feat(errors): Also handle errors as RFC 7807 problems in reverse proxy

engine/engine.go

@@ -315,6 +315,11 @@ func (e *Engine) ReverseProxyAndValidate(w http.ResponseWriter, r *http.Request,
 		r.Out.Header.Set(HeaderBaseURL, e.Config.BaseURL.String())
 	}
 
+	errorHandler := func(w http.ResponseWriter, _ *http.Request, err error) {
+		log.Printf("failed to proxy request: %v", err)
+		RenderProblem(ProblemBadGateway, w)
+	}
+
 	modifyResponse := func(proxyRes *http.Response) error {
 		if prefer204 {
 			// OGC spec: If the tile has no content due to lack of data in the area, but is within the data
@@ -334,7 +339,6 @@ func (e *Engine) ReverseProxyAndValidate(w http.ResponseWriter, r *http.Request,
 			if proxyRes.Header.Get(HeaderContentEncoding) == FormatGzip {
 				reader, err = gzip.NewReader(proxyRes.Body)
 				if err != nil {
-					log.Printf("%v", err.Error())
 					return err
 				}
 			} else {
@@ -343,15 +347,18 @@ func (e *Engine) ReverseProxyAndValidate(w http.ResponseWriter, r *http.Request,
 			defer reader.Close()
 			res, err := io.ReadAll(reader)
 			if err != nil {
-				log.Printf("%v", err.Error())
 				return err
 			}
 			e.ServeResponse(w, r, false, true, contentType, res)
 		}
 		return nil
 	}
 
-	reverseProxy := &httputil.ReverseProxy{Rewrite: rewrite, ModifyResponse: modifyResponse}
+	reverseProxy := &httputil.ReverseProxy{
+		Rewrite:        rewrite,
+		ModifyResponse: modifyResponse,
+		ErrorHandler:   errorHandler,
+	}
 	reverseProxy.ServeHTTP(w, r)
 }
 

engine/engine_test.go

@@ -63,7 +63,7 @@ func TestEngine_ReverseProxy(t *testing.T) {
 	defer mockTargetServer.Close()
 
 	engine, targetURL := makeEngine(mockTargetServer)
-	rec, req := makeAPICall(t, mockTargetServer)
+	rec, req := makeAPICall(t, mockTargetServer.URL)
 
 	// when
 	engine.ReverseProxy(rec, req, targetURL, false, "")
@@ -85,7 +85,7 @@ func TestEngine_ReverseProxyAndValidate(t *testing.T) {
 	defer mockTargetServer.Close()
 
 	engine, targetURL := makeEngine(mockTargetServer)
-	rec, req := makeAPICall(t, mockTargetServer)
+	rec, req := makeAPICall(t, mockTargetServer.URL)
 
 	// when
 	engine.ReverseProxyAndValidate(rec, req, targetURL, false, MediaTypeJSON, true)
@@ -103,7 +103,7 @@ func TestEngine_ReverseProxy_Status204(t *testing.T) {
 	defer mockTargetServer.Close()
 
 	engine, targetURL := makeEngine(mockTargetServer)
-	rec, req := makeAPICall(t, mockTargetServer)
+	rec, req := makeAPICall(t, mockTargetServer.URL)
 
 	// when
 	engine.ReverseProxy(rec, req, targetURL, true, "audio/wav")
@@ -126,9 +126,9 @@ func makeEngine(mockTargetServer *httptest.Server) (*Engine, *url.URL) {
 	return engine, targetURL
 }
 
-func makeAPICall(t *testing.T, mockTargetServer *httptest.Server) (*httptest.ResponseRecorder, *http.Request) {
+func makeAPICall(t *testing.T, mockTargetServer string) (*httptest.ResponseRecorder, *http.Request) {
 	rec := httptest.NewRecorder()
-	req, err := http.NewRequest(http.MethodGet, mockTargetServer.URL+"/some/path", nil)
+	req, err := http.NewRequest(http.MethodGet, mockTargetServer+"/some/path", nil)
 	if err != nil {
 		t.Fatal(err)
 	}

engine/problems.go

@@ -9,16 +9,20 @@ import (
 )
 
 const (
-	timestampKey          = "timestamp"
-	messageInternalServer = "An unexpected error has occurred, try again or contact support if the problem persists"
+	timestampKey             = "timestamp"
+	defaultMessageServerErr  = "An unexpected error has occurred, try again or contact support if the problem persists"
+	defaultMessageBadGateway = "Failed to proxy request, try again or contact support if the problem persists"
 )
 
+var Now = time.Now // allow mocking
+
+// The following problems should be added to openapi/problems.go.json
 var (
-	Now                  = time.Now // allow mocking
-	ProblemServerError   = problem.Of(http.StatusInternalServerError).Append(problem.Detail(messageInternalServer))
 	ProblemBadRequest    = problem.Of(http.StatusBadRequest)
 	ProblemNotFound      = problem.Of(http.StatusNotFound)
 	ProblemNotAcceptable = problem.Of(http.StatusNotAcceptable)
+	ProblemServerError   = problem.Of(http.StatusInternalServerError).Append(problem.Detail(defaultMessageServerErr))
+	ProblemBadGateway    = problem.Of(http.StatusBadGateway).Append(problem.Detail(defaultMessageBadGateway))
 )
 
 func RenderProblem(p *problem.Problem, w http.ResponseWriter, details ...string) {

engine/templates/openapi/problems.go.json

@@ -39,4 +39,14 @@
       }
     }
 }
+"502": {
+    "description": "Bad Gateway: An unexpected error occurred while forwarding/proxying the request to another server.",
+    "content": {
+      "application/problem+json": {
+        "schema": {
+          "$ref": "#/components/schemas/exception"
+        }
+      }
+    }
+}
 {{ end }}