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Implement file.Watcher

Browse source 
Signed-off-by: Knut Ahlers <knut@ahlers.me>
This commit is contained in:
Knut Ahlers 2023-01-28 18:43:04 +01:00
parent 9eea964145
commit 36c4490cff
Signed by: luzifer
GPG key ID: D91C3E91E4CAD6F5
5 changed files with 508 additions and 10 deletions
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141
file/watcher.go Normal file
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@ -0,0 +1,141 @@
package file
import (
"crypto/sha256"
"sync"
"time"
"github.com/pkg/errors"
)
type (
// Watcher creates a background routine and emits events when the
// watched file changes on its C channel. If an error occurs the
// loop is stopped and the error is exposed on the Err property.
Watcher struct {
C <-chan WatcherEvent
CheckInterval time.Duration
Err error
FilePath string
c chan WatcherEvent
checks []WatcherCheck
lock sync.RWMutex
stateCache map[string]any
}
// WatcherCheck is an interface to implement own checks
WatcherCheck func(*Watcher) (WatcherEvent, error)
// WatcherEvent is the detected change to be signeld through the
// channel within the Watcher
WatcherEvent uint
)
const (
WatcherEventInvalid WatcherEvent = iota
WatcherEventNoChange
WatcherEventFileAppeared
WatcherEventFileModified
WatcherEventFileVanished
)
// NewCryptographicWatcher is a wrapper around NewWatcher to configure
// the Watcher with presence and sha256 hash checks.
func NewCryptographicWatcher(filePath string, interval time.Duration) (*Watcher, error) {
return NewWatcher(filePath, interval, WatcherCheckPresence, WatcherCheckHash(sha256.New))
}
// NewSimpleWatcher is a wrapper around NewWatcher to configure the
// Watcher with presence, size and mtime checks.
func NewSimpleWatcher(filePath string, interval time.Duration) (*Watcher, error) {
return NewWatcher(filePath, interval, WatcherCheckPresence, WatcherCheckSize, WatcherCheckMtime)
}
// NewWatcher creates a new Watcher configured with the given filePath,
// interval and checks given. The checks are executed once during
// initialization and will not cause an event to be sent. The created
// Watcher will automatically start its periodic check and the C
// channel should immediately be watched for changes. If the channel
// is not listened on the check loop will be paused until events are
// retrieved. If during the initial checks an error is detected the
// loop is NOT started and the watcher needs to be initialized again.
func NewWatcher(filePath string, interval time.Duration, checks ...WatcherCheck) (*Watcher, error) {
w, err := newWatcher(filePath, interval, checks...)
if err == nil {
go w.loop()
}
return w, err
}
func newWatcher(filePath string, interval time.Duration, checks ...WatcherCheck) (*Watcher, error) {
notify := make(chan WatcherEvent, 1)
w := &Watcher{
C: notify,
CheckInterval: interval,
FilePath: filePath,
c: notify,
checks: checks,
stateCache: make(map[string]any),
}
// Initially run checks once
_, err := w.runStateChecks(true)
return w, errors.Wrap(err, "executing initial checks")
}
// GetState is a helper to retrieve state from the internal store for
// usage in checks to have their state retained.
func (w *Watcher) GetState(key string) any {
w.lock.RLock()
defer w.lock.RUnlock()
return w.stateCache[key]
}
// SetState is a helper to set state into the internal store for
// usage in checks to have their state retained.
func (w *Watcher) SetState(key string, value any) {
w.lock.Lock()
defer w.lock.Unlock()
w.stateCache[key] = value
}
func (w *Watcher) loop() {
for {
evt, err := w.runStateChecks(false)
if err != nil {
w.Err = err
break
}
if evt != WatcherEventNoChange && evt != WatcherEventInvalid {
// On "no change" and "invalid" events sending the new event is skipped
w.c <- evt
}
time.Sleep(w.CheckInterval)
}
}
func (w *Watcher) runStateChecks(runAll bool) (WatcherEvent, error) {
for _, c := range w.checks {
evt, err := c(w)
if err != nil {
return WatcherEventInvalid, errors.Wrap(err, "checking file state")
}
if evt == WatcherEventNoChange && !runAll {
continue
}
return evt, nil
}
return WatcherEventNoChange, nil
}

