net/http: implement sniffing for some fonts

Implement sniffing for fonts:
* MS Font object  --> "application/vnd.ms-fontobject"
* ttf		  --> "application/font-ttf"

* off		  --> "application/font-off"
* otf		  --> "application/font-off"

* cff		  --> "application/font-cff"
* woff		  --> "application/font-woff"

Fixes #20808

Change-Id: Ibe02a87d3c9d610c6a30e1b6c03f4e520404e70f
Reviewed-on: https://go-review.googlesource.com/47553
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/sniff.go

@@ -91,6 +91,7 @@ var sniffSignatures = []sniffSig{
 		ct:   "image/webp",
 	},
 	&exactSig{[]byte("\x00\x00\x01\x00"), "image/vnd.microsoft.icon"},
+
 	&maskedSig{
 		mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
 		pat:  []byte("RIFF\x00\x00\x00\x00WAVE"),
@@ -126,6 +127,20 @@ var sniffSignatures = []sniffSig{
 		pat:  []byte("RIFF\x00\x00\x00\x00AVI "),
 		ct:   "video/avi",
 	},
+
+	// Fonts
+	&maskedSig{
+		// 34 NULL bytes followed by the string "LP"
+		pat: []byte("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x4C\x50"),
+		// 34 NULL bytes followed by \xF\xF
+		mask: []byte("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xFF\xFF"),
+		ct:   "application/vnd.ms-fontobject",
+	},
+	&exactSig{[]byte("\x00\x01\x00\x00"), "application/font-ttf"},
+	&exactSig{[]byte("OTTO"), "application/font-off"},
+	&exactSig{[]byte("ttcf"), "application/font-cff"},
+	&exactSig{[]byte("wOFF"), "application/font-woff"},
+
 	&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"},

src/net/http/sniff_test.go

@@ -54,6 +54,17 @@ var sniffTests = []struct {
 	{"MP4 video", []byte("\x00\x00\x00\x18ftypmp42\x00\x00\x00\x00mp42isom<\x06t\xbfmdat"), "video/mp4"},
 	{"AVI video #1", []byte("RIFF,O\n\x00AVI LISTÀ"), "video/avi"},
 	{"AVI video #2", []byte("RIFF,\n\x00\x00AVI LISTÀ"), "video/avi"},
+
+	// Font types.
+	// {"MS.FontObject", []byte("\x00\x00")},
+	{"TTF sample  I", []byte("\x00\x01\x00\x00\x00\x17\x01\x00\x00\x04\x01\x60\x4f"), "application/font-ttf"},
+	{"TTF sample II", []byte("\x00\x01\x00\x00\x00\x0e\x00\x80\x00\x03\x00\x60\x46"), "application/font-ttf"},
+
+	{"OTTO sample  I", []byte("\x4f\x54\x54\x4f\x00\x0e\x00\x80\x00\x03\x00\x60\x42\x41\x53\x45"), "application/font-off"},
+
+	{"woff sample  I", []byte("\x77\x4f\x46\x46\x00\x01\x00\x00\x00\x00\x30\x54\x00\x0d\x00\x00"), "application/font-woff"},
+	// Woff2 is not yet recognized, change this test once mime-sniff working group adds woff2
+	{"woff2 not recognized", []byte("\x77\x4f\x46\x32\x00\x01\x00\x00\x00"), "application/octet-stream"},
 }
 
 func TestDetectContentType(t *testing.T) {