feat: implement partial media downloads

src/Tests/test.media-download.ts

@@ -0,0 +1,64 @@
+import { MediaType, DownloadableMessage } from '../Types'
+import { downloadContentFromMessage } from '../Utils'
+import { proto } from '../../WAProto'
+import { readFileSync } from 'fs'
+
+type TestVector = {
+	type: MediaType
+	message: DownloadableMessage
+	plaintext: Buffer
+}
+
+const TEST_VECTORS: TestVector[] = [
+	{
+		type: 'image',
+		message: proto.ImageMessage.decode(
+			Buffer.from(
+				'Ck1odHRwczovL21tZy53aGF0c2FwcC5uZXQvZC9mL0FwaHR4WG9fWXZZcDZlUVNSa0tjOHE5d2ozVUpleWdoY3poM3ExX3I0ektnLmVuYxIKaW1hZ2UvanBlZyIgKTuVFyxDc6mTm4GXPlO3Z911Wd8RBeTrPLSWAEdqW8MomcUBQiB7wH5a4nXMKyLOT0A2nFgnnM/DUH8YjQf8QtkCIekaSkogTB+BXKCWDFrmNzozY0DCPn0L4VKd7yG1ZbZwbgRhzVc=',
+				'base64'
+			)
+		),
+		plaintext: readFileSync('./Media/cat.jpeg')
+	}
+]
+
+describe('Media Download Tests', () => {
+
+	it('should download a full encrypted media correctly', async() => {
+		for(const { type, message, plaintext } of TEST_VECTORS) {
+			const readPipe = await downloadContentFromMessage(message, type)
+			
+			let buffer = Buffer.alloc(0)
+			for await(const read of readPipe) {
+				buffer = Buffer.concat([ buffer, read ])
+			}
+
+			expect(buffer).toEqual(plaintext)
+		}
+	})
+
+	it('should download an encrypted media correctly piece', async() => {
+		for(const { type, message, plaintext } of TEST_VECTORS) {
+			// check all edge cases
+			const ranges = [
+				{ startByte: 51, endByte: plaintext.length-100 }, // random numbers
+				{ startByte: 1024, endByte: 2038 }, // larger random multiples of 16
+				{ startByte: 1, endByte: plaintext.length-1 } // borders
+			]
+			for(const range of ranges) {
+				const readPipe = await downloadContentFromMessage(message, type, range)
+			
+				let buffer = Buffer.alloc(0)
+				for await(const read of readPipe) {
+					buffer = Buffer.concat([ buffer, read ])
+				}
+
+				const hex = buffer.toString('hex')
+				const expectedHex = plaintext.slice(range.startByte || 0, range.endByte || undefined).toString('hex')
+				expect(hex).toBe(expectedHex)
+
+				console.log('success on ', range)
+			}
+		}
+	})
+})