feat: add op_drop to wasm-miniscript

Issue: BTC-1451

Author: OttoAllmendinger

packages/wasm-miniscript/Cargo.lock

@@ -9,4 +9,4 @@ crate-type = ["cdylib"]
 [dependencies]
 wasm-bindgen = "0.2"
 js-sys = "0.3"
-miniscript = { version = "12.2.0" }
+miniscript = { git = "https://github.com/BitGo/rust-miniscript", branch = "opdrop" }

packages/wasm-miniscript/Cargo.toml

@@ -158,6 +158,7 @@ impl<Pk: MiniscriptKey + TryIntoJsValue, Ctx: ScriptContext> TryIntoJsValue for
             Terminal::Check(node) => js_obj!("Check" => node),
             Terminal::DupIf(node) => js_obj!("DupIf" => node),
             Terminal::Verify(node) => js_obj!("Verify" => node),
+            Terminal::Drop(node) => js_obj!("Drop" => node),
             Terminal::NonZero(node) => js_obj!("NonZero" => node),
             Terminal::ZeroNotEqual(node) => js_obj!("ZeroNotEqual" => node),
             Terminal::AndV(a, b) => js_obj!("AndV" => js_arr!(a, b)),

packages/wasm-miniscript/src/try_into_js_value.rs

@@ -0,0 +1,11 @@
+import * as fs from "fs/promises";
+export async function getFixture(path: string, defaultValue: unknown): Promise<unknown> {
+  try {
+    return JSON.parse(await fs.readFile(path, "utf8"));
+  } catch (e) {
+    if (e.code === "ENOENT") {
+      await fs.writeFile(path, JSON.stringify(defaultValue, null, 2));
+      throw new Error(`Fixture not found at ${path}, created a new one`);
+    }
+  }
+}

packages/wasm-miniscript/test/fixtures.ts

@@ -0,0 +1 @@
+"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"

packages/wasm-miniscript/test/fixtures/opdrop.json

@@ -0,0 +1,96 @@
+import * as assert from "assert";
+import * as utxolib from "@bitgo/utxo-lib";
+import { Descriptor } from "../js";
+import { finalizePsbt, updateInputWithDescriptor } from "./psbt.util";
+import { getFixture } from "./fixtures";
+
+const rootWalletKeys = new utxolib.bitgo.RootWalletKeys(utxolib.testutil.getKeyTriple("wasm"));
+
+function getDescriptorOpDropP2ms(locktime: number, keys: utxolib.BIP32Interface[]) {
+  const xpubs = keys.map((key) => key.toBase58() + "/*");
+  // the `r:` prefix is a custom BitGo modification of miniscript to allow OP_DROP
+  return `wsh(and_v(r:after(${locktime}),multi(2,${xpubs.join(",")})))`;
+}
+
+describe("CLV with OP_DROP", () => {
+  const locktime = 1024;
+  const descriptor = Descriptor.fromString(
+    getDescriptorOpDropP2ms(locktime, rootWalletKeys.triple),
+    "derivable",
+  );
+  it("has expected AST", () => {
+    assert.deepStrictEqual(descriptor.node(), {
+      Wsh: {
+        Ms: {
+          AndV: [
+            {
+              Drop: {
+                After: {
+                  absLockTime: 1024,
+                },
+              },
+            },
+            {
+              Multi: [
+                2,
+                {
+                  XPub: "xpub661MyMwAqRbcFNusVUbSN3nbanHMtJjLgZGrs1wxH6f77kKQd6Vq4HfkZQNPC1vSbN6RTiBWJJV6FwJtCfBon2SgaT2J3MSkydukstKjwbJ/*",
+                },
+                {
+                  XPub: "xpub661MyMwAqRbcFo3t7PUqvbgvAcEuuoeVib5aapsg52inrG6KGF5aNtR5ey1FNCt1zJpMQiNec5XpofQmLNRhHvQRbhkc8UsWwwMwsXW6ogU/*",
+                },
+                {
+                  XPub: "xpub661MyMwAqRbcGg7f22Kcg2gy1F4jBjWR3xQTECVeJPHmxvhg5gUAZC6EYFtnyi6aMDQir1kV8HzCqC2FzTowGgEZqRh7rinqUCDeNDdmYzH/*",
+                },
+              ],
+            },
+          ],
+        },
+      },
+    });
+  });
+
+  it("has expected asm", () => {
+    assert.deepStrictEqual(descriptor.atDerivationIndex(0).toAsmString().split(" "), [
+      "OP_PUSHBYTES_2",
+      "0004",
+      "OP_CLTV",
+      "OP_DROP",
+      "OP_PUSHNUM_2",
+      "OP_PUSHBYTES_33",
+      "02ae7c3c0ebc315a33151a1985ebb1fdcae72b3b91c38e3193c40ebabfffe9c343",
+      "OP_PUSHBYTES_33",
+      "0260ba2407f7c75d525db9f171e9b2f3cf5ba3f0d7fc6067b20d4b91585432f974",
+      "OP_PUSHBYTES_33",
+      "03eadd6e4300dac62f1d4cf1131a06c5e140911f04245c64934c27510e93dbe843",
+      "OP_PUSHNUM_3",
+      "OP_CHECKMULTISIG",
+    ]);
+  });
+
+  it("can be signed", async function () {
+    const psbt = Object.assign(new utxolib.Psbt({ network: utxolib.networks.bitcoin }), {
+      locktime,
+    });
+    const signers = rootWalletKeys.triple.slice(0, 2);
+    const descriptorAt0 = descriptor.atDerivationIndex(0);
+    const script = Buffer.from(descriptorAt0.scriptPubkey());
+    psbt.addInput({
+      hash: Buffer.alloc(32),
+      index: 0,
+      sequence: 0xfffffffe,
+      witnessUtxo: { script, value: BigInt(1e8) },
+    });
+    psbt.addOutput({ script, value: BigInt(1e8) });
+    updateInputWithDescriptor(psbt, 0, descriptorAt0);
+    for (const signer of signers) {
+      psbt.signAllInputsHD(signer);
+    }
+    finalizePsbt(psbt);
+    const signedTx = psbt.extractTransaction().toBuffer();
+    assert.strictEqual(
+      signedTx.toString("hex"),
+      await getFixture("test/fixtures/opdrop.json", signedTx.toString("hex")),
+    );
+  });
+});