file/file.go

/*
Copyright 2016 Google LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package file provides utility file operations.
package file

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
	"runtime"

	"github.com/bazelbuild/buildtools/wspace"
	"github.com/google/safeopen"
)

// ReadFile can be updated from the caller to change the API
// for reading a file.
var ReadFile = readFile

// WriteFile can be updated from the caller to change the API
// for writing a file.
var WriteFile = writeFile

// WriteFileMode can be updated from the caller to change the API
// for writing a file with a specific mode.
var WriteFileMode = writeFileMode

// OpenReadFile can be updated from the caller to change the API
// for opening a file.
var OpenReadFile = openReadFile

// DisableSymlinkSafety disables symlink safety checks for WriteFile and WriteFileMode.
var DisableSymlinkSafety bool

// readFile is like os.ReadFile.
func readFile(name string) ([]byte, os.FileInfo, error) {
	fi, err := os.Stat(name)
	if err != nil {
		return nil, nil, err
	}

	data, err := os.ReadFile(name)
	return data, fi, err
}

// writeFile is like os.WriteFile.
func writeFile(name string, data []byte) error {
	return WriteFileMode(name, data, 0644)
}

// writeFile is like os.WriteFile.
func writeFileMode(name string, data []byte, mode os.FileMode) error {
	if DisableSymlinkSafety || runtime.GOOS != "linux" {
		return os.WriteFile(name, data, mode)
	}
	// If we are in a workspace, we allow writes to any symlinked file within the workspace.
	if wsRoot, _ := wspace.FindWorkspaceRoot(name); wsRoot != "" {
		relPath, err := filepath.Rel(wsRoot, name)
		if err != nil {
			return err
		}
		return safeopen.WriteFileBeneath(wsRoot, relPath, data, mode)
	}
	dir, file := filepath.Split(name)
	absDir, err := filepath.Abs(dir)
	if err != nil {
		return err
	}
	// If we are not in a workspace, we only allow writes to the directory where the file is located.
	return safeopen.WriteFileBeneath(absDir, file, data, mode)
}

// openReadFile is like os.Open.
func openReadFile(name string) io.ReadCloser {
	f, err := os.Open(name)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Could not open %s\n", name)
		os.Exit(1)
	}
	return f
}