first commit

exif/exif.go

@@ -0,0 +1,55 @@
+package exif
+
+import "io"
+
+type (
+	writerSkipper struct {
+		io.Writer
+		bytesToSkip int
+	}
+)
+
+func NewWriterExif(w io.Writer, exif []byte) (io.Writer, error) {
+	writer := &writerSkipper{
+		Writer:      w,
+		bytesToSkip: 2,
+	}
+	soi := []byte{0xff, 0xd8}
+	if _, err := w.Write(soi); err != nil {
+		return nil, err
+	}
+
+	if exif != nil {
+		app1Marker := 0xe1
+		markerlen := 2 + len(exif)
+		marker := []byte{0xff, uint8(app1Marker), uint8(markerlen >> 8), uint8(markerlen & 0xff)}
+		if _, err := w.Write(marker); err != nil {
+			return nil, err
+		}
+
+		if _, err := w.Write(exif); err != nil {
+			return nil, err
+		}
+	}
+
+	return writer, nil
+}
+
+func (w *writerSkipper) Write(data []byte) (int, error) {
+	if w.bytesToSkip <= 0 {
+		return w.Writer.Write(data)
+	}
+
+	if dataLen := len(data); dataLen < w.bytesToSkip {
+		w.bytesToSkip -= dataLen
+		return dataLen, nil
+	}
+
+	if n, err := w.Writer.Write(data[w.bytesToSkip:]); err == nil {
+		n += w.bytesToSkip
+		w.bytesToSkip = 0
+		return n, nil
+	} else {
+		return n, err
+	}
+}