Disable Content-Type auto-detection by default

docs/content/middlewares/http/contenttype.md

@@ -1,6 +1,6 @@
 ---
 title: "Traefik ContentType Documentation"
-description: "Traefik Proxy's HTTP middleware can automatically specify the content-type header if it has not been defined by the backend. Read the technical documentation."
+description: "Traefik Proxy's HTTP middleware automatically sets the `Content-Type` header value when it is not set by the backend. Read the technical documentation."
 ---
 
 # ContentType
@@ -8,84 +8,59 @@ description: "Traefik Proxy's HTTP middleware can automatically specify the cont
 Handling Content-Type auto-detection
 {: .subtitle }
 
-The Content-Type middleware - or rather its `autoDetect` option -
+The Content-Type middleware sets the `Content-Type` header value to the media type detected from the response content,
-specifies whether to let the `Content-Type` header,
+when it is not set by the backend.
-if it has not been defined by the backend,
-be automatically set to a value derived from the contents of the response.
-
-As a proxy, the default behavior should be to leave the header alone,
-regardless of what the backend did with it.
-However, the historic default was to always auto-detect and set the header if it was not already defined,
-and altering this behavior would be a breaking change which would impact many users.
-
-This middleware exists to enable the correct behavior until at least the default one can be changed in a future version.
 
 !!! info
 
-    As explained above, for compatibility reasons the default behavior on a router (without this middleware),
-    is still to automatically set the `Content-Type` header.
-    Therefore, given the default value of the `autoDetect` option (false),
-    simply enabling this middleware for a router switches the router's behavior.
-
     The scope of the Content-Type middleware is the MIME type detection done by the core of Traefik (the server part).
     Therefore, it has no effect against any other `Content-Type` header modifications (e.g.: in another middleware such as compress).
 
 ## Configuration Examples
 
 ```yaml tab="Docker"
-# Disable auto-detection
+# Enable auto-detection
 labels:
-  - "traefik.http.middlewares.autodetect.contenttype.autodetect=false"
+  - "traefik.http.middlewares.autodetect.contenttype=true"
 ```
 
 ```yaml tab="Kubernetes"
-# Disable auto-detection
+# Enable auto-detection
 apiVersion: traefik.containo.us/v1alpha1
 kind: Middleware
 metadata:
   name: autodetect
 spec:
-  contentType:
+  contentType: {}
-    autoDetect: false
 ```
 
 ```yaml tab="Consul Catalog"
-# Disable auto-detection
+# Enable auto-detection
-- "traefik.http.middlewares.autodetect.contenttype.autodetect=false"
+- "traefik.http.middlewares.autodetect.contenttype=true"
 ```
 
 ```json tab="Marathon"
 "labels": {
-  "traefik.http.middlewares.autodetect.contenttype.autodetect": "false"
+  "traefik.http.middlewares.autodetect.contenttype": "true"
 }
 ```
 
 ```yaml tab="Rancher"
-# Disable auto-detection
+# Enable auto-detection
 labels:
-  - "traefik.http.middlewares.autodetect.contenttype.autodetect=false"
+  - "traefik.http.middlewares.autodetect.contenttype=true"
 ```
 
 ```yaml tab="File (YAML)"
-# Disable auto-detection
+# Enable auto-detection
 http:
   middlewares:
     autodetect:
-      contentType:
+      contentType: {}
-        autoDetect: false
 ```
 
 ```toml tab="File (TOML)"
-# Disable auto-detection
+# Enable auto-detection
 [http.middlewares]
   [http.middlewares.autodetect.contentType]
-     autoDetect=false
 ```
-
-## Configuration Options
-
-### `autoDetect`
-
-`autoDetect` specifies whether to let the `Content-Type` header,
-if it has not been set by the backend,
-be automatically set to a value derived from the contents of the response.

docs/content/migration/v2-to-v3.md

@@ -45,3 +45,8 @@ and should be explicitly combined using logical operators to mimic previous beha
 `Query` can take a single value to match is the query value that has no value (e.g. `/search?mobile`).
 
 `HostHeader` has been removed, use `Host` instead.
+
+## Content-Type Auto-Detection
+
+In v3, the `Content-Type` header is not auto-detected anymore when it is not set by the backend.
+One should use the `ContentType` middleware to enable the `Content-Type` header value auto-detection.

