0.8.2: add SCALE-compact length prefix to v4 extrinsic on the wire

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## 0.8.2
+
+### Fixed
+
+- **`handleCreateTransaction` now prepends the SCALE-compact length prefix** to the returned bytes. `0.8.1` returned the bare `[0x84][signer][sig][extras][callData]` frame, which is the *inner* extrinsic body — RPC and polkadot-api decoders expect the outer wire form `[compact len][0x84]…`, so a length-prefixed decoder reads byte 0 as part of the length and fails. The handler now produces the wire form directly.
+- Integration test #45 was updated to strip the compact prefix before asserting on the v4 frame, so the test would have caught the missing prefix.
+
 ## 0.8.1
 
 ### Fixed

forum-post.md

@@ -349,23 +349,23 @@ _Thanks to [@TarikGul](https://github.com/TarikGul) for spotting and fixing this
 
 ---
 
-# host-api-test-sdk 0.8.1
+# host-api-test-sdk 0.8.2
 
-Bumps `@novasamatech/*` to `0.7.9-4` and fixes `handleCreateTransaction` to return a real signed v4 extrinsic. In `0.8.0` it echoed `params.callData` back — fine for `result.ok === true` checks, broken the moment a product tried to submit the bytes.
+Bumps `@novasamatech/*` to `0.7.9-4` and fixes `handleCreateTransaction` to return a real signed v4 extrinsic on the wire. Earlier `0.8.x` releases either echoed `callData` back or returned the inner extrinsic frame without its SCALE-compact length prefix — both of which fail the moment a product tries to submit the bytes through polkadot-api / RPC.
 
 ## What changed
 
 - **`handleCreateTransaction` / `handleCreateTransactionWithLegacyAccount`** — the request is now a flat object (`signer`, `genesisHash`, `callData`, `extensions`, `txExtVersion`); no more tuple wrapping, no `context` block, all fields are `Uint8Array`. Exports `VersionedPublicTxPayload` / `TxPayloadV1Public` are gone — use `ProductAccountTransaction` / `LegacyTransaction`.
-- The handler now signs `callData || extras || additionalSigned` sr25519 and returns a v4 signed-extrinsic frame: `[0x84][MultiAddress::Id + AccountId32][Sr25519 + sig][extras][callData]`. v5 is not emitted yet (paseo-asset-hub-next runs `extrinsic.version: [4]` only).
+- The handler signs `callData || extras || additionalSigned` with sr25519 and returns the full v4 wire form: `[compact len][0x84][MultiAddress::Id + AccountId32][Sr25519 + sig][extras][callData]`. v5 is not emitted yet (paseo-asset-hub-next runs `extrinsic.version: [4]` only).
 - Upstream also removed the attestation service and simplified SSO; `@novasamatech/product-sdk` is being renamed to `@novasamatech/host-api-wrapper` (`0.7.9-5+` is under the new name; we stay on `product-sdk@0.7.9-4` for this release).
 
 ## What you need to do
 
-- Upgrade to `0.8.1`. No product-side code change required — the wrapper API didn't move.
+- Upgrade to `0.8.2`. No product-side code change required — the wrapper API didn't move.
 - If you constructed `createTransaction` requests by hand, switch to the flat `ProductAccountTransaction` shape and include `genesisHash`.
 - If your tests asserted on the bytes being equal to `callData`, drop that assumption and decode the response as a v4 extrinsic instead.
 - If your runtime negotiates v5 general extrinsics, file an issue — v5 support is a follow-up.
 
-`0.8.0` is deprecated on npm; upgrade.
+`0.8.0` and `0.8.1` are superseded; skip straight to `0.8.2`.
 