145
file/watcher_checks.go Normal file
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@ -0,0 +1,145 @@
package file
import (
"crypto/sha512"
"fmt"
"hash"
"io"
"io/fs"
"os"
"github.com/pkg/errors"
)
const (
keyWatcherCheckHash = "WatcherCheckHash"
keyWatcherCheckMtime = "WatcherCheckMtime"
keyWatcherCheckPresence = "WatcherCheckPresence"
keyWatcherCheckSize = "WatcherCheckSize"
)
// WatcherCheckHash returns a WatcherCheck configured with the given
// hash method (i.e. provide md5.New, sha1.New, ...). If the file is
// not present at the time of the check the check is skipped and will
// NOT cause an error.
func WatcherCheckHash(hcf func() hash.Hash) WatcherCheck {
return func(w *Watcher) (WatcherEvent, error) {
var lastHash string
if v, ok := w.GetState(keyWatcherCheckHash).(string); ok {
lastHash = v
}
if _, err := os.Stat(w.FilePath); errors.Is(err, fs.ErrNotExist) {
return WatcherEventInvalid, nil
}
f, err := os.Open(w.FilePath)
if err != nil {
return WatcherEventInvalid, errors.Wrap(err, "opening file")
}
defer f.Close()
h := hcf()
if _, err = io.Copy(h, f); err != nil {
return WatcherEventInvalid, errors.Wrap(err, "reading file")
}
currentHash := fmt.Sprintf("%x", h.Sum(nil))
if lastHash == currentHash {
return WatcherEventNoChange, nil
}
w.SetState(keyWatcherCheckHash, currentHash)
return WatcherEventFileModified, nil
}
}
var _ WatcherCheck = WatcherCheckHash(sha512.New)
// WatcherCheckMtime checks whether the mtime attribute of the file
// has changed. If the file is not present at the time of the check
// the check is skipped and will NOT cause an error.
func WatcherCheckMtime(w *Watcher) (WatcherEvent, error) {
var lastChange int64
if v, ok := w.GetState(keyWatcherCheckMtime).(int64); ok {
lastChange = v
}
s, err := os.Stat(w.FilePath)
switch {
case err == nil:
// handle size change
case errors.Is(err, fs.ErrNotExist):
return WatcherEventInvalid, nil
default:
return WatcherEventInvalid, errors.Wrap(err, "getting file stat")
}
if s.ModTime().UnixNano() == lastChange {
return WatcherEventNoChange, nil
}
w.SetState(keyWatcherCheckMtime, s.ModTime().UnixNano())
return WatcherEventFileModified, nil
}
var _ WatcherCheck = WatcherCheckMtime
// WatcherCheckPresence simply checks whether the file is present and
// allows to emit WatcherEventFileAppeared / WatcherEventFileVanished
// events when the file existence state changes.
func WatcherCheckPresence(w *Watcher) (WatcherEvent, error) {
var wasPresent bool
if v, ok := w.GetState(keyWatcherCheckPresence).(bool); ok {
wasPresent = v
}
_, err := os.Stat(w.FilePath)
if err != nil && !errors.Is(err, fs.ErrNotExist) {
// Some weird error occurred
return WatcherEventInvalid, errors.Wrap(err, "getting file stat")
}
isPresent := err == nil
w.SetState(keyWatcherCheckPresence, isPresent)
switch {
case !wasPresent && isPresent:
return WatcherEventFileAppeared, nil
case wasPresent && !isPresent:
return WatcherEventFileVanished, nil
default:
return WatcherEventNoChange, nil
}
}
var _ WatcherCheck = WatcherCheckPresence
// WatcherCheckSize checks whether the size of the file has changed.
// If the file is not present at the time of the check the check is
// skipped and will NOT cause an error.
func WatcherCheckSize(w *Watcher) (WatcherEvent, error) {
var knownSize int64
if v, ok := w.GetState(keyWatcherCheckSize).(int64); ok {
knownSize = v
}
s, err := os.Stat(w.FilePath)
switch {
case err == nil:
// handle size change
case errors.Is(err, fs.ErrNotExist):
return WatcherEventInvalid, nil
default:
return WatcherEventInvalid, errors.Wrap(err, "getting file stat")
}
if s.Size() == knownSize {
return WatcherEventNoChange, nil
}
w.SetState(keyWatcherCheckSize, s.Size())
return WatcherEventFileModified, nil
}
var _ WatcherCheck = WatcherCheckSize