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

@@ -17,7 +17,7 @@
 - "traefik.http.middlewares.middleware05.compress=true"
 - "traefik.http.middlewares.middleware05.compress.excludedcontenttypes=foobar, foobar"
 - "traefik.http.middlewares.middleware05.compress.minresponsebodybytes=42"
-- "traefik.http.middlewares.middleware06.contenttype.autodetect=true"
+- "traefik.http.middlewares.middleware06.contenttype=true"
 - "traefik.http.middlewares.middleware07.digestauth.headerfield=foobar"
 - "traefik.http.middlewares.middleware07.digestauth.realm=foobar"
 - "traefik.http.middlewares.middleware07.digestauth.removeheader=true"

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

@@ -137,7 +137,6 @@
         minResponseBodyBytes = 42
     [http.middlewares.Middleware06]
       [http.middlewares.Middleware06.contentType]
-        autoDetect = true
     [http.middlewares.Middleware07]
       [http.middlewares.Middleware07.digestAuth]
         users = ["foobar", "foobar"]

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

@@ -141,8 +141,7 @@ http:
           - foobar
         minResponseBodyBytes: 42
     Middleware06:
-      contentType:
+      contentType: {}
-        autoDetect: true
     Middleware07:
       digestAuth:
         users:

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

@@ -762,19 +762,9 @@ spec:
                 type: object
               contentType:
                 description: ContentType holds the content-type middleware configuration.
-                  This middleware exists to enable the correct behavior until at least
+                  This middleware sets the `Content-Type` header value to the media
-                  the default one can be changed in a future version.
+                  type detected from the response content, when it is not set by the
-                properties:
+                  backend.
-                  autoDetect:
-                    description: AutoDetect specifies whether to let the `Content-Type`
-                      header, if it has not been set by the backend, be automatically
-                      set to a value derived from the contents of the response. As
-                      a proxy, the default behavior should be to leave the header
-                      alone, regardless of what the backend did with it. However,
-                      the historic default was to always auto-detect and set the header
-                      if it was nil, and it is going to be kept that way in order
-                      to support users currently relying on it.
-                    type: boolean
                 type: object
               digestAuth:
                 description: 'DigestAuth holds the digest auth middleware configuration.

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

@@ -19,7 +19,7 @@
 | `traefik/http/middlewares/Middleware05/compress/excludedContentTypes/0` | `foobar` |
 | `traefik/http/middlewares/Middleware05/compress/excludedContentTypes/1` | `foobar` |
 | `traefik/http/middlewares/Middleware05/compress/minResponseBodyBytes` | `42` |
-| `traefik/http/middlewares/Middleware06/contentType/autoDetect` | `true` |
+| `traefik/http/middlewares/Middleware06/contentType` | `` |
 | `traefik/http/middlewares/Middleware07/digestAuth/headerField` | `foobar` |
 | `traefik/http/middlewares/Middleware07/digestAuth/realm` | `foobar` |
 | `traefik/http/middlewares/Middleware07/digestAuth/removeHeader` | `true` |

docs/content/reference/dynamic-configuration/marathon-labels.json

@@ -17,7 +17,7 @@
 "traefik.http.middlewares.middleware05.compress": "true",
 "traefik.http.middlewares.middleware05.compress.excludedcontenttypes": "foobar, foobar",
 "traefik.http.middlewares.middleware05.compress.minresponsebodybytes": "42",
-"traefik.http.middlewares.middleware06.contenttype.autodetect": "true",
+"traefik.http.middlewares.middleware06.contenttype": "true",
 "traefik.http.middlewares.middleware07.digestauth.headerfield": "foobar",
 "traefik.http.middlewares.middleware07.digestauth.realm": "foobar",
 "traefik.http.middlewares.middleware07.digestauth.removeheader": "true",

docs/content/reference/dynamic-configuration/traefik.containo.us_middlewares.yaml

@@ -185,19 +185,9 @@ spec:
                 type: object
               contentType:
                 description: ContentType holds the content-type middleware configuration.
-                  This middleware exists to enable the correct behavior until at least
+                  This middleware sets the `Content-Type` header value to the media
-                  the default one can be changed in a future version.
+                  type detected from the response content, when it is not set by the
-                properties:
+                  backend.
-                  autoDetect:
-                    description: AutoDetect specifies whether to let the `Content-Type`
-                      header, if it has not been set by the backend, be automatically
-                      set to a value derived from the contents of the response. As
-                      a proxy, the default behavior should be to leave the header
-                      alone, regardless of what the backend did with it. However,
-                      the historic default was to always auto-detect and set the header
-                      if it was nil, and it is going to be kept that way in order
-                      to support users currently relying on it.
-                    type: boolean
                 type: object
               digestAuth:
                 description: 'DigestAuth holds the digest auth middleware configuration.

