Ensure BlameReaders close at end of request (#12102)

#11716 reports multiple git blame processes hanging around
this was thought to be due to timeouts, however on closer look this
appears to be due to the Close() function of the BlameReader hanging
with a blocked stdout pipe.

This PR fixes this Close function to:

* Cancel the context of the cmd
* Close the StdoutReader - ensuring that the output pipe is closed

Further it makes the context of the `git blame` command a child of the
request context - ensuring that even if Close() is not called, on
cancellation of the Request the blame is command will also be cancelled.

Fixes #11716
Closes #11727

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/git/blame.go

@@ -79,7 +79,9 @@ func (r *BlameReader) NextPart() (*BlamePart, error) {
 // Close BlameReader - don't run NextPart after invoking that
 func (r *BlameReader) Close() error {
 	defer process.GetManager().Remove(r.pid)
-	defer r.cancel()
+	r.cancel()
+
+	_ = r.output.Close()
 
 	if err := r.cmd.Wait(); err != nil {
 		return fmt.Errorf("Wait: %v", err)
@@ -89,19 +91,19 @@ func (r *BlameReader) Close() error {
 }
 
 // CreateBlameReader creates reader for given repository, commit and file
-func CreateBlameReader(repoPath, commitID, file string) (*BlameReader, error) {
+func CreateBlameReader(ctx context.Context, repoPath, commitID, file string) (*BlameReader, error) {
 	gitRepo, err := OpenRepository(repoPath)
 	if err != nil {
 		return nil, err
 	}
 	gitRepo.Close()
 
-	return createBlameReader(repoPath, GitExecutable, "blame", commitID, "--porcelain", "--", file)
+	return createBlameReader(ctx, repoPath, GitExecutable, "blame", commitID, "--porcelain", "--", file)
 }
 
-func createBlameReader(dir string, command ...string) (*BlameReader, error) {
-	// FIXME: graceful: This should have a timeout
-	ctx, cancel := context.WithCancel(DefaultContext)
+func createBlameReader(ctx context.Context, dir string, command ...string) (*BlameReader, error) {
+	// Here we use the provided context - this should be tied to the request performing the blame so that it does not hang around.
+	ctx, cancel := context.WithCancel(ctx)
 	cmd := exec.CommandContext(ctx, command[0], command[1:]...)
 	cmd.Dir = dir
 	cmd.Stderr = os.Stderr

modules/git/blame_test.go

@@ -5,6 +5,7 @@
 package git
 
 import (
+	"context"
 	"io/ioutil"
 	"testing"
 
@@ -93,8 +94,10 @@ func TestReadingBlameOutput(t *testing.T) {
 	if _, err = tempFile.WriteString(exampleBlame); err != nil {
 		panic(err)
 	}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
 
-	blameReader, err := createBlameReader("", "cat", tempFile.Name())
+	blameReader, err := createBlameReader(ctx, "", "cat", tempFile.Name())
 	if err != nil {
 		panic(err)
 	}

routers/repo/blame.go

@@ -123,7 +123,7 @@ func RefBlame(ctx *context.Context) {
 		return
 	}
 
-	blameReader, err := git.CreateBlameReader(models.RepoPath(userName, repoName), commitID, fileName)
+	blameReader, err := git.CreateBlameReader(ctx.Req.Context(), models.RepoPath(userName, repoName), commitID, fileName)
 	if err != nil {
 		ctx.NotFound("CreateBlameReader", err)
 		return