fix(artifacts): compare package signatures without ASCII folding (#2069)

src/application/BinaryTargetResolver.ts

@@ -299,7 +299,7 @@ const detectArtifactFormat = async (
   if (
     lower.endsWith(".pkg") &&
     observed.bytesRead >= 4 &&
-    magic.subarray(0, 4).toString("ascii") === "xar!"
+    magic.subarray(0, 4).equals(Buffer.from("xar!"))
   )
     return "pkg";
   if (lower.endsWith(".dmg")) {
@@ -310,7 +310,7 @@ const detectArtifactFormat = async (
       const trailer = Buffer.alloc(4);
       const read = await handle.read(trailer, 0, trailer.length, size - 512);
       throwIfTargetResolutionCancelled(signal);
-      if (read.bytesRead === 4 && trailer.toString("ascii") === "koly")
+      if (read.bytesRead === 4 && trailer.equals(Buffer.from("koly")))
         return "dmg";
     }
   }

src/artifacts/inventory/classify.ts

@@ -152,7 +152,7 @@ const classifyRootFormat = async (
   if (hasZipSignature(prefix)) return zipRootPackageFormat(lower);
   if (
     lower.endsWith(".pkg") &&
-    prefix.subarray(0, 4).toString("ascii") === "xar!"
+    prefix.subarray(0, 4).equals(Buffer.from("xar!"))
   )
     return "pkg";
   if (lower.endsWith(".dmg") && (await hasKolyTrailer(handle))) return "dmg";
@@ -172,5 +172,5 @@ const hasKolyTrailer = async (handle: FileHandle): Promise<boolean> => {
   if (size < 512) return false;
   const trailer = Buffer.alloc(4);
   const read = await handle.read(trailer, 0, trailer.length, size - 512);
-  return read.bytesRead === 4 && trailer.toString("ascii") === "koly";
+  return read.bytesRead === 4 && trailer.equals(Buffer.from("koly"));
 };

tests/boundary/filesystem/zipDetection.test.ts

@@ -199,3 +199,38 @@ describe("nested container family", () => {
     },
   );
 });
+
+describe("package signature byte identity", () => {
+  it.each([
+    { extension: "pkg", signature: "xar!", offset: 0, size: 4 },
+    { extension: "dmg", signature: "koly", offset: 0, size: 512 },
+  ])(
+    "rejects high-bit aliases of $extension magic at both admission boundaries",
+    async ({ extension, signature, offset, size }) => {
+      const root = await createTestTempDirectory("rea-package-magic-");
+      const path = join(root, `input.${extension}`);
+      const bytes = Buffer.alloc(size);
+      bytes.write(signature, offset, "ascii");
+      await writeFile(path, bytes);
+      expect(
+        (await classifyAndHashRoot(path, false, await lstat(path))).format,
+      ).toBe(extension);
+      expect(await parseBinaryTarget(path)).toMatchObject({
+        ok: true,
+        value: { format: extension },
+      });
+      for (let index = 0; index < signature.length; index += 1) {
+        const changed = Buffer.from(bytes);
+        changed[offset + index] = changed[offset + index]! | 0x80;
+        await writeFile(path, changed);
+        expect(
+          (await classifyAndHashRoot(path, false, await lstat(path))).format,
+        ).toBe("file");
+        expect(await parseBinaryTarget(path)).toMatchObject({
+          ok: false,
+          error: { _tag: "BinaryTargetError" },
+        });
+      }
+    },
+  );
+});