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

@@ -762,19 +762,9 @@ spec:
                 type: object
               contentType:
                 description: ContentType holds the content-type middleware configuration.
-                  This middleware exists to enable the correct behavior until at least
+                  This middleware sets the `Content-Type` header value to the media
-                  the default one can be changed in a future version.
+                  type detected from the response content, when it is not set by the
-                properties:
+                  backend.
-                  autoDetect:
-                    description: AutoDetect specifies whether to let the `Content-Type`
-                      header, if it has not been set by the backend, be automatically
-                      set to a value derived from the contents of the response. As
-                      a proxy, the default behavior should be to leave the header
-                      alone, regardless of what the backend did with it. However,
-                      the historic default was to always auto-detect and set the header
-                      if it was nil, and it is going to be kept that way in order
-                      to support users currently relying on it.
-                    type: boolean
                 type: object
               digestAuth:
                 description: 'DigestAuth holds the digest auth middleware configuration.

integration/fixtures/simple_contenttype.toml

@@ -21,32 +21,12 @@
 [http.routers]
   [http.routers.router1]
     service = "service1"
-    rule = "PathPrefix(`/css/ct/nomiddleware`) || PathPrefix(`/pdf/ct/nomiddleware`)"
+    rule = "PathPrefix(`/`)"
 
   [http.routers.router2]
     service = "service1"
     middlewares = ["autodetect"]
-    rule = "PathPrefix(`/css/ct/middlewareauto`) || PathPrefix(`/pdf/ct/middlewareauto`)"
+    rule = "PathPrefix(`/autodetect`)"
-
-  [http.routers.router3]
-    service = "service1"
-    middlewares = ["noautodetect"]
-    rule = "PathPrefix(`/css/ct/middlewarenoauto`) || PathPrefix(`/pdf/ct/middlewarenoauto`)"
-
-  [http.routers.router4]
-    service = "service1"
-    rule = "PathPrefix(`/css/noct/nomiddleware`) || PathPrefix(`/pdf/noct/nomiddleware`)"
-
-  [http.routers.router5]
-    service = "service1"
-    middlewares = ["autodetect"]
-    rule = "PathPrefix(`/css/noct/middlewareauto`) || PathPrefix(`/pdf/noct/middlewareauto`)"
-
-  [http.routers.router6]
-    service = "service1"
-    middlewares = ["noautodetect"]
-    rule = "PathPrefix(`/css/noct/middlewarenoauto`) || PathPrefix(`/pdf/noct/middlewarenoauto`)"
-
 
 [http.services]
   [http.services.service1]
@@ -56,7 +36,3 @@
         url = "{{ .Server }}"
 
 [http.middlewares.autodetect.contentType]
-autoDetect=true
-
-[http.middlewares.noautodetect.contentType]
-autoDetect=false

integration/simple_test.go

@@ -1166,9 +1166,10 @@ func (s *SimpleSuite) TestSecureAPI(c *check.C) {
 func (s *SimpleSuite) TestContentTypeDisableAutoDetect(c *check.C) {
 	srv1 := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
 		rw.Header()["Content-Type"] = nil
-		switch req.URL.Path[:4] {
+		path := strings.TrimPrefix(req.URL.Path, "/autodetect")
+		switch path[:4] {
 		case "/css":
-			if !strings.Contains(req.URL.Path, "noct") {
+			if strings.Contains(req.URL.Path, "/ct") {
 				rw.Header().Set("Content-Type", "text/css")
 			}
 
@@ -1177,7 +1178,7 @@ func (s *SimpleSuite) TestContentTypeDisableAutoDetect(c *check.C) {
 			_, err := rw.Write([]byte(".testcss { }"))
 			c.Assert(err, checker.IsNil)
 		case "/pdf":
-			if !strings.Contains(req.URL.Path, "noct") {
+			if strings.Contains(req.URL.Path, "/ct") {
 				rw.Header().Set("Content-Type", "application/pdf")
 			}
 
