reexec: add "CommandContext"

Adds a CommandContext command, to provide the equivalent of
exec.CommandContext.

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

reexec/reexec.go

@@ -7,6 +7,7 @@
 package reexec
 
 import (
+	"context"
 	"fmt"
 	"os"
 	"os/exec"
@@ -52,6 +53,23 @@ func Command(args ...string) *exec.Cmd {
 	return command(args...)
 }
 
+// CommandContext is like [Command] but includes a context. It uses
+// [exec.CommandContext] under the hood.
+//
+// The provided context is used to interrupt the process
+// (by calling cmd.Cancel or [os.Process.Kill])
+// if the context becomes done before the command completes on its own.
+//
+// CommandContext sets the command's Cancel function to invoke the Kill method
+// on its Process, and leaves its WaitDelay unset. The caller may change the
+// cancellation behavior by modifying those fields before starting the command.
+func CommandContext(ctx context.Context, args ...string) *exec.Cmd {
+	if ctx == nil {
+		panic("nil Context")
+	}
+	return commandContext(ctx, args...)
+}
+
 // Self returns the path to the current process's binary.
 //
 // On Linux, it returns "/proc/self/exe", which provides the in-memory version

reexec/reexec_linux.go

@@ -1,6 +1,7 @@
 package reexec
 
 import (
+	"context"
 	"os/exec"
 	"syscall"
 )
@@ -16,3 +17,15 @@ func command(args ...string) *exec.Cmd {
 	}
 	return cmd
 }
+
+func commandContext(ctx context.Context, args ...string) *exec.Cmd {
+	// We try to stay close to exec.Command's behavior, but after
+	// constructing the cmd, we remove "Self()" from cmd.Args, which
+	// is prepended by exec.Command.
+	cmd := exec.CommandContext(ctx, Self(), args...)
+	cmd.Args = cmd.Args[1:]
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Pdeathsig: syscall.SIGTERM,
+	}
+	return cmd
+}

reexec/reexec_other.go

@@ -3,6 +3,7 @@
 package reexec
 
 import (
+	"context"
 	"os/exec"
 )
 
@@ -14,3 +15,12 @@ func command(args ...string) *exec.Cmd {
 	cmd.Args = cmd.Args[1:]
 	return cmd
 }
+
+func commandContext(ctx context.Context, args ...string) *exec.Cmd {
+	// We try to stay close to exec.Command's behavior, but after
+	// constructing the cmd, we remove "Self()" from cmd.Args, which
+	// is prepended by exec.Command.
+	cmd := exec.CommandContext(ctx, Self(), args...)
+	cmd.Args = cmd.Args[1:]
+	return cmd
+}

reexec/reexec_test.go

@@ -1,18 +1,22 @@
 package reexec
 
 import (
+	"context"
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 )
 
 const (
 	testReExec  = "test-reexec"
 	testReExec2 = "test-reexec2"
+	testReExec3 = "test-reexec3"
 )
 
 func init() {
@@ -27,6 +31,11 @@ func init() {
 		fmt.Println("Hello", testReExec2, args)
 		os.Exit(0)
 	})
+	Register(testReExec3, func() {
+		fmt.Println("Hello " + testReExec3)
+		time.Sleep(1 * time.Second)
+		os.Exit(0)
+	})
 	Init()
 }
 
@@ -112,6 +121,83 @@ func TestCommand(t *testing.T) {
 	}
 }
 
+func TestCommandContext(t *testing.T) {
+	tests := []struct {
+		doc        string
+		cmdAndArgs []string
+		cancel     bool
+		expOut     string
+		expError   bool
+	}{
+		{
+			doc:        "basename",
+			cmdAndArgs: []string{testReExec2},
+			expOut:     "Hello test-reexec2",
+		},
+		{
+			doc:        "full path",
+			cmdAndArgs: []string{filepath.Join("something", testReExec2)},
+			expOut:     "Hello test-reexec2",
+		},
+		{
+			doc:        "command with args",
+			cmdAndArgs: []string{testReExec2, "--some-flag", "some-value", "arg1", "arg2"},
+			expOut:     `Hello test-reexec2 (args: []string{"--some-flag", "some-value", "arg1", "arg2"})`,
+		},
+		{
+			doc:        "context canceled",
+			cancel:     true,
+			cmdAndArgs: []string{testReExec2},
+			expError:   true,
+		},
+		{
+			doc:        "context timeout",
+			cmdAndArgs: []string{testReExec3},
+			expOut:     "Hello test-reexec3",
+			expError:   true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.doc, func(t *testing.T) {
+			ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+			defer cancel()
+
+			cmd := CommandContext(ctx, tc.cmdAndArgs...)
+			if !reflect.DeepEqual(cmd.Args, tc.cmdAndArgs) {
+				t.Fatalf("got %+v, want %+v", cmd.Args, tc.cmdAndArgs)
+			}
+
+			w, err := cmd.StdinPipe()
+			if err != nil {
+				t.Fatalf("Error on pipe creation: %v", err)
+			}
+			defer func() { _ = w.Close() }()
+			if tc.cancel {
+				cancel()
+			}
+			out, err := cmd.CombinedOutput()
+			if tc.cancel {
+				if !errors.Is(err, context.Canceled) {
+					t.Errorf("got %[1]v (%[1]T), want %v", err, context.Canceled)
+				}
+			}
+			if tc.expError {
+				if err == nil {
+					t.Errorf("expected error, got nil")
+				}
+			} else if err != nil {
+				t.Errorf("error on re-exec cmd: %v, out: %v", err, string(out))
+			}
+
+			actual := strings.TrimSpace(string(out))
+			if actual != tc.expOut {
+				t.Errorf("got %v, want %v", actual, tc.expOut)
+			}
+		})
+	}
+}
+
 func TestNaiveSelf(t *testing.T) {
 	if os.Getenv("TEST_CHECK") == "1" {
 		os.Exit(2)