209
file/watcher_test.go Normal file
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@ -0,0 +1,209 @@
package file
import (
"crypto/sha256"
"os"
"path"
"testing"
"time"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
)
func TestWatcherCheckHash(t *testing.T) {
testDir, err := os.MkdirTemp("", "")
require.NoError(t, err, "creating test-tempdir")
t.Cleanup(func() {
if err := os.RemoveAll(testDir); err != nil {
t.Logf("failed to clean tempdir %q: %s", testDir, err)
}
})
testFile := path.Join(testDir, "test.txt")
w, err := newWatcher(testFile, time.Second, WatcherCheckHash(sha256.New))
require.NoError(t, err, "initial check should not error on non existing file")
evt, err := w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventInvalid, evt, "expect invalid as file is still missing")
err = os.WriteFile(testFile, []byte("test"), 0o644)
require.NoError(t, err, "creating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileModified, evt, "expect change as file now exists and has hash change")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventNoChange, evt, "expect no change as the file has the same hash")
err = os.WriteFile(testFile, []byte("hello world"), 0o644)
require.NoError(t, err, "updating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileModified, evt, "expect change as file was modified")
err = os.Remove(testFile)
require.NoError(t, err, "deleting test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventInvalid, evt, "expect check to be invalid as file is no longer there")
err = os.WriteFile(testFile, []byte("hello world"), 0o644)
require.NoError(t, err, "updating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventNoChange, evt, "expect change as file has same hash")
}
func TestWatcherCheckMtime(t *testing.T) {
testDir, err := os.MkdirTemp("", "")
require.NoError(t, err, "creating test-tempdir")
t.Cleanup(func() {
if err := os.RemoveAll(testDir); err != nil {
t.Logf("failed to clean tempdir %q: %s", testDir, err)
}
})
testFile := path.Join(testDir, "test.txt")
w, err := newWatcher(testFile, time.Second, WatcherCheckMtime)
require.NoError(t, err, "initial check should not error on non existing file")
evt, err := w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventInvalid, evt, "expect invalid as file is still missing")
err = os.WriteFile(testFile, []byte("test"), 0o644)
require.NoError(t, err, "creating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileModified, evt, "expect change as file now exists and has mtime change")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventNoChange, evt, "expect no change as the file has the same mtime")
time.Sleep(time.Second) // Unix mtime is second-based, wait a moment
err = os.WriteFile(testFile, []byte("hello world"), 0o644)
require.NoError(t, err, "updating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileModified, evt, "expect change as file was modified")
err = os.Remove(testFile)
require.NoError(t, err, "deleting test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventInvalid, evt, "expect check to be invalid as file is no longer there")
time.Sleep(time.Second) // Unix mtime is second-based, wait a moment
err = os.WriteFile(testFile, []byte("hello world"), 0o644)
require.NoError(t, err, "updating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileModified, evt, "expect change as file is newer")
}
func TestWatcherCheckPresence(t *testing.T) {
testDir, err := os.MkdirTemp("", "")
require.NoError(t, err, "creating test-tempdir")
t.Cleanup(func() {
if err := os.RemoveAll(testDir); err != nil {
t.Logf("failed to clean tempdir %q: %s", testDir, err)
}
})
testFile := path.Join(testDir, "test.txt")
w, err := newWatcher(testFile, time.Second, WatcherCheckPresence)
require.NoError(t, err, "initial check should not error on non existing file")
evt, err := w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventNoChange, evt, "expect no change as file is still missing")
err = os.WriteFile(testFile, []byte("test"), 0o644)
require.NoError(t, err, "creating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileAppeared, evt, "expect check to state file is now there")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventNoChange, evt, "expect check to state nothing changed")
err = os.Remove(testFile)
require.NoError(t, err, "deleting test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventFileVanished, evt, "expect check to state file vanished again")
}
func TestWatcherCheckSize(t *testing.T) {
testDir, err := os.MkdirTemp("", "")
require.NoError(t, err, "creating test-tempdir")
t.Cleanup(func() {
if err := os.RemoveAll(testDir); err != nil {
t.Logf("failed to clean tempdir %q: %s", testDir, err)
}
})
testFile := path.Join(testDir, "test.txt")
w, err := newWatcher(testFile, time.Second, WatcherCheckSize)
require.NoError(t, err, "initial check should not error on non existing file")
evt, err := w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventInvalid, evt, "expect invalid as file is still missing")
err = os.WriteFile(testFile, []byte("test"), 0o644)
require.NoError(t, err, "creating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileModified, evt, "expect change as file has now 4 instead of 0 bytes")
err = os.WriteFile(testFile, []byte("tset"), 0o644)
require.NoError(t, err, "updating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventNoChange, evt, "expect no change as the file has the same size")
err = os.WriteFile(testFile, []byte("hello world"), 0o644)
require.NoError(t, err, "updating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventFileModified, evt, "expect change as we went from 4 to 11 chars")
err = os.Remove(testFile)
require.NoError(t, err, "deleting test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on non existing file")
assert.Equal(t, WatcherEventInvalid, evt, "expect check to be invalid as file is no longer there")
err = os.WriteFile(testFile, []byte("hello world"), 0o644)
require.NoError(t, err, "updating test file")
evt, err = w.runStateChecks(false)
require.NoError(t, err, "check should not error on existing file")
assert.Equal(t, WatcherEventNoChange, evt, "expect no change as we restored the file with same content")
}

