Add support for Brotli

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>
Co-authored-by: Tom Moulard <tom.moulard@traefik.io>
Co-authored-by: Romain <rtribotte@users.noreply.github.com>
Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

pkg/middlewares/compress/brotli/brotli.go

@@ -0,0 +1,338 @@
+package brotli
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"mime"
+	"net"
+	"net/http"
+
+	"github.com/andybalholm/brotli"
+)
+
+const (
+	vary            = "Vary"
+	acceptEncoding  = "Accept-Encoding"
+	contentEncoding = "Content-Encoding"
+	contentLength   = "Content-Length"
+	contentType     = "Content-Type"
+)
+
+// Config is the Brotli handler configuration.
+type Config struct {
+	// ExcludedContentTypes is the list of content types for which we should not compress.
+	ExcludedContentTypes []string
+	// MinSize is the minimum size (in bytes) required to enable compression.
+	MinSize int
+}
+
+// NewWrapper returns a new Brotli compressing wrapper.
+func NewWrapper(cfg Config) (func(http.Handler) http.HandlerFunc, error) {
+	if cfg.MinSize < 0 {
+		return nil, fmt.Errorf("minimum size must be greater than or equal to zero")
+	}
+
+	var contentTypes []parsedContentType
+	for _, v := range cfg.ExcludedContentTypes {
+		mediaType, params, err := mime.ParseMediaType(v)
+		if err != nil {
+			return nil, fmt.Errorf("parsing media type: %w", err)
+		}
+
+		contentTypes = append(contentTypes, parsedContentType{mediaType, params})
+	}
+
+	return func(h http.Handler) http.HandlerFunc {
+		return func(rw http.ResponseWriter, r *http.Request) {
+			rw.Header().Add(vary, acceptEncoding)
+
+			brw := &responseWriter{
+				rw:                   rw,
+				bw:                   brotli.NewWriter(rw),
+				minSize:              cfg.MinSize,
+				statusCode:           http.StatusOK,
+				excludedContentTypes: contentTypes,
+			}
+			defer brw.close()
+
+			h.ServeHTTP(brw, r)
+		}
+	}, nil
+}
+
+// TODO: check whether we want to implement content-type sniffing (as gzip does)
+// TODO: check whether we should support Accept-Ranges (as gzip does, see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Ranges)
+type responseWriter struct {
+	rw http.ResponseWriter
+	bw *brotli.Writer
+
+	minSize              int
+	excludedContentTypes []parsedContentType
+
+	buf                 []byte
+	hijacked            bool
+	compressionStarted  bool
+	compressionDisabled bool
+	headersSent         bool
+
+	// Mostly needed to avoid calling bw.Flush/bw.Close when no data was
+	// written in bw.
+	seenData bool
+
+	statusCodeSet bool
+	statusCode    int
+}
+
+func (r *responseWriter) Header() http.Header {
+	return r.rw.Header()
+}
+
+func (r *responseWriter) WriteHeader(statusCode int) {
+	if r.statusCodeSet {
+		return
+	}
+
+	r.statusCode = statusCode
+	r.statusCodeSet = true
+}
+
+func (r *responseWriter) Write(p []byte) (int, error) {
+	// i.e. has write ever been called at least once with non nil data.
+	if !r.seenData && len(p) > 0 {
+		r.seenData = true
+	}
+
+	// We do not compress, either for contentEncoding or contentType reasons.
+	if r.compressionDisabled {
+		return r.rw.Write(p)
+	}
+
+	// We have already buffered more than minSize,
+	// We are now in compression cruise mode until the end of times.
+	if r.compressionStarted {
+		// If compressionStarted we assume we have sent headers already
+		return r.bw.Write(p)
+	}
+
+	// If we detect a contentEncoding, we know we are never going to compress.
+	if r.rw.Header().Get(contentEncoding) != "" {
+		r.compressionDisabled = true
+		return r.rw.Write(p)
+	}
+
+	// Disable compression according to user wishes in excludedContentTypes.
