[receiver/filestats] add file.count metric (open-telemetry#30191)

**Description:**
Add a file.count metric to filestatsreceiver that reports the number of
files matched by the receiver

**Link to tracking Issue:**
Fixes open-telemetry#24651

---------

Co-authored-by: Dmitrii Anoshin <[email protected]>

.chloggen/filestats_filecount.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: filestatsreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add a file.count metric to filestatsreceiver that reports the number of files matched by the receiver
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [24651]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/filestatsreceiver/documentation.md

@@ -46,6 +46,14 @@ Elapsed time since last access of the file or folder, in seconds since Epoch.
 | ---- | ----------- | ---------- | ----------------------- | --------- |
 | s | Sum | Int | Cumulative | false |
 
+### file.count
+
+The number of files matched
+
+| Unit | Metric Type | Value Type |
+| ---- | ----------- | ---------- |
+| {file} | Gauge | Int |
+
 ### file.ctime
 
 Elapsed time since the last change of the file or folder, in seconds since Epoch. In addition to `file.mtime`, this metric tracks metadata changes such as permissions or renaming the file.

receiver/filestatsreceiver/internal/metadata/testdata/config.yaml

@@ -3,6 +3,8 @@ all_set:
   metrics:
     file.atime:
       enabled: true
+    file.count:
+      enabled: true
     file.ctime:
       enabled: true
     file.mtime:
@@ -18,6 +20,8 @@ none_set:
   metrics:
     file.atime:
       enabled: false
+    file.count:
+      enabled: false
     file.ctime:
       enabled: false
     file.mtime:

receiver/filestatsreceiver/metadata.yaml

@@ -57,5 +57,11 @@ metrics:
     gauge:
       value_type: int
     unit: "b"
+  file.count:
+    description: The number of files matched
+    enabled: false
+    gauge:
+      value_type: int
+    unit: "{file}"
 tests:
   config:

receiver/filestatsreceiver/scraper.go

@@ -57,6 +57,9 @@ func (s *scraper) scrape(_ context.Context) (pmetric.Metrics, error) {
 		s.mb.EmitForResource(metadata.WithResource(rb.Emit()))
 	}
 
+	s.mb.RecordFileCountDataPoint(now, int64(len(matches)))
+	s.mb.EmitForResource()
+
 	if len(scrapeErrors) > 0 {
 		return s.mb.Emit(), scrapererror.NewPartialScrapeError(multierr.Combine(scrapeErrors...), len(scrapeErrors))
 	}

receiver/filestatsreceiver/scraper_test.go

@@ -52,11 +52,15 @@ func Test_Scrape_All(t *testing.T) {
 	cfg.Include = filepath.Join(tmpDir, "*.log")
 	cfg.Metrics.FileAtime.Enabled = true
 	cfg.Metrics.FileCtime.Enabled = true
+	cfg.Metrics.FileCount.Enabled = true
 
 	s := newScraper(cfg, receivertest.NewNopCreateSettings())
 	metrics, err := s.scrape(context.Background())
 	require.NoError(t, err)
-	require.Equal(t, 0, metrics.ResourceMetrics().Len())
+	require.Equal(t, 1, metrics.ResourceMetrics().Len())
+	fileCount := metrics.ResourceMetrics().At(0).ScopeMetrics().At(0).Metrics().At(0)
+	require.Equal(t, int64(0), fileCount.Gauge().DataPoints().At(0).IntValue())
+	require.Equal(t, "file.count", fileCount.Name())
 	logFile := filepath.Join(tmpDir, "my.log")
 	err = os.WriteFile(logFile, []byte("something"), 0600)
 	t.Cleanup(func() {
@@ -71,8 +75,9 @@ func Test_Scrape_All(t *testing.T) {
 	require.Equal(t, []string{logFile}, matches)
 	metrics, err = s.scrape(context.Background())
 	require.NoError(t, err)
-	require.Equal(t, 1, metrics.ResourceMetrics().Len())
+	require.Equal(t, 2, metrics.ResourceMetrics().Len())
 	require.Equal(t, 4, metrics.ResourceMetrics().At(0).ScopeMetrics().At(0).Metrics().Len())
+	require.Equal(t, 1, metrics.ResourceMetrics().At(1).ScopeMetrics().At(0).Metrics().Len())
 	aTimeMetric := metrics.ResourceMetrics().At(0).ScopeMetrics().At(0).Metrics().At(0)
 	require.Equal(t, "file.atime", aTimeMetric.Name())
 	require.Equal(t, fileinfo.ModTime().Unix(), aTimeMetric.Sum().DataPoints().At(0).IntValue())
@@ -85,4 +90,7 @@ func Test_Scrape_All(t *testing.T) {
 	sizeMetric := metrics.ResourceMetrics().At(0).ScopeMetrics().At(0).Metrics().At(3)
 	require.Equal(t, "file.size", sizeMetric.Name())
 	require.Equal(t, int64(9), sizeMetric.Gauge().DataPoints().At(0).IntValue())
+	fileCount = metrics.ResourceMetrics().At(1).ScopeMetrics().At(0).Metrics().At(0)
+	require.Equal(t, "file.count", fileCount.Name())
+	require.Equal(t, int64(1), fileCount.Gauge().DataPoints().At(0).IntValue())
 }