 ---

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@parity/host-api-test-sdk",
-  "version": "0.8.1",
+  "version": "0.8.2",
   "description": "Lightweight test host for Spektr product E2E testing — embeds dapps with auto-signing dev accounts, no Docker needed",
   "license": "MIT",
   "repository": {

src/browser/host-runtime.ts

@@ -31,7 +31,7 @@ import {
 import { Keyring } from "@polkadot/keyring";
 import type { KeyringPair } from "@polkadot/keyring/types";
 import { TypeRegistry } from "@polkadot/types";
-import { u8aToHex } from "@polkadot/util";
+import { compactToU8a, u8aToHex } from "@polkadot/util";
 import { blake2AsHex, blake2AsU8a, cryptoWaitReady } from "@polkadot/util-crypto";
 import { ResultAsync } from "neverthrow";
 import { getWsProvider } from "polkadot-api/ws";
@@ -172,7 +172,9 @@ function getPairByPublicKey(pubkey: Uint8Array): KeyringPair | undefined {
  * Build a v4 signed extrinsic from a SCALE-encoded call plus per-extension
  * `extra` / `additionalSigned` blobs, signed sr25519 by `pair`.
  *
- * Layout (no outer compact length prefix):
+ * Layout (with outer SCALE-compact length prefix — what RPC and polkadot-api
+ * decoders expect on the wire):
+ *   [compact len]                   length of the bytes that follow
  *   [0x84]                          version 4 + signed bit
  *   [0x00][AccountId32]             MultiAddress::Id
  *   [0x01][signature 64B]           MultiSignature::Sr25519
@@ -208,13 +210,18 @@ function buildSignedV4Extrinsic(
   const toSign = payload.length > 256 ? blake2AsU8a(payload, 256) : payload;
   const signature = pair.sign(toSign); // sr25519, 64 bytes
 
-  const out = new Uint8Array(1 + 1 + 32 + 1 + 64 + extras.length + callData.length);
+  const inner = new Uint8Array(1 + 1 + 32 + 1 + 64 + extras.length + callData.length);
   let p = 0;
-  out[p++] = 0x84;
-  out[p++] = 0x00; out.set(pair.publicKey, p); p += 32;
-  out[p++] = 0x01; out.set(signature, p); p += 64;
-  out.set(extras, p); p += extras.length;
-  out.set(callData, p);
+  inner[p++] = 0x84;
+  inner[p++] = 0x00; inner.set(pair.publicKey, p); p += 32;
+  inner[p++] = 0x01; inner.set(signature, p); p += 64;
+  inner.set(extras, p); p += extras.length;
+  inner.set(callData, p);
+
+  const lenPrefix = compactToU8a(inner.length);
+  const out = new Uint8Array(lenPrefix.length + inner.length);
+  out.set(lenPrefix, 0);
+  out.set(inner, lenPrefix.length);
   return out;
 }
 

test/integration.spec.ts

@@ -15,7 +15,7 @@ import { join, dirname } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { Keyring } from '@polkadot/keyring';
 import { cryptoWaitReady, sr25519Verify } from '@polkadot/util-crypto';
-import { hexToU8a, u8aToHex } from '@polkadot/util';
+import { compactFromU8a, hexToU8a, u8aToHex } from '@polkadot/util';
 import { createTestHostServer } from '../dist/index.js';
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
@@ -1298,8 +1298,11 @@ test.describe('Create transaction', () => {
       expect(result.signedHex).toBeDefined();
 
       // test-product sends callData = [0, 0], no extensions
-      // expected layout: [0x84][0x00 + 32B pubkey][0x01 + 64B sig][0 extras][2B callData]
-      const bytes = hexToU8a(result.signedHex!);
+      // wire layout: [compact len][0x84][0x00 + 32B pubkey][0x01 + 64B sig][0 extras][2B callData]
+      const wire = hexToU8a(result.signedHex!);
+      const [offset, innerLen] = compactFromU8a(wire); // [bytesUsed, BN value]
+      const bytes = wire.slice(offset);
+      expect(bytes.length).toBe(innerLen.toNumber());
       expect(bytes.length).toBe(1 + 1 + 32 + 1 + 64 + 2);
       expect(bytes[0]).toBe(0x84);   // v4 + signed bit
       expect(bytes[1]).toBe(0x00);   // MultiAddress::Id