Make appendPadding infer file size

ts/AttachmentCrypto.ts

@@ -11,8 +11,8 @@ import {
   randomBytes,
 } from 'crypto';
 import type { Decipher, Hash, Hmac } from 'crypto';
-import type { TransformCallback } from 'stream';
 import { Transform } from 'stream';
+import type { Readable } from 'stream';
 import { pipeline } from 'stream/promises';
 import { ensureFile } from 'fs-extra';
 import * as log from './logging/log';
@@ -55,12 +55,10 @@ export type DecryptedAttachmentV2 = {
 export async function encryptAttachmentV2({
   keys,
   plaintextAbsolutePath,
-  size,
   dangerousTestOnlyIv,
 }: {
   keys: Readonly<Uint8Array>;
   plaintextAbsolutePath: string;
-  size: number;
   dangerousTestOnlyIv?: Readonly<Uint8Array>;
 }): Promise<EncryptedAttachmentV2> {
   const logId = 'encryptAttachmentV2';
@@ -98,7 +96,7 @@ export async function encryptAttachmentV2({
     await pipeline(
       readFd.createReadStream(),
       peekAndUpdateHash(plaintextHash),
-      appendPadding(size),
+      appendPadding(),
       createCipheriv(CipherType.AES256CBC, aesKey, iv),
       prependIv(iv),
       appendMac(macKey),
@@ -402,52 +400,57 @@ function* generatePadding(size: number) {
   }
 }
 
-/**
- * Appends zero-padding to the stream to a target bucket size.
- */
-function appendPadding(fileSize: number) {
-  const iterator = generatePadding(fileSize);
-  let bytesWritten = 0;
-  let finalCallback: TransformCallback;
-
 // Push as much padding as we can. If we reach the end
-  // of the padding, call the callback.
-  function pushPadding(transform: Transform) {
+// of the padding, return true.
+function pushPadding(
+  paddingIterator: Iterator<Uint8Array>,
+  readable: Readable
+): boolean {
   // eslint-disable-next-line no-constant-condition
   while (true) {
-      const result = iterator.next();
+    const result = paddingIterator.next();
     if (result.done) {
       break;
     }
-      const keepGoing = transform.push(result.value);
+    const keepGoing = readable.push(result.value);
     if (!keepGoing) {
-        return;
+      return false;
     }
   }
-    finalCallback();
+  return true;
 }
 
+/**
+ * Appends zero-padding to the stream to a target bucket size.
+ */
+function appendPadding() {
+  let onReadableDrained: undefined | (() => void);
+  let fileSize = 0;
+
   return new Transform({
     read(size) {
       // When in the process of pushing padding, we pause and wait for
       // read to be called again.
-      if (finalCallback != null) {
-        pushPadding(this);
+      if (onReadableDrained != null) {
+        onReadableDrained();
       }
       // Always call _read, even if we're done.
       Transform.prototype._read.call(this, size);
     },
     transform(chunk, _encoding, callback) {
-      bytesWritten += chunk.byteLength;
-      // Once we reach the end of the file, start pushing padding.
-      if (bytesWritten >= fileSize) {
-        this.push(chunk);
-        finalCallback = callback;
-        pushPadding(this);
-        return;
-      }
+      fileSize += chunk.byteLength;
       callback(null, chunk);
     },
+    flush(callback) {
+      const iterator = generatePadding(fileSize);
+
+      onReadableDrained = () => {
+        if (pushPadding(iterator, this)) {
+          callback();
+        }
+      };
+      onReadableDrained();
+    },
   });
 }
 

ts/test-electron/Crypto_test.ts

@@ -1,8 +1,6 @@
 // Copyright 2015 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-/* eslint-disable @typescript-eslint/no-non-null-assertion */
-
 import { assert } from 'chai';
 import { readFileSync, unlinkSync, writeFileSync } from 'fs';
 import { join } from 'path';
@@ -30,6 +28,7 @@ import {
   deriveMasterKeyFromGroupV1,
   encryptSymmetric,
   decryptSymmetric,
+  sha256,
   hmacSha256,
   verifyHmacSha256,
   randomInt,
@@ -609,7 +608,7 @@ describe('Crypto', () => {
   describe('attachments', () => {
     const FILE_PATH = join(__dirname, '../../fixtures/ghost-kitty.mp4');
     const FILE_CONTENTS = readFileSync(FILE_PATH);
-    let tempDir: string | undefined;
+    let tempDir: string;
 
