116 lines
3.3 KiB
Go
116 lines
3.3 KiB
Go
package web
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import (
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"compress/gzip"
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"net/http"
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"strings"
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"sync"
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)
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// 可压缩的响应类型。图片（迷雾 PNG、图标）本身已是压缩格式，再压纯属浪费 CPU。
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func compressible(ct string) bool {
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ct = strings.ToLower(ct)
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if i := strings.IndexByte(ct, ';'); i >= 0 {
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ct = ct[:i]
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}
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ct = strings.TrimSpace(ct)
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switch ct {
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case "text/html", "text/css", "text/plain", "text/javascript",
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"application/javascript", "application/json", "application/x-javascript",
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"image/svg+xml", "application/manifest+json", "application/xml":
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return true
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}
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return strings.HasPrefix(ct, "text/") && ct != "text/cache-manifest"
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}
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type gzipWriter struct {
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http.ResponseWriter
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gz *gzip.Writer
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comp bool
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seen bool // 首部是否已定下来（WriteHeader 已调用，或首字节已写）
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}
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var gzipPool = sync.Pool{New: func() any {
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return gzip.NewWriter(nil)
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}}
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// WriteHeader 必须在首部提交前决定压不压。静态文件由 http.FileServer 提供，
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// 它会先设好 Content-Length 再显式 WriteHeader(200/206)；若拖到 Write 里再改首部，
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// 首部早已提交，会出现「声明长度 ≠ 实际压缩后长度」，浏览器报
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// ERR_CONTENT_LENGTH_MISMATCH 并把 CSS/JS 截断。只有 200 才压缩，
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// 206（Range）/304 等自带长度语义，一律原样透传。
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func (g *gzipWriter) WriteHeader(code int) {
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if g.seen {
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return
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}
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g.seen = true
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if code == http.StatusOK && compressible(g.Header().Get("Content-Type")) {
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g.comp = true
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g.Header().Set("Content-Encoding", "gzip")
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g.Header().Set("Vary", "Accept-Encoding")
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g.Header().Del("Content-Length")
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}
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g.ResponseWriter.WriteHeader(code)
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}
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func (g *gzipWriter) Write(b []byte) (int, error) {
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if !g.seen {
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g.seen = true
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// 上游没有显式 WriteHeader 时，首字节写入才能确定内容类型，此时决定压不压
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ct := g.Header().Get("Content-Type")
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if ct == "" {
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ct = http.DetectContentType(b)
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g.Header().Set("Content-Type", ct)
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}
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if compressible(ct) {
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g.comp = true
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g.Header().Set("Content-Encoding", "gzip")
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g.Header().Set("Vary", "Accept-Encoding")
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g.Header().Del("Content-Length")
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}
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}
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if !g.comp {
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return g.ResponseWriter.Write(b)
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}
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if g.gz == nil {
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g.gz = gzipPool.Get().(*gzip.Writer)
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g.gz.Reset(g.ResponseWriter)
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}
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return g.gz.Write(b)
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}
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func (g *gzipWriter) Flush() {
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if g.gz != nil {
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g.gz.Flush()
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}
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if f, ok := g.ResponseWriter.(http.Flusher); ok {
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f.Flush()
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}
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}
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func (g *gzipWriter) close() {
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if g.gz != nil {
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g.gz.Close()
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gzipPool.Put(g.gz)
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g.gz = nil
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}
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}
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// gzipHandler 对声明了 gzip 且内容类型可压缩的响应做在线压缩。
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func gzipHandler(next http.Handler) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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// 带 Range 的请求（浏览器校验 / 续传 immutable 缓存的静态资源）会返回 206 并自带
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// Content-Length，gzip 无法在首部已提交后再改写长度，会导致浏览器把 CSS/JS 截断
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// （ERR_CONTENT_LENGTH_MISMATCH）。这类请求直接透传、不压缩。
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if !strings.Contains(r.Header.Get("Accept-Encoding"), "gzip") ||
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r.Header.Get("Upgrade") != "" ||
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r.Header.Get("Range") != "" {
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next.ServeHTTP(w, r)
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return
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}
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gw := &gzipWriter{ResponseWriter: w}
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defer gw.close()
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next.ServeHTTP(gw, r)
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})
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}
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