Support Media Message (#9)

pkg/util/dat2img/dat2img.go

@@ -0,0 +1,60 @@
+package dat2img
+
+// copy from: https://github.com/tujiaw/wechat_dat_to_image
+
+import (
+	"fmt"
+)
+
+type Format struct {
+	Header []byte
+	Ext    string
+}
+
+var (
+	JPG     = Format{Header: []byte{0xFF, 0xD8, 0xFF}, Ext: "jpg"}
+	PNG     = Format{Header: []byte{0x89, 0x50, 0x4E, 0x47}, Ext: "png"}
+	GIF     = Format{Header: []byte{0x47, 0x49, 0x46, 0x38}, Ext: "gif"}
+	TIFF    = Format{Header: []byte{0x49, 0x49, 0x2A, 0x00}, Ext: "tiff"}
+	BMP     = Format{Header: []byte{0x42, 0x4D}, Ext: "bmp"}
+	Formats = []Format{JPG, PNG, GIF, TIFF, BMP}
+)
+
+func Dat2Image(data []byte) ([]byte, string, error) {
+
+	if len(data) < 4 {
+		return nil, "", fmt.Errorf("data length is too short: %d", len(data))
+	}
+
+	findFormat := func(data []byte, header []byte) bool {
+		xorBit := data[0] ^ header[0]
+		for i := 0; i < len(header); i++ {
+			if data[i]^header[i] != xorBit {
+				return false
+			}
+		}
+		return true
+	}
+
+	var xorBit byte
+	var find bool
+	var ext string
+	for _, format := range Formats {
+		if find = findFormat(data, format.Header); find {
+			xorBit = data[0] ^ format.Header[0]
+			ext = format.Ext
+			break
+		}
+	}
+
+	if !find {
+		return nil, "", fmt.Errorf("unknown image type: %x %x", data[0], data[1])
+	}
+
+	out := make([]byte, len(data))
+	for i := range data {
+		out[i] = data[i] ^ xorBit
+	}
+
+	return out, ext, nil
+}