Add support for CAD DWG format.

Author: gabriel-vasile

internal/matchers/image.go

@@ -59,3 +59,35 @@ func Tiff(in []byte) bool {
 func Bpg(in []byte) bool {
 	return bytes.HasPrefix(in, []byte{0x42, 0x50, 0x47, 0xFB})
 }
+
+// Dwg matches a CAD drawing file.
+func Dwg(in []byte) bool {
+	if in[0] != 0x41 || in[1] != 0x43 || len(in) < 6 {
+		return false
+	}
+	dwgVersions := [][]byte{
+		{0x31, 0x2E, 0x34, 0x30},
+		{0x31, 0x2E, 0x35, 0x30},
+		{0x32, 0x2E, 0x31, 0x30},
+		{0x31, 0x30, 0x30, 0x32},
+		{0x31, 0x30, 0x30, 0x33},
+		{0x31, 0x30, 0x30, 0x34},
+		{0x31, 0x30, 0x30, 0x36},
+		{0x31, 0x30, 0x30, 0x39},
+		{0x31, 0x30, 0x31, 0x32},
+		{0x31, 0x30, 0x31, 0x34},
+		{0x31, 0x30, 0x31, 0x35},
+		{0x31, 0x30, 0x31, 0x38},
+		{0x31, 0x30, 0x32, 0x31},
+		{0x31, 0x30, 0x32, 0x34},
+		{0x31, 0x30, 0x33, 0x32},
+	}
+
+	for _, d := range dwgVersions {
+		if bytes.Equal(in[2:6], d) {
+			return true
+		}
+	}
+
+	return false
+}

mime_test.go

@@ -135,6 +135,8 @@ var files = map[string]*node{
 	"dbf.dbf": dbf,
 
 	"sqlite3.sqlite3": sqlite3,
+	"dwg.dwg":         dwg,
+	"dwg.1.dwg":       dwg,
 }
 
 func TestMatching(t *testing.T) {

supported_mimes.md

@@ -1,4 +1,4 @@
-## 104 Supported MIME types
+## 105 Supported MIME types
 This file is automatically generated when running tests. Do not edit manually.
 
 Extension | MIME type
@@ -107,3 +107,4 @@ Extension | MIME type
 **lit** | application/x-ms-reader
 **bpg** | image/bpg
 **sqlite** | application/x-sqlite3
+**dwg** | image/vnd.dwg

testdata/dwg.1.dwg

@@ -10,7 +10,7 @@ var root = newNode("application/octet-stream", "", matchers.True,
 	ar, tar, xar, bz2, fits, tiff, bmp, ico, mp3, flac, midi, ape, musePack, amr,
 	wav, aiff, au, mpeg, quickTime, mqv, mp4, webM, threeGP, threeG2, avi, flv,
 	mkv, asf, aMp4, m4a, txt, gzip, class, swf, crx, woff, woff2, wasm, shx, dbf,
-	dcm, rar, djvu, mobi, lit, bpg, sqlite3,
+	dcm, rar, djvu, mobi, lit, bpg, sqlite3, dwg,
 )
 
 // The list of nodes appended to the root node
@@ -118,4 +118,5 @@ var (
 	mobi      = newNode("application/x-mobipocket-ebook", "mobi", matchers.Mobi)
 	lit       = newNode("application/x-ms-reader", "lit", matchers.Lit)
 	sqlite3   = newNode("application/x-sqlite3", "sqlite", matchers.Sqlite)
+	dwg       = newNode("image/vnd.dwg", "dwg", matchers.Dwg)
 )