vendor/github.com/NYTimes/gziphandler/gzip.go - cloudstack-kubernetes-provider - Git at Google

 package gziphandler

 import (
 	"bufio"
 	"compress/gzip"
 	"fmt"
 	"io"
 	"net"
 	"net/http"
 	"strconv"
 	"strings"
 	"sync"
 )

 const (
 	vary            = "Vary"
 	acceptEncoding  = "Accept-Encoding"
 	contentEncoding = "Content-Encoding"
 	contentType     = "Content-Type"
 	contentLength   = "Content-Length"
 )

 type codings map[string]float64

 const (
 	// DefaultQValue is the default qvalue to assign to an encoding if no explicit qvalue is set.
 	// This is actually kind of ambiguous in RFC 2616, so hopefully it's correct.
 	// The examples seem to indicate that it is.
 	DefaultQValue = 1.0

 	// 1500 bytes is the MTU size for the internet since that is the largest size allowed at the network layer.
 	// If you take a file that is 1300 bytes and compress it to 800 bytes, it’s still transmitted in that same 1500 byte packet regardless, so you’ve gained nothing.
 	// That being the case, you should restrict the gzip compression to files with a size greater than a single packet, 1400 bytes (1.4KB) is a safe value.
 	DefaultMinSize = 1400
 )

 // gzipWriterPools stores a sync.Pool for each compression level for reuse of
 // gzip.Writers. Use poolIndex to covert a compression level to an index into
 // gzipWriterPools.
 var gzipWriterPools [gzip.BestCompression - gzip.BestSpeed + 2]*sync.Pool

 func init() {
 	for i := gzip.BestSpeed; i <= gzip.BestCompression; i++ {
 		addLevelPool(i)
 	}
 	addLevelPool(gzip.DefaultCompression)
 }

 // poolIndex maps a compression level to its index into gzipWriterPools. It
 // assumes that level is a valid gzip compression level.
 func poolIndex(level int) int {
 	// gzip.DefaultCompression == -1, so we need to treat it special.
 	if level == gzip.DefaultCompression {
 		return gzip.BestCompression - gzip.BestSpeed + 1
 	}
 	return level - gzip.BestSpeed
 }

 func addLevelPool(level int) {
 	gzipWriterPools[poolIndex(level)] = &sync.Pool{
 		New: func() interface{} {
 			// NewWriterLevel only returns error on a bad level, we are guaranteeing
 			// that this will be a valid level so it is okay to ignore the returned
 			// error.
 			w, _ := gzip.NewWriterLevel(nil, level)
 			return w
 		},
 	}
 }

 // GzipResponseWriter provides an http.ResponseWriter interface, which gzips
 // bytes before writing them to the underlying response. This doesn't close the
 // writers, so don't forget to do that.
 // It can be configured to skip response smaller than minSize.
 type GzipResponseWriter struct {
 	http.ResponseWriter
 	index int // Index for gzipWriterPools.
 	gw    *gzip.Writer

 	code int // Saves the WriteHeader value.

 	minSize int    // Specifed 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.

 	contentTypes []string // Only compress if the response is one of these content-types. All are accepted if empty.
 }

 type GzipResponseWriterWithCloseNotify struct {
 	*GzipResponseWriter
 }

 func (w GzipResponseWriterWithCloseNotify) CloseNotify() <-chan bool {
 	return w.ResponseWriter.(http.CloseNotifier).CloseNotify()
 }

 // Write appends data to the gzip writer.
 func (w *GzipResponseWriter) Write(b []byte) (int, error) {
 	// If content type is not set.
 	if _, ok := w.Header()[contentType]; !ok {
 		// It infer it from the uncompressed body.
 		w.Header().Set(contentType, http.DetectContentType(b))
 	}

 	// GZIP responseWriter is initialized. Use the GZIP responseWriter.
 	if w.gw != nil {
 		n, err := w.gw.Write(b)
 		return n, err
 	}

 	// Save the write into a buffer for later use in GZIP responseWriter (if content is long enough) or at close with regular responseWriter.
 	// On the first write, w.buf changes from nil to a valid slice
 	w.buf = append(w.buf, b...)

