261 lines
7.9 KiB
Go
261 lines
7.9 KiB
Go
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package gziphandler
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import (
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"bufio"
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"compress/gzip"
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"fmt"
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"net"
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"net/http"
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"strconv"
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"strings"
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"sync"
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)
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const (
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vary = "Vary"
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acceptEncoding = "Accept-Encoding"
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contentEncoding = "Content-Encoding"
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contentType = "Content-Type"
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contentLength = "Content-Length"
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)
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type codings map[string]float64
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// The default qvalue to assign to an encoding if no explicit qvalue is set.
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// This is actually kind of ambiguous in RFC 2616, so hopefully it's correct.
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// The examples seem to indicate that it is.
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const DEFAULT_QVALUE = 1.0
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// gzipWriterPools stores a sync.Pool for each compression level for reuse of
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// gzip.Writers. Use poolIndex to covert a compression level to an index into
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// gzipWriterPools.
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var gzipWriterPools [gzip.BestCompression - gzip.BestSpeed + 2]*sync.Pool
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func init() {
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for i := gzip.BestSpeed; i <= gzip.BestCompression; i++ {
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addLevelPool(i)
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}
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addLevelPool(gzip.DefaultCompression)
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}
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// poolIndex maps a compression level to its index into gzipWriterPools. It
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// assumes that level is a valid gzip compression level.
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func poolIndex(level int) int {
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// gzip.DefaultCompression == -1, so we need to treat it special.
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if level == gzip.DefaultCompression {
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return gzip.BestCompression - gzip.BestSpeed + 1
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}
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return level - gzip.BestSpeed
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}
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func addLevelPool(level int) {
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gzipWriterPools[poolIndex(level)] = &sync.Pool{
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New: func() interface{} {
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// NewWriterLevel only returns error on a bad level, we are guaranteeing
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// that this will be a valid level so it is okay to ignore the returned
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// error.
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w, _ := gzip.NewWriterLevel(nil, level)
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return w
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},
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}
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}
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// GzipResponseWriter provides an http.ResponseWriter interface, which gzips
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// bytes before writing them to the underlying response. This doesn't close the
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// writers, so don't forget to do that.
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type GzipResponseWriter struct {
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http.ResponseWriter
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index int // Index for gzipWriterPools.
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gw *gzip.Writer
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}
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// Write appends data to the gzip writer.
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func (w *GzipResponseWriter) Write(b []byte) (int, error) {
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// Lazily create the gzip.Writer, this allows empty bodies to be actually
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// empty, for example in the case of status code 204 (no content).
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if w.gw == nil {
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w.init()
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}
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if _, ok := w.Header()[contentType]; !ok {
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// If content type is not set, infer it from the uncompressed body.
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w.Header().Set(contentType, http.DetectContentType(b))
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}
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return w.gw.Write(b)
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}
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// WriteHeader will check if the gzip writer needs to be lazily initiated and
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// then pass the code along to the underlying ResponseWriter.
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func (w *GzipResponseWriter) WriteHeader(code int) {
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if w.gw == nil &&
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code != http.StatusNotModified && code != http.StatusNoContent {
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w.init()
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}
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w.ResponseWriter.WriteHeader(code)
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}
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// init graps a new gzip writer from the gzipWriterPool and writes the correct
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// content encoding header.
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func (w *GzipResponseWriter) init() {
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// Bytes written during ServeHTTP are redirected to this gzip writer
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// before being written to the underlying response.
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gzw := gzipWriterPools[w.index].Get().(*gzip.Writer)
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gzw.Reset(w.ResponseWriter)
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w.gw = gzw
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w.ResponseWriter.Header().Set(contentEncoding, "gzip")
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// if the Content-Length is already set, then calls to Write on gzip
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// will fail to set the Content-Length header since its already set
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// See: https://github.com/golang/go/issues/14975
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w.ResponseWriter.Header().Del(contentLength)
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}
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// Close will close the gzip.Writer and will put it back in the gzipWriterPool.
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func (w *GzipResponseWriter) Close() error {
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if w.gw == nil {
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return nil
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}
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err := w.gw.Close()
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gzipWriterPools[w.index].Put(w.gw)
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return err
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}
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// Flush flushes the underlying *gzip.Writer and then the underlying
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// http.ResponseWriter if it is an http.Flusher. This makes GzipResponseWriter
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// an http.Flusher.
