fix: enable serialization of unsigned transactions

web3.js/src/transaction.js

@@ -16,6 +16,13 @@ import type {Blockhash} from './blockhash';
  */
 export type TransactionSignature = string;
 
+/**
+ * Default (empty) signature
+ *
+ * Signatures are 64 bytes in length
+ */
+const DEFAULT_SIGNATURE = Array(64).fill(0);
+
 /**
  * Maximum over-the-wire size of a Transaction
  *
@@ -164,7 +171,6 @@ export class Transaction {
     }
 
     const keys = this.signatures.map(({publicKey}) => publicKey.toString());
-    let numRequiredSignatures = 0;
     let numCreditOnlySignedAccounts = 0;
     let numCreditOnlyUnsignedAccounts = 0;
 
@@ -175,7 +181,10 @@ export class Transaction {
         const keyStr = keySignerPair.pubkey.toString();
         if (!keys.includes(keyStr)) {
           if (keySignerPair.isSigner) {
-            numRequiredSignatures += 1;
+            this.signatures.push({
+              signature: null,
+              publicKey: keySignerPair.pubkey,
+            });
             if (!keySignerPair.isDebitable) {
               numCreditOnlySignedAccounts += 1;
             }
@@ -201,12 +210,6 @@ export class Transaction {
       }
     });
 
-    if (numRequiredSignatures > this.signatures.length) {
-      throw new Error(
-        `Insufficent signatures: expected ${numRequiredSignatures} but got ${this.signatures.length}`,
-      );
-    }
-
     let keyCount = [];
     shortvec.encodeLength(keyCount, keys.length);
 
@@ -391,12 +394,13 @@ export class Transaction {
     invariant(signatures.length < 256);
     Buffer.from(signatureCount).copy(wireTransaction, 0);
     signatures.forEach(({signature}, index) => {
-      invariant(signature !== null, `null signature`);
-      invariant(signature.length === 64, `signature has invalid length`);
-      Buffer.from(signature).copy(
-        wireTransaction,
-        signatureCount.length + index * 64,
-      );
+      if (signature !== null) {
+        invariant(signature.length === 64, `signature has invalid length`);
+        Buffer.from(signature).copy(
+          wireTransaction,
+          signatureCount.length + index * 64,
+        );
+      }
     });
     signData.copy(
       wireTransaction,
@@ -506,7 +510,10 @@ export class Transaction {
     transaction.recentBlockhash = new PublicKey(recentBlockhash).toBase58();
     for (let i = 0; i < signatureCount; i++) {
       const sigPubkeyPair = {
-        signature: Buffer.from(signatures[i]),
+        signature:
+          signatures[i].toString() == DEFAULT_SIGNATURE.toString()
+            ? null
+            : Buffer.from(signatures[i]),
         publicKey: new PublicKey(accounts[i]),
       };
       transaction.signatures.push(sigPubkeyPair);