Improve recovery from corrupted downloads

ts/AttachmentCrypto.ts

@@ -19,6 +19,7 @@ import {
   ValidatingPassThrough,
 } from '@signalapp/libsignal-client/dist/incremental_mac';
 import type { ChunkSizeChoice } from '@signalapp/libsignal-client/dist/incremental_mac';
+import { isAbsolute } from 'path';
 
 import * as log from './logging/log';
 import {
@@ -37,7 +38,7 @@ import { finalStream } from './util/finalStream';
 import { getIvAndDecipher } from './util/getIvAndDecipher';
 import { getMacAndUpdateHmac } from './util/getMacAndUpdateHmac';
 import { trimPadding } from './util/trimPadding';
-import { strictAssert } from './util/assert';
+import { assertDev, strictAssert } from './util/assert';
 import * as Errors from './types/errors';
 import { isNotNil } from './util/isNotNil';
 import { missingCaseError } from './util/missingCaseError';
@@ -733,11 +734,17 @@ export function getPlaintextHashForInMemoryAttachment(
  * Unlinks a file without throwing an error if it doesn't exist.
  * Throws an error if it fails to unlink for any other reason.
  */
-export async function safeUnlink(filePath: string): Promise<void> {
+export async function safeUnlink(absoluteFilePath: string): Promise<void> {
+  assertDev(
+    isAbsolute(absoluteFilePath),
+    'safeUnlink: a relative path was passed instead of an absolute one'
+  );
+
   try {
-    await unlink(filePath);
+    await unlink(absoluteFilePath);
   } catch (error) {
     // Ignore if file doesn't exist
+
     if (error.code !== 'ENOENT') {
       log.error('Failed to unlink', error);
       throw error;

ts/test-electron/util/ensureAttachmentIsReencryptable_test.ts

@@ -134,7 +134,9 @@ describe('utils/ensureAttachmentIsReencryptable', async () => {
 
     after(async () => {
       if (path) {
-        await safeUnlink(path);
+        await safeUnlink(
+          window.Signal.Migrations.getAbsoluteAttachmentPath(path)
+        );
       }
     });
 

ts/textsecure/downloadAttachment.ts

@@ -126,10 +126,12 @@ export async function downloadAttachment(
   let downloadResult: Awaited<ReturnType<typeof downloadToDisk>>;
 
   let { downloadPath } = attachment;
+  const absoluteDownloadPath = downloadPath
+    ? window.Signal.Migrations.getAbsoluteAttachmentPath(downloadPath)
+    : undefined;
   let downloadOffset = 0;
-  if (downloadPath) {
-    const absoluteDownloadPath =
-      window.Signal.Migrations.getAbsoluteDownloadsPath(downloadPath);
+
+  if (absoluteDownloadPath) {
     try {
       ({ size: downloadOffset } = await stat(absoluteDownloadPath));
     } catch (error) {
@@ -139,7 +141,7 @@ export async function downloadAttachment(
           Errors.toLogFormat(error)
         );
         try {
-          await safeUnlink(downloadPath);
+          await safeUnlink(absoluteDownloadPath);
         } catch {
           downloadPath = undefined;
         }
@@ -148,9 +150,9 @@ export async function downloadAttachment(
   }
 
   // Start over if we go over the size
-  if (downloadOffset >= size && downloadPath) {
+  if (downloadOffset >= size && absoluteDownloadPath) {
     log.warn('downloadAttachment: went over, retrying');
-    await safeUnlink(downloadPath);
+    await safeUnlink(absoluteDownloadPath);
     downloadOffset = 0;
   }