Bug 1902020 - Fix a math error in calculating binary blob content length when it divides evenly by chunk size. r=backup-reviewers,fchasen

Differential Revision: https://phabricator.services.mozilla.com/D213481

browser/components/backup/Archive.worker.mjs

@@ -100,6 +100,8 @@ class ArchiveWorker {
    *   The path on the file system where the compressed backup file is located.
    * @param {EncryptionArgs} [params.encryptionArgs=undefined]
    *   Optional EncryptionArgs, which will be used to encrypt this archive.
+   * @param {number} params.chunkSize
+   *   The size of the chunks to break the byte stream into for encoding.
    * @returns {Promise<undefined>}
    */
   async constructArchive({
@@ -108,6 +110,7 @@ class ArchiveWorker {
     backupMetadata,
     compressedBackupSnapshotPath,
     encryptionArgs,
+    chunkSize,
   }) {
     let encryptor = null;
     if (encryptionArgs) {
@@ -177,30 +180,30 @@ ${JSON.stringify(jsonBlock)}
 
     // To calculate the Content-Length of the base64 block, we start by
     // computing how many newlines we'll be adding...
-    let totalNewlines = Math.ceil(
-      totalBytesToRead / ArchiveUtils.ARCHIVE_CHUNK_MAX_BYTES_SIZE
-    );
+    let totalNewlines = Math.ceil(totalBytesToRead / chunkSize);
 
-    // Next, we determine how many full-sized chunks of
-    // ARCHIVE_CHUNK_MAX_BYTES_SIZE we'll be using, and multiply that by the
-    // number of base64 bytes that such a chunk will require.
+    // Next, we determine how many full-sized chunks of chunkSize we'll be
+    // using, and multiply that by the number of base64 bytes that such a chunk
+    // will require.
     let fullSizeChunks = totalNewlines - 1;
     let fullSizeChunkBase64Bytes = this.#computeChunkBase64Bytes(
-      ArchiveUtils.ARCHIVE_CHUNK_MAX_BYTES_SIZE,
+      chunkSize,
       !!encryptor
     );
     let totalBase64Bytes = fullSizeChunks * fullSizeChunkBase64Bytes;
 
-    // Finally, if there are any leftover bytes that are less than
-    // ARCHIVE_CHUNK_MAX_BYTES_SIZE, determine how many bytes those will
-    // require, and add it to our total.
-    let leftoverChunkBytes =
-      totalBytesToRead % ArchiveUtils.ARCHIVE_CHUNK_MAX_BYTES_SIZE;
+    // Finally, if there are any leftover bytes that are less than chunkSize,
+    // determine how many bytes those will require, and add it to our total.
+    let leftoverChunkBytes = totalBytesToRead % chunkSize;
     if (leftoverChunkBytes) {
       totalBase64Bytes += this.#computeChunkBase64Bytes(
         leftoverChunkBytes,
         !!encryptor
       );
+    } else {
+      // We divided perfectly by chunkSize, so add another
+      // fullSizeChunkBase64Bytes to the total.
+      totalBase64Bytes += fullSizeChunkBase64Bytes;
     }
 
     await IOUtils.writeUTF8(
@@ -220,10 +223,7 @@ Content-Length: ${totalBase64Bytes}
     // encryption will be done.
     let currentIndex = 0;
     while (currentIndex < totalBytesToRead) {
-      let bytesToRead = Math.min(
-        ArchiveUtils.ARCHIVE_CHUNK_MAX_BYTES_SIZE,
-        totalBytesToRead - currentIndex
-      );
+      let bytesToRead = Math.min(chunkSize, totalBytesToRead - currentIndex);
       if (bytesToRead <= 0) {
         throw new Error(
           "Failed to calculate the right number of bytes to read."
@@ -236,8 +236,7 @@ Content-Length: ${totalBase64Bytes}
       let bytesToWrite;
 
       if (encryptor) {
-        let isLastChunk =
-          bytesToRead < ArchiveUtils.ARCHIVE_CHUNK_MAX_BYTES_SIZE;
+        let isLastChunk = bytesToRead < chunkSize;
         bytesToWrite = await encryptor.encrypt(buffer, isLastChunk);
       } else {
         bytesToWrite = buffer;

