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|
package brotli
import (
"compress/gzip"
"io"
"net/http"
"strings"
)
// HTTPCompressor chooses a compression method (brotli, gzip, or none) based on
// the Accept-Encoding header, sets the Content-Encoding header, and returns a
// WriteCloser that implements that compression. The Close method must be called
// before the current HTTP handler returns.
func HTTPCompressor(w http.ResponseWriter, r *http.Request) io.WriteCloser {
if w.Header().Get("Vary") == "" {
w.Header().Set("Vary", "Accept-Encoding")
}
encoding := negotiateContentEncoding(r, []string{"br", "gzip"})
switch encoding {
case "br":
w.Header().Set("Content-Encoding", "br")
return NewWriterV2(w, DefaultCompression)
case "gzip":
w.Header().Set("Content-Encoding", "gzip")
return gzip.NewWriter(w)
}
return nopCloser{w}
}
// negotiateContentEncoding returns the best offered content encoding for the
// request's Accept-Encoding header. If two offers match with equal weight and
// then the offer earlier in the list is preferred. If no offers are
// acceptable, then "" is returned.
func negotiateContentEncoding(r *http.Request, offers []string) string {
bestOffer := "identity"
bestQ := -1.0
specs := parseAccept(r.Header, "Accept-Encoding")
for _, offer := range offers {
for _, spec := range specs {
if spec.Q > bestQ &&
(spec.Value == "*" || spec.Value == offer) {
bestQ = spec.Q
bestOffer = offer
}
}
}
if bestQ == 0 {
bestOffer = ""
}
return bestOffer
}
// acceptSpec describes an Accept* header.
type acceptSpec struct {
Value string
Q float64
}
// parseAccept parses Accept* headers.
func parseAccept(header http.Header, key string) (specs []acceptSpec) {
loop:
for _, s := range header[key] {
for {
var spec acceptSpec
spec.Value, s = expectTokenSlash(s)
if spec.Value == "" {
continue loop
}
spec.Q = 1.0
s = skipSpace(s)
if strings.HasPrefix(s, ";") {
s = skipSpace(s[1:])
if !strings.HasPrefix(s, "q=") {
continue loop
}
spec.Q, s = expectQuality(s[2:])
if spec.Q < 0.0 {
continue loop
}
}
specs = append(specs, spec)
s = skipSpace(s)
if !strings.HasPrefix(s, ",") {
continue loop
}
s = skipSpace(s[1:])
}
}
return
}
func skipSpace(s string) (rest string) {
i := 0
for ; i < len(s); i++ {
if octetTypes[s[i]]&isSpace == 0 {
break
}
}
return s[i:]
}
func expectTokenSlash(s string) (token, rest string) {
i := 0
for ; i < len(s); i++ {
b := s[i]
if (octetTypes[b]&isToken == 0) && b != '/' {
break
}
}
return s[:i], s[i:]
}
func expectQuality(s string) (q float64, rest string) {
switch {
case len(s) == 0:
return -1, ""
case s[0] == '0':
q = 0
case s[0] == '1':
q = 1
default:
return -1, ""
}
s = s[1:]
if !strings.HasPrefix(s, ".") {
return q, s
}
s = s[1:]
i := 0
n := 0
d := 1
for ; i < len(s); i++ {
b := s[i]
if b < '0' || b > '9' {
break
}
n = n*10 + int(b) - '0'
d *= 10
}
return q + float64(n)/float64(d), s[i:]
}
// Octet types from RFC 2616.
var octetTypes [256]octetType
type octetType byte
const (
isToken octetType = 1 << iota
isSpace
)
func init() {
// OCTET = <any 8-bit sequence of data>
// CHAR = <any US-ASCII character (octets 0 - 127)>
// CTL = <any US-ASCII control character (octets 0 - 31) and DEL (127)>
// CR = <US-ASCII CR, carriage return (13)>
// LF = <US-ASCII LF, linefeed (10)>
// SP = <US-ASCII SP, space (32)>
// HT = <US-ASCII HT, horizontal-tab (9)>
// <"> = <US-ASCII double-quote mark (34)>
// CRLF = CR LF
// LWS = [CRLF] 1*( SP | HT )
// TEXT = <any OCTET except CTLs, but including LWS>
// separators = "(" | ")" | "<" | ">" | "@" | "," | ";" | ":" | "\" | <">
// | "/" | "[" | "]" | "?" | "=" | "{" | "}" | SP | HT
// token = 1*<any CHAR except CTLs or separators>
// qdtext = <any TEXT except <">>
for c := 0; c < 256; c++ {
var t octetType
isCtl := c <= 31 || c == 127
isChar := 0 <= c && c <= 127
isSeparator := strings.ContainsRune(" \t\"(),/:;<=>?@[]\\{}", rune(c))
if strings.ContainsRune(" \t\r\n", rune(c)) {
t |= isSpace
}
if isChar && !isCtl && !isSeparator {
t |= isToken
}
octetTypes[c] = t
}
}
|
