watcher.go

/*-
 * Copyright 2015 Square Inc.
 *
 * 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
 *
 *     http://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 main

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"io/ioutil"
	"path"
	"time"
)

// Watch files with a periodic timer, for filesystems that don't do
// inotify correctly (e.g. some fuse filesystems or other custom stuff).
func watchFiles(files []string, duration time.Duration, notify chan bool) {
	hashes := hashFiles(files)
	ticker := time.Tick(duration)

	for {
		<-ticker
		logger.Printf("running timed reload (timer fired)")

		change := false
		for _, file := range files {
			if fileChanged(hashes, file) {
				logger.Printf("detected change on %s, reloading", path.Base(file))
				change = true
			}
		}

		if change {
			notify <- true
		} else {
			logger.Printf("nothing changed, not reloading")
		}
	}
}

// Hash initial state of files we're watching
func hashFiles(files []string) map[string][32]byte {
	hashes := make(map[string][32]byte)

	for _, file := range files {
		hash, err := hashFile(file)
		if err != nil {
			logger.Printf("error reading file: %s", err)
			continue
		}

		name := path.Base(file)
		logger.Printf("sha256(%s) = %s", name, hex.EncodeToString(hash[:]))
		hashes[name] = hash
	}

	return hashes
}

// Read & hash a single file
func hashFile(file string) ([32]byte, error) {
	data, err := ioutil.ReadFile(file)
	if err != nil {
		return [32]byte{}, err
	}

	return sha256.Sum256(data), nil
}

// Check if a file has changed contents, update hash
func fileChanged(hashes map[string][32]byte, file string) bool {
	newHash, err := hashFile(file)
	if err != nil {
		logger.Printf("error reading file: %s", err)
		return false
	}

	name := path.Base(file)
	oldHash := hashes[name]
	if !bytes.Equal(oldHash[:], newHash[:]) {
		logger.Printf("sha256(%s) = %s", name, hex.EncodeToString(newHash[:]))
		hashes[name] = newHash
		return true
	}

	return false
}