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

refs #196

zfs/zfscmd/zfscmd.go

@@ -0,0 +1,143 @@
+// Package zfscmd provides a wrapper around packate os/exec.
+// Functionality provided by the wrapper:
+// - logging start and end of command execution
+// - status report of active commands
+// - prometheus metrics of runtimes
+package zfscmd
+
+import (
+	"context"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/zrepl/zrepl/util/circlog"
+)
+
+type Cmd struct {
+	cmd                       *exec.Cmd
+	ctx                       context.Context
+	mtx                       sync.RWMutex
+	startedAt, waitReturnedAt time.Time
+}
+
+func CommandContext(ctx context.Context, name string, arg ...string) *Cmd {
+	cmd := exec.CommandContext(ctx, name, arg...)
+	return &Cmd{cmd: cmd, ctx: ctx}
+}
+
+// err.(*exec.ExitError).Stderr will NOT be set
+func (c *Cmd) CombinedOutput() (o []byte, err error) {
+	c.startPre()
+	c.startPost(nil)
+	c.waitPre()
+	o, err = c.cmd.CombinedOutput()
+	c.waitPost(err)
+	return
+}
+
+// err.(*exec.ExitError).Stderr will be set
+func (c *Cmd) Output() (o []byte, err error) {
+	c.startPre()
+	c.startPost(nil)
+	c.waitPre()
+	o, err = c.cmd.Output()
+	c.waitPost(err)
+	return
+}
+
+// Careful: err.(*exec.ExitError).Stderr will not be set, even if you don't open an StderrPipe
+func (c *Cmd) StdoutPipeWithErrorBuf() (p io.ReadCloser, errBuf *circlog.CircularLog, err error) {
+	p, err = c.cmd.StdoutPipe()
+	errBuf = circlog.MustNewCircularLog(1 << 15)
+	c.cmd.Stderr = errBuf
+	return p, errBuf, err
+}
+
+type Stdio struct {
+	Stdin  io.ReadCloser
+	Stdout io.Writer
+	Stderr io.Writer
+}
+
+func (c *Cmd) SetStdio(stdio Stdio) {
+	c.cmd.Stdin = stdio.Stdin
+	c.cmd.Stderr = stdio.Stderr
+	c.cmd.Stdout = stdio.Stdout
+}
+
+func (c *Cmd) String() string {
+	return strings.Join(c.cmd.Args, " ") // includes argv[0] if initialized with CommandContext, that's the only way we o it
+}
+
+func (c *Cmd) log() Logger {
+	return getLogger(c.ctx).WithField("cmd", c.String())
+}
+
+func (c *Cmd) Start() (err error) {
+	c.startPre()
+	err = c.cmd.Start()
+	c.startPost(err)
+	return err
+}
+
+// only call this after a successful call to .Start()
+func (c *Cmd) Process() *os.Process {
+	if c.startedAt.IsZero() {
+		panic("calling Process() only allowed after successful call to Start()")
+	}
+	return c.cmd.Process
+}
+
+func (c *Cmd) Wait() (err error) {
+	c.waitPre()
+	err = c.cmd.Wait()
+	if !c.waitReturnedAt.IsZero() {
+		// ignore duplicate waits
+		return err
+	}
+	c.waitPost(err)
+	return err
+}
+
+func (c *Cmd) startPre() {
+	startPreLogging(c, time.Now())
+}
+
+func (c *Cmd) startPost(err error) {
+	now := time.Now()
+
+	c.mtx.Lock()
+	c.startedAt = now
+	c.mtx.Unlock()
+
+	startPostReport(c, err, now)
+	startPostLogging(c, err, now)
+}
+
+func (c *Cmd) waitPre() {
+	waitPreLogging(c, time.Now())
+}
+
+func (c *Cmd) waitPost(err error) {
+	now := time.Now()
+
+	c.mtx.Lock()
+	c.waitReturnedAt = now
+	c.mtx.Unlock()
+
+	waitPostReport(c, now)
+	waitPostLogging(c, err, now)
+	waitPostPrometheus(c, err, now)
+}
+
+// returns 0 if the command did not yet finish
+func (c *Cmd) Runtime() time.Duration {
+	if c.waitReturnedAt.IsZero() {
+		return 0
+	}
+	return c.waitReturnedAt.Sub(c.startedAt)
+}