executils.go

// This file is part of arduino-cli.
//
// Copyright 2020 ARDUINO SA (http://www.arduino.cc/)
//
// This software is released under the GNU General Public License version 3,
// which covers the main part of arduino-cli.
// The terms of this license can be found at:
// https://www.gnu.org/licenses/gpl-3.0.en.html
//
// You can be released from the requirements of the above licenses by purchasing
// a commercial license. Buying such a license is mandatory if you want to
// modify or otherwise use the software for commercial activities involving the
// Arduino software without disclosing the source code of your own applications.
// To purchase a commercial license, send an email to license@arduino.cc.

package executils

import (
	"bytes"
	"fmt"
	"io"
	"os/exec"
)

// PipeCommands executes the commands received as input by feeding the output of
// one to the input of the other, exactly like Unix Pipe (|).
// Returns the output of the final command and the eventual error.
//
// code inspired by https://gist.github.com/tyndyll/89fbb2c2273f83a074dc
func PipeCommands(commands ...*exec.Cmd) ([]byte, error) {
	var errorBuffer, outputBuffer bytes.Buffer
	pipeStack := make([]*io.PipeWriter, len(commands)-1)
	i := 0
	for ; i < len(commands)-1; i++ {
		stdinPipe, stdoutPipe := io.Pipe()
		commands[i].Stdout = stdoutPipe
		commands[i].Stderr = &errorBuffer
		commands[i+1].Stdin = stdinPipe
		pipeStack[i] = stdoutPipe
	}
	commands[i].Stdout = &outputBuffer
	commands[i].Stderr = &errorBuffer

	if err := call(commands, pipeStack); err != nil {
		return nil, err
	}

	return outputBuffer.Bytes(), nil
}

func call(stack []*exec.Cmd, pipes []*io.PipeWriter) (err error) {
	if stack[0].Process == nil {
		if err = stack[0].Start(); err != nil {
			return err
		}
	}
	if len(stack) > 1 {
		if err = stack[1].Start(); err != nil {
			return err
		}
		defer func() {
			pipes[0].Close()
			err = call(stack[1:], pipes[1:])
		}()
	}
	return stack[0].Wait()
}

// TellCommandNotToSpawnShell avoids that the specified Cmd display a small
// command prompt while runnning on Windows. It has no effects on other OS.
func TellCommandNotToSpawnShell(cmd *exec.Cmd) {
	tellCommandNotToSpawnShell(cmd)
}

// Command creates a command with the provided command line arguments.
// The first argument is the path to the executable, the remainder are the
// arguments to the command.
func Command(args []string) (*exec.Cmd, error) {
	if args == nil || len(args) == 0 {
		return nil, fmt.Errorf("no executable specified")
	}
	cmd := exec.Command(args[0], args[1:]...)
	TellCommandNotToSpawnShell(cmd)

	// This is required because some tools detects if the program is running
	// from terminal by looking at the stdin/out bindings.
	// https://github.com/arduino/arduino-cli/issues/844
	cmd.Stdin = NullReader
	return cmd, nil
}