 	// If the global writes are bigger than the minSize and we're about to write
 	// a response containing a content type we want to handle, enable
 	// compression.
 	if len(w.buf) >= w.minSize && handleContentType(w.contentTypes, w) && w.Header().Get(contentEncoding) == "" {
 		err := w.startGzip()
 		if err != nil {
 			return 0, err
 		}
 	}

 	return len(b), nil
 }

 // startGzip initialize any GZIP specific informations.
 func (w *GzipResponseWriter) startGzip() error {

 	// Set the GZIP header.
 	w.Header().Set(contentEncoding, "gzip")

 	// if the Content-Length is already set, then calls to Write on gzip
 	// will fail to set the Content-Length header since its already set
 	// See: https://github.com/golang/go/issues/14975.
 	w.Header().Del(contentLength)

 	// Write the header to gzip response.
 	if w.code != 0 {
 		w.ResponseWriter.WriteHeader(w.code)
 	}

 	// Initialize the GZIP response.
 	w.init()

 	// Flush the buffer into the gzip response.
 	n, err := w.gw.Write(w.buf)

 	// This should never happen (per io.Writer docs), but if the write didn't
 	// accept the entire buffer but returned no specific error, we have no clue
 	// what's going on, so abort just to be safe.
 	if err == nil && n < len(w.buf) {
 		return io.ErrShortWrite
 	}

 	w.buf = nil
 	return err
 }

 // WriteHeader just saves the response code until close or GZIP effective writes.
 func (w *GzipResponseWriter) WriteHeader(code int) {
 	if w.code == 0 {
 		w.code = code
 	}
 }

 // init graps a new gzip writer from the gzipWriterPool and writes the correct
 // content encoding header.
 func (w *GzipResponseWriter) init() {
 	// Bytes written during ServeHTTP are redirected to this gzip writer
 	// before being written to the underlying response.
 	gzw := gzipWriterPools[w.index].Get().(*gzip.Writer)
 	gzw.Reset(w.ResponseWriter)
 	w.gw = gzw
 }

 // Close will close the gzip.Writer and will put it back in the gzipWriterPool.
 func (w *GzipResponseWriter) Close() error {
 	if w.gw == nil {
 		// Gzip not trigged yet, write out regular response.
 		if w.code != 0 {
 			w.ResponseWriter.WriteHeader(w.code)
 		}
 		if w.buf != nil {
 			_, writeErr := w.ResponseWriter.Write(w.buf)
 			// Returns the error if any at write.
 			if writeErr != nil {
 				return fmt.Errorf("gziphandler: write to regular responseWriter at close gets error: %q", writeErr.Error())
 			}
 		}
 		return nil
 	}

 	err := w.gw.Close()
 	gzipWriterPools[w.index].Put(w.gw)
 	w.gw = nil
 	return err
 }

 // Flush flushes the underlying *gzip.Writer and then the underlying
 // http.ResponseWriter if it is an http.Flusher. This makes GzipResponseWriter
 // an http.Flusher.
 func (w *GzipResponseWriter) Flush() {
 	if w.gw == nil {
 		// Only flush once startGzip has been called.
 		//
 		// Flush is thus a no-op until the written body
 		// exceeds minSize.
 		return
 	}

 	w.gw.Flush()

 	if fw, ok := w.ResponseWriter.(http.Flusher); ok {
 		fw.Flush()
 	}
 }

 // Hijack implements http.Hijacker. If the underlying ResponseWriter is a
 // Hijacker, its Hijack method is returned. Otherwise an error is returned.
 func (w *GzipResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
 	if hj, ok := w.ResponseWriter.(http.Hijacker); ok {
 		return hj.Hijack()
 	}
 	return nil, nil, fmt.Errorf("http.Hijacker interface is not supported")
 }

 // verify Hijacker interface implementation
 var _ http.Hijacker = &GzipResponseWriter{}

 // MustNewGzipLevelHandler behaves just like NewGzipLevelHandler except that in
 // an error case it panics rather than returning an error.
 func MustNewGzipLevelHandler(level int) func(http.Handler) http.Handler {
 	wrap, err := NewGzipLevelHandler(level)
 	if err != nil {
 		panic(err)
 	}
 	return wrap
 }

 // NewGzipLevelHandler returns a wrapper function (often known as middleware)
 // which can be used to wrap an HTTP handler to transparently gzip the response
 // body if the client supports it (via the Accept-Encoding header). Responses will
 // be encoded at the given gzip compression level. An error will be returned only
 // if an invalid gzip compression level is given, so if one can ensure the level
 // is valid, the returned error can be safely ignored.
 func NewGzipLevelHandler(level int) (func(http.Handler) http.Handler, error) {
 	return NewGzipLevelAndMinSize(level, DefaultMinSize)
 }

