pkg/shell: Add cancellable versions of Run and RunWithExitCode

A subsequent commit will use this to ensure that the user can still
interact with the image download prompt while 'skopeo inspect' fetches
the image size from the remote registry.  Initially, the prompt will be
shown without the imagesize.  If the user responds before the size is
fetched, then the pending 'skopeo inspect' will be cancelled.

#752
#1263

src/pkg/shell/shell.go

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2019 – 2022 Red Hat Inc.
+ * Copyright © 2019 – 2023 Red Hat Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package shell
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"io"
@@ -27,7 +28,13 @@ import (
 )
 
 func Run(name string, stdin io.Reader, stdout, stderr io.Writer, arg ...string) error {
-	exitCode, err := RunWithExitCode(name, stdin, stdout, stderr, arg...)
+	ctx := context.Background()
+	err := RunContext(ctx, name, stdin, stdout, stderr, arg...)
+	return err
+}
+
+func RunContext(ctx context.Context, name string, stdin io.Reader, stdout, stderr io.Writer, arg ...string) error {
+	exitCode, err := RunContextWithExitCode(ctx, name, stdin, stdout, stderr, arg...)
 	if err != nil {
 		return err
 	}
@@ -37,13 +44,18 @@ func Run(name string, stdin io.Reader, stdout, stderr io.Writer, arg ...string)
 	return nil
 }
 
-func RunWithExitCode(name string, stdin io.Reader, stdout, stderr io.Writer, arg ...string) (int, error) {
+func RunContextWithExitCode(ctx context.Context,
+	name string,
+	stdin io.Reader,
+	stdout, stderr io.Writer,
+	arg ...string) (int, error) {
+
 	logLevel := logrus.GetLevel()
 	if stderr == nil && logLevel >= logrus.DebugLevel {
 		stderr = os.Stderr
 	}
 
-	cmd := exec.Command(name, arg...)
+	cmd := exec.CommandContext(ctx, name, arg...)
 	cmd.Stdin = stdin
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr
@@ -53,6 +65,10 @@ func RunWithExitCode(name string, stdin io.Reader, stdout, stderr io.Writer, arg
 			return 1, fmt.Errorf("%s(1) not found", name)
 		}
 
+		if ctxErr := ctx.Err(); ctxErr != nil {
+			return 1, ctxErr
+		}
+
 		var exitErr *exec.ExitError
 		if errors.As(err, &exitErr) {
 			exitCode := exitErr.ExitCode()
@@ -64,3 +80,9 @@ func RunWithExitCode(name string, stdin io.Reader, stdout, stderr io.Writer, arg
 
 	return 0, nil
 }
+
+func RunWithExitCode(name string, stdin io.Reader, stdout, stderr io.Writer, arg ...string) (int, error) {
+	ctx := context.Background()
+	exitCode, err := RunContextWithExitCode(ctx, name, stdin, stdout, stderr, arg...)
+	return exitCode, err
+}