track referers

Signed-off-by: Xe Iaso <me@xeiaso.net>

1 files changed, 23 insertions, 0 deletions

diff --git a/internal/referer.go b/internal/referer.go
new file mode 100644
index 0000000..ec8c2be
--- /dev/null
+++ b/internal/referer.go
@@ -0,0 +1,23 @@
+package internal
+
+import (
+	"expvar"
+	"net/http"
+
+	"tailscale.com/metrics"
+)
+
+var (
+	referers = &metrics.LabelMap{Label: "referer"}
+)
+
+func init() {
+	expvar.Publish("gauge_xesite_referer", referers)
+}
+
+func RefererMiddleware(next http.Handler) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		referers.Add(r.Header.Get("Referer"), 1)
+		next.ServeHTTP(w, r)
+	}
+}