Fix premature close of build output on pull

The build job will sometimes trigger a pull job when the base image
does not exist. Now that engine jobs properly close their output by default
the pull job would also close the build job's stdout in a cascading close
upon completion of the pull.

This patch corrects this by wrapping the `pull` job's stdout with a
nopCloseWriter which will not close the stdout of the `build` job.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

builder/internals.go

@@ -25,6 +25,7 @@ import (
 	imagepkg "github.com/docker/docker/image"
 	"github.com/docker/docker/pkg/archive"
 	"github.com/docker/docker/pkg/chrootarchive"
+	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/docker/pkg/parsers"
 	"github.com/docker/docker/pkg/symlink"
 	"github.com/docker/docker/pkg/system"
@@ -433,7 +434,7 @@ func (b *Builder) pullImage(name string) (*imagepkg.Image, error) {
 	job.SetenvBool("json", b.StreamFormatter.Json())
 	job.SetenvBool("parallel", true)
 	job.SetenvJson("authConfig", pullRegistryAuth)
-	job.Stdout.Add(b.OutOld)
+	job.Stdout.Add(ioutils.NopWriteCloser(b.OutOld))
 	if err := job.Run(); err != nil {
 		return nil, err
 	}

engine/engine_test.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"strings"
 	"testing"
+
+	"github.com/docker/docker/pkg/ioutils"
 )
 
 func TestRegister(t *testing.T) {
@@ -150,3 +152,85 @@ func TestCatchallEmptyName(t *testing.T) {
 		t.Fatalf("Engine.Job(\"\").Run() should return an error")
 	}
 }
+
+// Ensure that a job within a job both using the same underlying standard
+// output writer does not close the output of the outer job when the inner
+// job's stdout is wrapped with a NopCloser. When not wrapped, it should
+// close the outer job's output.
+func TestNestedJobSharedOutput(t *testing.T) {
+	var (
+		outerHandler Handler
+		innerHandler Handler
+		wrapOutput   bool
+	)
+
+	outerHandler = func(job *Job) Status {
+		job.Stdout.Write([]byte("outer1"))
+
+		innerJob := job.Eng.Job("innerJob")
+
+		if wrapOutput {
+			innerJob.Stdout.Add(ioutils.NopWriteCloser(job.Stdout))
+		} else {
+			innerJob.Stdout.Add(job.Stdout)
+		}
+
+		if err := innerJob.Run(); err != nil {
+			t.Fatal(err)
+		}
+
+		// If wrapOutput was *false* this write will do nothing.
+		// FIXME (jlhawn): It should cause an error to write to
+		// closed output.
+		job.Stdout.Write([]byte(" outer2"))
+
+		return StatusOK
+	}
+
+	innerHandler = func(job *Job) Status {
+		job.Stdout.Write([]byte(" inner"))
+
+		return StatusOK
+	}
+
+	eng := New()
+	eng.Register("outerJob", outerHandler)
+	eng.Register("innerJob", innerHandler)
+
+	// wrapOutput starts *false* so the expected
+	// output of running the outer job will be:
+	//
+	//     "outer1 inner"
+	//
+	outBuf := new(bytes.Buffer)
+	outerJob := eng.Job("outerJob")
+	outerJob.Stdout.Add(outBuf)
+
+	if err := outerJob.Run(); err != nil {
+		t.Fatal(err)
+	}
+
+	expectedOutput := "outer1 inner"
+	if outBuf.String() != expectedOutput {
+		t.Fatalf("expected job output to be %q, got %q", expectedOutput, outBuf.String())
+	}
+
+	// Set wrapOutput to true so that the expected
+	// output of running the outer job will be:
+	//
+	//     "outer1 inner outer2"
+	//
+	wrapOutput = true
+	outBuf.Reset()
+	outerJob = eng.Job("outerJob")
+	outerJob.Stdout.Add(outBuf)
+
+	if err := outerJob.Run(); err != nil {
+		t.Fatal(err)
+	}
+
+	expectedOutput = "outer1 inner outer2"
+	if outBuf.String() != expectedOutput {
+		t.Fatalf("expected job output to be %q, got %q", expectedOutput, outBuf.String())
+	}
+}