Fix another upload-pack deadlock

Thanks Nick for pointing out that exec.Cmd can take care of all the
copying for us.

internal/git/git-http.go

@@ -14,6 +14,7 @@ import (
 	"path"
 	"path/filepath"
 	"strings"
+	"sync"
 
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/api"
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/helper"
@@ -27,19 +28,18 @@ func UploadPack(a *api.API) http.Handler {
 	return postRPCHandler(a, "handleUploadPack", handleUploadPack)
 }
 
-func postRPCHandler(a *api.API, name string, handler func(*GitHttpResponseWriter, *http.Request, *api.Response) (int64, error)) http.Handler {
+func postRPCHandler(a *api.API, name string, handler func(*GitHttpResponseWriter, *http.Request, *api.Response) error) http.Handler {
 	return repoPreAuthorizeHandler(a, func(rw http.ResponseWriter, r *http.Request, ar *api.Response) {
-		var writtenIn int64
-		var err error
+		cr := &countReadCloser{ReadCloser: r.Body}
+		r.Body = cr
 
 		w := NewGitHttpResponseWriter(rw)
 		defer func() {
-			w.Log(r, writtenIn)
+			w.Log(r, cr.Count())
 		}()
 
-		writtenIn, err = handler(w, r, ar)
-		if err != nil {
-			helper.LogError(r, fmt.Errorf("%s: %v", name, err))
+		if err := handler(w, r, ar); err != nil {
+			helper.Fail500(w, r, fmt.Errorf("%s: %v", name, err))
 		}
 	})
 }
@@ -70,46 +70,25 @@ func repoPreAuthorizeHandler(myAPI *api.API, handleFunc api.HandleFunc) http.Han
 	}, "")
 }
 
-func setupGitCommand(action string, a *api.Response, options ...string) (cmd *exec.Cmd, stdin io.WriteCloser, stdout io.ReadCloser, err error) {
-	// Don't leak pipes when we return early after an error
-	defer func() {
-		if err == nil {
-			return
-		}
-		if stdin != nil {
-			stdin.Close()
-		}
-		if stdout != nil {
-			stdout.Close()
-		}
-	}()
-
+func startGitCommand(a *api.Response, stdin io.Reader, stdout io.Writer, action string, options ...string) (cmd *exec.Cmd, err error) {
 	// Prepare our Git subprocess
 	args := []string{subCommand(action), "--stateless-rpc"}
 	args = append(args, options...)
 	args = append(args, a.RepoPath)
 	cmd = gitCommand(a.GL_ID, "git", args...)
-	stdout, err = cmd.StdoutPipe()
-	if err != nil {
-		return nil, nil, nil, fmt.Errorf("stdout pipe: %v", err)
-	}
-
-	stdin, err = cmd.StdinPipe()
-	if err != nil {
-		return nil, nil, nil, fmt.Errorf("stdin pipe: %v", err)
-	}
+	cmd.Stdin = stdin
+	cmd.Stdout = stdout
 
 	if err = cmd.Start(); err != nil {
-		return nil, nil, nil, fmt.Errorf("start %v: %v", cmd.Args, err)
+		return nil, fmt.Errorf("start %v: %v", cmd.Args, err)
 	}
 
-	return cmd, stdin, stdout, nil
+	return cmd, nil
 }
 
 func writePostRPCHeader(w http.ResponseWriter, action string) {
 	w.Header().Set("Content-Type", fmt.Sprintf("application/x-%s-result", action))
 	w.Header().Set("Cache-Control", "no-cache")
-	w.WriteHeader(200) // Don't bother with HTTP 500 from this point on, just return
 }
 
 func getService(r *http.Request) string {
@@ -127,3 +106,25 @@ func isExitError(err error) bool {
 func subCommand(rpc string) string {
 	return strings.TrimPrefix(rpc, "git-")
 }
+
+type countReadCloser struct {
+	n int64
+	io.ReadCloser
+	sync.Mutex
+}
+
+func (c *countReadCloser) Read(p []byte) (n int, err error) {
+	n, err = c.ReadCloser.Read(p)
+
+	c.Lock()
+	defer c.Unlock()
+	c.n += int64(n)
+
+	return n, err
+}
+
+func (c *countReadCloser) Count() int64 {
+	c.Lock()
+	defer c.Unlock()
+	return c.n
+}

internal/git/git-http_test.go

@@ -39,7 +39,7 @@ func TestHandleReceivePack(t *testing.T) {
 	testHandlePostRpc(t, "git-receive-pack", handleReceivePack)
 }
 
