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>
2022-11-15 02:56:08 -07:00 · 2022-11-15 02:56:08 -07:00 · 67d9c8da0b
parent 1a1cfd1adc
commit 67d9c8da0b
11 changed files with 1201 additions and 39 deletions
--- a/docs/content/middlewares/http/compress.md
+++ b/docs/content/middlewares/http/compress.md
@ -5,23 +5,24 @@ description: "Traefik Proxy's HTTP middleware lets you compress responses before

 # Compress

-Compress Responses before Sending them to the Client
+Compress Allows Compressing Responses before Sending them to the Client
 {: .subtitle }

 ![Compress](../../assets/img/middleware/compress.png)

-The Compress middleware uses gzip compression.
+The Compress middleware supports gzip and Brotli compression.
+The activation of compression, and the compression method choice rely (among other things) on the request's `Accept-Encoding` header.

 ## Configuration Examples

 ```yaml tab="Docker"
-# Enable gzip compression
+# Enable compression
 labels:
  - "traefik.http.middlewares.test-compress.compress=true"
 ```

 ```yaml tab="Kubernetes"
-# Enable gzip compression
+# Enable compression
 apiVersion: traefik.containo.us/v1alpha1
 kind: Middleware
 metadata:
@ -31,7 +32,7 @@ spec:
 ```

 ```yaml tab="Consul Catalog"
-# Enable gzip compression
+# Enable compression
 - "traefik.http.middlewares.test-compress.compress=true"
 ```

@ -42,13 +43,13 @@ spec:
 ```

 ```yaml tab="Rancher"
-# Enable gzip compression
+# Enable compression
 labels:
  - "traefik.http.middlewares.test-compress.compress=true"
 ```

 ```yaml tab="File (YAML)"
-# Enable gzip compression
+# Enable compression
 http:
  middlewares:
    test-compress:
@ -56,7 +57,7 @@ http:
 ```

 ```toml tab="File (TOML)"
-# Enable gzip compression
+# Enable compression
 [http.middlewares]
  [http.middlewares.test-compress.compress]
 ```
@ -65,23 +66,34 @@ http:

    Responses are compressed when the following criteria are all met:

-    * The response body is larger than the configured minimum amount of bytes (default is `1024`).
-    * The `Accept-Encoding` request header contains `gzip`.
+    * The `Accept-Encoding` request header contains `gzip`, `*`, and/or `br` with or without [quality values](https://developer.mozilla.org/en-US/docs/Glossary/Quality_values).
+    If the `Accept-Encoding` request header is absent, it is meant as br compression is requested.
+    If it is present, but its value is the empty string, then compression is disabled.
    * The response is not already compressed, i.e. the `Content-Encoding` response header is not already set.
-
-    If the `Content-Type` header is not defined, or empty, the compress middleware will automatically [detect](https://mimesniff.spec.whatwg.org/) a content type.
-    It will also set the `Content-Type` header according to the detected MIME type.
+    * The response`Content-Type` header is not one among the [excludedContentTypes options](#excludedcontenttypes).
+    * The response body is larger than the [configured minimum amount of bytes](#minresponsebodybytes) (default is `1024`).

 ## Configuration Options

 ### `excludedContentTypes`

+_Optional, Default=""_ 
+
 `excludedContentTypes` specifies a list of content types to compare the `Content-Type` header of the incoming requests and responses before compressing.

 The responses with content types defined in `excludedContentTypes` are not compressed.

 Content types are compared in a case-insensitive, whitespace-ignored manner.

+!!! info "In the case of gzip"
+
+    If the `Content-Type` header is not defined, or empty, the compress middleware will automatically [detect](https://mimesniff.spec.whatwg.org/) a content type.
+    It will also set the `Content-Type` header according to the detected MIME type.
+
+!!! info "gRPC"
+
+    Note that `application/grpc` is never compressed.
+
 ```yaml tab="Docker"
 labels:
  - "traefik.http.middlewares.test-compress.compress.excludedcontenttypes=text/event-stream"
@ -130,9 +142,9 @@ http:

 ### `minResponseBodyBytes`

-`minResponseBodyBytes` specifies the minimum amount of bytes a response body must have to be compressed.
+_Optional, Default=1024_

-The default value is `1024`, which should be a reasonable value for most cases.
+`minResponseBodyBytes` specifies the minimum amount of bytes a response body must have to be compressed.

