Support rewriting status codes in error page middleware

docs/content/middlewares/http/errorpages.md

@@ -102,6 +102,19 @@ The status code ranges are inclusive (`505-599` will trigger with every code bet
     The comma-separated syntax is only available for label-based providers.
     The examples above demonstrate which syntax is appropriate for each provider.
 
+### `statusRewrites`
+
+An optional mapping of status codes to be rewritten. For example, if a service returns a 418, you might want to rewrite it to a 404.
+You can map individual status codes or even ranges to a different status code. The syntax for ranges follows the same rules as the `status` option.
+
+Here is an example:
+
+```yml
+statusRewrites:
+  "500-503": 500
+  "418": 404
+```
+
 ### `service`
 
 The service that will serve the new requested error page.
@@ -124,6 +137,7 @@ There are multiple variables that can be placed in the `query` option to insert
 The table below lists all the available variables and their associated values.
 
 | Variable           | Value                                                                                      |
-|------------|--------------------------------------------------------------------|
+|--------------------|--------------------------------------------------------------------------------------------|
-| `{status}` | The response status code.                                          |
+| `{status}`         | The response status code. It may be rewritten when using the `statusRewrites` option.      |
+| `{originalStatus}` | The original response status code, if it has been modified by the `statusRewrites` option. |
 | `{url}`            | The [escaped](https://pkg.go.dev/net/url#QueryEscape) request URL.                         |

docs/content/reference/dynamic-configuration/docker-labels.yml

@@ -33,6 +33,8 @@
 - "traefik.http.middlewares.middleware09.errors.query=foobar"
 - "traefik.http.middlewares.middleware09.errors.service=foobar"
 - "traefik.http.middlewares.middleware09.errors.status=foobar, foobar"
+- "traefik.http.middlewares.middleware09.errors.statusrewrites.name0=42"
+- "traefik.http.middlewares.middleware09.errors.statusrewrites.name1=42"
 - "traefik.http.middlewares.middleware10.forwardauth.addauthcookiestoresponse=foobar, foobar"
 - "traefik.http.middlewares.middleware10.forwardauth.address=foobar"
 - "traefik.http.middlewares.middleware10.forwardauth.authrequestheaders=foobar, foobar"

docs/content/reference/dynamic-configuration/file.toml

@@ -173,6 +173,9 @@
         status = ["foobar", "foobar"]
         service = "foobar"
         query = "foobar"
+        [http.middlewares.Middleware09.errors.statusRewrites]
+          name0 = 42
+          name1 = 42
     [http.middlewares.Middleware10]
       [http.middlewares.Middleware10.forwardAuth]
         address = "foobar"

docs/content/reference/dynamic-configuration/file.yaml

@@ -186,6 +186,9 @@ http:
         status:
           - foobar
           - foobar
+        statusRewrites:
+          name0: 42
+          name1: 42
         service: foobar
         query: foobar
     Middleware10:

docs/content/reference/dynamic-configuration/kubernetes-crd-definition-v1.yml

@@ -1003,6 +1003,8 @@ spec:
                     description: |-
                       Query defines the URL for the error page (hosted by service).
                       The {status} variable can be used in order to insert the status code in the URL.
+                      The {originalStatus} variable can be used in order to insert the upstream status code in the URL.
+                      The {url} variable can be used in order to insert the escaped request URL.
                     type: string
                   service:
                     description: |-
@@ -1199,6 +1201,13 @@ spec:
                     items:
                       type: string
                     type: array
+                  statusRewrites:
+                    additionalProperties:
+                      type: integer
+                    description: |-
+                      StatusRewrites defines a mapping of status codes that should be returned instead of the original error status codes.
+                      For example: "418": 404 or "410-418": 404
+                    type: object
                 type: object
               forwardAuth:
                 description: |-

