web3.js: Implement addSignature in VersionedTransaction

web3.js/src/transaction/versioned.ts

@@ -7,6 +7,7 @@ import {SIGNATURE_LENGTH_IN_BYTES} from './constants';
 import * as shortvec from '../utils/shortvec-encoding';
 import * as Layout from '../layout';
 import {sign} from '../utils/ed25519';
+import {PublicKey} from '../publickey';
 
 export type TransactionVersion = 'legacy' | 0;
 
@@ -106,4 +107,20 @@ export class VersionedTransaction {
       this.signatures[signerIndex] = sign(messageData, signer.secretKey);
     }
   }
+
+  addSignature(publicKey: PublicKey, signature: Uint8Array) {
+    assert(signature.byteLength === 64, 'Signature must be 64 bytes long');
+    const signerPubkeys = this.message.staticAccountKeys.slice(
+      0,
+      this.message.header.numRequiredSignatures,
+    );
+    const signerIndex = signerPubkeys.findIndex(pubkey =>
+      pubkey.equals(publicKey),
+    );
+    assert(
+      signerIndex >= 0,
+      `Can not add signature; \`${publicKey.toBase58()}\` is not required to sign this transaction`,
+    );
+    this.signatures[signerIndex] = signature;
+  }
 }

web3.js/test/transaction.test.ts

@@ -8,6 +8,7 @@ import {PublicKey} from '../src/publickey';
 import {
   Transaction,
   TransactionInstruction,
+  TransactionMessage,
   VersionedTransaction,
 } from '../src/transaction';
 import {StakeProgram, SystemProgram} from '../src/programs';
@@ -962,4 +963,48 @@ describe('Transaction', () => {
     t1.partialSign(signer);
     t1.serialize();
   });
+
+  it('externally signed versioned transaction', () => {
+    const signer = Keypair.generate();
+    const invalidSigner = Keypair.generate();
+
+    const recentBlockhash = new PublicKey(3).toBuffer();
+
+    const message = new TransactionMessage({
+      payerKey: signer.publicKey,
+      instructions: [
+        new TransactionInstruction({
+          data: Buffer.from('Hello!'),
+          keys: [
+            {
+              pubkey: signer.publicKey,
+              isSigner: true,
+              isWritable: true,
+            },
+          ],
+          programId: new PublicKey(
+            'MemoSq4gqABAXKb96qnH8TysNcWxMyWCqXgDLGmfcHr',
+          ),
+        }),
+      ],
+      recentBlockhash: bs58.encode(recentBlockhash),
+    });
+
+    const transaction = new VersionedTransaction(message.compileToV0Message());
+
+    const signature = sign(transaction.message.serialize(), signer.secretKey);
+
+    transaction.addSignature(signer.publicKey, signature);
+
+    expect(transaction.signatures).to.have.length(1);
+    expect(transaction.signatures[0]).to.eq(signature);
+    expect(() => {
+      transaction.addSignature(signer.publicKey, new Uint8Array(32));
+    }).to.throw('Signature must be 64 bytes long');
+    expect(() => {
+      transaction.addSignature(invalidSigner.publicKey, new Uint8Array(64));
+    }).to.throw(
+      `Can not add signature; \`${invalidSigner.publicKey.toBase58()}\` is not required to sign this transaction`,
+    );
+  });
 });