TransactionInput: make field scriptBytes immutable

Because tweaking is necessary for transaction signing, these usages
have been changed to produce new inputs instead and replace them in
transactions as needed.

core/src/main/java/org/bitcoinj/core/Transaction.java

@@ -902,20 +902,20 @@ public TransactionInput addSignedInput(TransactionOutPoint prevOut, Script scrip
         if (ScriptPattern.isP2PK(scriptPubKey)) {
             TransactionSignature signature = calculateSignature(inputIndex, sigKey, scriptPubKey, sigHash,
                     anyoneCanPay);
-            input.setScriptSig(ScriptBuilder.createInputScript(signature));
+            input = input.withScriptSig(ScriptBuilder.createInputScript(signature));
             input = input.withoutWitness();
             replaceInput(inputIndex, input);
         } else if (ScriptPattern.isP2PKH(scriptPubKey)) {
             TransactionSignature signature = calculateSignature(inputIndex, sigKey, scriptPubKey, sigHash,
                     anyoneCanPay);
-            input.setScriptSig(ScriptBuilder.createInputScript(signature, sigKey));
+            input = input.withScriptSig(ScriptBuilder.createInputScript(signature, sigKey));
             input = input.withoutWitness();
             replaceInput(inputIndex, input);
         } else if (ScriptPattern.isP2WPKH(scriptPubKey)) {
             Script scriptCode = ScriptBuilder.createP2PKHOutputScript(sigKey);
             TransactionSignature signature = calculateWitnessSignature(inputIndex, sigKey, scriptCode, input.getValue(),
                     sigHash, anyoneCanPay);
-            input.setScriptSig(ScriptBuilder.createEmpty());
+            input = input.withScriptSig(ScriptBuilder.createEmpty());
             input = input.withWitness(TransactionWitness.redeemP2WPKH(signature, sigKey));
             replaceInput(inputIndex, input);
         } else {
@@ -1195,7 +1195,7 @@ public Sha256Hash hashForSignature(int inputIndex, byte[] connectedScript, byte
             // EC math so we'll do it anyway.
             for (int i = 0; i < tx.inputs.size(); i++) {
                 TransactionInput input = tx.getInput(i);
-                input.clearScriptBytes();
+                input = input.withoutScriptBytes();
                 input = input.withoutWitness();
                 tx.replaceInput(i, input);
             }
@@ -1212,8 +1212,9 @@ public Sha256Hash hashForSignature(int inputIndex, byte[] connectedScript, byte
             // Set the input to the script of its output. Bitcoin Core does this but the step has no obvious purpose as
             // the signature covers the hash of the prevout transaction which obviously includes the output script
             // already. Perhaps it felt safer to him in some way, or is another leftover from how the code was written.
-            TransactionInput input = tx.inputs.get(inputIndex);
-            input.setScriptBytes(connectedScript);
+            TransactionInput input = tx.getInput(inputIndex);
+            input = input.withScriptBytes(connectedScript);
+            tx.replaceInput(inputIndex, input);
 
             if ((sigHashType & 0x1f) == SigHash.NONE.value) {
                 // SIGHASH_NONE means no outputs are signed at all - the signature is effectively for a "blank cheque".

core/src/main/java/org/bitcoinj/core/TransactionInput.java

@@ -79,7 +79,7 @@ public class TransactionInput {
     // The "script bytes" might not actually be a script. In coinbase transactions where new coins are minted there
     // is no input transaction, so instead the scriptBytes contains some extra stuff (like a rollover nonce) that we
     // don't care about much. The bytes are turned into a Script object (cached below) on demand via a getter.
-    private byte[] scriptBytes;
+    private final byte[] scriptBytes;
     // The Script object obtained from parsing scriptBytes. Only filled in on demand and if the transaction is not
     // coinbase.
     private WeakReference<Script> scriptSig;
@@ -231,11 +231,16 @@ public Script getScriptSig() throws ScriptException {
         return script;
     }
 