docs/content/reference/dynamic-configuration/kv-ref.md

@@ -40,6 +40,8 @@ THIS FILE MUST NOT BE EDITED BY HAND
 | `traefik/http/middlewares/Middleware09/errors/service` | `foobar` |
 | `traefik/http/middlewares/Middleware09/errors/status/0` | `foobar` |
 | `traefik/http/middlewares/Middleware09/errors/status/1` | `foobar` |
+| `traefik/http/middlewares/Middleware09/errors/statusRewrites/name0` | `42` |
+| `traefik/http/middlewares/Middleware09/errors/statusRewrites/name1` | `42` |
 | `traefik/http/middlewares/Middleware10/forwardAuth/addAuthCookiesToResponse/0` | `foobar` |
 | `traefik/http/middlewares/Middleware10/forwardAuth/addAuthCookiesToResponse/1` | `foobar` |
 | `traefik/http/middlewares/Middleware10/forwardAuth/address` | `foobar` |

docs/content/reference/dynamic-configuration/traefik.io_middlewares.yaml

@@ -261,6 +261,8 @@ spec:
                     description: |-
                       Query defines the URL for the error page (hosted by service).
                       The {status} variable can be used in order to insert the status code in the URL.
+                      The {originalStatus} variable can be used in order to insert the upstream status code in the URL.
+                      The {url} variable can be used in order to insert the escaped request URL.
                     type: string
                   service:
                     description: |-
@@ -457,6 +459,13 @@ spec:
                     items:
                       type: string
                     type: array
+                  statusRewrites:
+                    additionalProperties:
+                      type: integer
+                    description: |-
+                      StatusRewrites defines a mapping of status codes that should be returned instead of the original error status codes.
+                      For example: "418": 404 or "410-418": 404
+                    type: object
                 type: object
               forwardAuth:
                 description: |-

integration/error_pages_test.go

@@ -69,6 +69,30 @@ func (s *ErrorPagesSuite) TestErrorPage() {
 	require.NoError(s.T(), err)
 }
 
+func (s *ErrorPagesSuite) TestStatusRewrites() {
+	// The `statusRewrites.toml` file contains a misconfigured backend host and some status code rewrites.
+	file := s.adaptFile("fixtures/error_pages/statusRewrites.toml", struct {
+		Server1 string
+		Server2 string
+	}{s.BackendIP, s.ErrorPageIP})
+
+	s.traefikCmd(withConfigFile(file))
+
+	frontendReq, err := http.NewRequest(http.MethodGet, "http://127.0.0.1:8080", nil)
+	require.NoError(s.T(), err)
+	frontendReq.Host = "test502.local"
+
+	err = try.Request(frontendReq, 2*time.Second, try.BodyContains("An error occurred."), try.StatusCodeIs(404))
+	require.NoError(s.T(), err)
+
+	frontendReq, err = http.NewRequest(http.MethodGet, "http://127.0.0.1:8080", nil)
+	require.NoError(s.T(), err)
+	frontendReq.Host = "test418.local"
+
+	err = try.Request(frontendReq, 2*time.Second, try.BodyContains("An error occurred."), try.StatusCodeIs(400))
+	require.NoError(s.T(), err)
+}
+
 func (s *ErrorPagesSuite) TestErrorPageFlush() {
 	srv := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
 		rw.Header().Add("Transfer-Encoding", "chunked")

integration/fixtures/error_pages/statusRewrites.toml

@@ -0,0 +1,45 @@
+[global]
+  checkNewVersion = false
+  sendAnonymousUsage = false
+
+[log]
+  level = "DEBUG"
+  noColor = true
+
+[entryPoints]
+  [entryPoints.web]
+    address = ":8080"
+
+[providers.file]
+  filename = "{{ .SelfFilename }}"
+
+## dynamic configuration ##
+
+[http.routers]
+  [http.routers.router1]
+    rule = "Host(`test502.local`)"
+    service = "service1"
+    middlewares = ["error"]
+  [http.routers.router2]
+    rule = "Host(`test418.local`)"
+    service = "noop@internal"
+    middlewares = ["error"]
+
+[http.middlewares]
+  [http.middlewares.error.errors]
+    status = ["500-502", "503-599", "418"]
+    service = "error"
+    query = "/50x.html"
+    [http.middlewares.error.errors.statusRewrites]
+      "418" = 400
+      "500-502" = 404
+
+[http.services]
+  [http.services.service1.loadBalancer]
+    passHostHeader = true
+    [[http.services.service1.loadBalancer.servers]]
+      url = "http://{{.Server1}}:8989474"
+
+  [http.services.error.loadBalancer]
+    [[http.services.error.loadBalancer.servers]]
+      url = "http://{{.Server2}}:80"