 // NewGzipLevelAndMinSize behave as NewGzipLevelHandler except it let the caller
 // specify the minimum size before compression.
 func NewGzipLevelAndMinSize(level, minSize int) (func(http.Handler) http.Handler, error) {
 	return GzipHandlerWithOpts(CompressionLevel(level), MinSize(minSize))
 }

 func GzipHandlerWithOpts(opts ...option) (func(http.Handler) http.Handler, error) {
 	c := &config{
 		level:   gzip.DefaultCompression,
 		minSize: DefaultMinSize,
 	}

 	for _, o := range opts {
 		o(c)
 	}

 	if err := c.validate(); err != nil {
 		return nil, err
 	}

 	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,
 				}
 				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
 }

 // Used for functional configuration.
 type config struct {
 	minSize      int
 	level        int
 	contentTypes []string
 }

 func (c *config) validate() error {
 	if c.level != gzip.DefaultCompression && (c.level < gzip.BestSpeed || c.level > gzip.BestCompression) {
 		return fmt.Errorf("invalid compression level requested: %d", c.level)
 	}

 	if c.minSize < 0 {
 		return fmt.Errorf("minimum size must be more than zero")
 	}

 	return nil
 }

 type option func(c *config)

 func MinSize(size int) option {
 	return func(c *config) {
 		c.minSize = size
 	}
 }

 func CompressionLevel(level int) option {
 	return func(c *config) {
 		c.level = level
 	}
 }

 func ContentTypes(types []string) option {
 	return func(c *config) {
 		c.contentTypes = []string{}
 		for _, v := range types {
 			c.contentTypes = append(c.contentTypes, strings.ToLower(v))
 		}
 	}
 }

 // GzipHandler wraps an HTTP handler, to transparently gzip the response body if
 // the client supports it (via the Accept-Encoding header). This will compress at
 // the default compression level.
 func GzipHandler(h http.Handler) http.Handler {
 	wrapper, _ := NewGzipLevelHandler(gzip.DefaultCompression)
 	return wrapper(h)
 }

 // acceptsGzip returns true if the given HTTP request indicates that it will
 // accept a gzipped response.
 func acceptsGzip(r *http.Request) bool {
 	acceptedEncodings, _ := parseEncodings(r.Header.Get(acceptEncoding))
 	return acceptedEncodings["gzip"] > 0.0
 }

 // returns true if we've been configured to compress the specific content type.
 func handleContentType(contentTypes []string, w http.ResponseWriter) bool {
 	// If contentTypes is empty we handle all content types.
 	if len(contentTypes) == 0 {
 		return true
 	}

 	ct := strings.ToLower(w.Header().Get(contentType))
 	for _, c := range contentTypes {
 		if c == ct {
 			return true
 		}
 	}

 	return false
 }

 // parseEncodings attempts to parse a list of codings, per RFC 2616, as might
 // appear in an Accept-Encoding header. It returns a map of content-codings to
 // quality values, and an error containing the errors encountered. It's probably
 // safe to ignore those, because silently ignoring errors is how the internet
 // works.
 //
 // See: http://tools.ietf.org/html/rfc2616#section-14.3.
 func parseEncodings(s string) (codings, error) {
 	c := make(codings)
 	var e []string

 	for _, ss := range strings.Split(s, ",") {
 		coding, qvalue, err := parseCoding(ss)

 		if err != nil {
 			e = append(e, err.Error())
 		} else {
 			c[coding] = qvalue
 		}
 	}

 	// TODO (adammck): Use a proper multi-error struct, so the individual errors
 	//                 can be extracted if anyone cares.
 	if len(e) > 0 {
 		return c, fmt.Errorf("errors while parsing encodings: %s", strings.Join(e, ", "))
 	}

 	return c, nil
 }

 // parseCoding parses a single conding (content-coding with an optional qvalue),
 // as might appear in an Accept-Encoding header. It attempts to forgive minor
 // formatting errors.
 func parseCoding(s string) (coding string, qvalue float64, err error) {
 	for n, part := range strings.Split(s, ";") {
 		part = strings.TrimSpace(part)
 		qvalue = DefaultQValue

 		if n == 0 {
 			coding = strings.ToLower(part)
 		} else if strings.HasPrefix(part, "q=") {
 			qvalue, err = strconv.ParseFloat(strings.TrimPrefix(part, "q="), 64)