+	if ct := r.rw.Header().Get(contentType); ct != "" {
+		mediaType, params, err := mime.ParseMediaType(ct)
+		if err != nil {
+			return 0, fmt.Errorf("parsing media type: %w", err)
+		}
+
+		for _, excludedContentType := range r.excludedContentTypes {
+			if excludedContentType.equals(mediaType, params) {
+				r.compressionDisabled = true
+				return r.rw.Write(p)
+			}
+		}
+	}
+
+	// We buffer until we know whether to compress (i.e. when we reach minSize received).
+	if len(r.buf)+len(p) < r.minSize {
+		r.buf = append(r.buf, p...)
+		return len(p), nil
+	}
+
+	// If we ever make it here, we have received at least minSize, which means we want to compress,
+	// and we are going to send headers right away.
+	r.compressionStarted = true
+
+	// Since we know we are going to compress we will never be able to know the actual length.
+	r.rw.Header().Del(contentLength)
+
+	r.rw.Header().Set(contentEncoding, "br")
+	r.rw.WriteHeader(r.statusCode)
+	r.headersSent = true
+
+	// Start with sending what we have previously buffered, before actually writing
+	// the bytes in argument.
+	n, err := r.bw.Write(r.buf)
+	if err != nil {
+		r.buf = r.buf[n:]
+		// Return zero because we haven't taken care of the bytes in argument yet.
+		return 0, err
+	}
+
+	// If we wrote less than what we wanted, we need to reclaim the leftovers + the bytes in argument,
+	// and keep them for a subsequent Write.
+	if n < len(r.buf) {
+		r.buf = r.buf[n:]
+		r.buf = append(r.buf, p...)
+		return len(p), nil
+	}
+
+	// Otherwise just reset the buffer.
+	r.buf = r.buf[:0]
+
+	// Now that we emptied the buffer, we can actually write the given bytes.
+	return r.bw.Write(p)
+}
+
+// Flush flushes data to the appropriate underlying writer(s), although it does
+// not guarantee that all buffered data will be sent.
+// If not enough bytes have been written to determine whether to enable compression,
+// no flushing will take place.
+func (r *responseWriter) Flush() {
+	if !r.seenData {
+		// we should not flush if there never was any data, because flushing the bw
+		// (just like closing) would send some extra end of compressionStarted stream bytes.
+		return
+	}
+
+	// It was already established by Write that compression is disabled, we only
+	// have to flush the uncompressed writer.
+	if r.compressionDisabled {
+		if rw, ok := r.rw.(http.Flusher); ok {
+			rw.Flush()
+		}
+
+		return
+	}
+
+	// Here, nothing was ever written either to rw or to bw (since we're still
+	// waiting to decide whether to compress), so we do not need to flush anything.
+	// Note that we diverge with klauspost's gzip behavior, where they instead
+	// force compression and flush whatever was in the buffer in this case.
+	if !r.compressionStarted {
+		return
+	}
+
+	// Conversely, we here know that something was already written to bw (or is
+	// going to be written right after anyway), so bw will have to be flushed.
+	// Also, since we know that bw writes to rw, but (apparently) never flushes it,
+	// we have to do it ourselves.
+	defer func() {
+		// because we also ignore the error returned by Write anyway
+		_ = r.bw.Flush()
+
+		if rw, ok := r.rw.(http.Flusher); ok {
+			rw.Flush()
+		}
+	}()
+
+	// We empty whatever is left of the buffer that Write never took care of.
+	n, err := r.bw.Write(r.buf)
+	if err != nil {
+		return
+	}
+
+	// And just like in Write we also handle "short writes".
+	if n < len(r.buf) {
+		r.buf = r.buf[n:]
+		return
+	}
+
+	r.buf = r.buf[:0]
+}
+
+func (r *responseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	if hijacker, ok := r.rw.(http.Hijacker); ok {
+		// We only make use of r.hijacked in close (and not in Write/WriteHeader)
+		// because we want to let the stdlib catch the error on writes, as
+		// they already do a good job of logging it.
