitDiffCmd, err))
+		return
+	}
+}

internal/upstream/routes.go

@@ -48,6 +48,7 @@ func (u *Upstream) configureRoutes() {
 		)),
 		git.SendArchive,
 		git.SendBlob,
+		git.SendDiff,
 	)
 
 	u.Routes = []route{

main_test.go

@@ -621,6 +621,50 @@ func TestGetGitBlob(t *testing.T) {
 	}
 }
 
+func TestGetGitDiff(t *testing.T) {
+	fromSha := "be93687618e4b132087f430a4d8fc3a609c9b77c"
+	toSha := "54fcc214b94e78d7a41a9a8fe6d87a5e59500e51"
+	headerKey := http.CanonicalHeaderKey("Gitlab-Workhorse-Send-Data")
+
+	ts := testhelper.TestServerWithHandler(regexp.MustCompile(`.`), func(w http.ResponseWriter, r *http.Request) {
+		responseJSON := fmt.Sprintf(`{"RepoPath":"%s","ShaFrom":"%s","ShaTo":"%s"}`, path.Join(testRepoRoot, testRepo), fromSha, toSha)
+		encodedJSON := base64.StdEncoding.EncodeToString([]byte(responseJSON))
+		w.Header().Set(headerKey, "git-diff:"+encodedJSON)
+		return
+	})
+	defer ts.Close()
+
+	ws := startWorkhorseServer(ts.URL)
+	defer ws.Close()
+
+	resourcePath := "/something"
+	resp, err := http.Get(ws.URL + resourcePath)
+	if err != nil {
+		t.Error(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		t.Errorf("GET %q: expected 200, got %d", resourcePath, resp.StatusCode)
+	}
+	if len(resp.Header[headerKey]) != 0 {
+		t.Fatalf("Unexpected response header: %s: %q", headerKey, resp.Header.Get(headerKey))
+	}
+
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !strings.HasPrefix(string(body), "diff --git a/README b/README") {
+		t.Fatalf("diff --git a/README b/README, got %q", body)
+	}
+
+	bodyLengthBytes := len(body)
+	if bodyLengthBytes != 155 {
+		t.Fatal("Expected the body to consist of 155 bytes, got %v", bodyLengthBytes)
+	}
+}
+
 func setupStaticFile(fpath, content string) error {
 	cwd, err := os.Getwd()
 	if err != nil {