1 files changed, 214 insertions, 0 deletions
diff --git a/src/net/http/sniff.go b/src/net/http/sniff.go
new file mode 100644
index 000000000..68f519b05
--- /dev/null
+++ b/src/net/http/sniff.go
@@ -0,0 +1,214 @@
+// 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 (
+	"bytes"
+	"encoding/binary"
+)
+
+// The algorithm uses at most sniffLen bytes to make its decision.
+const sniffLen = 512
+
+// DetectContentType implements the algorithm described
+// at http://mimesniff.spec.whatwg.org/ to determine the
+// Content-Type of the given data.  It considers at most the
+// first 512 bytes of data.  DetectContentType always returns
+// a valid MIME type: if it cannot determine a more specific one, it
+// returns "application/octet-stream".
+func DetectContentType(data []byte) string {
+	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\r "), 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("<!DOCTYPE HTML"),
+	htmlSig("<HTML"),
+	htmlSig("<HEAD"),
+	htmlSig("<SCRIPT"),
+	htmlSig("<IFRAME"),
+	htmlSig("<H1"),
+	htmlSig("<DIV"),
+	htmlSig("<FONT"),
+	htmlSig("<TABLE"),
+	htmlSig("<A"),
+	htmlSig("<STYLE"),
+	htmlSig("<TITLE"),
+	htmlSig("<B"),
+	htmlSig("<BODY"),
+	htmlSig("<BR"),
+	htmlSig("<P"),
+	htmlSig("<!--"),
+
+	&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): Re-enable this when the spec is sorted w.r.t. MP4.
+	//mp4Sig(0),
+
+	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"
+}
+
+type mp4Sig int
+
+func (mp4Sig) match(data []byte, firstNonWS int) string {
+	// c.f. section 6.1.
+	if len(data) < 8 {
+		return ""
+	}
+	boxSize := int(binary.BigEndian.Uint32(data[:4]))
+	if boxSize%4 != 0 || len(data) < boxSize {
+		return ""
+	}
+	if !bytes.Equal(data[4:8], []byte("ftyp")) {
+		return ""
+	}
+	for st := 8; st < boxSize; st += 4 {
+		if st == 12 {
+			// minor version number
+			continue
+		}
+		seg := string(data[st : st+3])
+		switch seg {
+		case "mp4", "iso", "M4V", "M4P", "M4B":
+			return "video/mp4"
+			/* The remainder are not in the spec.
+			case "M4A":
+				return "audio/mp4"
+			case "3gp":
+				return "video/3gpp"
+			case "jp2":
+				return "image/jp2" // JPEG 2000
+			*/
+		}
+	}
+	return ""
+}
+
+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"
+}