Viewer: re-run a transaction's scripts in the browser (Script Lab)

applications/viewer/README.md

@@ -8,8 +8,10 @@ A live Cardano explorer for your Yaci DevKit devnet, or any [Yaci Store](https:/
   transaction, address, stake address, pool, DRep, policy, asset, fingerprint, script, datum or epoch.
 - **Transactions you can read:** inputs flow into outputs, scripts show their execution budget, redeemers and datums
   are decoded from CBOR, plus mints, metadata, collateral, reference inputs and the raw JSON.
-- **Script Lab:** decode any Plutus script into searchable UPLC, see the builtins it uses and verify its hash. It runs
-  in your browser with the [julc](https://github.com/bloxbean/julc) WebAssembly engine.
+- **Script Lab:** in your browser, with the [julc](https://github.com/bloxbean/julc) WebAssembly engine:
+  - decode any Plutus script into searchable UPLC, see the builtins it uses and verify its hash;
+  - re-run every script of a transaction with the cost model of its epoch, compare the budget with what was declared
+    on chain, and see the exact ScriptContext the validator received.
 - Addresses, stake accounts, assets, epochs and protocol parameters, pools, rewards, certificates, Ada pots and
   Conway governance.
 - Light and dark themes; works on a phone.
@@ -69,7 +71,12 @@ into `static/julc/` (git-ignored). The engine is only downloaded by the browser
   release's `julc-wasm-<version>-SHA256SUMS.txt`.
 - The engine needs WebAssembly GC and exception handling (exnref): current Chrome, Edge, Firefox and Safari. Other
   browsers get a message instead. Playwright's bundled Chromium is too old, so run the Script Lab test with Chrome:
-  `SCRIPT_LAB_HASH=<plutus script hash> PW_CHANNEL=chrome npx playwright test script-lab`.
+  `SCRIPT_LAB_HASH=<plutus script hash> SCRIPT_LAB_TX=<tx with redeemers> PW_CHANNEL=chrome npx playwright test script-lab`.
+- Re-runs rebuild the transaction from Yaci Store data (`src/lib/julc/replay/`). Until julc builds contexts exactly
+  as the ledger does ([julc#244](https://github.com/bloxbean/julc/issues/244)), the viewer corrects julc's context
+  (asset order, the other redeemers, datums given by hash, Plutus V1 shapes) and runs the script again; each result
+  says what was corrected. Proposal (guardrail) scripts and most certificate kinds aren't replayed yet, and Plutus V1
+  (pre-2023 history) is partly reproduced.
 
 SvelteKit 2, Svelte 5 and Tailwind. Shared code lives in `src/lib`: `api/` (Yaci Store client), `live/` (WebSocket
 with a polling fallback), `ui/` (components), `shell/` (layout, navigation, search), `julc/` (Script Lab) and `format.ts`, `cbor.ts`,

applications/viewer/src/lib/cbor.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest';
-import { decodePlutusData, tryDecodePlutusData } from './cbor';
+import { decodePlutusData, encodePlutusData, tryDecodePlutusData, type PlutusData } from './cbor';
 
 describe('decodePlutusData', () => {
 	it('decodes constructors', () => {
@@ -28,3 +28,29 @@ describe('decodePlutusData', () => {
 		expect(tryDecodePlutusData(null)).toBeNull();
 	});
 });
+
+describe('encodePlutusData', () => {
+	it('encodes the way the Plutus libraries do', () => {
+		expect(encodePlutusData({ constructor: 0, fields: [] })).toBe('d87980');
+		expect(encodePlutusData({ constructor: 0, fields: [{ int: '42' }, { bytes: 'cafe' }] })).toBe('d8799f182a42cafeff');
+		expect(encodePlutusData({ constructor: 7, fields: [] })).toBe('d9050080');
+		expect(encodePlutusData({ constructor: 200, fields: [] })).toBe('d8668218c880');
+		expect(encodePlutusData({ int: '-1' })).toBe('20');
+		expect(encodePlutusData({ map: [{ k: { int: '1' }, v: { int: '2' } }] })).toBe('a10102');
+		expect(encodePlutusData({ int: (1n << 64n).toString() })).toBe('c249010000000000000000');
+		expect(encodePlutusData({ int: (-(1n << 64n) - 1n).toString() })).toBe('c349010000000000000000');
+		expect(encodePlutusData({ int: (-(1n << 64n)).toString() })).toBe('3bffffffffffffffff');
+	});
+
+	it('round-trips through the decoder, including chunked bytes', () => {
+		const samples: PlutusData[] = [
+			{ bytes: 'ab'.repeat(100) },
+			{ constructor: 2, fields: [{ list: [{ map: [] }, { int: '18446744073709551615' }, { int: '-18446744073709551617' }] }] },
+			{ map: [{ k: { bytes: '' }, v: { constructor: 130, fields: [{ int: '0' }] } }, { k: { bytes: '' }, v: { list: [] } }] }
+		];
+		for (const d of samples) expect(decodePlutusData(encodePlutusData(d))).toEqual(d);
+		const long = encodePlutusData({ bytes: 'ab'.repeat(100) });
+		expect(long.startsWith('5f5840')).toBe(true);
+		expect(long.endsWith('ff')).toBe(true);
+	});
+});

