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Update OSFileWatcher to support symlinks #6172

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merged 1 commit into from
Sep 18, 2020
Merged

Update OSFileWatcher to support symlinks #6172

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26 changes: 22 additions & 4 deletions internal/watch/file_watcher.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,9 @@ package watch

import (
"log"
"os"
"path"
"path/filepath"
"strings"

"github.com/fsnotify/fsnotify"
Expand Down Expand Up @@ -60,15 +62,31 @@ func (f *OSFileWatcher) watch() error {
}
f.watcher = watcher

realFile, err := filepath.EvalSymlinks(f.file)
if err != nil {
return err
}

dir, file := path.Split(f.file)
go func(file string) {
for {
select {
case event := <-watcher.Events:
if (event.Op&fsnotify.Write == fsnotify.Write ||
event.Op&fsnotify.Create == fsnotify.Create) &&
strings.HasSuffix(event.Name, file) {
f.onEvent()
if event.Op&fsnotify.Create == fsnotify.Create ||
event.Op&fsnotify.Write == fsnotify.Write {
if finfo, err := os.Lstat(event.Name); err != nil {
log.Printf("can not lstat file: %v\n", err)
} else if finfo.Mode()&os.ModeSymlink != 0 {
if currentRealFile, err := filepath.EvalSymlinks(f.file); err == nil &&
currentRealFile != realFile {
f.onEvent()
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@ElvinEfendi ElvinEfendi Sep 17, 2020 •
edited
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Do you not have to condition this on strings.HasSuffix(event.Name, file)? Why?

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the FileWatcher watches the entire directory (that's not new behaviour). Using the example in the PR description, the watcher will watch $dir/ca.crt, which is a symlink to $dir/..data/ca.crt, which is a symlink to $dir/..<dated_dir>/ca.crt. The CREATE event in $dir is not for a file called ca.crt (which would have the correct suffix), but for a directory called ..data which symlinks to the dated directory. However, the watcher should detect that the top-level symlink ($dir/ca.crt) now points to a different file, and trigger an event.
tl;dr when any file is created in the directory being watched, this FileWatcher should confirm if the symlink it was told to monitor has been updated somewhere within the directory (maybe deeper than 1 level).

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More details: this comment shows the internal order of events.

realFile = currentRealFile
}
continue
}
if strings.HasSuffix(event.Name, file) {
f.onEvent()
}
}
case err := <-watcher.Errors:
if err != nil {
Expand Down
72 changes: 72 additions & 0 deletions internal/watch/file_watcher_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@ package watch
import (
"io/ioutil"
"os"
"path"
"path/filepath"
"testing"
"time"

Expand Down Expand Up @@ -67,3 +69,73 @@ func TestFileWatcher(t *testing.T) {
t.Fatalf("expected an event shortly after writing a file")
}
}

func TestFileWatcherWithNestedSymlink(t *testing.T) {
target1, err := ioutil.TempFile("", "t1")
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
defer target1.Close()
defer os.Remove(target1.Name())
dir := path.Dir(target1.Name())

innerLink := path.Join(dir, "innerLink")
if err = os.Symlink(target1.Name(), innerLink); err != nil {
t.Fatalf("unexpected error: %v", err)
}
defer os.Remove(innerLink)
mainLink := path.Join(dir, "mainLink")
if err = os.Symlink(innerLink, mainLink); err != nil {
t.Fatalf("unexpected error: %v", err)
}
defer os.Remove(mainLink)

targetName, err := filepath.EvalSymlinks(mainLink)
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
if targetName != target1.Name() {
t.Fatalf("expected symlink to point to %v, not %v", target1.Name(), targetName)
}

count := 0
events := make(chan bool, 10)
fw, err := NewFileWatcher(mainLink, func() {
count++
if count != 1 {
t.Fatalf("expected 1 but returned %v", count)
}
if targetName, err = filepath.EvalSymlinks(mainLink); err != nil {
t.Fatalf("unexpected error: %v", err)
}
events <- true
})
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
defer fw.Close()

target2, err := ioutil.TempFile("", "t2")
if err != nil {
t.Fatalf("unexpected error: %v", err)
}
defer target2.Close()
defer os.Remove(target2.Name())

if err = os.Remove(innerLink); err != nil {
t.Fatalf("unexpected error: %v", err)
}
if err = os.Symlink(target2.Name(), innerLink); err != nil {
t.Fatalf("unexpected error: %v", err)
}

timeoutChan := prepareTimeout()
select {
case <-events:
case <-timeoutChan:
t.Fatalf("expected an event shortly after creating a file and relinking")
}
if targetName != target2.Name() {
t.Fatalf("expected symlink to point to %v, not %v", target2.Name(), targetName)
}
}