 Responses smaller than the specified values will not be compressed.

--- a/docs/content/reference/dynamic-configuration/kubernetes-crd-definition-v1.yml
+++ b/docs/content/reference/dynamic-configuration/kubernetes-crd-definition-v1.yml
@ -749,7 +749,8 @@ spec:
                  excludedContentTypes:
                    description: ExcludedContentTypes defines the list of content
                      types to compare the Content-Type header of the incoming requests
-                      and responses before compressing.
+                      and responses before compressing. `application/grpc` is always
+                      excluded.
                    items:
                      type: string
                    type: array
--- a/docs/content/reference/dynamic-configuration/traefik.containo.us_middlewares.yaml
+++ b/docs/content/reference/dynamic-configuration/traefik.containo.us_middlewares.yaml
@ -172,7 +172,8 @@ spec:
                  excludedContentTypes:
                    description: ExcludedContentTypes defines the list of content
                      types to compare the Content-Type header of the incoming requests
-                      and responses before compressing.
+                      and responses before compressing. `application/grpc` is always
+                      excluded.
                    items:
                      type: string
                    type: array
--- a/go.mod
+++ b/go.mod
@ -7,6 +7,7 @@ require (
 	github.com/ExpediaDotCom/haystack-client-go v0.0.0-20190315171017-e7edbdf53a61
 	github.com/Masterminds/sprig/v3 v3.2.2
 	github.com/abbot/go-http-auth v0.0.0-00010101000000-000000000000
+	github.com/andybalholm/brotli v1.0.4
 	github.com/aws/aws-sdk-go v1.44.47
 	github.com/cenkalti/backoff/v4 v4.1.3
 	github.com/compose-spec/compose-go v1.0.3
--- a/go.sum
+++ b/go.sum
@ -212,6 +212,8 @@ github.com/aliyun/alibaba-cloud-sdk-go v1.61.1755/go.mod h1:RcDobYh8k5VP6TNybz9m
 github.com/andres-erbsen/clock v0.0.0-20160526145045-9e14626cd129 h1:MzBOUgng9orim59UnfUTLRjMpd09C5uEVQ6RPGeCaVI=
 github.com/andres-erbsen/clock v0.0.0-20160526145045-9e14626cd129/go.mod h1:rFgpPQZYZ8vdbc+48xibu8ALc3yeyd64IhHS+PU6Yyg=
 github.com/andybalholm/brotli v1.0.2/go.mod h1:loMXtMfwqflxFJPmdbJO0a3KNoPuLBgiu3qAvBg8x/Y=
+github.com/andybalholm/brotli v1.0.4 h1:V7DdXeJtZscaqfNuAdSRuRFzuiKlHSC/Zh3zl9qY3JY=
+github.com/andybalholm/brotli v1.0.4/go.mod h1:fO7iG3H7G2nSZ7m0zPUDn85XEX2GTukHGRSepvi9Eig=
 github.com/anmitsu/go-shlex v0.0.0-20161002113705-648efa622239/go.mod h1:2FmKhYUyUczH0OGQWaF5ceTx0UBShxjsH6f8oGKYe2c=
 github.com/antihax/optional v1.0.0/go.mod h1:uupD/76wgC+ih3iEmQUL+0Ugr19nfwCT1kdvxnR2qWY=
 github.com/apache/thrift v0.12.0/go.mod h1:cp2SuWMxlEZw2r+iP2GNCdIi4C1qmUzdZFSVb+bacwQ=
--- a/integration/fixtures/k8s/01-traefik-crd.yml
+++ b/integration/fixtures/k8s/01-traefik-crd.yml
@ -749,7 +749,8 @@ spec:
                  excludedContentTypes:
                    description: ExcludedContentTypes defines the list of content
                      types to compare the Content-Type header of the incoming requests
-                      and responses before compressing.
+                      and responses before compressing. `application/grpc` is always
+                      excluded.
                    items:
                      type: string
                    type: array
--- a/pkg/config/dynamic/middlewares.go
+++ b/pkg/config/dynamic/middlewares.go
@ -161,6 +161,7 @@ func (c *CircuitBreaker) SetDefaults() {
 // More info: https://doc.traefik.io/traefik/v2.9/middlewares/http/compress/
 type Compress struct {
 	// ExcludedContentTypes defines the list of content types to compare the Content-Type header of the incoming requests and responses before compressing.
+	// `application/grpc` is always excluded.
 	ExcludedContentTypes []string `json:"excludedContentTypes,omitempty" toml:"excludedContentTypes,omitempty" yaml:"excludedContentTypes,omitempty" export:"true"`
 	// MinResponseBodyBytes defines the minimum amount of bytes a response body must have to be compressed.
 	// Default: 1024.
--- a/pkg/middlewares/compress/brotli/brotli.go
+++ b/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
+}
--- a/pkg/middlewares/compress/brotli/brotli_test.go
+++ b/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))
+		})
+	}
+}
--- a/pkg/middlewares/compress/compress.go
+++ b/pkg/middlewares/compress/compress.go
@ -1,22 +1,26 @@
 package compress

