Add a util/exec interface for testing execs.

pkg/util/exec/doc.go

+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package exec provides an injectable interface and implementations for running commands.
+package exec

pkg/util/exec/exec.go

+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package exec
+
+import (
+	osexec "os/exec"
+	"syscall"
+)
+
+// Interface is an interface that presents a subset of the os/exec API.  Use this
+// when you want to inject fakeable/mockable exec behavior.
+type Interface interface {
+	// Command returns a Cmd instance which can be used to run a single command.
+	// This follows the pattern of package os/exec.
+	Command(cmd string, args ...string) Cmd
+}
+
+// Cmd is an interface that presents an API that is very similar to Cmd from os/exec.
+// As more functionality is needed, this can grow.  Since Cmd is a struct, we will have
+// to replace fields with get/set method pairs.
+type Cmd interface {
+	// CombinedOutput runs the command and returns its combined standard output
+	// and standard error.  This follows the pattern of package os/exec.
+	CombinedOutput() ([]byte, error)
+}
+
+// ExitError is an interface that presents an API similar to os.ProcessState, which is
+// what ExitError from os/exec is.  This is designed to make testing a bit easier and
+// probably loses some of the cross-platform properties of the underlying library.
+type ExitError interface {
+	String() string
+	Error() string
+	Exited() bool
+	ExitStatus() int
+}
+
+// Implements Interface in terms of really exec()ing.
+type executor struct{}
+
+// New returns a new Interface which will os/exec to run commands.
+func New() Interface {
+	return &executor{}
+}
+
+// Command is part of the Interface interface.
+func (executor *executor) Command(cmd string, args ...string) Cmd {
+	return (*cmdWrapper)(osexec.Command(cmd, args...))
+}
+
+// Wraps exec.Cmd so we can capture errors.
+type cmdWrapper osexec.Cmd
+
+// CombinedOutput is part of the Cmd interface.
+func (cmd *cmdWrapper) CombinedOutput() ([]byte, error) {
+	out, err := (*osexec.Cmd)(cmd).CombinedOutput()
+	if err != nil {
+		ee, ok := err.(*osexec.ExitError)
+		if !ok {
+			return out, err
+		}
+		// Force a compile fail if exitErrorWrapper can't convert to ExitError.
+		var x ExitError = &exitErrorWrapper{ee}
+		return out, x
+	}
+	return out, nil
+}
+
+// exitErrorWrapper is an implementation of ExitError in terms of os/exec ExitError.
+// Note: standard exec.ExitError is type *os.ProcessState, which already implements Exited().
+type exitErrorWrapper struct {
+	*osexec.ExitError
+}
+
+// ExitStatus is part of the ExitError interface.
+func (eew exitErrorWrapper) ExitStatus() int {
+	ws, ok := eew.Sys().(syscall.WaitStatus)
+	if !ok {
+		panic("can't call ExitStatus() on a non-WaitStatus exitErrorWrapper")
+	}
+	return ws.ExitStatus()
+}

pkg/util/exec/exec_test.go

+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package exec
+
+import (
+	"testing"
+)
+
+func TestExecutorNoArgs(t *testing.T) {
+	ex := New()
+
+	cmd := ex.Command("/bin/true")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Errorf("expected success, got %+v", err)
+	}
+	if len(out) != 0 {
+		t.Errorf("expected no output, got %q", string(out))
+	}
+
+	cmd = ex.Command("/bin/false")
+	out, err = cmd.CombinedOutput()
+	if err == nil {
+		t.Errorf("expected failure, got nil error")
+	}
+	if len(out) != 0 {
+		t.Errorf("expected no output, got %q", string(out))
+	}
+	ee, ok := err.(ExitError)
+	if !ok {
+		t.Errorf("expected an ExitError, got %+v", err)
+	}
+	if ee.Exited() {
+		if code := ee.ExitStatus(); code != 1 {
+			t.Errorf("expected exit status 1, got %d", code)
+		}
+	}
+
+	cmd = ex.Command("/does/not/exist")
+	out, err = cmd.CombinedOutput()
+	if err == nil {
+		t.Errorf("expected failure, got nil error")
+	}
+	if ee, ok := err.(ExitError); ok {
+		t.Errorf("expected non-ExitError, got %+v", ee)
+	}
+}
+
+func TestExecutorWithArgs(t *testing.T) {
+	ex := New()
+
+	cmd := ex.Command("/bin/echo", "stdout")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Errorf("expected success, got %+v", err)
+	}
+	if string(out) != "stdout\n" {
+		t.Errorf("unexpected output: %q", string(out))
+	}
+
+	cmd = ex.Command("/bin/sh", "-c", "echo stderr > /dev/stderr")
+	out, err = cmd.CombinedOutput()
+	if err != nil {
+		t.Errorf("expected success, got %+v", err)
+	}
+	if string(out) != "stderr\n" {
+		t.Errorf("unexpected output: %q", string(out))
+	}
+}