Add Heal The Breach support

gzip.go

@@ -3,8 +3,10 @@ package gziphandler // import "github.com/NYTimes/gziphandler"
 import (
 	"bufio"
 	"compress/gzip"
+	"crypto/rand"
 	"fmt"
 	"io"
+	"math/big"
 	"mime"
 	"net"
 	"net/http"
@@ -41,6 +43,9 @@ const (
 // gzipWriterPools.
 var gzipWriterPools [gzip.BestCompression - gzip.BestSpeed + 2]*sync.Pool
 
+// ascii is used to create pseudo random file names for HTB.
+var ascii = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
+
 func init() {
 	for i := gzip.BestSpeed; i <= gzip.BestCompression; i++ {
 		addLevelPool(i)
@@ -81,9 +86,10 @@ type GzipResponseWriter struct {
 
 	code int // Saves the WriteHeader value.
 
-	minSize int    // Specifies the minimum response size to gzip. If the response length is bigger than this value, it is compressed.
-	buf     []byte // Holds the first part of the write before reaching the minSize or the end of the write.
-	ignore  bool   // If true, then we immediately passthru writes to the underlying ResponseWriter.
+	minSize     int                    // Specifies the minimum response size to gzip. If the response length is bigger than this value, it is compressed.
+	htbFileName func() (string, error) // Holds a function that returns a random string for HTB. Setting a function enables dependency injection.
+	buf         []byte                 // Holds the first part of the write before reaching the minSize or the end of the write.
+	ignore      bool                   // If true, then we immediately passthru writes to the underlying ResponseWriter.
 
 	contentTypes []parsedContentType // Only compress if the response is one of these content-types. All are accepted if empty.
 }
@@ -169,6 +175,16 @@ func (w *GzipResponseWriter) startGzip() error {
 	if len(w.buf) > 0 {
 		// Initialize the GZIP response.
 		w.init()
+
+		// Handle HTB. Modifying the header needs to happen before the first call to write.
+		if w.htbFileName != nil {
+			htbName, err := w.htbFileName()
+			if err != nil {
+				return fmt.Errorf("gziphandler: generating HTB file name: %w", err)
+			}
+			w.gw.Header.Name = htbName
+		}
+
 		n, err := w.gw.Write(w.buf)
 
 		// This should never happen (per io.Writer docs), but if the write didn't
@@ -182,6 +198,25 @@ func (w *GzipResponseWriter) startGzip() error {
 	return nil
 }
 
+func htbFileName(maxSize int) (string, error) {
+	// Get a random size
+	size, err := rand.Int(rand.Reader, big.NewInt(int64(maxSize)))
+	if err != nil {
+		return "", err
+	}
+
+	// Create the string
+	b := make([]rune, size.Int64())
+	for i := range b {
+		n, err := rand.Int(rand.Reader, big.NewInt(int64(len(ascii))))
+		if err != nil {
+			return "", err
+		}
+		b[i] = ascii[n.Int64()]
+	}
+	return string(b), nil
+}
+
 // startPlain writes to sent bytes and buffer the underlying ResponseWriter without gzip.
 func (w *GzipResponseWriter) startPlain() error {
 	if w.code != 0 {
@@ -329,6 +364,11 @@ func GzipHandlerWithOpts(opts ...option) (func(http.Handler) http.Handler, error
 					minSize:        c.minSize,
 					contentTypes:   c.contentTypes,
 				}
+				if c.htbSize > 0 {
+					gw.htbFileName = func() (string, error) {
+						return htbFileName(c.htbSize)
+					}
+				}
 				defer gw.Close()
 
 				if _, ok := w.(http.CloseNotifier); ok {
@@ -378,6 +418,7 @@ func (pct parsedContentType) equals(mediaType string, params map[string]string)
 type config struct {
 	minSize      int
 	level        int
+	htbSize      int
 	contentTypes []parsedContentType
 }
 
@@ -407,6 +448,14 @@ func CompressionLevel(level int) option {
 	}
 }
 
+// HTBSize lets you specify the maximum size for Heal The Breach.
+// See https://ieeexplore.ieee.org/document/9754554
+func HTBSize(size int) option {
+	return func(c *config) {
+		c.htbSize = size
+	}
+}
+
 // ContentTypes specifies a list of content types to compare
 // the Content-Type header to before compressing. If none
 // match, the response will be returned as-is.

gzip_test.go

@@ -79,6 +79,28 @@ func TestGzipHandler(t *testing.T) {
 	handler.ServeHTTP(res3, req3)
 
 	assert.Equal(t, http.DetectContentType([]byte(testBody)), res3.Header().Get("Content-Type"))
+
+	// Test with an HTB function
+
+	req4, _ := http.NewRequest("GET", "/whatever", nil)
+	req4.Header.Set("Accept-Encoding", "gzip")
+	resp4 := httptest.NewRecorder()
+
+	htbFileName := "12345"
+	wrapper, _ := handlerWithCustomHTB(func() (string, error) {
+		return htbFileName, nil
+	})
+	htbHandler := wrapper(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		io.WriteString(w, testBody)
+
+	}))
+	htbHandler.ServeHTTP(resp4, req4)
+	res4 := resp4.Result()
+
+	assert.Equal(t, 200, res4.StatusCode)
+	assert.Equal(t, "gzip", res4.Header.Get("Content-Encoding"))
+	assert.Equal(t, "Accept-Encoding", res4.Header.Get("Vary"))
+	assert.Equal(t, gzipStrLevelWithFileName(testBody, htbFileName, gzip.DefaultCompression), resp4.Body.Bytes())
 }
 
 func TestGzipHandlerSmallBodyNoCompression(t *testing.T) {
@@ -625,6 +647,15 @@ func gzipStrLevel(s string, lvl int) []byte {
 	return b.Bytes()
 }
 
+func gzipStrLevelWithFileName(s, n string, lvl int) []byte {
+	var b bytes.Buffer
+	w, _ := gzip.NewWriterLevel(&b, lvl)
+	w.Header.Name = n
+	io.WriteString(w, s)
+	w.Close()
+	return b.Bytes()
+}
+
 func benchmark(b *testing.B, parallel bool, size int) {
 	bin, err := ioutil.ReadFile("testdata/benchmark.json")
 	if err != nil {
@@ -671,3 +702,37 @@ func newTestHandler(body string) http.Handler {
 		}
 	}))
 }
+
+func handlerWithCustomHTB(htb func() (string, error)) (func(http.Handler) http.Handler, error) {
+	c := &config{
+		level:   gzip.DefaultCompression,
+		minSize: DefaultMinSize,
+	}
+	return func(h http.Handler) http.Handler {
+		index := poolIndex(c.level)
+
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Add(vary, acceptEncoding)
+			if acceptsGzip(r) {
+				gw := &GzipResponseWriter{
+					ResponseWriter: w,
+					index:          index,
+					minSize:        c.minSize,
+					contentTypes:   c.contentTypes,
+					htbFileName:    htb,
+				}
+				defer gw.Close()
+
+				if _, ok := w.(http.CloseNotifier); ok {
+					gwcn := GzipResponseWriterWithCloseNotify{gw}
+					h.ServeHTTP(gwcn, r)
+				} else {
+					h.ServeHTTP(gw, r)
+				}
+
+			} else {
+				h.ServeHTTP(w, r)
+			}
+		})
+	}, nil
+}