-func testHandlePostRpc(t *testing.T, action string, handler func(*GitHttpResponseWriter, *http.Request, *api.Response) (int64, error)) {
+func testHandlePostRpc(t *testing.T, action string, handler func(*GitHttpResponseWriter, *http.Request, *api.Response) error) {
 	execCommand = fakeExecCommand
 	defer func() { execCommand = exec.Command }()
 

internal/git/info-refs.go

@@ -2,7 +2,6 @@ package git
 
 import (
 	"fmt"
-	"io"
 	"net/http"
 	"path"
 
@@ -45,36 +44,31 @@ func handleGetInfoRefs(rw http.ResponseWriter, r *http.Request, a *api.Response)
 		return
 	}
 
-	cmd, stdin, stdout, err := setupGitCommand(rpc, a, "--advertise-refs")
-	if err != nil {
-		helper.Fail500(w, r, fmt.Errorf("handleGetInfoRefs: setupGitCommand: %v", err))
-		return
-	}
-	defer helper.CleanUpProcessGroup(cmd) // Ensure brute force subprocess clean-up
-	stdin.Close()                         // Not needed for this request
-	defer stdout.Close()
-
-	// Start writing the response
 	w.Header().Set("Content-Type", fmt.Sprintf("application/x-%s-advertisement", rpc))
 	w.Header().Set("Cache-Control", "no-cache")
-	w.WriteHeader(200) // Don't bother with HTTP 500 from this point on, just return
+
+	if err := writeBody(w, a, rpc); err != nil {
+		helper.LogError(r, fmt.Errorf("handleGetInfoRefs: %v", err))
+	}
+}
+
+func writeBody(w http.ResponseWriter, a *api.Response, rpc string) error {
 	if err := pktLine(w, fmt.Sprintf("# service=%s\n", rpc)); err != nil {
-		helper.LogError(r, fmt.Errorf("handleGetInfoRefs: pktLine: %v", err))
-		return
+		return fmt.Errorf("pktLine: %v", err)
 	}
 	if err := pktFlush(w); err != nil {
-		helper.LogError(r, fmt.Errorf("handleGetInfoRefs: pktFlush: %v", err))
-		return
+		return fmt.Errorf("pktFlush: %v", err)
 	}
-	if _, err := io.Copy(w, stdout); err != nil {
-		helper.LogError(
-			r,
-			&copyError{fmt.Errorf("handleGetInfoRefs: copy output of %v: %v", cmd.Args, err)},
-		)
-		return
+
+	cmd, err := startGitCommand(a, nil, w, rpc, "--advertise-refs")
+	if err != nil {
+		return fmt.Errorf("startGitCommand: %v", err)
 	}
+	defer helper.CleanUpProcessGroup(cmd) // Ensure brute force subprocess clean-up
+
 	if err := cmd.Wait(); err != nil {
-		helper.LogError(r, fmt.Errorf("handleGetInfoRefs: wait for %v: %v", cmd.Args, err))
-		return
+		return fmt.Errorf("wait for %v: %v", cmd.Args, err)
 	}
+
+	return nil
 }

internal/git/receive-pack.go

@@ -2,53 +2,29 @@ package git
 
 import (
 	"fmt"
-	"io"
 	"net/http"
 
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/api"
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/helper"
 )
 
-func handleReceivePack(w *GitHttpResponseWriter, r *http.Request, a *api.Response) (writtenIn int64, err error) {
+// Will not return a non-nil error after the response body has been
+// written to.
+func handleReceivePack(w *GitHttpResponseWriter, r *http.Request, a *api.Response) error {
 	action := getService(r)
-	cmd, stdin, stdout, err := setupGitCommand(action, a)
-
-	if err != nil {
-		fail500(w)
-		return writtenIn, fmt.Errorf("setupGitCommand: %v", err)
-	}
-
-	defer stdout.Close()
-	defer stdin.Close()
-	defer helper.CleanUpProcessGroup(cmd) // Ensure brute force subprocess clean-up
-
-	writtenIn, err = io.Copy(stdin, r.Body)
-
-	if err != nil {
-		fail500(w)
-		return writtenIn, fmt.Errorf("write to %v: %v", cmd.Args, err)
-	}
-	// Signal to the Git subprocess that no more data is coming
-	stdin.Close()
-
-	// It may take a while before we return and the deferred closes happen
-	// so let's free up some resources already.
-	r.Body.Close()
-
 	writePostRPCHeader(w, action)
 