@@ -1211,37 +1212,13 @@ func (s *SimpleSuite) TestContentTypeDisableAutoDetect(c *check.C) {
 	err = try.GetRequest("http://127.0.0.1:8080/api/rawdata", 10*time.Second, try.BodyContains("127.0.0.1"))
 	c.Assert(err, checker.IsNil)
 
-	err = try.GetRequest("http://127.0.0.1:8000/css/ct/nomiddleware", time.Second, try.HasHeaderValue("Content-Type", "text/css", false))
+	err = try.GetRequest("http://127.0.0.1:8000/css/ct", time.Second, try.HasHeaderValue("Content-Type", "text/css", false))
 	c.Assert(err, checker.IsNil)
 
-	err = try.GetRequest("http://127.0.0.1:8000/pdf/ct/nomiddleware", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
+	err = try.GetRequest("http://127.0.0.1:8000/pdf/ct", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
 	c.Assert(err, checker.IsNil)
 
-	err = try.GetRequest("http://127.0.0.1:8000/css/ct/middlewareauto", time.Second, try.HasHeaderValue("Content-Type", "text/css", false))
+	err = try.GetRequest("http://127.0.0.1:8000/css/noct", time.Second, func(res *http.Response) error {
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/pdf/ct/nomiddlewareauto", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/css/ct/middlewarenoauto", time.Second, try.HasHeaderValue("Content-Type", "text/css", false))
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/pdf/ct/nomiddlewarenoauto", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/css/noct/nomiddleware", time.Second, try.HasHeaderValue("Content-Type", "text/plain; charset=utf-8", false))
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/pdf/noct/nomiddleware", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/css/noct/middlewareauto", time.Second, try.HasHeaderValue("Content-Type", "text/plain; charset=utf-8", false))
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/pdf/noct/nomiddlewareauto", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
-	c.Assert(err, checker.IsNil)
-
-	err = try.GetRequest("http://127.0.0.1:8000/css/noct/middlewarenoauto", time.Second, func(res *http.Response) error {
 		if ct, ok := res.Header["Content-Type"]; ok {
 			return fmt.Errorf("should have no content type and %s is present", ct)
 		}
@@ -1249,13 +1226,25 @@ func (s *SimpleSuite) TestContentTypeDisableAutoDetect(c *check.C) {
 	})
 	c.Assert(err, checker.IsNil)
 
-	err = try.GetRequest("http://127.0.0.1:8000/pdf/noct/middlewarenoauto", time.Second, func(res *http.Response) error {
+	err = try.GetRequest("http://127.0.0.1:8000/pdf/noct", time.Second, func(res *http.Response) error {
 		if ct, ok := res.Header["Content-Type"]; ok {
 			return fmt.Errorf("should have no content type and %s is present", ct)
 		}
 		return nil
 	})
 	c.Assert(err, checker.IsNil)
+
+	err = try.GetRequest("http://127.0.0.1:8000/autodetect/css/ct", time.Second, try.HasHeaderValue("Content-Type", "text/css", false))
+	c.Assert(err, checker.IsNil)
+
+	err = try.GetRequest("http://127.0.0.1:8000/autodetect/pdf/ct", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
+	c.Assert(err, checker.IsNil)
+
+	err = try.GetRequest("http://127.0.0.1:8000/autodetect/css/noct", time.Second, try.HasHeaderValue("Content-Type", "text/plain; charset=utf-8", false))
+	c.Assert(err, checker.IsNil)
+
+	err = try.GetRequest("http://127.0.0.1:8000/autodetect/pdf/noct", time.Second, try.HasHeaderValue("Content-Type", "application/pdf", false))
+	c.Assert(err, checker.IsNil)
 }
 