+		r.hijacked = true
+		return hijacker.Hijack()
+	}
+
+	return nil, nil, fmt.Errorf("%T is not a http.Hijacker", r.rw)
+}
+
+// close closes the underlying writers if/when appropriate.
+// Note that the compressed writer should not be closed if we never used it,
+// as it would otherwise send some extra "end of compression" bytes.
+// Close also makes sure to flush whatever was left to write from the buffer.
+func (r *responseWriter) close() error {
+	if r.hijacked {
+		return nil
+	}
+
+	// We have to take care of statusCode ourselves (in case there was never any
+	// call to Write or WriteHeader before us) as it's the only header we buffer.
+	if !r.headersSent {
+		r.rw.WriteHeader(r.statusCode)
+		r.headersSent = true
+	}
+
+	// Nothing was ever written anywhere, nothing to flush.
+	if !r.seenData {
+		return nil
+	}
+
+	// If compression was disabled, there never was anything in the buffer to flush,
+	// and nothing was ever written to bw.
+	if r.compressionDisabled {
+		return nil
+	}
+
+	if len(r.buf) == 0 {
+		// If we got here we know compression has started, so we can safely flush on bw.
+		return r.bw.Close()
+	}
+
+	// There is still data in the buffer, because we never reached minSize (to
+	// determine whether to compress). We therefore flush it uncompressed.
+	if !r.compressionStarted {
+		n, err := r.rw.Write(r.buf)
+		if err != nil {
+			return err
+		}
+		if n < len(r.buf) {
+			return io.ErrShortWrite
+		}
+		return nil
+	}
+
+	// There is still data in the buffer, simply because Write did not take care of it all.
+	// We flush it to the compressed writer.
+	n, err := r.bw.Write(r.buf)
+	if err != nil {
+		r.bw.Close()
+		return err
+	}
+	if n < len(r.buf) {
+		r.bw.Close()
+		return io.ErrShortWrite
+	}
+	return r.bw.Close()
+}
+
+// parsedContentType is the parsed representation of one of the inputs to ContentTypes.
+// From https://github.com/klauspost/compress/blob/master/gzhttp/compress.go#L401.
+type parsedContentType struct {
+	mediaType string
+	params    map[string]string
+}
+
+// equals returns whether this content type matches another content type.
+func (p parsedContentType) equals(mediaType string, params map[string]string) bool {
+	if p.mediaType != mediaType {
+		return false
+	}
+
+	// if p has no params, don't care about other's params
+	if len(p.params) == 0 {
+		return true
+	}
+
+	// if p has any params, they must be identical to other's.
+	if len(p.params) != len(params) {
+		return false
+	}
+
+	for k, v := range p.params {
+		if w, ok := params[k]; !ok || v != w {
+			return false
+		}
+	}
+
+	return true
+}

pkg/middlewares/compress/brotli/brotli_test.go

@@ -0,0 +1,618 @@
+package brotli
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/andybalholm/brotli"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	smallTestBody = []byte("aaabbc" + strings.Repeat("aaabbbccc", 9) + "aaabbbc")
+	bigTestBody   = []byte(strings.Repeat(strings.Repeat("aaabbbccc", 66)+" ", 6) + strings.Repeat("aaabbbccc", 66))
+)
+
+func Test_Vary(t *testing.T) {
+	h := newTestHandler(t, smallTestBody)
+
+	req, _ := http.NewRequest(http.MethodGet, "/whatever", nil)
+	req.Header.Set(acceptEncoding, "br")
+
+	rw := httptest.NewRecorder()
+	h.ServeHTTP(rw, req)
+
+	assert.Equal(t, http.StatusOK, rw.Code)
+	assert.Equal(t, acceptEncoding, rw.Header().Get(vary))
+}
+
+func Test_SmallBodyNoCompression(t *testing.T) {
+	h := newTestHandler(t, smallTestBody)
+
+	req, _ := http.NewRequest(http.MethodGet, "/whatever", nil)
+	req.Header.Set(acceptEncoding, "br")
+
+	rw := httptest.NewRecorder()
+	h.ServeHTTP(rw, req)
+
+	// With less than 1024 bytes the response should not be compressed.
