diff.go

// Copyright (c) 2018 Uber Technologies, Inc.
//
// 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.

// Primarily adapted from https://github.com/golang/go/blob/e86168430f0aab8f971763e4b00c2aae7bec55f0/src/cmd/gofmt/gofmt.go.
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package diff

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

// Do does a diff between an input and output.
func Do(input []byte, output []byte, filename string) ([]byte, error) {
	f1, err := writeTempFile("", "prototool-diff", input)
	if err != nil {
		return nil, err
	}
	defer func() { _ = os.Remove(f1) }()

	f2, err := writeTempFile("", "prototool-diff", output)
	if err != nil {
		return nil, err
	}
	defer func() { _ = os.Remove(f2) }()

	cmd := "diff"
	if runtime.GOOS == "plan9" {
		cmd = "/bin/ape/diff"
	}

	data, err := exec.Command(cmd, "-u", f1, f2).CombinedOutput()
	if len(data) > 0 {
		// diff exits with a non-zero status when the files don't match.
		// Ignore that failure as long as we get output.
		return replaceTempFilename(data, filename)
	}
	return nil, err
}

func writeTempFile(dir, prefix string, data []byte) (string, error) {
	file, err := ioutil.TempFile(dir, prefix)
	if err != nil {
		return "", err
	}
	_, err = file.Write(data)
	if err1 := file.Close(); err == nil {
		err = err1
	}
	if err != nil {
		_ = os.Remove(file.Name())
		return "", err
	}
	return file.Name(), nil
}

// replaceTempFilename replaces temporary filenames in diff with actual one.
//
//   --- /tmp/gofmt316145376	2017-02-03 19:13:00.280468375 -0500
//   +++ /tmp/gofmt617882815	2017-02-03 19:13:00.280468375 -0500
//   ...
//   ->
//   --- path/to/file.go.orig	2017-02-03 19:13:00.280468375 -0500
//   +++ path/to/file.go	2017-02-03 19:13:00.280468375 -0500
//   ...
func replaceTempFilename(diff []byte, filename string) ([]byte, error) {
	bs := bytes.SplitN(diff, []byte{'\n'}, 3)
	if len(bs) < 3 {
		return nil, fmt.Errorf("got unexpected diff for %s", filename)
	}
	// Preserve timestamps.
	var t0, t1 []byte
	if i := bytes.LastIndexByte(bs[0], '\t'); i != -1 {
		t0 = bs[0][i:]
	}
	if i := bytes.LastIndexByte(bs[1], '\t'); i != -1 {
		t1 = bs[1][i:]
	}
	// Always print filepath with slash separator.
	f := filepath.ToSlash(filename)
	bs[0] = []byte(fmt.Sprintf("--- %s%s", f+".orig", t0))
	bs[1] = []byte(fmt.Sprintf("+++ %s%s", f, t1))
	return bytes.Join(bs, []byte{'\n'}), nil
}