run.go

// SPDX-License-Identifier: MIT
//
// Copyright (c) 2019 GitHub Inc.
//               2022 Unikraft GmbH.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package run

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

// Runnable is typically an exec.Cmd or its stub in tests
type Runnable interface {
	Output() ([]byte, error)
	Run() error
}

// PrepareCmd extends exec.Cmd with extra error reporting features and provides
// a hook to stub command execution in tests
var PrepareCmd = func(cmd *exec.Cmd) Runnable {
	return &cmdWithStderr{cmd}
}

// cmdWithStderr augments exec.Cmd by adding stderr to the error message
type cmdWithStderr struct {
	*exec.Cmd
}

func (c cmdWithStderr) Output() ([]byte, error) {
	if os.Getenv("DEBUG") != "" {
		_ = printArgs(os.Stderr, c.Cmd.Args)
	}
	if c.Cmd.Stderr != nil {
		return c.Cmd.Output()
	}
	errStream := &bytes.Buffer{}
	c.Cmd.Stderr = errStream
	out, err := c.Cmd.Output()
	if err != nil {
		err = &CmdError{errStream, c.Cmd.Args, err}
	}
	return out, err
}

func (c cmdWithStderr) Run() error {
	if os.Getenv("DEBUG") != "" {
		_ = printArgs(os.Stderr, c.Cmd.Args)
	}
	if c.Cmd.Stderr != nil {
		return c.Cmd.Run()
	}
	errStream := &bytes.Buffer{}
	c.Cmd.Stderr = errStream
	err := c.Cmd.Run()
	if err != nil {
		err = &CmdError{errStream, c.Cmd.Args, err}
	}
	return err
}

// CmdError provides more visibility into why an exec.Cmd had failed
type CmdError struct {
	Stderr *bytes.Buffer
	Args   []string
	Err    error
}

func (e CmdError) Error() string {
	msg := e.Stderr.String()
	if msg != "" && !strings.HasSuffix(msg, "\n") {
		msg += "\n"
	}
	return fmt.Sprintf("%s%s: %s", msg, e.Args[0], e.Err)
}

func printArgs(w io.Writer, args []string) error {
	if len(args) > 0 {
		// print commands, but omit the full path to an executable
		args = append([]string{filepath.Base(args[0])}, args[1:]...)
	}
	_, err := fmt.Fprintf(w, "%v\n", args)
	return err
}