+	assert.Equal(t, http.StatusOK, rw.Code)
+	assert.Empty(t, rw.Header().Get(contentEncoding))
+	assert.Equal(t, smallTestBody, rw.Body.Bytes())
+}
+
+func Test_AlreadyCompressed(t *testing.T) {
+	h := newTestHandler(t, bigTestBody)
+
+	req, _ := http.NewRequest(http.MethodGet, "/compressed", nil)
+	req.Header.Set(acceptEncoding, "br")
+
+	rw := httptest.NewRecorder()
+	h.ServeHTTP(rw, req)
+
+	assert.Equal(t, bigTestBody, rw.Body.Bytes())
+}
+
+func Test_NoBody(t *testing.T) {
+	testCases := []struct {
+		desc       string
+		statusCode int
+		body       []byte
+	}{
+		{
+			desc:       "status no content",
+			statusCode: http.StatusNoContent,
+			body:       nil,
+		},
+		{
+			desc:       "status not modified",
+			statusCode: http.StatusNotModified,
+			body:       nil,
+		},
+		{
+			desc:       "status OK with empty body",
+			statusCode: http.StatusOK,
+			body:       []byte{},
+		},
+		{
+			desc:       "status OK with nil body",
+			statusCode: http.StatusOK,
+			body:       nil,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			h := mustNewWrapper(t, Config{MinSize: 1024})(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				rw.WriteHeader(test.statusCode)
+
+				_, err := rw.Write(test.body)
+				require.NoError(t, err)
+			}))
+
+			req := httptest.NewRequest(http.MethodGet, "/", nil)
+			req.Header.Set(acceptEncoding, "br")
+
+			rw := httptest.NewRecorder()
+			h.ServeHTTP(rw, req)
+
+			body, err := io.ReadAll(rw.Body)
+			require.NoError(t, err)
+
+			assert.Empty(t, rw.Header().Get(contentEncoding))
+			assert.Empty(t, body)
+		})
+	}
+}
+
+func Test_MinSize(t *testing.T) {
+	cfg := Config{
+		MinSize: 128,
+	}
+
+	var bodySize int
+	h := mustNewWrapper(t, cfg)(http.HandlerFunc(
+		func(rw http.ResponseWriter, req *http.Request) {
+			for i := 0; i < bodySize; i++ {
+				// We make sure to Write at least once less than minSize so that both
+				// cases below go through the same algo: i.e. they start buffering
+				// because they haven't reached minSize.
+				_, err := rw.Write([]byte{'x'})
+				require.NoError(t, err)
+			}
+		},
+	))
+
+	req, _ := http.NewRequest(http.MethodGet, "/whatever", &bytes.Buffer{})
+	req.Header.Add(acceptEncoding, "br")
+
+	// Short response is not compressed
+	bodySize = cfg.MinSize - 1
+	rw := httptest.NewRecorder()
+	h.ServeHTTP(rw, req)
+
+	assert.Empty(t, rw.Result().Header.Get(contentEncoding))
+
+	// Long response is compressed
+	bodySize = cfg.MinSize
+	rw = httptest.NewRecorder()
+	h.ServeHTTP(rw, req)
+
+	assert.Equal(t, "br", rw.Result().Header.Get(contentEncoding))
+}
+
+func Test_MultipleWriteHeader(t *testing.T) {
+	h := mustNewWrapper(t, Config{MinSize: 1024})(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		// We ensure that the subsequent call to WriteHeader is a noop.
