2 files changed, 59 insertions, 2 deletions

diff --git a/src/pkg/os/exec/exec.go b/src/pkg/os/exec/exec.go
index a3bbcf3005..582930f2c4 100644
--- a/src/pkg/os/exec/exec.go
+++ b/src/pkg/os/exec/exec.go
@@ -13,6 +13,7 @@ import (
 	"io"
 	"os"
 	"strconv"
+	"sync"
 	"syscall"
 )
 
@@ -357,6 +358,8 @@ func (c *Cmd) CombinedOutput() ([]byte, error) {
 
 // StdinPipe returns a pipe that will be connected to the command's
 // standard input when the command starts.
+// If the returned WriteCloser is not closed before Wait is called,
+// Wait will close it.
 func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
 	if c.Stdin != nil {
 		return nil, errors.New("exec: Stdin already set")
@@ -370,8 +373,23 @@ func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
 	}
 	c.Stdin = pr
 	c.closeAfterStart = append(c.closeAfterStart, pr)
-	c.closeAfterWait = append(c.closeAfterWait, pw)
-	return pw, nil
+	wc := &closeOnce{File: pw}
+	c.closeAfterWait = append(c.closeAfterWait, wc)
+	return wc, nil
+}
+
+type closeOnce struct {
+	*os.File
+
+	close    sync.Once
+	closeErr error
+}
+
+func (c *closeOnce) Close() error {
+	c.close.Do(func() {
+		c.closeErr = c.File.Close()
+	})
+	return c.closeErr
 }
 
 // StdoutPipe returns a pipe that will be connected to the command's
diff --git a/src/pkg/os/exec/exec_test.go b/src/pkg/os/exec/exec_test.go
index d7e8573a08..c380d6506c 100644
--- a/src/pkg/os/exec/exec_test.go
+++ b/src/pkg/os/exec/exec_test.go
@@ -152,6 +152,34 @@ func TestPipes(t *testing.T) {
 	check("Wait", err)
 }
 
+const stdinCloseTestString = "Some test string."
+
+// Issue 6270.
+func TestStdinClose(t *testing.T) {
+	check := func(what string, err error) {
+		if err != nil {
+			t.Fatalf("%s: %v", what, err)
+		}
+	}
+	cmd := helperCommand("stdinClose")
+	stdin, err := cmd.StdinPipe()
+	check("StdinPipe", err)
+	// Check that we can access methods of the underlying os.File.`
+	if _, ok := stdin.(interface {
+		Fd() uintptr
+	}); !ok {
+		t.Error("can't access methods of underlying *os.File")
+	}
+	check("Start", cmd.Start())
+	go func() {
+		_, err := io.Copy(stdin, strings.NewReader(stdinCloseTestString))
+		check("Copy", err)
+		// Before the fix, this next line would race with cmd.Wait.
+		check("Close", stdin.Close())
+	}()
+	check("Wait", cmd.Wait())
+}
+
 // Issue 5071
 func TestPipeLookPathLeak(t *testing.T) {
 	fd0 := numOpenFDS(t)
@@ -507,6 +535,17 @@ func TestHelperProcess(*testing.T) {
 				os.Exit(1)
 			}
 		}
+	case "stdinClose":
+		b, err := ioutil.ReadAll(os.Stdin)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+		if s := string(b); s != stdinCloseTestString {
+			fmt.Fprintf(os.Stderr, "Error: Read %q, want %q", s, stdinCloseTestString)
+			os.Exit(1)
+		}
+		os.Exit(0)
 	case "read3": // read fd 3
 		fd3 := os.NewFile(3, "fd3")
 		bs, err := ioutil.ReadAll(fd3)