feat: add proxy backend errors interceptor

pkg/middleware/error-interceptor.go

@@ -0,0 +1,94 @@
+package middleware
+
+/*
+ * Copyright 2024 Jonas Kaninda
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+import (
+	"bytes"
+	"encoding/json"
+	"github.com/jkaninda/goma-gateway/internal/logger"
+	"io"
+	"net/http"
+)
+
+// InterceptErrors contains backend status code errors to intercept
+type InterceptErrors struct {
+	Errors []int
+}
+
+// responseRecorder intercepts the response body and status code
+type responseRecorder struct {
+	http.ResponseWriter
+	statusCode int
+	body       *bytes.Buffer
+}
+
+func newResponseRecorder(w http.ResponseWriter) *responseRecorder {
+	return &responseRecorder{
+		ResponseWriter: w,
+		statusCode:     http.StatusOK,
+		body:           &bytes.Buffer{},
+	}
+}
+
+func (rec *responseRecorder) WriteHeader(code int) {
+	rec.statusCode = code
+}
+
+func (rec *responseRecorder) Write(data []byte) (int, error) {
+	return rec.body.Write(data)
+}
+
+// ErrorInterceptor Middleware intercepts backend errors
+func (intercept InterceptErrors) ErrorInterceptor(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		rec := newResponseRecorder(w)
+		next.ServeHTTP(rec, r)
+		if canIntercept(rec.statusCode, intercept.Errors) {
+			logger.Debug("Backend error intercepted")
+			logger.Debug("An error occurred in the backend, %d", rec.statusCode)
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(rec.statusCode)
+			err := json.NewEncoder(w).Encode(ProxyResponseError{
+				Success: false,
+				Code:    rec.statusCode,
+				Message: http.StatusText(rec.statusCode),
+			})
+			if err != nil {
+				return
+			}
+		} else {
+			// No error: write buffered response to client
+			w.WriteHeader(rec.statusCode)
+			_, err := io.Copy(w, rec.body)
+			if err != nil {
+				return
+			}
+
+		}
+
+	})
+}
+func canIntercept(code int, errors []int) bool {
+	for _, er := range errors {
+		if er == code {
+			return true
+		}
+		continue
+
+	}
+	return false
+}