integration/fixtures/k8s/01-traefik-crd.yml

@@ -1003,6 +1003,8 @@ spec:
                     description: |-
                       Query defines the URL for the error page (hosted by service).
                       The {status} variable can be used in order to insert the status code in the URL.
+                      The {originalStatus} variable can be used in order to insert the upstream status code in the URL.
+                      The {url} variable can be used in order to insert the escaped request URL.
                     type: string
                   service:
                     description: |-
@@ -1199,6 +1201,13 @@ spec:
                     items:
                       type: string
                     type: array
+                  statusRewrites:
+                    additionalProperties:
+                      type: integer
+                    description: |-
+                      StatusRewrites defines a mapping of status codes that should be returned instead of the original error status codes.
+                      For example: "418": 404 or "410-418": 404
+                    type: object
                 type: object
               forwardAuth:
                 description: |-

pkg/config/dynamic/middlewares.go

@@ -222,10 +222,15 @@ type ErrorPage struct {
 	// as ranges by separating two codes with a dash (500-599),
 	// or a combination of the two (404,418,500-599).
 	Status []string `json:"status,omitempty" toml:"status,omitempty" yaml:"status,omitempty" export:"true"`
+	// StatusRewrites defines a mapping of status codes that should be returned instead of the original error status codes.
+	// For example: "418": 404 or "410-418": 404
+	StatusRewrites map[string]int `json:"statusRewrites,omitempty" toml:"statusRewrites,omitempty" yaml:"statusRewrites,omitempty" export:"true"`
 	// Service defines the name of the service that will serve the error page.
 	Service string `json:"service,omitempty" toml:"service,omitempty" yaml:"service,omitempty" export:"true"`
 	// Query defines the URL for the error page (hosted by service).
 	// The {status} variable can be used in order to insert the status code in the URL.
+	// The {originalStatus} variable can be used in order to insert the upstream status code in the URL.
+	// The {url} variable can be used in order to insert the escaped request URL.
 	Query string `json:"query,omitempty" toml:"query,omitempty" yaml:"query,omitempty" export:"true"`
 }
 

pkg/config/dynamic/zz_generated.deepcopy.go

@@ -313,6 +313,13 @@ func (in *ErrorPage) DeepCopyInto(out *ErrorPage) {
 		*out = make([]string, len(*in))
 		copy(*out, *in)
 	}
+	if in.StatusRewrites != nil {
+		in, out := &in.StatusRewrites, &out.StatusRewrites
+		*out = make(map[string]int, len(*in))
+		for key, val := range *in {
+			(*out)[key] = val
+		}
+	}
 	return
 }
 

pkg/middlewares/customerrors/custom_errors.go

@@ -37,6 +37,12 @@ type customErrors struct {
 	backendHandler http.Handler
 	httpCodeRanges types.HTTPCodeRanges
 	backendQuery   string
+	statusRewrites []statusRewrite
+}
+
+type statusRewrite struct {
+	fromCodes types.HTTPCodeRanges
+	toCode    int
 }
 
 // New creates a new custom error pages middleware.
@@ -53,12 +59,27 @@ func New(ctx context.Context, next http.Handler, config dynamic.ErrorPage, servi
 		return nil, err
 	}
 
+	// Parse StatusRewrites
+	statusRewrites := make([]statusRewrite, 0, len(config.StatusRewrites))
+	for k, v := range config.StatusRewrites {
+		ranges, err := types.NewHTTPCodeRanges([]string{k})
+		if err != nil {
+			return nil, err
+		}
+
+		statusRewrites = append(statusRewrites, statusRewrite{
+			fromCodes: ranges,
+			toCode:    v,
+		})
+	}
+
 	return &customErrors{
 		name:           name,
 		next:           next,
 		backendHandler: backend,
 		httpCodeRanges: httpCodeRanges,
 		backendQuery:   config.Query,
+		statusRewrites: statusRewrites,
 	}, nil
 }
 