 func (s *SimpleSuite) TestMuxer(c *check.C) {

pkg/config/dynamic/middlewares.go

@@ -33,7 +33,7 @@ type Middleware struct {
 	Compress          *Compress          `json:"compress,omitempty" toml:"compress,omitempty" yaml:"compress,omitempty" label:"allowEmpty" file:"allowEmpty" kv:"allowEmpty" export:"true"`
 	PassTLSClientCert *PassTLSClientCert `json:"passTLSClientCert,omitempty" toml:"passTLSClientCert,omitempty" yaml:"passTLSClientCert,omitempty" export:"true"`
 	Retry             *Retry             `json:"retry,omitempty" toml:"retry,omitempty" yaml:"retry,omitempty" export:"true"`
-	ContentType       *ContentType       `json:"contentType,omitempty" toml:"contentType,omitempty" yaml:"contentType,omitempty" export:"true"`
+	ContentType       *ContentType       `json:"contentType,omitempty" toml:"contentType,omitempty" yaml:"contentType,omitempty" label:"allowEmpty" file:"allowEmpty" kv:"allowEmpty" export:"true"`
 	GrpcWeb           *GrpcWeb           `json:"grpcWeb,omitempty" toml:"grpcWeb,omitempty" yaml:"grpcWeb,omitempty" export:"true"`
 
 	Plugin map[string]PluginConf `json:"plugin,omitempty" toml:"plugin,omitempty" yaml:"plugin,omitempty" export:"true"`
@@ -52,15 +52,9 @@ type GrpcWeb struct {
 // +k8s:deepcopy-gen=true
 
 // ContentType holds the content-type middleware configuration.
-// This middleware exists to enable the correct behavior until at least the default one can be changed in a future version.
+// This middleware sets the `Content-Type` header value to the media type detected from the response content,
-type ContentType struct {
+// when it is not set by the backend.
-	// AutoDetect specifies whether to let the `Content-Type` header, if it has not been set by the backend,
+type ContentType struct{}
-	// be automatically set to a value derived from the contents of the response.
-	// As a proxy, the default behavior should be to leave the header alone, regardless of what the backend did with it.
-	// However, the historic default was to always auto-detect and set the header if it was nil,
-	// and it is going to be kept that way in order to support users currently relying on it.
-	AutoDetect bool `json:"autoDetect,omitempty" toml:"autoDetect,omitempty" yaml:"autoDetect,omitempty" export:"true"`
-}
 
 // +k8s:deepcopy-gen=true
 

pkg/middlewares/contenttype/content_type.go

@@ -0,0 +1,46 @@
+package contenttype
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/traefik/traefik/v2/pkg/middlewares"
+)
+
+const (
+	typeName = "ContentType"
+)
+
+// ContentType is a middleware used to activate Content-Type auto-detection.
+type contentType struct {
+	next http.Handler
+	name string
+}
+
+// New creates a new handler.
+func New(ctx context.Context, next http.Handler, name string) (http.Handler, error) {
+	middlewares.GetLogger(ctx, name, typeName).Debug().Msg("Creating middleware")
+	return &contentType{next: next, name: name}, nil
+}
+
+func (c *contentType) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	// Re-enable auto-detection.
+	if ct, ok := rw.Header()["Content-Type"]; ok && ct == nil {
+		middlewares.GetLogger(req.Context(), c.name, typeName).
+			Debug().Msg("Enable Content-Type auto-detection.")
+		delete(rw.Header(), "Content-Type")
+	}
+
+	c.next.ServeHTTP(rw, req)
+}
+
+func DisableAutoDetection(next http.Handler) http.HandlerFunc {
+	return func(rw http.ResponseWriter, req *http.Request) {
+		// Prevent Content-Type auto-detection.
+		if _, ok := rw.Header()["Content-Type"]; !ok {
+			rw.Header()["Content-Type"] = nil
+		}
+
+		next.ServeHTTP(rw, req)
+	}
+}

