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http: sniffing algorithm.
This follows draft-ietf-websec-mime-sniff-03 in its intent, though not its algorithmic specification. R=rsc CC=golang-dev https://golang.org/cl/4746042
This commit is contained in:
David Symonds
parent
7911965fe9
commit
78c89d21bc
@ -359,10 +359,7 @@ func (w *response) sniff() {
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w.needSniff = false
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data := w.conn.body
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ctype := detectContentType(data)
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if ctype != "" {
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fmt.Fprintf(w.conn.buf, "Content-Type: %s\r\n", ctype)
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}
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fmt.Fprintf(w.conn.buf, "Content-Type: %s\r\n", DetectContentType(data))
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io.WriteString(w.conn.buf, "\r\n")
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if w.chunking && len(data) > 0 {
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@ -4,15 +4,173 @@
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package http
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import (
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"bytes"
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)
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// Content-type sniffing algorithm.
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// http://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03
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// References in this file refer to this draft specification:
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// http://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03
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// The algorithm prefers to use sniffLen bytes to make its decision.
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const sniffLen = 1024
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const sniffLen = 512
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// detectContentType returns the sniffed Content-Type string
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// for the given data.
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func detectContentType(data []byte) string {
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// TODO(dsymonds,rsc): Implement algorithm from draft.
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// DetectContentType returns the sniffed Content-Type string
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// for the given data. This function always returns a valid MIME type.
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func DetectContentType(data []byte) string {
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if len(data) > sniffLen {
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data = data[:sniffLen]
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}
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// Index of the first non-whitespace byte in data.
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firstNonWS := 0
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for ; firstNonWS < len(data) && isWS(data[firstNonWS]); firstNonWS++ {
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}
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for _, sig := range sniffSignatures {
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if ct := sig.match(data, firstNonWS); ct != "" {
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return ct
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}
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}
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return "application/octet-stream" // fallback
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}
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func isWS(b byte) bool {
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return bytes.IndexByte([]byte("\t\n\x0C\n "), b) != -1
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}
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type sniffSig interface {
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// match returns the MIME type of the data, or "" if unknown.
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match(data []byte, firstNonWS int) string
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}
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// Data matching the table in section 6.
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var sniffSignatures = []sniffSig{
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htmlSig([]byte("<!DOCTYPE HTML")),
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htmlSig([]byte("<HTML")),
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htmlSig([]byte("<HEAD")),
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htmlSig([]byte("<SCRIPT")),
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htmlSig([]byte("<IFRAME")),
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htmlSig([]byte("<H1")),
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htmlSig([]byte("<DIV")),
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htmlSig([]byte("<FONT")),
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htmlSig([]byte("<TABLE")),
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htmlSig([]byte("<A")),
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htmlSig([]byte("<STYLE")),
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htmlSig([]byte("<TITLE")),
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htmlSig([]byte("<B")),
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htmlSig([]byte("<BODY")),
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htmlSig([]byte("<BR")),
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htmlSig([]byte("<P")),
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htmlSig([]byte("<!--")),
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&maskedSig{mask: []byte("\xFF\xFF\xFF\xFF\xFF"), pat: []byte("<?xml"), skipWS: true, ct: "text/xml; charset=utf-8"},
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&exactSig{[]byte("%PDF-"), "application/pdf"},
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&exactSig{[]byte("%!PS-Adobe-"), "application/postscript"},
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// UTF BOMs.