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func (w *GzipResponseWriter) Flush() {
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if w.gw != nil {
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w.gw.Flush()
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}
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if fw, ok := w.ResponseWriter.(http.Flusher); ok {
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fw.Flush()
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}
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}
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// Hijack implements http.Hijacker. If the underlying ResponseWriter is a
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// Hijacker, its Hijack method is returned. Otherwise an error is returned.
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func (w *GzipResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
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if hj, ok := w.ResponseWriter.(http.Hijacker); ok {
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return hj.Hijack()
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}
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return nil, nil, fmt.Errorf("http.Hijacker interface is not supported")
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}
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// verify Hijacker interface implementation
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var _ http.Hijacker = &GzipResponseWriter{}
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// MustNewGzipLevelHandler behaves just like NewGzipLevelHandler except that in
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// an error case it panics rather than returning an error.
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func MustNewGzipLevelHandler(level int) func(http.Handler) http.Handler {
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wrap, err := NewGzipLevelHandler(level)
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if err != nil {
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panic(err)
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}
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return wrap
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}
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// NewGzipLevelHandler returns a wrapper function (often known as middleware)
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// which can be used to wrap an HTTP handler to transparently gzip the response
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// body if the client supports it (via the Accept-Encoding header). Responses will
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// be encoded at the given gzip compression level. An error will be returned only
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// if an invalid gzip compression level is given, so if one can ensure the level
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// is valid, the returned error can be safely ignored.
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func NewGzipLevelHandler(level int) (func(http.Handler) http.Handler, error) {
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if level != gzip.DefaultCompression && (level < gzip.BestSpeed || level > gzip.BestCompression) {
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return nil, fmt.Errorf("invalid compression level requested: %d", level)
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}
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return func(h http.Handler) http.Handler {
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index := poolIndex(level)
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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w.Header().Add(vary, acceptEncoding)
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if acceptsGzip(r) {
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gw := &GzipResponseWriter{
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ResponseWriter: w,
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index: index,
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}
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defer gw.Close()
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h.ServeHTTP(gw, r)
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} else {
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h.ServeHTTP(w, r)
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}
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})
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}, nil
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}
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// GzipHandler wraps an HTTP handler, to transparently gzip the response body if
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// the client supports it (via the Accept-Encoding header). This will compress at
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// the default compression level.
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func GzipHandler(h http.Handler) http.Handler {
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wrapper, _ := NewGzipLevelHandler(gzip.DefaultCompression)
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return wrapper(h)
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}
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// acceptsGzip returns true if the given HTTP request indicates that it will
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// accept a gzipped response.
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func acceptsGzip(r *http.Request) bool {
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acceptedEncodings, _ := parseEncodings(r.Header.Get(acceptEncoding))
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return acceptedEncodings["gzip"] > 0.0
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}
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// parseEncodings attempts to parse a list of codings, per RFC 2616, as might
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// appear in an Accept-Encoding header. It returns a map of content-codings to
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// quality values, and an error containing the errors encountered. It's probably
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// safe to ignore those, because silently ignoring errors is how the internet
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// works.
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//
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// See: http://tools.ietf.org/html/rfc2616#section-14.3.
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func parseEncodings(s string) (codings, error) {
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c := make(codings)
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var e []string
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for _, ss := range strings.Split(s, ",") {
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coding, qvalue, err := parseCoding(ss)
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if err != nil {
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e = append(e, err.Error())
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} else {
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c[coding] = qvalue
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}
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}
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// TODO (adammck): Use a proper multi-error struct, so the individual errors
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// can be extracted if anyone cares.
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if len(e) > 0 {
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return c, fmt.Errorf("errors while parsing encodings: %s", strings.Join(e, ", "))
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}
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return c, nil
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}
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// parseCoding parses a single conding (content-coding with an optional qvalue),
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// as might appear in an Accept-Encoding header. It attempts to forgive minor
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// formatting errors.
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func parseCoding(s string) (coding string, qvalue float64, err error) {
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for n, part := range strings.Split(s, ";") {
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part = strings.TrimSpace(part)
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qvalue = DEFAULT_QVALUE
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if n == 0 {
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coding = strings.ToLower(part)
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} else if strings.HasPrefix(part, "q=") {
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qvalue, err = strconv.ParseFloat(strings.TrimPrefix(part, "q="), 64)
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if qvalue < 0.0 {
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qvalue = 0.0
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} else if qvalue > 1.0 {
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qvalue = 1.0
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}
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}
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}
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if coding == "" {
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err = fmt.Errorf("empty content-coding")
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}
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return
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}
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