gzhttp: Use strings for randomJitter to skip a copy (#767)

* gzhttp: Use strings for randomJitter to skip a copy

* gzhttp: Use crc32.Update instead of crc32.New

Skips another allocation:

name        old time/op    new time/op    delta
2kJitter-8    29.4µs ± 4%    29.0µs ± 3%  -1.30%  (p=0.006 n=24+24)

name        old speed      new speed      delta
2kJitter-8  69.7MB/s ± 4%  70.6MB/s ± 3%  +1.30%  (p=0.006 n=24+24)

name        old alloc/op   new alloc/op   delta
2kJitter-8    3.40kB ± 4%    3.34kB ± 4%  -1.94%  (p=0.001 n=25+25)

name        old allocs/op  new allocs/op  delta
2kJitter-8      16.0 ± 0%      15.0 ± 0%  -6.25%  (p=0.000 n=25+25)

gzhttp/compress.go

@@ -2,7 +2,6 @@ package gzhttp
 
 import (
 	"bufio"
-	"bytes"
 	"crypto/rand"
 	"crypto/sha256"
 	"encoding/binary"
@@ -76,7 +75,7 @@ type GzipResponseWriter struct {
 	suffixETag       string // Suffix to add to ETag header if response is compressed.
 	dropETag         bool   // Drop ETag header if response is compressed (supersedes suffixETag).
 	sha256Jitter     bool   // Use sha256 for jitter.
-	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.
@@ -216,7 +215,7 @@ 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 CRC or SHA-256 of current buffer.
 		// Before first write.
 		if len(w.randomJitter) > 0 {
 			var jitRNG uint32
@@ -232,20 +231,19 @@ func (w *GzipResponseWriter) startGzip(remain []byte) error {
 						}
 						h.Write(remain)
 					}
-					var tmp [sha256.BlockSize]byte
+					var tmp [sha256.Size]byte
 					jitRNG = binary.LittleEndian.Uint32(h.Sum(tmp[:0]))
 				} else {
-					h := crc32.New(castagnoliTable)
-					h.Write(w.buf)
+					h := crc32.Update(0, castagnoliTable, w.buf)
 					// Use only up to "w.jitterBuffer", otherwise the output depends on write sizes.
 					if len(remain) > 0 && len(w.buf) < w.jitterBuffer {
 						remain := remain
 						if len(remain)+len(w.buf) > w.jitterBuffer {
 							remain = remain[:w.jitterBuffer-len(w.buf)]
 						}
-						h.Write(remain)
+						h = crc32.Update(h, castagnoliTable, remain)
 					}
-					jitRNG = bits.RotateLeft32(h.Sum32(), 19) ^ 0xab0755de
+					jitRNG = bits.RotateLeft32(h, 19) ^ 0xab0755de
 				}
 			} else {
 				// Get from rand.Reader
@@ -526,7 +524,7 @@ type config struct {
 	suffixETag       string
 	dropETag         bool
 	jitterBuffer     int
-	randomJitter     []byte
+	randomJitter     string
 	sha256Jitter     bool
 }
 
@@ -721,14 +719,13 @@ func RandomJitter(n, buffer int, paranoid bool) option {
 	return func(c *config) {
 		if n > 0 {
 			c.sha256Jitter = paranoid
-			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
 		}
 	}

gzhttp/writer/gzkp/gzkp.go

@@ -61,23 +61,13 @@ func NewWriter(w io.Writer, level int) writer.GzipWriter {
 	}
 }
 
-// SetHeader will override header with any non-nil values.
+// SetHeader will override the gzip header on pw.
 func (pw *pooledWriter) SetHeader(h writer.Header) {
-	if h.Name != nil {
-		pw.Name = string(h.Name)
-	}
-	if h.Extra != nil {
-		pw.Extra = *h.Extra
-	}
-	if h.Comment != nil {
-		pw.Comment = string(h.Comment)
-	}
-	if h.ModTime != nil {
-		pw.ModTime = *h.ModTime
-	}
-	if h.OS != nil {
-		pw.OS = *h.OS
-	}
+	pw.Name = h.Name
+	pw.Extra = h.Extra
+	pw.Comment = h.Comment
+	pw.ModTime = h.ModTime
+	pw.OS = h.OS
 }
 
 func Levels() (min, max int) {

gzhttp/writer/gzstd/stdlib.go

@@ -61,23 +61,13 @@ func NewWriter(w io.Writer, level int) writer.GzipWriter {
 	}
 }
 
-// SetHeader will override header with any non-nil values.
+// SetHeader will override the gzip header on pw.
 func (pw *pooledWriter) SetHeader(h writer.Header) {
-	if h.Name != nil {
-		pw.Name = string(h.Name)
-	}
-	if h.Extra != nil {
-		pw.Extra = *h.Extra
-	}
-	if h.Comment != nil {
-		pw.Comment = string(h.Comment)
-	}
-	if h.ModTime != nil {
-		pw.ModTime = *h.ModTime
-	}
-	if h.OS != nil {
-		pw.OS = *h.OS
-	}
+	pw.Name = h.Name
+	pw.Extra = h.Extra
+	pw.Comment = h.Comment
+	pw.ModTime = h.ModTime
+	pw.OS = h.OS
 }
 
 func Levels() (min, max int) {

gzhttp/writer/interface.go

@@ -21,13 +21,13 @@ type GzipWriterExt interface {
 	SetHeader(h Header)
 }
 
-// Header provides nillable header fields.
+// Header is a gzip header.
 type Header struct {
-	Comment []byte     // comment, converted to string if set.
-	Extra   *[]byte    // "extra data"
-	ModTime *time.Time // modification time
-	Name    []byte     // file name, converted to string if set.
-	OS      *byte      // operating system type
+	Comment string    // comment
+	Extra   []byte    // "extra data"
+	ModTime time.Time // modification time
+	Name    string    // file name
+	OS      byte      // operating system type
 }
 
 // GzipWriterFactory contains the information needed for custom gzip implementations.