-    /** Set the given program as the scriptSig that is supposed to satisfy the connected output script. */
-    public void setScriptSig(Script scriptSig) {
-        this.scriptSig = new WeakReference<>(Objects.requireNonNull(scriptSig));
-        // TODO: This should all be cleaned up so we have a consistent internal representation.
-        setScriptBytes(scriptSig.program());
+    /**
+     * Returns a clone of this input, with given scriptSig. The typical use case is transaction signing.
+     *
+     * @param scriptSig scriptSig for the clone
+     * @return clone of input, with given scriptSig
+     */
+    public TransactionInput withScriptSig(Script scriptSig) {
+        Objects.requireNonNull(scriptSig);
+        return new TransactionInput(this.parent, scriptSig, scriptSig.program(), this.outpoint, this.sequence,
+                this.value, this.witness);
     }
 
     /**
@@ -282,20 +287,29 @@ public TransactionOutPoint getOutpoint() {
      * @return the scriptBytes
      */
     public byte[] getScriptBytes() {
-        return scriptBytes;
+        return Arrays.copyOf(scriptBytes, scriptBytes.length);
     }
 
-    /** Clear input scripts, e.g. in preparation for signing. */
-    public void clearScriptBytes() {
-        setScriptBytes(TransactionInput.EMPTY_ARRAY);
+    /**
+     * Returns a clone of this input, without script bytes. The typical use case is transaction signing.
+     *
+     * @return clone of input, without script bytes
+     */
+    public TransactionInput withoutScriptBytes() {
+        return new TransactionInput(this.parent, null, TransactionInput.EMPTY_ARRAY, this.outpoint, this.sequence,
+                this.value, this.witness);
     }
 
     /**
-     * @param scriptBytes the scriptBytes to set
+     * Returns a clone of this input, with given script bytes. The typical use case is transaction signing.
+     *
+     * @param scriptBytes script bytes for the clone
+     * @return clone of input, with given script bytes
      */
-    void setScriptBytes(byte[] scriptBytes) {
-        this.scriptSig = null;
-        this.scriptBytes = scriptBytes;
+    public TransactionInput withScriptBytes(byte[] scriptBytes) {
+        Objects.requireNonNull(scriptBytes);
+        return new TransactionInput(this.parent, null, scriptBytes, this.outpoint, this.sequence, this.value,
+                this.witness);
     }
 
     /**

core/src/main/java/org/bitcoinj/signers/CustomTransactionSigner.java

@@ -93,7 +93,8 @@ public boolean signInputs(ProposedTransaction propTx, KeyBag keyBag) {
             TransactionSignature txSig = new TransactionSignature(sigKey.sig, Transaction.SigHash.ALL, false);
             int sigIndex = inputScript.getSigInsertionIndex(sighash, sigKey.pubKey);
             inputScript = scriptPubKey.getScriptSigWithSignature(inputScript, txSig.encodeToBitcoin(), sigIndex);
-            txIn.setScriptSig(inputScript);
+            txIn = txIn.withScriptSig(inputScript);
+            tx.replaceInput(i, txIn);
         }
         return true;
     }

core/src/main/java/org/bitcoinj/signers/LocalTransactionSigner.java

@@ -127,14 +127,14 @@ public boolean signInputs(ProposedTransaction propTx, KeyBag keyBag) {
                     int sigIndex = 0;
                     inputScript = scriptPubKey.getScriptSigWithSignature(inputScript, signature.encodeToBitcoin(),
                             sigIndex);
-                    txIn.setScriptSig(inputScript);
+                    txIn = txIn.withScriptSig(inputScript);
                     txIn = txIn.withoutWitness();
                 } else if (ScriptPattern.isP2WPKH(scriptPubKey)) {
                     Script scriptCode = ScriptBuilder.createP2PKHOutputScript(key);
                     Coin value = txIn.getValue();
                     TransactionSignature signature = tx.calculateWitnessSignature(i, key, scriptCode, value,
                             Transaction.SigHash.ALL, false);
-                    txIn.setScriptSig(ScriptBuilder.createEmpty());
+                    txIn = txIn.withScriptSig(ScriptBuilder.createEmpty());
                     txIn = txIn.withWitness(TransactionWitness.redeemP2WPKH(signature, key));
                 } else {
                     throw new IllegalStateException(script.toString());

