Add support for APNG

index.d.ts

@@ -5,6 +5,7 @@ declare namespace fileType {
 	type FileType =
 		| 'jpg'
 		| 'png'
+		| 'apng'
 		| 'gif'
 		| 'webp'
 		| 'flif'

index.js

@@ -47,6 +47,24 @@ const fileType = input => {
 	}
 
 	if (check([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A])) {
+		// APNG format (https://wiki.mozilla.org/APNG_Specification)
+		// 1. Find the first IDAT (image data) chunk (49 44 41 54)
+		// 2. Check if there is an "acTL" chunk before the IDAT one (61 63 54 4C)
+
+		// Offset calculated as follows:
+		// - 8 bytes: PNG signature
+		// - 4 (length) + 4 (chunk type) + 13 (chunk data) + 4 (CRC): IHDR chunk
+		const startIndex = 33;
+		const firstImageDataChunkIndex = buffer.findIndex((el, i) => i >= startIndex && buffer[i] === 0x49 && buffer[i + 1] === 0x44 && buffer[i + 2] === 0x41 && buffer[i + 3] === 0x54);
+		const sliced = buffer.subarray(startIndex, firstImageDataChunkIndex);
+
+		if (sliced.findIndex((el, i) => sliced[i] === 0x61 && sliced[i + 1] === 0x63 && sliced[i + 2] === 0x54 && sliced[i + 3] === 0x4C) >= 0) {
+			return {
+				ext: 'apng',
+				mime: 'image/apng'
+			};
+		}
+
 		return {
 			ext: 'png',
 			mime: 'image/png'

package.json

@@ -42,6 +42,7 @@
 		"uint8array",
 		"jpg",
 		"png",
+		"apng",
 		"gif",
 		"webp",
 		"flif",

readme.md

@@ -124,6 +124,7 @@ Type: [`stream.Readable`](https://nodejs.org/api/stream.html#stream_class_stream
 
 - [`jpg`](https://en.wikipedia.org/wiki/JPEG)
 - [`png`](https://en.wikipedia.org/wiki/Portable_Network_Graphics)
+- [`apng`](https://en.wikipedia.org/wiki/APNG) - Animated Portable Network Graphics
 - [`gif`](https://en.wikipedia.org/wiki/GIF)
 - [`webp`](https://en.wikipedia.org/wiki/WebP)
 - [`flif`](https://en.wikipedia.org/wiki/Free_Lossless_Image_Format)

test.js

@@ -10,6 +10,7 @@ import fileType from '.';
 const types = [
 	'jpg',
 	'png',
+	'apng',
 	'gif',
 	'webp',
 	'flif',