pkg/middlewares/contenttype/content_type_test.go

@@ -0,0 +1,79 @@
+package contenttype
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v2/pkg/testhelpers"
+)
+
+func TestAutoDetection(t *testing.T) {
+	testCases := []struct {
+		desc            string
+		autoDetect      bool
+		contentType     string
+		wantContentType string
+	}{
+		{
+			desc:            "Keep the Content-Type returned by the server",
+			autoDetect:      false,
+			contentType:     "application/json",
+			wantContentType: "application/json",
+		},
+		{
+			desc:            "Don't auto-detect Content-Type header by default when not set by the server",
+			autoDetect:      false,
+			contentType:     "",
+			wantContentType: "",
+		},
+		{
+			desc:            "Keep the Content-Type returned by the server with auto-detection middleware",
+			autoDetect:      true,
+			contentType:     "application/json",
+			wantContentType: "application/json",
+		},
+		{
+			desc:            "Auto-detect when Content-Type header is not already set by the server with auto-detection middleware",
+			autoDetect:      true,
+			contentType:     "",
+			wantContentType: "text/plain; charset=utf-8",
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var next http.Handler
+			next = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				if test.contentType != "" {
+					w.Header().Set("Content-Type", test.contentType)
+				}
+				w.WriteHeader(http.StatusOK)
+				_, _ = w.Write([]byte("Test"))
+			})
+
+			if test.autoDetect {
+				var err error
+				next, err = New(context.Background(), next, "foo-content-type")
+				require.NoError(t, err)
+			}
+
+			server := httptest.NewServer(
+				DisableAutoDetection(next),
+			)
+			t.Cleanup(server.Close)
+
+			req := testhelpers.MustNewRequest(http.MethodGet, server.URL, nil)
+			res, err := server.Client().Do(req)
+			require.NoError(t, err)
+
+			assert.Equal(t, test.wantContentType, res.Header.Get("Content-Type"))
+		})
+	}
+}

pkg/redactor/redactor_config_test.go

@@ -337,9 +337,7 @@ func init() {
 					Attempts:        42,
 					InitialInterval: 42,
 				},
-				ContentType: &dynamic.ContentType{
+				ContentType: &dynamic.ContentType{},
-					AutoDetect: true,
-				},
 				Plugin: map[string]dynamic.PluginConf{
 					"foo": {
 						"answer": struct{ Answer int }{

pkg/redactor/testdata/anonymized-dynamic-config.json

@@ -302,9 +302,7 @@
           "attempts": 42,
           "initialInterval": "42ns"
         },
-        "contentType": {
+        "contentType": {},
-          "autoDetect": true
-        },
         "plugin": {
           "foo": {
             "answer": {}

pkg/redactor/testdata/secured-dynamic-config.json

@@ -305,9 +305,7 @@
           "attempts": 42,
           "initialInterval": "42ns"
         },
-        "contentType": {
+        "contentType": {},
-          "autoDetect": true
-        },
         "plugin": {
           "foo": {
             "answer": {}

pkg/server/middleware/middlewares.go

@@ -16,6 +16,7 @@ import (
 	"github.com/traefik/traefik/v2/pkg/middlewares/chain"
 	"github.com/traefik/traefik/v2/pkg/middlewares/circuitbreaker"
 	"github.com/traefik/traefik/v2/pkg/middlewares/compress"
+	"github.com/traefik/traefik/v2/pkg/middlewares/contenttype"
 	"github.com/traefik/traefik/v2/pkg/middlewares/customerrors"
 	"github.com/traefik/traefik/v2/pkg/middlewares/grpcweb"
 	"github.com/traefik/traefik/v2/pkg/middlewares/headers"
@@ -181,12 +182,7 @@ func (b *Builder) buildConstructor(ctx context.Context, middlewareName string) (
 			return nil, badConf
 		}
 		middleware = func(next http.Handler) (http.Handler, error) {
-			return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+			return contenttype.New(ctx, next, middlewareName)
-				if !config.ContentType.AutoDetect {
-					rw.Header()["Content-Type"] = nil
-				}
-				next.ServeHTTP(rw, req)
-			}), nil
 		}
 	}
 

pkg/server/server_entrypoint_tcp.go

@@ -22,6 +22,7 @@ import (
 	"github.com/traefik/traefik/v2/pkg/ip"
 	"github.com/traefik/traefik/v2/pkg/logs"
 	"github.com/traefik/traefik/v2/pkg/middlewares"
+	"github.com/traefik/traefik/v2/pkg/middlewares/contenttype"
 	"github.com/traefik/traefik/v2/pkg/middlewares/forwardedheaders"
 	"github.com/traefik/traefik/v2/pkg/middlewares/requestdecorator"
 	"github.com/traefik/traefik/v2/pkg/safe"
@@ -537,6 +538,8 @@ func createHTTPServer(ctx context.Context, ln net.Listener, configuration *stati
 
 	handler = http.AllowQuerySemicolons(handler)
 
+	handler = contenttype.DisableAutoDetection(handler)
+
 	if withH2c {
 		handler = h2c.NewHandler(handler, &http2.Server{
 			MaxConcurrentStreams: uint32(configuration.HTTP2.MaxConcurrentStreams),