Add BMP support to imageSize

image_size/bmp.go

@@ -0,0 +1,48 @@
+package imageSize
+
+import (
+	"bytes"
+	"encoding/binary"
+	"io"
+)
+
+var bmpMagick = []byte("BM")
+
+type BmpFormatError string
+
+func (e BmpFormatError) Error() string { return "invalid BMP format: " + string(e) }
+
+func DecodeBmpMeta(r io.Reader) (*Meta, error) {
+	var tmp [26]byte
+
+	if _, err := io.ReadFull(r, tmp[:]); err != nil {
+		return nil, err
+	}
+
+	if !bytes.Equal(tmp[:2], bmpMagick) {
+		return nil, BmpFormatError("malformed header")
+	}
+
+	infoSize := binary.LittleEndian.Uint32(tmp[14:18])
+
+	var width, height int
+
+	if infoSize >= 40 {
+		width = int(binary.LittleEndian.Uint32(tmp[18:22]))
+		height = int(binary.LittleEndian.Uint32(tmp[22:26]))
+	} else {
+		// CORE
+		width = int(binary.LittleEndian.Uint16(tmp[18:20]))
+		height = int(binary.LittleEndian.Uint16(tmp[20:22]))
+	}
+
+	return &Meta{
+		Format: "bmp",
+		Width:  width,
+		Height: height,
+	}, nil
+}
+
+func init() {
+	RegisterFormat(string(bmpMagick), DecodeBmpMeta)
+}