Promtail: Fix excludepath not evaluated on newly added files (#9831)

**What this PR does / why we need it**:

In promtail, when a file matching the exclude path is created in a
directory that is being watched, this file should not be tailed by
promtail. However, previously this was the case. As described in #7115.
This change checks the filename to the excludePath and if it matches,
ignores the file.

**Which issue(s) this PR fixes**:
Fixes #7115

**Special notes for your reviewer**:
We tested manually this by running Promtail locally and creating a bunch
of files which should and should not be tailed by Promtail.

**Checklist**
- [x] Reviewed the
[`CONTRIBUTING.md`](https://github.com/grafana/loki/blob/main/CONTRIBUTING.md)
guide (**required**)
- [x] Tests updated
- [x] `CHANGELOG.md` updated
- [ ] If the change is worth mentioning in the release notes, add
`add-to-release-notes` label
- [ ] Changes that require user attention or interaction to upgrade are
documented in `docs/sources/upgrading/_index.md`

CHANGELOG.md

@@ -50,6 +50,7 @@
 ##### Fixes
 * [11074](https://github.com/grafana/loki/pull/11074) **hainenber** Fix panic in lambda-promtail due to mishandling of empty DROP_LABELS env var.
 * [11195](https://github.com/grafana/loki/pull/11195) **canuteson** Generate tsdb_shipper storage_config even if using_boltdb_shipper is false
+* [9831](https://github.com/grafana/loki/pull/9831) **sijmenhuizenga**: Fix Promtail excludepath not evaluated on newly added files.
 * [11551](https://github.com/grafana/loki/pull/11551) **dannykopping** Do not reflect label names in request metrics' "route" label.
 * [11601](https://github.com/grafana/loki/pull/11601) **dannykopping** Ruler: Fixed a panic that can be caused by concurrent read-write access of tenant configs when there are a large amount of rules.
 * [11606](https://github.com/grafana/loki/pull/11606) **dannykopping** Fixed regression adding newlines to HTTP error response bodies which may break client integrations.

clients/pkg/promtail/targets/file/filetarget.go

@@ -350,6 +350,20 @@ func (t *FileTarget) startTailing(ps []string) {
 			continue
 		}
 
+		if t.pathExclude != "" {
+			matched, err := doublestar.Match(t.pathExclude, p)
+			if err != nil {
+				level.Error(t.logger).Log("msg", "ignoring file, exclude pattern match failed", "error", err, "filename", p, "pathExclude", t.pathExclude)
+				t.metrics.totalBytes.DeleteLabelValues(p)
+				continue
+			}
+			if matched {
+				level.Info(t.logger).Log("msg", "ignoring file", "error", "file matches exclude pattern", "filename", p, "pathExclude", t.pathExclude)
+				t.metrics.totalBytes.DeleteLabelValues(p)
+				continue
+			}
+		}
+
 		var reader Reader
 		if t.decompressCfg != nil && t.decompressCfg.Enabled {
 			level.Debug(t.logger).Log("msg", "reading from compressed file", "filename", p)

clients/pkg/promtail/targets/file/filetarget_test.go

@@ -475,6 +475,7 @@ func TestHandleFileCreationEvent(t *testing.T) {
 	positionsFileName := filepath.Join(dirName, "positions.yml")
 	logDir := filepath.Join(dirName, "log")
 	logFile := filepath.Join(logDir, "test1.log")
+	logFileIgnored := filepath.Join(logDir, "test.donot.log")
 
 	if err := os.MkdirAll(logDir, 0750); err != nil {
 		t.Fatal(err)
@@ -511,7 +512,8 @@ func TestHandleFileCreationEvent(t *testing.T) {
 		}
 	}()
 
-	target, err := NewFileTarget(metrics, logger, client, ps, path, "", nil, nil, &Config{
+	pathExclude := "**/*.donot.log"
+	target, err := NewFileTarget(metrics, logger, client, ps, path, pathExclude, nil, nil, &Config{
 		// To handle file creation event from channel, set enough long time as sync period
 		SyncPeriod: 10 * time.Minute,
 	}, DefaultWatchConig, fakeFileHandler, fakeTargetHandler, "", nil)
@@ -523,10 +525,18 @@ func TestHandleFileCreationEvent(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	_, err = os.Create(logFileIgnored)
+	if err != nil {
+		t.Fatal(err)
+	}
 	fakeFileHandler <- fsnotify.Event{
 		Name: logFile,
 		Op:   fsnotify.Create,
 	}
+	fakeFileHandler <- fsnotify.Event{
+		Name: logFileIgnored,
+		Op:   fsnotify.Create,
+	}
 	requireEventually(t, func() bool {
 		return len(target.readers) == 1
 	}, "Expected tails to be 1 at this point in the test...")