chore(examples): add one example to log request body when the status …

…code is non 200 (#4108)

* chore(examples): add one example to log request body when the status code is non 200

* chore(examples): fix typo

* chore(deps): add logging the request body for a request doc

* chore(deps): update logging docs with some minor edits

docs/docs/operations/logging.md

@@ -0,0 +1,61 @@
+---
+layout: default
+title: Logging the request body pattern for a request
+nav_order: 5
+parent: Operations
+---
+
+# Logging the request body pattern for a request
+
+If you want to log the request body of incoming requests, you will need to buffer the body before it reaches the gateway. To log the request body, you can use a middleware `http.Handler` to buffer the request body before it's consumed.
+
+1. Create a `http.Handler` middleware. The `logRequestBody` example middleware logs the request body when the response status code is not 200.
+
+```go
+type logResponseWriter struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func (rsp *logResponseWriter) WriteHeader(code int) {
+	rsp.statusCode = code
+	rsp.ResponseWriter.WriteHeader(code)
+}
+
+func newLogResponseWriter(w http.ResponseWriter) *logResponseWriter {
+	return &logResponseWriter{w, http.StatusOK}
+}
+
+// logRequestBody logs the request body when the response status code is not 200.
+func logRequestBody(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		lw := newLogResponseWriter(w)
+
+		// Note that buffering the entire request body could consume a lot of memory.
+		body, err := io.ReadAll(r.Body)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("failed to read body: %v", err), http.StatusBadRequest)
+			return
+		}
+		clonedR := r.Clone(r.Context())
+		clonedR.Body = io.NopCloser(bytes.NewReader(body))
+
+		h.ServeHTTP(lw, clonedR)
+
+		if lw.statusCode != http.StatusOK {
+			grpclog.Errorf("http error %+v request body %+v", lw.statusCode, string(body))
+		}
+	})
+}
+```
+
+2. Wrap the gateway serve mux with the `logRequestBody` middleware:
+
+```go
+    mux := runtime.NewServeMux()
+    // Register generated gateway handlers
+
+    s := &http.Server{
+        Handler: logRequestBody(mux),
+    }
+```

examples/internal/gateway/handlers.go

@@ -1,7 +1,9 @@
 package gateway
 
 import (
+	"bytes"
 	"fmt"
+	"io"
 	"net/http"
 	"path"
 	"strings"
@@ -27,7 +29,7 @@ func openAPIServer(dir string) http.HandlerFunc {
 	}
 }
 
-// allowCORS allows Cross Origin Resoruce Sharing from any origin.
+// allowCORS allows Cross Origin Resource Sharing from any origin.
 // Don't do this without consideration in production systems.
 func allowCORS(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -64,3 +66,38 @@ func healthzServer(conn *grpc.ClientConn) http.HandlerFunc {
 		fmt.Fprintln(w, "ok")
 	}
 }
+
+type logResponseWriter struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func (rsp *logResponseWriter) WriteHeader(code int) {
+	rsp.statusCode = code
+	rsp.ResponseWriter.WriteHeader(code)
+}
+
+func newLogResponseWriter(w http.ResponseWriter) *logResponseWriter {
+	return &logResponseWriter{w, http.StatusOK}
+}
+
+// logRequestBody logs the request body when the response status code is not 200.
+// This addresses the issue of being unable to retrieve the request body in the customErrorHandler middleware.
+func logRequestBody(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		lw := newLogResponseWriter(w)
+		body, err := io.ReadAll(r.Body)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("grpc server read request body err %+v", err), http.StatusBadRequest)
+			return
+		}
+		clonedR := r.Clone(r.Context())
+		clonedR.Body = io.NopCloser(bytes.NewReader(body))
+
+		h.ServeHTTP(lw, clonedR)
+
+		if lw.statusCode != http.StatusOK {
+			grpclog.Errorf("http error %+v request body %+v", lw.statusCode, string(body))
+		}
+	})
+}

examples/internal/gateway/main.go

@@ -58,7 +58,7 @@ func Run(ctx context.Context, opts Options) error {
 
 	s := &http.Server{
 		Addr:    opts.Addr,
-		Handler: allowCORS(mux),
+		Handler: logRequestBody(allowCORS(mux)),
 	}
 	go func() {
 		<-ctx.Done()