internal: add middleware to track the use of accept-encoding headers

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

2 files changed, 24 insertions, 0 deletions

diff --git a/cmd/xesite/main.go b/cmd/xesite/main.go
index 3c0b2af..bf01514 100644
--- a/cmd/xesite/main.go
+++ b/cmd/xesite/main.go
@@ -120,6 +120,7 @@ func main() {
 	var h http.Handler = mux
 	h = internal.ClackSet(fs.Clacks()).Middleware(h)
 	h = internal.CacheHeader(h)
+	h = internal.AcceptEncodingMiddleware(h)
 
 	slog.Info("starting server", "bind", *bind)
 	log.Fatal(http.Serve(ln, h))
diff --git a/internal/accept_encoding.go b/internal/accept_encoding.go
new file mode 100644
index 0000000..9eca7ed
--- /dev/null
+++ b/internal/accept_encoding.go
@@ -0,0 +1,23 @@
+package internal
+
+import (
+	"expvar"
+	"net/http"
+
+	"tailscale.com/metrics"
+)
+
+var (
+	acceptEncodings = &metrics.LabelMap{Label: "encoding"}
+)
+
+func init() {
+	expvar.Publish("gauge_xesite_accept_encoding", acceptEncodings)
+}
+
+func AcceptEncodingMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		acceptEncodings.Add(r.Header.Get("Accept-Encoding"), 1)
+		next.ServeHTTP(w, r)
+	})
+}