Bugfix: only use io.Copy in hijack if attaching both stdout and stderr

Add regression tests to ensure issue is fixed.

Docker-DCO-1.1-Signed-off-by: Matt Heon <mheon@redhat.com> (github: mheon)

api/client/hijack.go

@@ -88,7 +88,7 @@ func (cli *DockerCli) hijack(method, path string, setRawTerminal bool, in io.Rea
 			}()
 
 			// When TTY is ON, use regular copy
-			if setRawTerminal {
+			if setRawTerminal && stdout != nil {
 				_, err = io.Copy(stdout, br)
 			} else {
 				_, err = utils.StdCopy(stdout, stderr, br)

integration-cli/docker_cli_run_test.go

@@ -1218,3 +1218,51 @@ func TestDnsOptionsBasedOnHostResolvConf(t *testing.T) {
 
 	logDone("run - dns options based on host resolv.conf")
 }
+
+// Regression test for #6983
+func TestAttachStdErrOnlyTTYMode(t *testing.T) {
+	cmd := exec.Command(dockerBinary, "run", "-t", "-a", "stderr", "busybox", "true")
+
+	exitCode, err := runCommand(cmd)
+	if err != nil {
+		t.Fatal(err)
+	} else if exitCode != 0 {
+		t.Fatalf("Container should have exited with error code 0")
+	}
+
+	deleteAllContainers()
+
+	logDone("run - Attach stderr only with -t")
+}
+
+// Regression test for #6983
+func TestAttachStdOutOnlyTTYMode(t *testing.T) {
+	cmd := exec.Command(dockerBinary, "run", "-t", "-a", "stdout", "busybox", "true")
+
+	exitCode, err := runCommand(cmd)
+	if err != nil {
+		t.Fatal(err)
+	} else if exitCode != 0 {
+		t.Fatalf("Container should have exited with error code 0")
+	}
+
+	deleteAllContainers()
+
+	logDone("run - Attach stdout only with -t")
+}
+
+// Regression test for #6983
+func TestAttachStdOutAndErrTTYMode(t *testing.T) {
+	cmd := exec.Command(dockerBinary, "run", "-t", "-a", "stdout", "-a", "stderr", "busybox", "true")
+
+	exitCode, err := runCommand(cmd)
+	if err != nil {
+		t.Fatal(err)
+	} else if exitCode != 0 {
+		t.Fatalf("Container should have exited with error code 0")
+	}
+
+	deleteAllContainers()
+
+	logDone("run - Attach stderr and stdout with -t")
+}