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)
Upstream-commit: 1476f295aca20e1c35383c133219d54a5373183f
Component: engine

components/engine/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")
+}