@@ -84,12 +105,28 @@ func (c *customErrors) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 
 	// check the recorder code against the configured http status code ranges
 	code := catcher.getCode()
+
+	originalCode := code
+
+	// Check if we need to rewrite the status code
+	for _, rsc := range c.statusRewrites {
+		if rsc.fromCodes.Contains(code) {
+			code = rsc.toCode
+			break
+		}
+	}
+
+	if code != originalCode {
+		logger.Debug().Msgf("Caught HTTP Status Code %d (rewritten to %d), returning error page", originalCode, code)
+	} else {
 		logger.Debug().Msgf("Caught HTTP Status Code %d, returning error page", code)
+	}
 
 	var query string
 	if len(c.backendQuery) > 0 {
 		query = "/" + strings.TrimPrefix(c.backendQuery, "/")
 		query = strings.ReplaceAll(query, "{status}", strconv.Itoa(code))
+		query = strings.ReplaceAll(query, "{originalStatus}", strconv.Itoa(originalCode))
 		query = strings.ReplaceAll(query, "{url}", url.QueryEscape(req.URL.String()))
 	}
 

pkg/provider/kubernetes/crd/fixtures/with_error_page.yml

@@ -9,6 +9,8 @@ spec:
     status:
     - "404"
     - "500"
+    statusRewrites:
+      404: 200
     query: query
     service:
       name: whoami

pkg/provider/kubernetes/crd/kubernetes.go

@@ -738,6 +738,7 @@ func (p *Provider) createErrorPageMiddleware(client Client, namespace string, er
 
 	errorPageMiddleware := &dynamic.ErrorPage{
 		Status:         errorPage.Status,
+		StatusRewrites: errorPage.StatusRewrites,
 		Query:          errorPage.Query,
 	}
 

pkg/provider/kubernetes/crd/kubernetes_test.go

@@ -4161,6 +4161,9 @@ func TestLoadIngressRoutes(t *testing.T) {
 						"default-errorpage": {
 							Errors: &dynamic.ErrorPage{
 								Status: []string{"404", "500"},
+								StatusRewrites: map[string]int{
+									"404": 200,
+								},
 								Service: "default-errorpage-errorpage-service",
 								Query:   "query",
 							},

pkg/provider/kubernetes/crd/traefikio/v1alpha1/middleware.go

@@ -68,11 +68,16 @@ type ErrorPage struct {
 	// as ranges by separating two codes with a dash (500-599),
 	// or a combination of the two (404,418,500-599).
 	Status []string `json:"status,omitempty"`
+	// StatusRewrites defines a mapping of status codes that should be returned instead of the original error status codes.
+	// For example: "418": 404 or "410-418": 404
+	StatusRewrites map[string]int `json:"statusRewrites,omitempty"`
 	// Service defines the reference to a Kubernetes Service that will serve the error page.
 	// More info: https://doc.traefik.io/traefik/v3.3/middlewares/http/errorpages/#service
 	Service Service `json:"service,omitempty"`
 	// Query defines the URL for the error page (hosted by service).
 	// The {status} variable can be used in order to insert the status code in the URL.
+	// The {originalStatus} variable can be used in order to insert the upstream status code in the URL.
+	// The {url} variable can be used in order to insert the escaped request URL.
 	Query string `json:"query,omitempty"`
 }
 

pkg/provider/kubernetes/crd/traefikio/v1alpha1/zz_generated.deepcopy.go

@@ -229,6 +229,13 @@ func (in *ErrorPage) DeepCopyInto(out *ErrorPage) {
 		*out = make([]string, len(*in))
 		copy(*out, *in)
 	}
+	if in.StatusRewrites != nil {
+		in, out := &in.StatusRewrites, &out.StatusRewrites
+		*out = make(map[string]int, len(*in))
+		for key, val := range *in {
+			(*out)[key] = val
+		}
+	}
 	in.Service.DeepCopyInto(&out.Service)
 	return
 }