zfs: introduce pkg zfs/zfscmd for command logging, status, prometheus metrics

refs #196

zfs/zfscmd/zfscmd_platform_test.go

@@ -0,0 +1,60 @@
+package zfscmd
+
+import (
+	"bytes"
+	"io"
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+const testBin = "./zfscmd_platform_test.bash"
+
+func TestCmdStderrBehaviorOutput(t *testing.T) {
+
+	stdout, err := exec.Command(testBin, "0").Output()
+	require.NoError(t, err)
+	require.Equal(t, []byte("to stdout\n"), stdout)
+
+	stdout, err = exec.Command(testBin, "1").Output()
+	assert.Equal(t, []byte("to stdout\n"), stdout)
+	require.Error(t, err)
+	ee, ok := err.(*exec.ExitError)
+	require.True(t, ok)
+	require.Equal(t, ee.Stderr, []byte("to stderr\n"))
+}
+
+func TestCmdStderrBehaviorCombinedOutput(t *testing.T) {
+
+	stdio, err := exec.Command(testBin, "0").CombinedOutput()
+	require.NoError(t, err)
+	require.Equal(t, "to stderr\nto stdout\n", string(stdio))
+
+	stdio, err = exec.Command(testBin, "1").CombinedOutput()
+	require.Equal(t, "to stderr\nto stdout\n", string(stdio))
+	require.Error(t, err)
+	ee, ok := err.(*exec.ExitError)
+	require.True(t, ok)
+	require.Empty(t, ee.Stderr) // !!!! maybe not what one would expect
+}
+
+func TestCmdStderrBehaviorStdoutPipe(t *testing.T) {
+	cmd := exec.Command(testBin, "1")
+	stdoutPipe, err := cmd.StdoutPipe()
+	require.NoError(t, err)
+	err = cmd.Start()
+	require.NoError(t, err)
+	defer cmd.Wait()
+	var stdout bytes.Buffer
+	_, err = io.Copy(&stdout, stdoutPipe)
+	require.NoError(t, err)
+	require.Equal(t, "to stdout\n", stdout.String())
+
+	err = cmd.Wait()
+	require.Error(t, err)
+	ee, ok := err.(*exec.ExitError)
+	require.True(t, ok)
+	require.Empty(t, ee.Stderr) // !!!!! probably not what one would expect if we only redirect stdout
+}