 			if qvalue < 0.0 {
 				qvalue = 0.0
 			} else if qvalue > 1.0 {
 				qvalue = 1.0
 			}
 		}
 	}

 	if coding == "" {
 		err = fmt.Errorf("empty content-coding")
 	}

 	return
 }
	package gziphandler

	import (
	"bufio"
	"compress/gzip"
	"fmt"
	"io"
	"net"
	"net/http"
	"strconv"
	"strings"
	"sync"
	)

	const (
	vary = "Vary"
	acceptEncoding = "Accept-Encoding"
	contentEncoding = "Content-Encoding"
	contentType = "Content-Type"
	contentLength = "Content-Length"
	)

	type codings map[string]float64

	const (
	// DefaultQValue is the default qvalue to assign to an encoding if no explicit qvalue is set.
	// This is actually kind of ambiguous in RFC 2616, so hopefully it's correct.
	// The examples seem to indicate that it is.
	DefaultQValue = 1.0

	// 1500 bytes is the MTU size for the internet since that is the largest size allowed at the network layer.
	// If you take a file that is 1300 bytes and compress it to 800 bytes, it’s still transmitted in that same 1500 byte packet regardless, so you’ve gained nothing.
	// That being the case, you should restrict the gzip compression to files with a size greater than a single packet, 1400 bytes (1.4KB) is a safe value.
	DefaultMinSize = 1400
	)

	// gzipWriterPools stores a sync.Pool for each compression level for reuse of
	// gzip.Writers. Use poolIndex to covert a compression level to an index into
	// gzipWriterPools.
	var gzipWriterPools [gzip.BestCompression - gzip.BestSpeed + 2]*sync.Pool

	func init() {
	for i := gzip.BestSpeed; i <= gzip.BestCompression; i++ {
	addLevelPool(i)
	}
	addLevelPool(gzip.DefaultCompression)
	}

	// poolIndex maps a compression level to its index into gzipWriterPools. It
	// assumes that level is a valid gzip compression level.
	func poolIndex(level int) int {
	// gzip.DefaultCompression == -1, so we need to treat it special.
	if level == gzip.DefaultCompression {
	return gzip.BestCompression - gzip.BestSpeed + 1
	}
	return level - gzip.BestSpeed
	}

	func addLevelPool(level int) {
	gzipWriterPools[poolIndex(level)] = &sync.Pool{
	New: func() interface{} {
	// NewWriterLevel only returns error on a bad level, we are guaranteeing
	// that this will be a valid level so it is okay to ignore the returned
	// error.
	w, _ := gzip.NewWriterLevel(nil, level)
	return w
	},
	}
	}

	// GzipResponseWriter provides an http.ResponseWriter interface, which gzips
	// bytes before writing them to the underlying response. This doesn't close the
	// writers, so don't forget to do that.
	// It can be configured to skip response smaller than minSize.
	type GzipResponseWriter struct {
	http.ResponseWriter
	index int // Index for gzipWriterPools.
	gw *gzip.Writer

	code int // Saves the WriteHeader value.

	minSize int // Specifed 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.

	contentTypes []string // Only compress if the response is one of these content-types. All are accepted if empty.
	}

	type GzipResponseWriterWithCloseNotify struct {
	*GzipResponseWriter
	}

	func (w GzipResponseWriterWithCloseNotify) CloseNotify() <-chan bool {
	return w.ResponseWriter.(http.CloseNotifier).CloseNotify()
	}

	// Write appends data to the gzip writer.
	func (w *GzipResponseWriter) Write(b []byte) (int, error) {
	// If content type is not set.
	if _, ok := w.Header()[contentType]; !ok {
	// It infer it from the uncompressed body.
	w.Header().Set(contentType, http.DetectContentType(b))
	}

	// GZIP responseWriter is initialized. Use the GZIP responseWriter.
	if w.gw != nil {
	n, err := w.gw.Write(b)
	return n, err
	}

	// Save the write into a buffer for later use in GZIP responseWriter (if content is long enough) or at close with regular responseWriter.
	// On the first write, w.buf changes from nil to a valid slice
	w.buf = append(w.buf, b...)