+		rw.WriteHeader(http.StatusInternalServerError)
+		rw.WriteHeader(http.StatusNotFound)
+	}))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.Header.Set(acceptEncoding, "br")
+
+	rw := httptest.NewRecorder()
+	h.ServeHTTP(rw, req)
+
+	assert.Equal(t, http.StatusInternalServerError, rw.Code)
+}
+
+func Test_FlushBeforeWrite(t *testing.T) {
+	srv := httptest.NewServer(mustNewWrapper(t, Config{MinSize: 1024})(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		rw.WriteHeader(http.StatusOK)
+		rw.(http.Flusher).Flush()
+
+		_, err := rw.Write(bigTestBody)
+		require.NoError(t, err)
+	})))
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodGet, srv.URL, http.NoBody)
+	require.NoError(t, err)
+
+	req.Header.Set(acceptEncoding, "br")
+
+	res, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+
+	defer res.Body.Close()
+
+	assert.Equal(t, http.StatusOK, res.StatusCode)
+	assert.Equal(t, "br", res.Header.Get(contentEncoding))
+
+	got, err := io.ReadAll(brotli.NewReader(res.Body))
+	require.NoError(t, err)
+	assert.Equal(t, bigTestBody, got)
+}
+
+func Test_FlushAfterWrite(t *testing.T) {
+	srv := httptest.NewServer(mustNewWrapper(t, Config{MinSize: 1024})(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		rw.WriteHeader(http.StatusOK)
+
+		_, err := rw.Write(bigTestBody[0:1])
+		require.NoError(t, err)
+
+		rw.(http.Flusher).Flush()
+		for _, b := range bigTestBody[1:] {
+			_, err := rw.Write([]byte{b})
+			require.NoError(t, err)
+		}
+	})))
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodGet, srv.URL, http.NoBody)
+	require.NoError(t, err)
+
+	req.Header.Set(acceptEncoding, "br")
+
+	res, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+
+	defer res.Body.Close()
+
+	assert.Equal(t, http.StatusOK, res.StatusCode)
+	assert.Equal(t, "br", res.Header.Get(contentEncoding))
+
+	got, err := io.ReadAll(brotli.NewReader(res.Body))
+	require.NoError(t, err)
+	assert.Equal(t, bigTestBody, got)
+}
+
+func Test_FlushAfterWriteNil(t *testing.T) {
+	srv := httptest.NewServer(mustNewWrapper(t, Config{MinSize: 1024})(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		rw.WriteHeader(http.StatusOK)
+
+		_, err := rw.Write(nil)
+		require.NoError(t, err)
+
+		rw.(http.Flusher).Flush()
+	})))
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodGet, srv.URL, http.NoBody)
+	require.NoError(t, err)
+
+	req.Header.Set(acceptEncoding, "br")
+
+	res, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+
+	defer res.Body.Close()
+
+	assert.Equal(t, http.StatusOK, res.StatusCode)
+	assert.Empty(t, res.Header.Get(contentEncoding))
+
+	got, err := io.ReadAll(brotli.NewReader(res.Body))
+	require.NoError(t, err)
+	assert.Empty(t, got)
+}
+
+func Test_FlushAfterAllWrites(t *testing.T) {
+	srv := httptest.NewServer(mustNewWrapper(t, Config{MinSize: 1024})(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		for i := range bigTestBody {
+			_, err := rw.Write(bigTestBody[i : i+1])
+			require.NoError(t, err)
+		}
+		rw.(http.Flusher).Flush()
+	})))
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodGet, srv.URL, http.NoBody)
+	require.NoError(t, err)
+
+	req.Header.Set(acceptEncoding, "br")
+
+	res, err := http.DefaultClient.Do(req)
+	require.NoError(t, err)
+
+	defer res.Body.Close()
+
+	assert.Equal(t, http.StatusOK, res.StatusCode)
+	assert.Equal(t, "br", res.Header.Get(contentEncoding))
+
+	got, err := io.ReadAll(brotli.NewReader(res.Body))
+	require.NoError(t, err)
+	assert.Equal(t, bigTestBody, got)
+}
+
+func Test_ExcludedContentTypes(t *testing.T) {
+	testCases := []struct {
+		desc                 string
+		contentType          string
+		excludedContentTypes []string
+		expCompression       bool
+	}{
+		{
+			desc:                 "Always compress when content types are empty",
+			contentType:          "",
+			excludedContentTypes: []string{},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match",
+			contentType:          "application/json",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME no match",
+			contentType:          "text/xml",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match with no other directive ignores non-MIME directives",
+			contentType:          "application/json; charset=utf-8",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME match with other directives requires all directives be equal, different charset",
+			contentType:          "application/json; charset=ascii",
+			excludedContentTypes: []string{"application/json; charset=utf-8"},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match with other directives requires all directives be equal, same charset",
+			contentType:          "application/json; charset=utf-8",
