Fix default for buffering middleware

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>
Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

pkg/middlewares/buffering/buffering_test.go

@@ -0,0 +1,72 @@
+package buffering
+
+import (
+	"bytes"
+	"context"
+	"math"
+	"math/rand"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v2/pkg/config/dynamic"
+)
+
+func TestBuffering(t *testing.T) {
+	payload := make([]byte, math.MaxInt8)
+	rand.Read(payload)
+
+	testCases := []struct {
+		desc         string
+		config       dynamic.Buffering
+		body         []byte
+		expectedCode int
+	}{
+		{
+			desc:         "Unlimited response and request body size",
+			body:         payload,
+			expectedCode: http.StatusOK,
+		},
+		{
+			desc: "Limited request body size",
+			config: dynamic.Buffering{
+				MaxRequestBodyBytes: 1,
+			},
+			body:         payload,
+			expectedCode: http.StatusRequestEntityTooLarge,
+		},
+		{
+			desc: "Limited response body size",
+			config: dynamic.Buffering{
+				MaxResponseBodyBytes: 1,
+			},
+			body:         payload,
+			expectedCode: http.StatusInternalServerError,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			next := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				rw.WriteHeader(http.StatusOK)
+				_, err := rw.Write(test.body)
+				require.NoError(t, err)
+			})
+
+			buffMiddleware, err := New(context.Background(), next, test.config, "foo")
+			require.NoError(t, err)
+
+			req := httptest.NewRequest(http.MethodPost, "http://localhost", bytes.NewBuffer(test.body))
+
+			recorder := httptest.NewRecorder()
+			buffMiddleware.ServeHTTP(recorder, req)
+
+			assert.Equal(t, test.expectedCode, recorder.Code)
+		})
+	}
+}