browser/components/backup/BackupService.sys.mjs

@@ -1023,19 +1023,27 @@ export class BackupService extends EventTarget {
    * @param {object} backupMetadata
    *   The metadata for the backup, which is also stored in the backup manifest
    *   of the compressed backup snapshot.
+   * @param {object} options
+   *   Options to pass to the worker, mainly for testing.
+   * @param {object} [options.chunkSize=ArchiveUtils.ARCHIVE_CHUNK_MAX_BYTES_SIZE]
+   *   The chunk size to break the bytes into.
    */
   async createArchive(
     archivePath,
     templateURI,
     compressedBackupSnapshotPath,
     encState,
-    backupMetadata
+    backupMetadata,
+    options = {}
   ) {
     let worker = new lazy.BasePromiseWorker(
       "resource:///modules/backup/Archive.worker.mjs",
       { type: "module" }
     );
 
+    let chunkSize =
+      options.chunkSize || lazy.ArchiveUtils.ARCHIVE_CHUNK_MAX_BYTES_SIZE;
+
     try {
       let encryptionArgs = encState
         ? {
@@ -1054,6 +1062,7 @@ export class BackupService extends EventTarget {
           backupMetadata,
           compressedBackupSnapshotPath,
           encryptionArgs,
+          chunkSize,
         },
       ]);
     } finally {

browser/components/backup/tests/xpcshell/test_BackupService_archive.js

@@ -164,3 +164,67 @@ add_task(async function test_createArchive_encrypted() {
   await IOUtils.remove(FAKE_ARCHIVE_PATH);
   await IOUtils.remove(EXTRACTION_PATH);
 });
+
+/**
+ * Tests that an archive can be created where the bytes of the archive are
+ * a multiple of 6, but the individual chunks of those bytes are not a multiple
+ * of 6 (which will necessitate base64 padding).
+ */
+add_task(async function test_createArchive_multiple_of_six_test() {
+  let bs = new BackupService();
+
+  const FAKE_ARCHIVE_PATH = PathUtils.join(
+    testProfilePath,
+    "fake-unencrypted-archive.html"
+  );
+  const FAKE_COMPRESSED_FILE = PathUtils.join(
+    testProfilePath,
+    "fake-compressed-staging.zip"
+  );
+
+  // Instead of generating a gigantic chunk of data to test this particular
+  // case, we'll override the default chunk size. We'll choose a chunk size of
+  // 500 bytes, which doesn't divide evenly by 6 - but we'll encode a set of
+  // 6 * 500 bytes, which will naturally divide evenly by 6.
+  const NOT_MULTIPLE_OF_SIX_OVERRIDE_CHUNK_SIZE = 500;
+  const MULTIPLE_OF_SIX_SIZE_IN_BYTES = 6 * 500;
+  let multipleOfSixBytes = new Uint8Array(MULTIPLE_OF_SIX_SIZE_IN_BYTES);
+
+  // seededRandomNumberGenerator is defined in head.js, but eslint doesn't seem
+  // happy about it. Maybe that's because it's a generator function.
+  // eslint-disable-next-line no-undef
+  let gen = seededRandomNumberGenerator();
+  for (let i = 0; i < MULTIPLE_OF_SIX_SIZE_IN_BYTES; ++i) {
+    multipleOfSixBytes.set(gen.next().value, i);
+  }
+
+  await IOUtils.write(FAKE_COMPRESSED_FILE, multipleOfSixBytes);
+
+  await bs.createArchive(
+    FAKE_ARCHIVE_PATH,
+    archiveTemplateURI,
+    FAKE_COMPRESSED_FILE,
+    null /* no ArchiveEncryptionState */,
+    FAKE_METADATA,
+    {
+      chunkSize: NOT_MULTIPLE_OF_SIX_OVERRIDE_CHUNK_SIZE,
+    }
+  );
+
+  const EXTRACTION_PATH = PathUtils.join(testProfilePath, "extraction.bin");
+  await bs.extractCompressedSnapshotFromArchive(
+    FAKE_ARCHIVE_PATH,
+    EXTRACTION_PATH
+  );
+
+  let writtenBytes = await IOUtils.read(EXTRACTION_PATH);
+  assertUint8ArraysSimilarity(
+    writtenBytes,
+    multipleOfSixBytes,
+    true /* expectSimilar */
+  );
+
+  await IOUtils.remove(FAKE_COMPRESSED_FILE);
+  await IOUtils.remove(FAKE_ARCHIVE_PATH);
+  await IOUtils.remove(EXTRACTION_PATH);
+});