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http: sniffing algorithm.

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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 2011-07-21 08:38:35 +10:00
parent 7911965fe9
commit 78c89d21bc
3 changed files with 205 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/pkg/http/server.go
View File

@ -359,10 +359,7 @@ func (w *response) sniff() {
w.needSniff = false w.needSniff = false
data := w.conn.body data := w.conn.body
ctype := detectContentType(data) fmt.Fprintf(w.conn.buf, "Content-Type: %s\r\n", DetectContentType(data))
if ctype != "" {
fmt.Fprintf(w.conn.buf, "Content-Type: %s\r\n", ctype)
}
io.WriteString(w.conn.buf, "\r\n") io.WriteString(w.conn.buf, "\r\n")
if w.chunking && len(data) > 0 { if w.chunking && len(data) > 0 {

170
src/pkg/http/sniff.go
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@ -4,15 +4,173 @@
package http package http
import (
"bytes"
)
// Content-type sniffing algorithm. // Content-type sniffing algorithm.
// http://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03 // References in this file refer to this draft specification:
// http://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03
// The algorithm prefers to use sniffLen bytes to make its decision. // The algorithm prefers to use sniffLen bytes to make its decision.
const sniffLen = 1024 const sniffLen = 512
// detectContentType returns the sniffed Content-Type string // DetectContentType returns the sniffed Content-Type string
// for the given data. // for the given data. This function always returns a valid MIME type.
func detectContentType(data []byte) string { func DetectContentType(data []byte) string {
// TODO(dsymonds,rsc): Implement algorithm from draft. if len(data) > sniffLen {
data = data[:sniffLen]
}
// Index of the first non-whitespace byte in data.
firstNonWS := 0
for ; firstNonWS < len(data) && isWS(data[firstNonWS]); firstNonWS++ {
}
for _, sig := range sniffSignatures {
if ct := sig.match(data, firstNonWS); ct != "" {
return ct
}
}
return "application/octet-stream" // fallback
}
func isWS(b byte) bool {
return bytes.IndexByte([]byte("\t\n\x0C\n "), b) != -1
}
type sniffSig interface {
// match returns the MIME type of the data, or "" if unknown.
match(data []byte, firstNonWS int) string
}
// Data matching the table in section 6.
var sniffSignatures = []sniffSig{
htmlSig([]byte("<!DOCTYPE HTML")),
htmlSig([]byte("<HTML")),
htmlSig([]byte("<HEAD")),
htmlSig([]byte("<SCRIPT")),
htmlSig([]byte("<IFRAME")),
htmlSig([]byte("<H1")),
htmlSig([]byte("<DIV")),
htmlSig([]byte("<FONT")),
htmlSig([]byte("<TABLE")),
htmlSig([]byte("<A")),
htmlSig([]byte("<STYLE")),
htmlSig([]byte("<TITLE")),
htmlSig([]byte("<B")),
htmlSig([]byte("<BODY")),
htmlSig([]byte("<BR")),
htmlSig([]byte("<P")),
htmlSig([]byte("<!--")),
&maskedSig{mask: []byte("\xFF\xFF\xFF\xFF\xFF"), pat: []byte("<?xml"), skipWS: true, ct: "text/xml; charset=utf-8"},
&exactSig{[]byte("%PDF-"), "application/pdf"},
&exactSig{[]byte("%!PS-Adobe-"), "application/postscript"},
// UTF BOMs.
&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFE\xFF\x00\x00"), ct: "text/plain; charset=utf-16be"},
&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFF\xFE\x00\x00"), ct: "text/plain; charset=utf-16le"},
&maskedSig{mask: []byte("\xFF\xFF\xFF\x00"), pat: []byte("\xEF\xBB\xBF\x00"), ct: "text/plain; charset=utf-8"},
&exactSig{[]byte("GIF87a"), "image/gif"},
&exactSig{[]byte("GIF89a"), "image/gif"},
&exactSig{[]byte("\x89\x50\x4E\x47\x0D\x0A\x1A\x0A"), "image/png"},
&exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"},
&exactSig{[]byte("BM"), "image/bmp"},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"),
pat: []byte("RIFF\x00\x00\x00\x00WEBPVP"),
ct: "image/webp",
},
&exactSig{[]byte("\x00\x00\x01\x00"), "image/vnd.microsoft.icon"},
&exactSig{[]byte("\x4F\x67\x67\x53\x00"), "application/ogg"},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
pat: []byte("RIFF\x00\x00\x00\x00WAVE"),
ct: "audio/wave",
},
&exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"},
&exactSig{[]byte("\x52\x61\x72\x20\x1A\x07\x00"), "application/x-rar-compressed"},
&exactSig{[]byte("\x50\x4B\x03\x04"), "application/zip"},
&exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"},
// TODO(dsymonds): MP4.
textSig(0), // should be last
}
type exactSig struct {
sig []byte
ct string
}
func (e *exactSig) match(data []byte, firstNonWS int) string {
if bytes.HasPrefix(data, e.sig) {
return e.ct
}
return ""
}
type maskedSig struct {
mask, pat []byte
skipWS bool
ct string
}
func (m *maskedSig) match(data []byte, firstNonWS int) string {
if m.skipWS {
data = data[firstNonWS:]
}
if len(data) < len(m.mask) {
return ""
}
for i, mask := range m.mask {
db := data[i] & mask
if db != m.pat[i] {
return ""
}
}
return m.ct
}
type htmlSig []byte
func (h htmlSig) match(data []byte, firstNonWS int) string {
data = data[firstNonWS:]
if len(data) < len(h)+1 {
return ""
}
for i, b := range h {
db := data[i]
if 'A' <= b && b <= 'Z' {
db &= 0xDF
}
if b != db {
return ""
}
}
// Next byte must be space or right angle bracket.
if db := data[len(h)]; db != ' ' && db != '>' {
return ""
}
return "text/html; charset=utf-8" return "text/html; charset=utf-8"
} }
type textSig int
func (textSig) match(data []byte, firstNonWS int) string {
// c.f. section 5, step 4.
for _, b := range data[firstNonWS:] {
switch {
case 0x00 <= b && b <= 0x08,
b == 0x0B,
0x0E <= b && b <= 0x1A,
0x1C <= b && b <= 0x1F:
return ""
}
}
return "text/plain; charset=utf-8"
}

40
src/pkg/http/sniff_test.go Normal file
View File

@ -0,0 +1,40 @@
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package http
import (
"testing"
)
var sniffTests = []struct {
desc string
data []byte
exp string
}{
// Some nonsense.
{"Empty", []byte{}, "text/plain; charset=utf-8"},
{"Binary", []byte{1, 2, 3}, "application/octet-stream"},
{"HTML document #1", []byte(`<HtMl><bOdY>blah blah blah</body></html>`), "text/html; charset=utf-8"},
{"HTML document #2", []byte(`<HTML></HTML>`), "text/html; charset=utf-8"},
{"HTML document #3 (leading whitespace)", []byte(` <!DOCTYPE HTML>...`), "text/html; charset=utf-8"},
{"Plain text", []byte(`This is not HTML. It has ☃ though.`), "text/plain; charset=utf-8"},
{"XML", []byte("\n<?xml!"), "text/xml; charset=utf-8"},
// Image types.
{"GIF 87a", []byte(`GIF87a`), "image/gif"},
{"GIF 89a", []byte(`GIF89a...`), "image/gif"},
}
func TestSniffing(t *testing.T) {
for _, st := range sniffTests {
got := DetectContentType(st.data)
if got != st.exp {
t.Errorf("%v: sniffed as %v, want %v", st.desc, got, st.exp)
}
}
}