feat: expose exif buffers

lib/decoder.js

@@ -657,6 +657,16 @@ var JpegImage = (function jpegImage() {
               }
             }
             // TODO APP1 - Exif
+            if (fileMarker === 0xFFE1) {
+              if (appData[0] === 0x45 &&
+                appData[1] === 0x78 &&
+                appData[2] === 0x69 &&
+                appData[3] === 0x66 &&
+                appData[4] === 0) { // 'EXIF\x00'
+                this.exifBuffer = appData.subarray(5, appData.length);
+              }
+            }
+
             if (fileMarker === 0xFFEE) {
               if (appData[0] === 0x41 && appData[1] === 0x64 && appData[2] === 0x6F &&
                 appData[3] === 0x62 && appData[4] === 0x65 && appData[5] === 0) { // 'Adobe\x00'
@@ -1050,6 +1060,7 @@ function decode(jpegData, opts) {
     var image = {
       width: decoder.width,
       height: decoder.height,
+      exifBuffer: decoder.exifBuffer,
       data: opts.useTArray ?
         new Uint8Array(bytesNeeded) :
         new Buffer(bytesNeeded)

lib/encoder.js

@@ -438,7 +438,33 @@ function JPEGEncoder(quality) {
 			writeByte(0); // thumbnwidth
 			writeByte(0); // thumbnheight
 		}
-
+
+		function writeAPP1(exifBuffer) {
+			if (!exifBuffer) return;
+
+			writeWord(0xFFE1); // APP1 marker
+
+			if (exifBuffer[0] === 0x45 &&
+					exifBuffer[1] === 0x78 &&
+					exifBuffer[2] === 0x69 &&
+					exifBuffer[3] === 0x66) {
+				// Buffer already starts with EXIF, just use it directly
+				writeWord(exifBuffer.length + 2); // length is buffer + length itself!
+			} else {
+				// Buffer doesn't start with EXIF, write it for them
+				writeWord(exifBuffer.length + 5 + 2); // length is buffer + EXIF\0 + length itself!
+				writeByte(0x45); // E
+				writeByte(0x78); // X
+				writeByte(0x69); // I
+				writeByte(0x66); // F
+				writeByte(0); // = "EXIF",'\0'
+			}
+
+			for (var i = 0; i < exifBuffer.length; i++) {
+				writeByte(exifBuffer[i]);
+			}
+		}
+
 		function writeSOF0(width, height)
 		{
 			writeWord(0xFFC0); // marker
@@ -599,6 +625,7 @@ function JPEGEncoder(quality) {
 			// Add JPEG headers
 			writeWord(0xFFD8); // SOI
 			writeAPP0();
+			writeAPP1(image.exifBuffer);
 			writeDQT();
 			writeSOF0(image.width,image.height);
 			writeDHT();

test/index.js

@@ -243,3 +243,13 @@ it('should be able to decode a JPEG into RGB', function(t) {
   t.assert(rawImageData.data instanceof Uint8Array, 'data is a typed array');
   t.end();
 });
+
+it('should be able to encode/decode image with exif data', function(t) {
+  var jpegData = fixture('grumpycat.jpg');
+  var imageData = jpeg.decode(new Uint8Array(jpegData));
+  t.assert(imageData.exifBuffer, 'decodes an exif buffer');
+  var encodedData = jpeg.encode(imageData);
+  var loopImageData = jpeg.decode(new Uint8Array(encodedData.data));
+  t.bufferEqual(loopImageData.exifBuffer, imageData.exifBuffer);
+  t.end();
+});