core/src/main/java/org/bitcoinj/signers/MissingSigResolutionSigner.java

@@ -80,7 +80,7 @@ public boolean signInputs(ProposedTransaction propTx, KeyBag keyBag) {
                         if (missingSigsMode == Wallet.MissingSigsMode.THROW) {
                             throw new MissingSignatureException();
                         } else if (missingSigsMode == Wallet.MissingSigsMode.USE_DUMMY_SIG) {
-                            txIn.setScriptSig(scriptPubKey.getScriptSigWithSignature(inputScript, dummySig, j - 1));
+                            txIn = txIn.withScriptSig(scriptPubKey.getScriptSigWithSignature(inputScript, dummySig, j - 1));
                         }
                     }
                 }
@@ -89,7 +89,7 @@ public boolean signInputs(ProposedTransaction propTx, KeyBag keyBag) {
                     if (missingSigsMode == Wallet.MissingSigsMode.THROW) {
                         throw new ECKey.MissingPrivateKeyException();
                     } else if (missingSigsMode == Wallet.MissingSigsMode.USE_DUMMY_SIG) {
-                        txIn.setScriptSig(scriptPubKey.getScriptSigWithSignature(inputScript, dummySig, 0));
+                        txIn = txIn.withScriptSig(scriptPubKey.getScriptSigWithSignature(inputScript, dummySig, 0));
                     }
                 }
             } else if (ScriptPattern.isP2WPKH(scriptPubKey)) {

core/src/main/java/org/bitcoinj/testing/FakeTxBuilder.java

@@ -97,7 +97,9 @@ public static Transaction createFakeTxWithChangeAddress(Coin value, Address to,
         TransactionOutput prevOut = new TransactionOutput(prevTx, value, to);
         prevTx.addOutput(prevOut);
         // Connect it.
-        t.addInput(prevOut).setScriptSig(ScriptBuilder.createInputScript(TransactionSignature.dummy()));
+        TransactionInput in = t.addInput(prevOut);
+        in = in.withScriptSig(ScriptBuilder.createInputScript(TransactionSignature.dummy()));
+        t.replaceInput(t.getInputs().size() - 1, in);
         // Fake signature.
         // Serialize/deserialize to ensure internal state is stripped, as if it had been read from the wire.
         return roundTripTransaction(t);
@@ -126,14 +128,18 @@ public static Transaction createFakeTxWithoutChangeAddress(Coin value, Address t
         TransactionOutput prevOut1 = new TransactionOutput(prevTx1, Coin.valueOf(split), to);
         prevTx1.addOutput(prevOut1);
         // Connect it.
-        t.addInput(prevOut1).setScriptSig(ScriptBuilder.createInputScript(TransactionSignature.dummy()));
+        TransactionInput in1 = t.addInput(prevOut1);
+        in1 = in1.withScriptSig(ScriptBuilder.createInputScript(TransactionSignature.dummy()));
+        t.replaceInput(t.getInputs().size() - 1, in1);
         // Fake signature.
 