	// If the global writes are bigger than the minSize and we're about to write
	// a response containing a content type we want to handle, enable
	// compression.
	if len(w.buf) >= w.minSize && handleContentType(w.contentTypes, w) && w.Header().Get(contentEncoding) == "" {
	err := w.startGzip()
	if err != nil {
	return 0, err
	}
	}

	return len(b), nil
	}

	// startGzip initialize any GZIP specific informations.
	func (w *GzipResponseWriter) startGzip() error {

	// Set the GZIP header.
	w.Header().Set(contentEncoding, "gzip")

	// if the Content-Length is already set, then calls to Write on gzip
	// will fail to set the Content-Length header since its already set
	// See: https://github.com/golang/go/issues/14975.
	w.Header().Del(contentLength)

	// Write the header to gzip response.
	if w.code != 0 {
	w.ResponseWriter.WriteHeader(w.code)
	}

	// Initialize the GZIP response.
	w.init()

	// Flush the buffer into the gzip response.
	n, err := w.gw.Write(w.buf)

	// This should never happen (per io.Writer docs), but if the write didn't
	// accept the entire buffer but returned no specific error, we have no clue
	// what's going on, so abort just to be safe.
	if err == nil && n < len(w.buf) {
	return io.ErrShortWrite
	}

	w.buf = nil
	return err
	}

	// WriteHeader just saves the response code until close or GZIP effective writes.
	func (w *GzipResponseWriter) WriteHeader(code int) {
	if w.code == 0 {
	w.code = code
	}
	}

	// init graps a new gzip writer from the gzipWriterPool and writes the correct
	// content encoding header.
	func (w *GzipResponseWriter) init() {
	// Bytes written during ServeHTTP are redirected to this gzip writer
	// before being written to the underlying response.
	gzw := gzipWriterPools[w.index].Get().(*gzip.Writer)
	gzw.Reset(w.ResponseWriter)
	w.gw = gzw
	}

	// Close will close the gzip.Writer and will put it back in the gzipWriterPool.
	func (w *GzipResponseWriter) Close() error {
	if w.gw == nil {
	// Gzip not trigged yet, write out regular response.
	if w.code != 0 {
	w.ResponseWriter.WriteHeader(w.code)
	}
	if w.buf != nil {
	_, writeErr := w.ResponseWriter.Write(w.buf)
	// Returns the error if any at write.
	if writeErr != nil {
	return fmt.Errorf("gziphandler: write to regular responseWriter at close gets error: %q", writeErr.Error())
	}
	}
	return nil
	}

	err := w.gw.Close()
	gzipWriterPools[w.index].Put(w.gw)
	w.gw = nil
	return err
	}

	// Flush flushes the underlying *gzip.Writer and then the underlying
	// http.ResponseWriter if it is an http.Flusher. This makes GzipResponseWriter
	// an http.Flusher.
	func (w *GzipResponseWriter) Flush() {
	if w.gw == nil {
	// Only flush once startGzip has been called.
	//
	// Flush is thus a no-op until the written body
	// exceeds minSize.
	return
	}

	w.gw.Flush()

	if fw, ok := w.ResponseWriter.(http.Flusher); ok {
	fw.Flush()
	}
	}

	// Hijack implements http.Hijacker. If the underlying ResponseWriter is a
	// Hijacker, its Hijack method is returned. Otherwise an error is returned.
	func (w GzipResponseWriter) Hijack() (net.Conn, bufio.ReadWriter, error) {
	if hj, ok := w.ResponseWriter.(http.Hijacker); ok {
	return hj.Hijack()
	}
	return nil, nil, fmt.Errorf("http.Hijacker interface is not supported")
	}

	// verify Hijacker interface implementation
	var _ http.Hijacker = &GzipResponseWriter{}

	// MustNewGzipLevelHandler behaves just like NewGzipLevelHandler except that in
	// an error case it panics rather than returning an error.
	func MustNewGzipLevelHandler(level int) func(http.Handler) http.Handler {
	wrap, err := NewGzipLevelHandler(level)
	if err != nil {
	panic(err)
	}
	return wrap
	}

	// NewGzipLevelHandler returns a wrapper function (often known as middleware)
	// which can be used to wrap an HTTP handler to transparently gzip the response
	// body if the client supports it (via the Accept-Encoding header). Responses will
	// be encoded at the given gzip compression level. An error will be returned only
	// if an invalid gzip compression level is given, so if one can ensure the level
	// is valid, the returned error can be safely ignored.
	func NewGzipLevelHandler(level int) (func(http.Handler) http.Handler, error) {
	return NewGzipLevelAndMinSize(level, DefaultMinSize)
	}