-	// This io.Copy may take a long time, both for Git push and pull.
-	_, err = io.Copy(w, stdout)
-
+	cmd, err := startGitCommand(a, r.Body, w, action)
 	if err != nil {
-		return writtenIn, &copyError{fmt.Errorf("copy output of %v: %v", cmd.Args, err)}
+		return fmt.Errorf("startGitCommand: %v", err)
 	}
+	defer helper.CleanUpProcessGroup(cmd)
 
-	err = cmd.Wait()
-
-	if err != nil {
-		return writtenIn, fmt.Errorf("wait for %v: %v", cmd.Args, err)
+	if err := cmd.Wait(); err != nil {
+		helper.LogError(r, fmt.Errorf("wait for %v: %v", cmd.Args, err))
+		// Return nil because the response body has been written to already.
+		return nil
 	}
 
-	return writtenIn, nil
+	return nil
 }

internal/git/upload-pack.go

@@ -9,68 +9,38 @@ import (
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/helper"
 )
 
-func handleUploadPack(w *GitHttpResponseWriter, r *http.Request, a *api.Response) (writtenIn int64, err error) {
+// Will not return a non-nil error after the response body has been
+// written to.
+func handleUploadPack(w *GitHttpResponseWriter, r *http.Request, a *api.Response) error {
 	// The body will consist almost entirely of 'have XXX' and 'want XXX'
 	// lines; these are about 50 bytes long. With a limit of 10MB the client
 	// can send over 200,000 have/want lines.
 	buffer, err := helper.ReadAllTempfile(io.LimitReader(r.Body, 10*1024*1024))
 	if err != nil {
-		fail500(w)
-		return writtenIn, fmt.Errorf("ReadAllTempfile: %v", err)
+		return fmt.Errorf("ReadAllTempfile: %v", err)
 	}
 	defer buffer.Close()
 	r.Body.Close()
 
 	isShallowClone := scanDeepen(buffer)
 	if _, err := buffer.Seek(0, 0); err != nil {
-		fail500(w)
-		return writtenIn, fmt.Errorf("seek tempfile: %v", err)
+		return fmt.Errorf("seek tempfile: %v", err)
 	}
 
 	action := getService(r)
-	cmd, stdin, stdout, err := setupGitCommand(action, a)
-
-	if err != nil {
-		fail500(w)
-		return writtenIn, fmt.Errorf("setupGitCommand: %v", err)
-	}
-
-	defer stdout.Close()
-	defer stdin.Close()
-	defer helper.CleanUpProcessGroup(cmd) // Ensure brute force subprocess clean-up
-
-	stdoutError := make(chan error, 1)
-	go func() {
 	writePostRPCHeader(w, action)
-		// Start reading from stdout already to avoid blocking while writing to
-		// stdin below.
-		_, err := io.Copy(w, stdout)
-		// This error may be lost if some other error prevents us from <-ing on this channel.
-		stdoutError <- err
-	}()
-
-	// Write the client request body to Git's standard input
-	if writtenIn, err = io.Copy(stdin, buffer); err != nil {
-		fail500(w)
-		return writtenIn, fmt.Errorf("write to %v: %v", cmd.Args, err)
-	}
-
-	// Signal to the Git subprocess that no more data is coming
-	stdin.Close()
 
-	if err := <-stdoutError; err != nil {
-		return writtenIn, &copyError{fmt.Errorf("copy output of %v: %v", cmd.Args, err)}
+	cmd, err := startGitCommand(a, buffer, w, action)
+	if err != nil {
+		return fmt.Errorf("startGitCommand: %v", err)
 	}
+	defer helper.CleanUpProcessGroup(cmd)
 
-	err = cmd.Wait()
-
-	if err != nil && !(isExitError(err) && isShallowClone) {
-		return writtenIn, fmt.Errorf("wait for %v: %v", cmd.Args, err)
+	if err := cmd.Wait(); err != nil && !(isExitError(err) && isShallowClone) {
+		helper.LogError(r, fmt.Errorf("wait for %v: %v", cmd.Args, err))
+		// Return nil because the response body has been written to already.
+		return nil
 	}
 
-	return writtenIn, nil
-}
-
-func fail500(w http.ResponseWriter) {
-	helper.Fail500(w, nil, nil)
+	return nil
 }