Sanitize file names taken from server metadata (closes #9)

A file title or album name decrypted from server data could name a path
outside the chosen directory (`../../.ssh/authorized_keys`). One module,
src/filename.ts, now makes such names safe for `quak get`/`get-thumb`
without `--out`, downloadFile/downloadThumbnail without outPath, and the
backup and metadata backup trees. Originals-cache extensions are limited to
letters and digits. A user-supplied path is still used as is. decryptFile
reads a missing or non-string title as "" and rejects metadata that is not
a JSON object.

Model: opus-5-5

test/cli/backup.test.ts

@@ -36,6 +36,7 @@ import {
     lstatSync,
     mkdirSync,
     mkdtempSync,
+    readdirSync,
     readFileSync,
     readlinkSync,
     rmSync,
@@ -107,6 +108,29 @@ class MockClient {
     }
 }
 
+// A server that names an album and a file so as to climb out of the backup
+// directory.
+class HostileClient extends MockClient {
+    override async collectionsSince(): Promise<CollectionsPage> {
+        const page = await super.collectionsSince();
+        return {
+            ...page,
+            collections: page.collections.length
+                ? [collection(3, "../escape")]
+                : [],
+        };
+    }
+    override async filesSince(args: {
+        collectionID: number;
+    }): Promise<FilesPage> {
+        const files =
+            args.collectionID === 3
+                ? [file(300, 3, "../../.ssh/authorized_keys")]
+                : [];
+        return { files, deleted: [], cursor: 1 };
+    }
+}
+
 // A content source that writes byte buffers of the expected length and can be
 // told to fail one fileID's original, to exercise per-file resilience.
 interface StubSource extends ContentSource {
@@ -136,9 +160,12 @@ const stubSource = (): StubSource => {
 
 let root: string;
 
-const openLibrary = (source: ContentSource): Promise<Library> =>
+const openLibrary = (
+    source: ContentSource,
+    client: MockClient = new MockClient(),
+): Promise<Library> =>
     Library.open({
-        client: new MockClient(),
+        client,
         cacheDirectory: join(root, "cache"),
         contentSource: source,
         refreshIntervalSeconds: 3600,
@@ -243,6 +270,30 @@ describe("lib.backup", () => {
         lib.close();
     });
 
+    it("keeps server-supplied album and file names inside the backup", async () => {
+        const lib = await openLibrary(stubSource(), new HostileClient());
+        const outDir = join(root, "backup");
+
+        const result = await lib.backup({ downloadDirectory: outDir });
+
+        expect(result.failed).toBe(0);
+        // The title has no usable extension, so the original is `.bin`.
+        expect(existsSync(join(outDir, "originals", "300.bin"))).toBe(true);
+        const link = join(
+            outDir,
+            "collections",
+            "__escape",
+            "__.._.ssh_authorized_keys",
+        );
+        expect(lstatSync(link).isSymbolicLink()).toBe(true);
+        expect(existsSync(join(outDir, "collections", "__escape.json"))).toBe(
+            true,
+        );
+        // Nothing landed beside or above the backup directory.
+        expect(readdirSync(root).sort()).toEqual(["backup", "cache"]);
+        lib.close();
+    });
+
     it("is an idempotent no-op when every original is already present", async () => {
         const source = stubSource();
         const lib = await openLibrary(source);

test/cli/metadata-backup.test.ts

@@ -165,14 +165,15 @@ const buildMetaMock = async (): Promise<MetaMockState> => {
         },
     };
 
-    // Collection 2: "Work" with no magic metadata
+    // Collection 2: "../Work" with no magic metadata. The server chose a name
+    // that tries to climb out of the backup directory.
     const ck2 = sodium.crypto_secretbox_keygen();
     const { ciphertext: encCK2, nonce: ck2N } = encryptSecretbox(
         ck2,
         masterKey,
     );
     const { ciphertext: encCN2, nonce: cn2N } = encryptSecretbox(
-        new TextEncoder().encode("Work"),
+        new TextEncoder().encode("../Work"),
         ck2,
     );
     const rawColl2 = {
@@ -496,7 +497,8 @@ describe("quak backup-metadata", () => {
         await runBackup(outDir);
 
         const collDirs = readdirSync(join(outDir, "collections"));
-        expect(collDirs.length).toBe(2);
+        // "../Work" is sanitized into one directory name.
+        expect(collDirs.sort()).toEqual(["10-Vacation", "20-__Work"]);
 
         // Find the Vacation collection dir (prefixed with ID)
         const vacDir = collDirs.find((d) => d.includes("Vacation"))!;

test/cli/output.test.ts

@@ -64,6 +64,24 @@ describe("CLI file output (issue #52)", () => {
         expect(thumbnailName(renamedFile)).toBe(`thumb_${RAW_TITLE}`);
     });
 
+    it("sanitizes the title when naming `quak get` downloads", () => {
+        // Without `--out`, the server-supplied title names the file, so it must
+        // not be able to point outside the working directory.
+        const hostile = {
+            ...renamedFile,
+            metadata: { ...renamedFile.metadata, title: "../../.bashrc" },
+        };
+        expect(originalName(hostile)).toBe("__.._.bashrc");
+        expect(thumbnailName(hostile)).toBe("thumb___.._.bashrc");
+
+        const untitled = {
+            ...renamedFile,
+            metadata: { ...renamedFile.metadata, title: "" },
+        };
+        expect(originalName(untitled)).toBe("file-100");
+        expect(thumbnailName(untitled)).toBe("thumb_file-100");
+    });
+
     it("does not use the editedName/editedTime projection", () => {
         const record = deriveRecords([], [renamedFile]).photos.get(100);
         // The projection prefers the edits and reports milliseconds; the CLI