refactoring process management: no more orphan processes and quicker chrome startup

internal/pkg/xexec/doc.go

@@ -1,6 +1,7 @@
 /*
 Package xexec helps creating exec.Cmd
-with logging.
+with logging and executing those commands
+without leaking orphan processes.
 
 All functions return our standard xerror.Error
 in case of error.

internal/pkg/xexec/xexec.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"os/exec"
 	"strings"
+	"syscall"
 
 	"github.com/thecodingmachine/gotenberg/internal/pkg/xerror"
 	"github.com/thecodingmachine/gotenberg/internal/pkg/xlog"
@@ -43,6 +44,61 @@ func CommandContext(ctx context.Context, logger xlog.Logger, binary string, args
 	return cmd, nil
 }
 
+/*
+Run runs a command.
+
+If command finishes or fails to finish
+before context.Context deadline, kill the
+corresponding process in a way which does
+not leak orphan processes.
+*/
+func Run(ctx context.Context, logger xlog.Logger, binary string, args ...string) error {
+	const op string = "xexec.Run"
+	resolver := func() error {
+		cmd, err := Command(
+			logger,
+			binary,
+			args...,
+		)
+		if err != nil {
+			return err
+		}
+		LogBeforeExecute(logger, cmd)
+		// see https://medium.com/@felixge/killing-a-child-process-and-all-of-its-children-in-go-54079af94773.
+		kill := func() {
+			err := syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
+			if err == nil {
+				return
+			}
+			if !strings.Contains(err.Error(), "no such process") {
+				logger.ErrorOp(op, err)
+			}
+		}
+		cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+		if err := cmd.Start(); err != nil {
+			return err
+		}
+		result := make(chan error, 1)
+		go func() {
+			result <- cmd.Wait()
+		}()
+		select {
+		case err := <-result:
+			logger.DebugfOp(op, "command '%s' finished", strings.Join(cmd.Args, " "))
+			kill()
+			return err
+		case <-ctx.Done():
+			logger.DebugfOp(op, "command '%s' failed to finish before context.Context deadline", strings.Join(cmd.Args, " "))
+			kill()
+			return ctx.Err()
+		}
+	}
+	if err := resolver(); err != nil {
+		return xerror.New(op, err)
+	}
+	return nil
+}
+
 // LogBeforeExecute logs a command before its execution.
 func LogBeforeExecute(logger xlog.Logger, cmd *exec.Cmd) {
 	const op string = "xexec.LogBeforeExecute"
@@ -87,7 +143,7 @@ func logCommandOutput(logger xlog.Logger, reader io.ReadCloser, outputType strin
 	for {
 		line, _, err := r.ReadLine()
 		if err != nil {
-			if err != io.EOF {
+			if err != io.EOF && !strings.Contains(err.Error(), "file already closed") {
 				logger.ErrorOp(op, err)
 			}
 			break

internal/pkg/xexec/xexec_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/thecodingmachine/gotenberg/internal/pkg/xcontext"
 	"github.com/thecodingmachine/gotenberg/test"
 )
 
@@ -37,3 +38,16 @@ func TestCommandContext(t *testing.T) {
 	LogBeforeExecute(logger, cmd)
 	assert.Nil(t, err)
 }
+
+func TestRun(t *testing.T) {
+	logger := test.DebugLogger()
+	// should run without issue.
+	err := Run(context.Background(), logger, "echo", "Hello", "World")
+	assert.Nil(t, err)
+	// should not be OK as context.Context
+	// should timeout.
+	ctx, cancel := xcontext.WithTimeout(logger, 0)
+	defer cancel()
+	err = Run(ctx, logger, "echo", "Hello", "World")
+	assert.NotNil(t, err)
+}