     function generateAttachmentKeys(): Uint8Array {
       return randomBytes(KEY_SET_LENGTH);
@@ -643,7 +642,7 @@ describe('Crypto', () => {
 
     it('v1 -> v2 (memory -> disk)', async () => {
       const keys = generateAttachmentKeys();
-      const ciphertextPath = join(tempDir!, 'file');
+      const ciphertextPath = join(tempDir, 'file');
       let plaintextPath;
 
       try {
@@ -679,7 +678,7 @@ describe('Crypto', () => {
       }
     });
 
-    it('v2 roundtrips (all on disk)', async () => {
+    it('v2 roundtrips smaller file (all on disk)', async () => {
       const keys = generateAttachmentKeys();
       let plaintextPath;
       let ciphertextPath;
@@ -688,7 +687,6 @@ describe('Crypto', () => {
         const encryptedAttachment = await encryptAttachmentV2({
           keys,
           plaintextAbsolutePath: FILE_PATH,
-          size: FILE_CONTENTS.byteLength,
         });
         ciphertextPath = window.Signal.Migrations.getAbsoluteAttachmentPath(
           encryptedAttachment.path
@@ -720,6 +718,60 @@ describe('Crypto', () => {
       }
     });
 
+    it('v2 roundtrips random data (all on disk)', async () => {
+      const sourcePath = join(tempDir, 'random');
+      // Get sufficient large file to have more than 64kb of padding and
+      // trigger push back on the streams.
+      const data = getRandomBytes(5 * 1024 * 1024);
+      const digest = sha256(data);
+
+      writeFileSync(sourcePath, data);
+
+      const keys = generateAttachmentKeys();
+      let plaintextPath;
+      let ciphertextPath;
+
+      try {
+        const encryptedAttachment = await encryptAttachmentV2({
+          keys,
+          plaintextAbsolutePath: sourcePath,
+        });
+        ciphertextPath = window.Signal.Migrations.getAbsoluteAttachmentPath(
+          encryptedAttachment.path
+        );
+        const decryptedAttachment = await decryptAttachmentV2({
+          ciphertextPath,
+          id: 'test',
+          keys,
+          size: data.byteLength,
+          theirDigest: encryptedAttachment.digest,
+        });
+        plaintextPath = window.Signal.Migrations.getAbsoluteAttachmentPath(
+          decryptedAttachment.path
+        );
+        const plaintext = readFileSync(plaintextPath);
+        assert.isTrue(constantTimeEqual(data, plaintext));
+        assert.strictEqual(
+          encryptedAttachment.plaintextHash,
+          Bytes.toHex(digest)
+        );
+        assert.strictEqual(
+          decryptedAttachment.plaintextHash,
+          encryptedAttachment.plaintextHash
+        );
+      } finally {
+        if (sourcePath) {
+          unlinkSync(sourcePath);
+        }
+        if (plaintextPath) {
+          unlinkSync(plaintextPath);
+        }
+        if (ciphertextPath) {
+          unlinkSync(ciphertextPath);
+        }
+      }
+    });
+
     it('v2 -> v1 (disk -> memory)', async () => {
       const keys = generateAttachmentKeys();
       let ciphertextPath;
@@ -728,7 +780,6 @@ describe('Crypto', () => {
         const encryptedAttachment = await encryptAttachmentV2({
           keys,
           plaintextAbsolutePath: FILE_PATH,
-          size: FILE_CONTENTS.byteLength,
         });
         ciphertextPath = window.Signal.Migrations.getAbsoluteAttachmentPath(
           encryptedAttachment.path
@@ -782,7 +833,6 @@ describe('Crypto', () => {
         const encryptedAttachmentV2 = await encryptAttachmentV2({
           keys,
           plaintextAbsolutePath: FILE_PATH,
-          size: FILE_CONTENTS.byteLength,
           dangerousTestOnlyIv,
         });
         ciphertextPath = window.Signal.Migrations.getAbsoluteAttachmentPath(