 import (
-	"compress/gzip"
 	"context"
+	"fmt"
 	"mime"
 	"net/http"
+	"strings"

 	"github.com/klauspost/compress/gzhttp"
 	"github.com/opentracing/opentracing-go/ext"
 	"github.com/traefik/traefik/v2/pkg/config/dynamic"
 	"github.com/traefik/traefik/v2/pkg/log"
 	"github.com/traefik/traefik/v2/pkg/middlewares"
+	"github.com/traefik/traefik/v2/pkg/middlewares/compress/brotli"
 	"github.com/traefik/traefik/v2/pkg/tracing"
 )

-const (
-	typeName = "Compress"
-)
+const typeName = "Compress"
+
+// DefaultMinSize is the default minimum size (in bytes) required to enable compression.
+// See https://github.com/klauspost/compress/blob/9559b037e79ad673c71f6ef7c732c00949014cd2/gzhttp/compress.go#L47.
+const DefaultMinSize = 1024

 // Compress is a middleware that allows to compress the response.
 type compress struct {
@ -24,6 +28,9 @@ type compress struct {
 	name     string
 	excludes []string
 	minSize  int
+
+	brotliHandler http.Handler
+	gzipHandler   http.Handler
 }

 // New creates a new compress middleware.
@ -40,42 +47,117 @@ func New(ctx context.Context, next http.Handler, conf dynamic.Compress, name str
 		excludes = append(excludes, mediaType)
 	}

-	minSize := gzhttp.DefaultMinSize
+	minSize := DefaultMinSize
 	if conf.MinResponseBodyBytes > 0 {
 		minSize = conf.MinResponseBodyBytes
 	}

-	return &compress{next: next, name: name, excludes: excludes, minSize: minSize}, nil
+	c := &compress{
+		next:     next,
+		name:     name,
+		excludes: excludes,
+		minSize:  minSize,
+	}
+
+	var err error
+	c.brotliHandler, err = c.newBrotliHandler()
+	if err != nil {
+		return nil, err
+	}
+
+	c.gzipHandler, err = c.newGzipHandler()
+	if err != nil {
+		return nil, err
+	}
+
+	return c, nil
 }

 func (c *compress) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
-	mediaType, _, err := mime.ParseMediaType(req.Header.Get("Content-Type"))
-	if err != nil {
-		log.FromContext(middlewares.GetLoggerCtx(context.Background(), c.name, typeName)).Debug(err)
+	logger := log.FromContext(middlewares.GetLoggerCtx(req.Context(), c.name, typeName))
+
+	if req.Method == http.MethodHead {
+		c.next.ServeHTTP(rw, req)
+		return
 	}