+			excludedContentTypes: []string{"application/json; charset=utf-8"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME match with other directives requires all directives be equal, missing charset",
+			contentType:          "application/json",
+			excludedContentTypes: []string{"application/json; charset=ascii"},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match case insensitive",
+			contentType:          "Application/Json",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME match ignore whitespace",
+			contentType:          "application/json;charset=utf-8",
+			excludedContentTypes: []string{"application/json;            charset=utf-8"},
+			expCompression:       false,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			cfg := Config{
+				MinSize:              1024,
+				ExcludedContentTypes: test.excludedContentTypes,
+			}
+			h := mustNewWrapper(t, cfg)(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				rw.Header().Set(contentType, test.contentType)
+
+				rw.WriteHeader(http.StatusOK)
+
+				_, err := rw.Write(bigTestBody)
+				require.NoError(t, err)
+			}))
+
+			req, _ := http.NewRequest(http.MethodGet, "/whatever", nil)
+			req.Header.Set(acceptEncoding, "br")
+
+			rw := httptest.NewRecorder()
+			h.ServeHTTP(rw, req)
+
+			assert.Equal(t, http.StatusOK, rw.Code)
+
+			if test.expCompression {
+				assert.Equal(t, "br", rw.Header().Get(contentEncoding))
+
+				got, err := io.ReadAll(brotli.NewReader(rw.Body))
+				assert.Nil(t, err)
+				assert.Equal(t, bigTestBody, got)
+			} else {
+				assert.NotEqual(t, "br", rw.Header().Get("Content-Encoding"))
+
+				got, err := io.ReadAll(rw.Body)
+				assert.Nil(t, err)
+				assert.Equal(t, bigTestBody, got)
+			}
+		})
+	}
+}
+
+func Test_FlushExcludedContentTypes(t *testing.T) {
+	testCases := []struct {
+		desc                 string
+		contentType          string
+		excludedContentTypes []string
+		expCompression       bool
+	}{
+		{
+			desc:                 "Always compress when content types are empty",
+			contentType:          "",
+			excludedContentTypes: []string{},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match",
+			contentType:          "application/json",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME no match",
+			contentType:          "text/xml",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match with no other directive ignores non-MIME directives",
+			contentType:          "application/json; charset=utf-8",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME match with other directives requires all directives be equal, different charset",
+			contentType:          "application/json; charset=ascii",
+			excludedContentTypes: []string{"application/json; charset=utf-8"},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match with other directives requires all directives be equal, same charset",
+			contentType:          "application/json; charset=utf-8",
+			excludedContentTypes: []string{"application/json; charset=utf-8"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME match with other directives requires all directives be equal, missing charset",
+			contentType:          "application/json",
+			excludedContentTypes: []string{"application/json; charset=ascii"},
+			expCompression:       true,
+		},
+		{
+			desc:                 "MIME match case insensitive",
+			contentType:          "Application/Json",
+			excludedContentTypes: []string{"application/json"},
+			expCompression:       false,
+		},
+		{
+			desc:                 "MIME match ignore whitespace",
+			contentType:          "application/json;charset=utf-8",
+			excludedContentTypes: []string{"application/json;            charset=utf-8"},
+			expCompression:       false,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			cfg := Config{
+				MinSize:              1024,
+				ExcludedContentTypes: test.excludedContentTypes,
+			}
+			h := mustNewWrapper(t, cfg)(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				rw.Header().Set(contentType, test.contentType)
+				rw.WriteHeader(http.StatusOK)
+
+				tb := bigTestBody
+				for len(tb) > 0 {
+					// Write 100 bytes per run
+					// Detection should not be affected (we send 100 bytes)
+					toWrite := 100
+					if toWrite > len(tb) {
+						toWrite = len(tb)
+					}
+
+					_, err := rw.Write(tb[:toWrite])
+					require.NoError(t, err)
+
+					// Flush between each write
+					rw.(http.Flusher).Flush()
+					tb = tb[toWrite:]
+				}
+			}))
+
+			req, _ := http.NewRequest(http.MethodGet, "/whatever", nil)
+			req.Header.Set(acceptEncoding, "br")
+
+			// This doesn't allow checking flushes, but we validate if content is correct.
