Add file size metric for disk serving

3 files changed, 56 insertions, 5 deletions

diff --git a/internal/serving/disk/reader.go b/internal/serving/disk/reader.go
index 0bc72646..38d055cf 100644
--- a/internal/serving/disk/reader.go
+++ b/internal/serving/disk/reader.go
@@ -10,11 +10,14 @@ import (
 	"strings"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
+
 	"gitlab.com/gitlab-org/gitlab-pages/internal/serving"
 )
 
 // Reader is a disk access driver
 type Reader struct {
+	fileSizeMetrics *prometheus.GaugeVec
 }
 
 func (reader *Reader) tryFile(h serving.Handler) error {
@@ -141,6 +144,8 @@ func (reader *Reader) serveFile(w http.ResponseWriter, r *http.Request, origPath
 		return err
 	}
 
+	reader.fileSizeMetrics.With(prometheus.Labels{"serving_type": "disk", "content_type": contentType}).Set(float64(fi.Size()))
+
 	w.Header().Set("Content-Type", contentType)
 	http.ServeContent(w, r, origPath, fi.ModTime(), file)
 
@@ -167,6 +172,8 @@ func (reader *Reader) serveCustomFile(w http.ResponseWriter, r *http.Request, co
 		return err
 	}
 
+	reader.fileSizeMetrics.With(prometheus.Labels{"serving_type": "disk", "content_type": contentType}).Set(float64(fi.Size()))
+
 	w.Header().Set("Content-Type", contentType)
 	w.Header().Set("Content-Length", strconv.FormatInt(fi.Size(), 10))
 	w.WriteHeader(code)
diff --git a/internal/serving/disk/serving.go b/internal/serving/disk/serving.go
index b4c1ba96..84945c8d 100644
--- a/internal/serving/disk/serving.go
+++ b/internal/serving/disk/serving.go
@@ -3,9 +3,14 @@ package disk
 import (
 	"gitlab.com/gitlab-org/gitlab-pages/internal/httperrors"
 	"gitlab.com/gitlab-org/gitlab-pages/internal/serving"
+	"gitlab.com/gitlab-org/gitlab-pages/metrics"
 )
 
-var disk *Disk = &Disk{}
+var disk = &Disk{
+	reader: Reader{
+		fileSizeMetrics: metrics.ServingFileSize,
+	},
+}
 
 // Disk describes a disk access serving
 type Disk struct {
@@ -31,9 +36,5 @@ func (s *Disk) ServeNotFoundHTTP(h serving.Handler) {
 // New returns a serving instance that is capable of reading files
 // from the disk
 func New() serving.Serving {
-	if disk == nil {
-		disk = &Disk{}
-	}
-
 	return disk
 }
diff --git a/internal/serving/disk/serving_test.go b/internal/serving/disk/serving_test.go
new file mode 100644
index 00000000..01a9a775
--- /dev/null
+++ b/internal/serving/disk/serving_test.go
@@ -0,0 +1,43 @@
+package disk
+
+import (
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
+	"github.com/stretchr/testify/require"
+
+	"gitlab.com/gitlab-org/gitlab-pages/internal/serving"
+	"gitlab.com/gitlab-org/gitlab-pages/metrics"
+)
+
+func TestDisk_ServeFileHTTP(t *testing.T) {
+	s := New()
+	w := httptest.NewRecorder()
+	r := httptest.NewRequest("GET", "http://group.gitlab-example.com/serving/index.html", nil)
+	handler := serving.Handler{
+		Writer:  w,
+		Request: r,
+		LookupPath: &serving.LookupPath{
+			Prefix: "/serving",
+			Path:   "../../../shared/pages/group/serving/public",
+		},
+		SubPath: "/index.html",
+	}
+
+	require.True(t, s.ServeFileHTTP(handler))
+
+	resp := w.Result()
+	defer resp.Body.Close()
+
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+	body, err := ioutil.ReadAll(resp.Body)
+	require.NoError(t, err)
+
+	require.Contains(t, string(body), "HTML Document")
+	gaugeValue := testutil.ToFloat64(metrics.ServingFileSize.With(prometheus.Labels{"serving_type": "disk", "content_type": resp.Header.Get("Content-Type")}))
+	require.Greater(t, gaugeValue, float64(0))
+}