proxyd: Add rate limit logging (#3173)

.changeset/strong-meals-impress.md

+---
+'@eth-optimism/proxyd': patch
+---
+
+Add logging/metrics

proxyd/integration_tests/rate_limit_test.go

 package integration_tests
 
 import (
-	"fmt"
 	"net/http"
 	"os"
 	"testing"
@@ -68,7 +67,6 @@ func TestFrontendMaxRPSLimit(t *testing.T) {
 		h.Set("Origin", "exempt_origin")
 		client := NewProxydClientWithHeaders("http://127.0.0.1:8545", h)
 		_, codes := spamReqs(t, client, 429)
-		fmt.Println(codes)
 		require.Equal(t, 3, codes[200])
 	})
 

proxyd/server.go

@@ -196,14 +196,16 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 	ctx, cancel = context.WithTimeout(ctx, s.timeout)
 	defer cancel()
 
-	exemptOrigin := s.limExemptOrigins[strings.ToLower(r.Header.Get("Origin"))]
-	exemptUserAgent := s.limExemptUserAgents[strings.ToLower(r.Header.Get("User-Agent"))]
+	origin := r.Header.Get("Origin")
+	userAgent := r.Header.Get("User-Agent")
+	exemptOrigin := s.limExemptOrigins[strings.ToLower(origin)]
+	exemptUserAgent := s.limExemptUserAgents[strings.ToLower(userAgent)]
+	// Use XFF in context since it will automatically be replaced by the remote IP
+	xff := stripXFF(GetXForwardedFor(ctx))
 	var ok bool
 	if exemptOrigin || exemptUserAgent {
 		ok = true
 	} else {
-		// Use XFF in context since it will automatically be replaced by the remote IP
-		xff := stripXFF(GetXForwardedFor(ctx))
 		if xff == "" {
 			log.Warn("rejecting request without XFF or remote IP")
 			ok = false
@@ -214,6 +216,15 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 	if !ok {
 		rpcErr := ErrOverRateLimit.Clone()
 		rpcErr.Message = s.limConfig.ErrorMessage
+		RecordRPCError(ctx, BackendProxyd, "unknown", rpcErr)
+		log.Warn(
+			"rate limited request",
+			"req_id", GetReqID(ctx),
+			"auth", GetAuthCtx(ctx),
+			"user_agent", userAgent,
+			"origin", origin,
+			"remote_ip", xff,
+		)
 		writeRPCError(ctx, w, nil, rpcErr)
 		return
 	}
@@ -222,7 +233,7 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 		"received RPC request",
 		"req_id", GetReqID(ctx),
 		"auth", GetAuthCtx(ctx),
-		"user_agent", r.Header.Get("user-agent"),
+		"user_agent", userAgent,
 	)
 
 	body, err := ioutil.ReadAll(io.LimitReader(r.Body, s.maxBodySize))