+			rw := httptest.NewRecorder()
+			h.ServeHTTP(rw, req)
+
+			assert.Equal(t, http.StatusOK, rw.Code)
+
+			if test.expCompression {
+				assert.Equal(t, "br", rw.Header().Get(contentEncoding))
+
+				got, err := io.ReadAll(brotli.NewReader(rw.Body))
+				assert.Nil(t, err)
+				assert.Equal(t, bigTestBody, got)
+			} else {
+				assert.NotEqual(t, "br", rw.Header().Get(contentEncoding))
+
+				got, err := io.ReadAll(rw.Body)
+				assert.Nil(t, err)
+				assert.Equal(t, bigTestBody, got)
+			}
+		})
+	}
+}
+
+func mustNewWrapper(t *testing.T, cfg Config) func(http.Handler) http.HandlerFunc {
+	t.Helper()
+
+	w, err := NewWrapper(cfg)
+	require.NoError(t, err)
+
+	return w
+}
+
+func newTestHandler(t *testing.T, body []byte) http.Handler {
+	t.Helper()
+
+	return mustNewWrapper(t, Config{MinSize: 1024})(
+		http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+			if req.URL.Path == "/compressed" {
+				rw.Header().Set("Content-Encoding", "br")
+			}
+
+			_, err := rw.Write(body)
+			require.NoError(t, err)
+		}),
+	)
+}
+
+func TestParseContentType_equals(t *testing.T) {
+	testCases := []struct {
+		desc      string
+		pct       parsedContentType
+		mediaType string
+		params    map[string]string
+		expect    assert.BoolAssertionFunc
+	}{
+		{
+			desc:   "empty parsed content type",
+			expect: assert.True,
+		},
+		{
+			desc: "simple content type",
+			pct: parsedContentType{
+				mediaType: "plain/text",
+			},
+			mediaType: "plain/text",
+			expect:    assert.True,
+		},
+		{
+			desc: "content type with params",
+			pct: parsedContentType{
+				mediaType: "plain/text",
+				params: map[string]string{
+					"charset": "utf8",
+				},
+			},
+			mediaType: "plain/text",
+			params: map[string]string{
+				"charset": "utf8",
+			},
+			expect: assert.True,
+		},
+		{
+			desc: "different content type",
+			pct: parsedContentType{
+				mediaType: "plain/text",
+			},
+			mediaType: "application/json",
+			expect:    assert.False,
+		},
+		{
+			desc: "content type with params",
+			pct: parsedContentType{
+				mediaType: "plain/text",
+				params: map[string]string{
+					"charset": "utf8",
+				},
+			},
+			mediaType: "plain/text",
+			params: map[string]string{
+				"charset": "latin-1",
+			},
+			expect: assert.False,
+		},
+		{
+			desc: "different number of parameters",
+			pct: parsedContentType{
+				mediaType: "plain/text",
+				params: map[string]string{
+					"charset": "utf8",
+				},
+			},
+			mediaType: "plain/text",
+			params: map[string]string{
+				"charset": "utf8",
+				"q":       "0.8",
+			},
+			expect: assert.False,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			test.expect(t, test.pct.equals(test.mediaType, test.params))
+		})
+	}
+}