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&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFE\xFF\x00\x00"), ct: "text/plain; charset=utf-16be"},
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&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFF\xFE\x00\x00"), ct: "text/plain; charset=utf-16le"},
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&maskedSig{mask: []byte("\xFF\xFF\xFF\x00"), pat: []byte("\xEF\xBB\xBF\x00"), ct: "text/plain; charset=utf-8"},
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&exactSig{[]byte("GIF87a"), "image/gif"},
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&exactSig{[]byte("GIF89a"), "image/gif"},
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&exactSig{[]byte("\x89\x50\x4E\x47\x0D\x0A\x1A\x0A"), "image/png"},
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&exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"},
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&exactSig{[]byte("BM"), "image/bmp"},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"),
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pat: []byte("RIFF\x00\x00\x00\x00WEBPVP"),
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ct: "image/webp",
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},
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&exactSig{[]byte("\x00\x00\x01\x00"), "image/vnd.microsoft.icon"},
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&exactSig{[]byte("\x4F\x67\x67\x53\x00"), "application/ogg"},
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&maskedSig{
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mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
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pat: []byte("RIFF\x00\x00\x00\x00WAVE"),
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ct: "audio/wave",
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},
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&exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"},
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&exactSig{[]byte("\x52\x61\x72\x20\x1A\x07\x00"), "application/x-rar-compressed"},
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&exactSig{[]byte("\x50\x4B\x03\x04"), "application/zip"},
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&exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"},
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// TODO(dsymonds): MP4.
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textSig(0), // should be last
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}
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type exactSig struct {
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sig []byte
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ct string
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}
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func (e *exactSig) match(data []byte, firstNonWS int) string {
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if bytes.HasPrefix(data, e.sig) {
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return e.ct
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}
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return ""
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}
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type maskedSig struct {
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mask, pat []byte
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skipWS bool
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ct string
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}
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func (m *maskedSig) match(data []byte, firstNonWS int) string {
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if m.skipWS {
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data = data[firstNonWS:]
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}
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if len(data) < len(m.mask) {
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return ""
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}
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for i, mask := range m.mask {
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db := data[i] & mask
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if db != m.pat[i] {
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return ""
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}
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}
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return m.ct
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}
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type htmlSig []byte
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func (h htmlSig) match(data []byte, firstNonWS int) string {
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data = data[firstNonWS:]
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if len(data) < len(h)+1 {
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return ""
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}
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for i, b := range h {
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db := data[i]
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if 'A' <= b && b <= 'Z' {
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db &= 0xDF
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}
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if b != db {
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return ""
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}
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}
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// Next byte must be space or right angle bracket.
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if db := data[len(h)]; db != ' ' && db != '>' {
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return ""
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}
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return "text/html; charset=utf-8"
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}
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type textSig int
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func (textSig) match(data []byte, firstNonWS int) string {
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// c.f. section 5, step 4.
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for _, b := range data[firstNonWS:] {
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switch {
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case 0x00 <= b && b <= 0x08,
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b == 0x0B,
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0x0E <= b && b <= 0x1A,
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0x1C <= b && b <= 0x1F:
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return ""
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}
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}
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return "text/plain; charset=utf-8"
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}
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40
src/pkg/http/sniff_test.go
Normal file
40
src/pkg/http/sniff_test.go
Normal file
@ -0,0 +1,40 @@
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package http
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import (
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"testing"
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)
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var sniffTests = []struct {
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desc string
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data []byte
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exp string
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}{
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// Some nonsense.
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{"Empty", []byte{}, "text/plain; charset=utf-8"},
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{"Binary", []byte{1, 2, 3}, "application/octet-stream"},
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{"HTML document #1", []byte(`<HtMl><bOdY>blah blah blah</body></html>`), "text/html; charset=utf-8"},
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{"HTML document #2", []byte(`<HTML></HTML>`), "text/html; charset=utf-8"},
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{"HTML document #3 (leading whitespace)", []byte(` <!DOCTYPE HTML>...`), "text/html; charset=utf-8"},
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{"Plain text", []byte(`This is not HTML. It has ☃ though.`), "text/plain; charset=utf-8"},
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{"XML", []byte("\n<?xml!"), "text/xml; charset=utf-8"},
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// Image types.
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{"GIF 87a", []byte(`GIF87a`), "image/gif"},
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{"GIF 89a", []byte(`GIF89a...`), "image/gif"},
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}
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func TestSniffing(t *testing.T) {
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for _, st := range sniffTests {
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got := DetectContentType(st.data)
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if got != st.exp {
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t.Errorf("%v: sniffed as %v, want %v", st.desc, got, st.exp)
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}
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}
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}
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