+	mediaType, _, err := mime.ParseMediaType(req.Header.Get("Content-Type"))
+	if err != nil {
+		logger.WithError(err).Debug("Unable to parse MIME type")
+	}
+
+	// Notably for text/event-stream requests the response should not be compressed.
+	// See https://github.com/traefik/traefik/issues/2576
 	if contains(c.excludes, mediaType) {
 		c.next.ServeHTTP(rw, req)
-	} else {
-		ctx := middlewares.GetLoggerCtx(req.Context(), c.name, typeName)
-		c.gzipHandler(ctx).ServeHTTP(rw, req)
+		return
 	}
+
+	// Client allows us to do whatever we want, so we br compress.
+	// See https://www.rfc-editor.org/rfc/rfc9110.html#section-12.5.3
+	acceptEncoding, ok := req.Header["Accept-Encoding"]
+	if !ok {
+		c.brotliHandler.ServeHTTP(rw, req)
+		return
+	}
+
+	if encodingAccepts(acceptEncoding, "br") {
+		c.brotliHandler.ServeHTTP(rw, req)
+		return
+	}
+
+	if encodingAccepts(acceptEncoding, "gzip") {
+		c.gzipHandler.ServeHTTP(rw, req)
+		return
+	}
+
+	c.next.ServeHTTP(rw, req)
 }

 func (c *compress) GetTracingInformation() (string, ext.SpanKindEnum) {
 	return c.name, tracing.SpanKindNoneEnum
 }

-func (c *compress) gzipHandler(ctx context.Context) http.Handler {
+func (c *compress) newGzipHandler() (http.Handler, error) {
 	wrapper, err := gzhttp.NewWrapper(
 		gzhttp.ExceptContentTypes(c.excludes),
-		gzhttp.CompressionLevel(gzip.DefaultCompression),
-		gzhttp.MinSize(c.minSize))
+		gzhttp.MinSize(c.minSize),
+	)
 	if err != nil {
-		log.FromContext(ctx).Error(err)
+		return nil, fmt.Errorf("new gzip wrapper: %w", err)
 	}

-	return wrapper(c.next)
+	return wrapper(c.next), nil
+}
+
+func (c *compress) newBrotliHandler() (http.Handler, error) {
+	cfg := brotli.Config{
+		ExcludedContentTypes: c.excludes,
+		MinSize:              c.minSize,
+	}
+
+	wrapper, err := brotli.NewWrapper(cfg)
+	if err != nil {
+		return nil, fmt.Errorf("new brotli wrapper: %w", err)
+	}
+
+	return wrapper(c.next), nil
+}
+
+func encodingAccepts(acceptEncoding []string, typ string) bool {
+	for _, ae := range acceptEncoding {
+		for _, e := range strings.Split(ae, ",") {
+			parsed := strings.Split(strings.TrimSpace(e), ";")
+			if len(parsed) == 0 {
+				continue
+			}
+			if parsed[0] == typ || parsed[0] == "*" {
+				return true
+			}
+		}
+	}
+
+	return false
 }

 func contains(values []string, val string) bool {
@ -84,5 +166,6 @@ func contains(values []string, val string) bool {
 			return true
 		}
 	}
+
 	return false
 }
--- a/pkg/middlewares/compress/compress_test.go
+++ b/pkg/middlewares/compress/compress_test.go
@ -1,12 +1,14 @@
 package compress

 import (
+	"compress/gzip"
 	"context"
 	"io"
 	"net/http"
 	"net/http/httptest"
 	"testing"

+	"github.com/andybalholm/brotli"
 	"github.com/klauspost/compress/gzhttp"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@ -20,8 +22,81 @@ const (
 	contentTypeHeader     = "Content-Type"
 	varyHeader            = "Vary"
 	gzipValue             = "gzip"
+	brotliValue           = "br"
 )

