super-graph/internal/serv/reload.go

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// Package reload offers lightweight automatic reloading of running processes.
//
// After initialisation with reload.Do() any changes to the binary will
// restart the process.
//
// Example:
//
// go func() {
// err := reload.Do(log.Printf)
// if err != nil {
// panic(err)
// }
// }()
//
// A list of additional directories to watch can be added:
//
// go func() {
// err := reload.Do(log.Printf, reload.Dir("tpl", reloadTpl)
// if err != nil {
// panic(err)
// }
// }()
//
// Note that this package won't prevent race conditions (e.g. when assigning to
// a global templates variable). You'll need to use sync.RWMutex yourself.
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package serv
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import (
"fmt"
"os"
"path/filepath"
"runtime"
"strings"
"syscall"
"time"
"github.com/fsnotify/fsnotify"
"github.com/pkg/errors"
)
var binSelf string
type dir struct {
path string
cb func()
}
// Dir is an additional directory to watch for changes. Directories are watched
// non-recursively.
//
// The second argument is the callback that to run when the directory changes.
// Use reload.ReExec() to restart the process.
func Dir(path string, cb func()) dir { return dir{path, cb} } // nolint: golint
// Do reload the current process when its binary changes.
//
// The log function is used to display an informational startup message and
// errors. It works well with e.g. the standard log package or Logrus.
//
// The error return will only return initialisation errors. Once initialized it
// will use the log function to print errors, rather than return.
func Do(log func(string, ...interface{}), additional ...dir) error {
watcher, err := fsnotify.NewWatcher()
if err != nil {
return errors.Wrap(err, "cannot setup watcher")
}
defer watcher.Close() // nolint: errcheck
binSelf, err = self()
if err != nil {
return err
}
// Watch the directory, because a recompile renames the existing
// file (rather than rewriting it), so we won't get events for that.
dirs := make([]string, len(additional)+1)
dirs[0] = filepath.Dir(binSelf)
for i := range additional {
path, err := filepath.Abs(additional[i].path)
if err != nil {
return errors.Wrapf(err, "cannot get absolute path to %q: %v",
additional[i].path, err)
}
s, err := os.Stat(path)
if err != nil {
return errors.Wrap(err, "os.Stat")
}
if !s.IsDir() {
return errors.Errorf("not a directory: %q; can only watch directories",
additional[i].path)
}
additional[i].path = path
dirs[i+1] = path
}
done := make(chan bool)
go func() {
for {
select {
case err := <-watcher.Errors:
// Standard logger doesn't have anything other than Print,
// Panic, and Fatal :-/ Printf() is probably best.
log("reload error: %v", err)
case event := <-watcher.Events:
// Ensure that we use the correct events, as they are not uniform across
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// platforms. See https://github.com/fsnotify/fsnotify/issues/74
if conf != nil && strings.HasSuffix(event.Name, "/allow.list") {
continue
}
if conf.Production {
continue
}
log("INF Reloading, file changed detected: %s", event)
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var trigger bool
switch runtime.GOOS {
case "darwin", "freebsd", "openbsd", "netbsd", "dragonfly":
trigger = event.Op&fsnotify.Create == fsnotify.Create
case "linux":
trigger = event.Op&fsnotify.Write == fsnotify.Write
default:
trigger = event.Op&fsnotify.Create == fsnotify.Create
log("reload: untested GOOS %q; this package may not work correctly", runtime.GOOS)
}
if !trigger {
continue
}
if event.Name == binSelf {
// Wait for writes to finish.
time.Sleep(100 * time.Millisecond)
ReExec()
}
for _, a := range additional {
if strings.HasPrefix(event.Name, a.path) {
time.Sleep(100 * time.Millisecond)
a.cb()
}
}
}
}
}()
for _, d := range dirs {
if err := watcher.Add(d); err != nil {
return errors.Wrapf(err, "cannot add %q to watcher", d)
}
}
add := ""
if len(additional) > 0 {
reldirs := make([]string, len(dirs)-1)
for i := range dirs[1:] {
reldirs[i] = relpath(dirs[i+1])
}
add = fmt.Sprintf(" (additional dirs: %s)", strings.Join(reldirs, ", "))
}
log("restarting %q when it changes%s", relpath(binSelf), add)
<-done
return nil
}
// Exec replaces the current process with a new copy of itself.
func ReExec() {
err := syscall.Exec(binSelf, append([]string{binSelf}, os.Args[1:]...), os.Environ())
if err != nil {
log.Fatalf("ERR cannot restart: %s", err)
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}
}
// Get location to executable.
func self() (string, error) {
bin := os.Args[0]
if !filepath.IsAbs(bin) {
var err error
bin, err = os.Executable()
if err != nil {
return "", errors.Wrapf(err,
"cannot get path to binary %q (launch with absolute path): %v",
os.Args[0], err)
}
}
return bin, nil
}