         // Do it again
         Transaction prevTx2 = new Transaction();
         TransactionOutput prevOut2 = new TransactionOutput(prevTx2, Coin.valueOf(value.getValue() - split), to);
         prevTx2.addOutput(prevOut2);
-        t.addInput(prevOut2).setScriptSig(ScriptBuilder.createInputScript(TransactionSignature.dummy()));
+        TransactionInput in2 = t.addInput(prevOut2);
+        in2 = in2.withScriptSig(ScriptBuilder.createInputScript(TransactionSignature.dummy()));
+        t.replaceInput(t.getInputs().size() - 1, in2);
 
         // Serialize/deserialize to ensure internal state is stripped, as if it had been read from the wire.
         return roundTripTransaction(t);

core/src/main/java/org/bitcoinj/wallet/Wallet.java

@@ -4564,7 +4564,8 @@ public void signTransaction(SendRequest req) throws BadWalletEncryptionKeyExcept
                 RedeemData redeemData = txIn.getConnectedRedeemData(maybeDecryptingKeyBag);
                 Objects.requireNonNull(redeemData, () ->
                         "Transaction exists in wallet that we cannot redeem: " + txIn.getOutpoint().hash());
-                txIn.setScriptSig(scriptPubKey.createEmptyInputScript(redeemData.keys.get(0), redeemData.redeemScript));
+                tx.replaceInput(i, txIn.withScriptSig(scriptPubKey.createEmptyInputScript(redeemData.keys.get(0),
+                        redeemData.redeemScript)));
             }
 
             TransactionSigner.ProposedTransaction proposal = new TransactionSigner.ProposedTransaction(tx);

core/src/test/java/org/bitcoinj/core/AbstractFullPrunedBlockChainTest.java

@@ -163,7 +163,8 @@ public void skipScripts() throws Exception {
         t.addOutput(new TransactionOutput(t, FIFTY_COINS, new byte[] {}));
         TransactionInput input = t.addInput(spendableOutput);
         // Invalid script.
-        input.clearScriptBytes();
+        input = input.withoutScriptBytes();
+        t.replaceInput(t.getInputs().size() - 1, input);
         rollingBlock.addTransaction(t);
         rollingBlock.solve();
         chain.setRunScripts(false);

core/src/test/java/org/bitcoinj/core/FullBlockTestGenerator.java

@@ -483,7 +483,7 @@ public boolean add(Rule element) {
         //
         NewBlock b26 = createNextBlock(b15, chainHeadHeight + 7, out6, null);
         // 1 is too small, but we already generate every other block with 2, so that is tested
-        b26.block.getTransactions().get(0).getInput(0).clearScriptBytes();
+        b26.block.getTransactions().get(0).replaceInput(0, b26.block.getTransactions().get(0).getInput(0).withoutScriptBytes());
         b26.block.setMerkleRoot(null);
         b26.solve();
         blocks.add(new BlockAndValidity(b26, false, true, b23.getHash(), chainHeadHeight + 7, "b26"));
@@ -496,7 +496,7 @@ public boolean add(Rule element) {
         {
             byte[] coinbase = new byte[101];
             Arrays.fill(coinbase, (byte)0);
-            b28.block.getTransactions().get(0).getInput(0).setScriptBytes(coinbase);
+            b28.block.getTransactions().get(0).replaceInput(0, b28.block.getTransactions().get(0).getInput(0).withScriptBytes(coinbase));
         }
         b28.block.setMerkleRoot(null);
         b28.solve();
@@ -510,7 +510,7 @@ public boolean add(Rule element) {
         {
             byte[] coinbase = new byte[100];
             Arrays.fill(coinbase, (byte)0);
-            b30.block.getTransactions().get(0).getInput(0).setScriptBytes(coinbase);
+            b30.block.getTransactions().get(0).replaceInput(0, b30.block.getTransactions().get(0).getInput(0).withScriptBytes(coinbase));
         }
         b30.block.setMerkleRoot(null);
         b30.solve();
@@ -761,6 +761,7 @@ public boolean add(Rule element) {
                 TransactionInput input = new TransactionInput(tx, new byte[]{},
                         new TransactionOutPoint(0, b39.block.getTransactions().get(i).getTxId()));
                 tx.addInput(input);
+                int inputIndex = tx.getInputs().size() - 1;
 
                 if (scriptSig == null) {
                     // Exploit the SigHash.SINGLE bug to avoid having to make more than one signature
@@ -784,7 +785,7 @@ public boolean add(Rule element) {
                     }
                 }
 