+func TestNegotiation(t *testing.T) {
+	testCases := []struct {
+		desc            string
+		acceptEncHeader string
+		expEncoding     string
+	}{
+		{
+			desc:        "no accept header",
+			expEncoding: "br",
+		},
+		{
+			desc:            "unsupported accept header",
+			acceptEncHeader: "notreal",
+			expEncoding:     "",
+		},
+		{
+			desc:            "accept any header",
+			acceptEncHeader: "*",
+			expEncoding:     "br",
+		},
+		{
+			desc:            "gzip accept header",
+			acceptEncHeader: "gzip",
+			expEncoding:     "gzip",
+		},
+		{
+			desc:            "br accept header",
+			acceptEncHeader: "br",
+			expEncoding:     "br",
+		},
+		{
+			desc:            "multi accept header, prefer br",
+			acceptEncHeader: "br;q=0.8, gzip;q=0.6",
+			expEncoding:     "br",
+		},
+		{
+			desc:            "multi accept header, prefer br",
+			acceptEncHeader: "gzip;q=1.0, br;q=0.8",
+			expEncoding:     "br",
+		},
+		{
+			desc:            "multi accept header list, prefer br",
+			acceptEncHeader: "gzip, br",
+			expEncoding:     "br",
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost", nil)
+			if test.acceptEncHeader != "" {
+				req.Header.Add(acceptEncodingHeader, test.acceptEncHeader)
+			}
+
+			next := http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+				_, _ = rw.Write(generateBytes(10))
+			})
+			handler, err := New(context.Background(), next, dynamic.Compress{MinResponseBodyBytes: 1}, "testing")
+			require.NoError(t, err)
+
+			rw := httptest.NewRecorder()
+			handler.ServeHTTP(rw, req)
+
+			assert.Equal(t, test.expEncoding, rw.Header().Get(contentEncodingHeader))
+		})
+	}
+}
+
 func TestShouldCompressWhenNoContentEncodingHeader(t *testing.T) {
 	req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost", nil)
 	req.Header.Add(acceptEncodingHeader, gzipValue)
@ -41,9 +116,12 @@ func TestShouldCompressWhenNoContentEncodingHeader(t *testing.T) {
 	assert.Equal(t, gzipValue, rw.Header().Get(contentEncodingHeader))
 	assert.Equal(t, acceptEncodingHeader, rw.Header().Get(varyHeader))

-	if assert.ObjectsAreEqualValues(rw.Body.Bytes(), baseBody) {
-		assert.Fail(t, "expected a compressed body", "got %v", rw.Body.Bytes())
-	}
+	gr, err := gzip.NewReader(rw.Body)
+	require.NoError(t, err)
+
+	got, err := io.ReadAll(gr)
+	require.NoError(t, err)
+	assert.Equal(t, got, baseBody)
 }

 func TestShouldNotCompressWhenContentEncodingHeader(t *testing.T) {
@ -71,7 +149,7 @@ func TestShouldNotCompressWhenContentEncodingHeader(t *testing.T) {
 	assert.EqualValues(t, rw.Body.Bytes(), fakeCompressedBody)
 }

-func TestShouldNotCompressWhenNoAcceptEncodingHeader(t *testing.T) {
+func TestShouldCompressWhenNoAcceptEncodingHeader(t *testing.T) {
 	req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost", nil)

 	fakeBody := generateBytes(gzhttp.DefaultMinSize)
@ -87,7 +165,33 @@ func TestShouldNotCompressWhenNoAcceptEncodingHeader(t *testing.T) {
 	rw := httptest.NewRecorder()
 	handler.ServeHTTP(rw, req)

+	assert.Equal(t, brotliValue, rw.Header().Get(contentEncodingHeader))
+	assert.Equal(t, acceptEncodingHeader, rw.Header().Get(varyHeader))
+
+	got, err := io.ReadAll(brotli.NewReader(rw.Body))
+	require.NoError(t, err)
+	assert.Equal(t, got, fakeBody)
+}
+
+func TestShouldNotCompressHeadRequest(t *testing.T) {
+	req := testhelpers.MustNewRequest(http.MethodHead, "http://localhost", nil)
+	req.Header.Add(acceptEncodingHeader, gzipValue)
+
+	fakeBody := generateBytes(gzhttp.DefaultMinSize)
+	next := http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		_, err := rw.Write(fakeBody)
+		if err != nil {
+			http.Error(rw, err.Error(), http.StatusInternalServerError)
+		}
+	})
+	handler, err := New(context.Background(), next, dynamic.Compress{}, "testing")
+	require.NoError(t, err)
+
+	rw := httptest.NewRecorder()
+	handler.ServeHTTP(rw, req)
+
 	assert.Empty(t, rw.Header().Get(contentEncodingHeader))
+	assert.Empty(t, rw.Header().Get(varyHeader))
 	assert.EqualValues(t, rw.Body.Bytes(), fakeBody)
 }