20
go.mod
View file

@ -1,24 +1,30 @@
module github.com/Luzifer/go_helpers/v2
go 1.15
go 1.19
require (
github.com/golang/protobuf v1.4.3 // indirect
github.com/google/go-cmp v0.5.4 // indirect
github.com/inconshreveable/go-update v0.0.0-20160112193335-8152e7eb6ccf
github.com/kr/text v0.2.0 // indirect
github.com/leekchan/gtf v0.0.0-20190214083521-5fba33c5b00b
github.com/nxadm/tail v1.4.6 // indirect
github.com/onsi/ginkgo v1.15.0
github.com/onsi/gomega v1.10.5
github.com/pkg/errors v0.9.1
github.com/sirupsen/logrus v1.7.0
github.com/stretchr/testify v1.7.0 // indirect
github.com/stretchr/testify v1.7.0
gopkg.in/yaml.v2 v2.4.0
)
require (
github.com/davecgh/go-spew v1.1.1 // indirect
github.com/fsnotify/fsnotify v1.4.9 // indirect
github.com/golang/protobuf v1.4.3 // indirect
github.com/kr/text v0.2.0 // indirect
github.com/nxadm/tail v1.4.6 // indirect
github.com/pmezard/go-difflib v1.0.0 // indirect
golang.org/x/net v0.0.0-20210119194325-5f4716e94777 // indirect
golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c // indirect
golang.org/x/text v0.3.5 // indirect
google.golang.org/protobuf v1.25.0 // indirect
gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
gopkg.in/yaml.v2 v2.4.0
gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 // indirect
gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
)

3
go.sum
View file

@ -29,8 +29,6 @@ github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMyw
github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
github.com/google/go-cmp v0.5.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
github.com/google/go-cmp v0.5.4 h1:L8R9j+yAqZuZjsqh/z+F1NCffTKKLShY6zXTItVIZ8M=
github.com/google/go-cmp v0.5.4/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
github.com/inconshreveable/go-update v0.0.0-20160112193335-8152e7eb6ccf h1:WfD7VjIE6z8dIvMsI4/s+1qr5EL+zoIGev1BQj1eoJ8=
github.com/inconshreveable/go-update v0.0.0-20160112193335-8152e7eb6ccf/go.mod h1:hyb9oH7vZsitZCiBt0ZvifOrB+qc8PS5IiilCIb87rg=
@ -119,7 +117,6 @@ golang.org/x/tools v0.0.0-20201224043029-2b0845dc783e/go.mod h1:emZCQorbCU4vsT4f
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=