applications/viewer/src/lib/cbor.ts

@@ -144,3 +144,75 @@ export function tryDecodePlutusData(hex: string | null | undefined): PlutusData
 		return null;
 	}
 }
+
+// Not `'constructor' in d`: every object inherits a `constructor` property.
+const isConstr = (d: PlutusData): d is { constructor: number; fields: PlutusData[] } => typeof (d as { constructor: unknown }).constructor === 'number';
+
+/*
+ * Encode Plutus data to CBOR hex the way the Plutus libraries do: indefinite-length lists (definite when empty),
+ * byte strings over 64 bytes in 64-byte chunks, integers beyond 64 bits as bignums, and constructor tags
+ * 121-127 / 1280-1400 / 102. Used to hand a modified ScriptContext back to the julc VM.
+ */
+export function encodePlutusData(d: PlutusData): string {
+	const out: number[] = [];
+	const head = (major: number, n: bigint) => {
+		const m = major << 5;
+		if (n < 24n) out.push(m | Number(n));
+		else if (n < 0x100n) out.push(m | 24, Number(n));
+		else if (n < 0x10000n) out.push(m | 25, Number(n >> 8n), Number(n & 0xffn));
+		else if (n < 0x100000000n) out.push(m | 26, ...[24n, 16n, 8n, 0n].map((s) => Number((n >> s) & 0xffn)));
+		else out.push(m | 27, ...[56n, 48n, 40n, 32n, 24n, 16n, 8n, 0n].map((s) => Number((n >> s) & 0xffn)));
+	};
+	const bytes = (b: number[]) => {
+		if (b.length <= 64) {
+			head(2, BigInt(b.length));
+			out.push(...b);
+			return;
+		}
+		out.push(0x5f);
+		for (let i = 0; i < b.length; i += 64) {
+			const chunk = b.slice(i, i + 64);
+			head(2, BigInt(chunk.length));
+			out.push(...chunk);
+		}
+		out.push(0xff);
+	};
+	const list = (items: PlutusData[]) => {
+		if (!items.length) return out.push(0x80);
+		out.push(0x9f);
+		items.forEach(write);
+		out.push(0xff);
+	};
+	const write = (x: PlutusData): void => {
+		if (isConstr(x)) {
+			const c = x.constructor;
+			if (c <= 6) head(6, BigInt(121 + c));
+			else if (c <= 127) head(6, BigInt(1280 + c - 7));
+			else {
+				head(6, 102n);
+				out.push(0x82);
+				head(0, BigInt(c));
+			}
+			list(x.fields);
+		} else if ('int' in x) {
+			const v = BigInt(x.int);
+			const n = v < 0n ? -1n - v : v;
+			if (n < 1n << 64n) head(v < 0n ? 1 : 0, n);
+			else {
+				head(6, v < 0n ? 3n : 2n);
+				const hex = n.toString(16);
+				bytes((hex.length % 2 ? '0' + hex : hex).match(/../g)!.map((h) => parseInt(h, 16)));
+			}
+		} else if ('bytes' in x) bytes((x.bytes.match(/../g) ?? []).map((h) => parseInt(h, 16)));
+		else if ('list' in x) list(x.list);
+		else {
+			head(5, BigInt(x.map.length));
+			for (const { k, v } of x.map) {
+				write(k);
+				write(v);
+			}
+		}
+	};
+	write(d);
+	return out.map((b) => b.toString(16).padStart(2, '0')).join('');
+}

applications/viewer/src/lib/julc/ScriptCode.svelte

@@ -96,7 +96,7 @@
 			</button>
 			<label class="mt-3 flex items-center gap-2 text-xs text-muted">
 				<input type="checkbox" class="accent-[rgb(var(--c-brand))]" checked={auto} onchange={(e) => toggleAuto(e.currentTarget.checked)} />
-				Always decode scripts automatically
+				Run Script Lab automatically
 			</label>
 		</div>
 	{:else if failure}