gzhttp: Use strings for randomJitter to skip a copy

gzhttp/compress.go

@@ -2,7 +2,6 @@ package gzhttp
 
 import (
 	"bufio"
-	"bytes"
 	"crypto/rand"
 	"crypto/sha256"
 	"encoding/binary"
@@ -73,7 +72,7 @@ type GzipResponseWriter struct {
 	setContentType   bool   // Add content type, if missing and detected.
 	suffixETag       string // Suffix to add to ETag header if response is compressed.
 	dropETag         bool   // Drop ETag header if response is compressed (supersedes suffixETag).
-	randomJitter     []byte // Add random bytes to output as header field.
+	randomJitter     string // Add random bytes to output as header field.
 	jitterBuffer     int    // Maximum buffer to accumulate before doing jitter.
 
 	contentTypeFilter func(ct string) bool // Only compress if the response is one of these content-types. All are accepted if empty.
@@ -211,7 +210,7 @@ func (w *GzipResponseWriter) startGzip(remain []byte) error {
 		// Initialize the GZIP response.
 		w.init()
 
-		// Set random jitter based on CRC of current buffer
+		// Set random jitter based on SHA-256 of current buffer
 		// Before first write.
 		if len(w.randomJitter) > 0 {
 			var jitRNG uint32
@@ -236,7 +235,7 @@ func (w *GzipResponseWriter) startGzip(remain []byte) error {
 				}
 				jitRNG = binary.LittleEndian.Uint32(tmp[:])
 			}
-			jit := string(w.randomJitter[:1+jitRNG%uint32(len(w.randomJitter)-1)])
+			jit := w.randomJitter[:1+jitRNG%uint32(len(w.randomJitter)-1)]
 			//fmt.Println("w.buf:", len(w.buf), "remain:", len(remain), "jitter:", len(jit))
 			w.gw.(writer.GzipWriterExt).SetHeader(writer.Header{Comment: &jit})
 		}
@@ -505,7 +504,7 @@ type config struct {
 	suffixETag       string
 	dropETag         bool
 	jitterBuffer     int
-	randomJitter     []byte
+	randomJitter     string
 }
 
 func (c *config) validate() error {
@@ -696,14 +695,13 @@ func DropETag() option {
 func RandomJitter(n, buffer int) option {
 	return func(c *config) {
 		if n > 0 {
-			c.randomJitter = bytes.Repeat([]byte("Padding-"), 1+(n/8))
-			c.randomJitter = c.randomJitter[:(n + 1)]
+			c.randomJitter = strings.Repeat("Padding-", 1+(n/8))[:n+1]
 			c.jitterBuffer = buffer
 			if c.jitterBuffer == 0 {
 				c.jitterBuffer = 64 << 10
 			}
 		} else {
-			c.randomJitter = nil
+			c.randomJitter = ""
 			c.jitterBuffer = 0
 		}
 	}