	// NewGzipLevelAndMinSize behave as NewGzipLevelHandler except it let the caller
	// specify the minimum size before compression.
	func NewGzipLevelAndMinSize(level, minSize int) (func(http.Handler) http.Handler, error) {
	return GzipHandlerWithOpts(CompressionLevel(level), MinSize(minSize))
	}

	func GzipHandlerWithOpts(opts ...option) (func(http.Handler) http.Handler, error) {
	c := &config{
	level: gzip.DefaultCompression,
	minSize: DefaultMinSize,
	}

	for _, o := range opts {
	o(c)
	}

	if err := c.validate(); err != nil {
	return nil, err
	}

	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,
	}
	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
	}

	// Used for functional configuration.
	type config struct {
	minSize int
	level int
	contentTypes []string
	}

	func (c *config) validate() error {
	if c.level != gzip.DefaultCompression && (c.level < gzip.BestSpeed \|\| c.level > gzip.BestCompression) {
	return fmt.Errorf("invalid compression level requested: %d", c.level)
	}

	if c.minSize < 0 {
	return fmt.Errorf("minimum size must be more than zero")
	}

	return nil
	}

	type option func(c *config)

	func MinSize(size int) option {
	return func(c *config) {
	c.minSize = size
	}
	}

	func CompressionLevel(level int) option {
	return func(c *config) {
	c.level = level
	}
	}

	func ContentTypes(types []string) option {
	return func(c *config) {
	c.contentTypes = []string{}
	for _, v := range types {
	c.contentTypes = append(c.contentTypes, strings.ToLower(v))
	}
	}
	}

	// GzipHandler wraps an HTTP handler, to transparently gzip the response body if
	// the client supports it (via the Accept-Encoding header). This will compress at
	// the default compression level.
	func GzipHandler(h http.Handler) http.Handler {
	wrapper, _ := NewGzipLevelHandler(gzip.DefaultCompression)
	return wrapper(h)
	}

	// acceptsGzip returns true if the given HTTP request indicates that it will
	// accept a gzipped response.
	func acceptsGzip(r *http.Request) bool {
	acceptedEncodings, _ := parseEncodings(r.Header.Get(acceptEncoding))
	return acceptedEncodings["gzip"] > 0.0
	}

	// returns true if we've been configured to compress the specific content type.
	func handleContentType(contentTypes []string, w http.ResponseWriter) bool {
	// If contentTypes is empty we handle all content types.
	if len(contentTypes) == 0 {
	return true
	}

	ct := strings.ToLower(w.Header().Get(contentType))
	for _, c := range contentTypes {
	if c == ct {
	return true
	}
	}

	return false
	}

	// parseEncodings attempts to parse a list of codings, per RFC 2616, as might
	// appear in an Accept-Encoding header. It returns a map of content-codings to
	// quality values, and an error containing the errors encountered. It's probably
	// safe to ignore those, because silently ignoring errors is how the internet
	// works.
	//
	// See: http://tools.ietf.org/html/rfc2616#section-14.3.
	func parseEncodings(s string) (codings, error) {
	c := make(codings)
	var e []string

	for _, ss := range strings.Split(s, ",") {
	coding, qvalue, err := parseCoding(ss)

	if err != nil {
	e = append(e, err.Error())
	} else {
	c[coding] = qvalue
	}
	}

	// TODO (adammck): Use a proper multi-error struct, so the individual errors
	// can be extracted if anyone cares.
	if len(e) > 0 {
	return c, fmt.Errorf("errors while parsing encodings: %s", strings.Join(e, ", "))
	}

	return c, nil
	}

	// parseCoding parses a single conding (content-coding with an optional qvalue),
	// as might appear in an Accept-Encoding header. It attempts to forgive minor
	// formatting errors.
	func parseCoding(s string) (coding string, qvalue float64, err error) {
	for n, part := range strings.Split(s, ";") {
	part = strings.TrimSpace(part)
	qvalue = DefaultQValue

	if n == 0 {
	coding = strings.ToLower(part)
	} else if strings.HasPrefix(part, "q=") {
	qvalue, err = strconv.ParseFloat(strings.TrimPrefix(part, "q="), 64)

	if qvalue < 0.0 {
	qvalue = 0.0
	} else if qvalue > 1.0 {
	qvalue = 1.0
	}
	}
	}

	if coding == "" {
	err = fmt.Errorf("empty content-coding")
	}

	return
	}