-                input.setScriptBytes(scriptSig);
+                tx.replaceInput(inputIndex, tx.getInput(inputIndex).withScriptBytes(scriptSig));
 
                 lastOutPoint = new TransactionOutPoint(0, tx.getTxId());
 
@@ -828,6 +829,7 @@ public boolean add(Rule element) {
                     TransactionInput input = new TransactionInput(tx, new byte[] {},
                             new TransactionOutPoint(0, b39.block.getTransactions().get(i).getTxId()));
                     tx.addInput(input);
+                    int inputIndex = tx.getInputs().size() - 1;
 
                     if (scriptSig == null) {
                         // Exploit the SigHash.SINGLE bug to avoid having to make more than one signature
@@ -857,7 +859,7 @@ public boolean add(Rule element) {
                         }
                     }
 
-                    input.setScriptBytes(scriptSig);
+                    tx.replaceInput(inputIndex, tx.getInput(inputIndex).withScriptBytes(scriptSig));
 
                     lastOutPoint = new TransactionOutPoint(0,
                             tx.getTxId());
@@ -1163,7 +1165,7 @@ public boolean add(Rule element) {
 
         NewBlock b61 = createNextBlock(b60, chainHeadHeight + 19, out18, null);
         {
-            b61.block.getTransactions().get(0).getInput(0).setScriptBytes(b60.block.getTransactions().get(0).getInput(0).getScriptBytes());
+            b61.block.getTransactions().get(0).replaceInput(0, b61.block.getTransactions().get(0).getInput(0).withScriptBytes(b60.block.getTransactions().get(0).getInput(0).getScriptBytes()));
             b61.block.unCache();
             checkState(b61.block.getTransactions().get(0).equals(b60.block.getTransactions().get(0)));
         }
@@ -1799,16 +1801,17 @@ private void addOnlyInputToTransaction(Transaction t, TransactionOutPointWithVal
         TransactionInput input = new TransactionInput(t, new byte[]{}, prevOut.outpoint);
         input = input.withSequence(sequence);
         t.addInput(input);
+        int inputIndex = t.getInputs().size() - 1;
 
         if (prevOut.scriptPubKey.chunks().get(0).equalsOpCode(OP_TRUE)) {
-            input.setScriptSig(new ScriptBuilder().op(OP_1).build());
+            t.replaceInput(inputIndex, input.withScriptSig(new ScriptBuilder().op(OP_1).build()));
         } else {
             // Sign input
             checkState(ScriptPattern.isP2PK(prevOut.scriptPubKey));
             Sha256Hash hash = t.hashForSignature(0, prevOut.scriptPubKey, SigHash.ALL, false);
-            input.setScriptSig(ScriptBuilder.createInputScript(
-                            new TransactionSignature(coinbaseOutKey.sign(hash), SigHash.ALL, false))
-            );
+            t.replaceInput(inputIndex, input.withScriptSig(ScriptBuilder.createInputScript(
+                    new TransactionSignature(coinbaseOutKey.sign(hash), SigHash.ALL, false))
+            ));
         }
     }
 

core/src/test/java/org/bitcoinj/core/TransactionTest.java

@@ -100,15 +100,15 @@ public void emptyInputs() {
     @Test(expected = VerificationException.LargerThanMaxBlockSize.class)
     public void tooHuge() {
         Transaction tx = FakeTxBuilder.createFakeTx(TESTNET.network());
-        tx.getInput(0).setScriptBytes(new byte[Block.MAX_BLOCK_SIZE]);
+        tx.replaceInput(0, tx.getInput(0).withScriptBytes(new byte[Block.MAX_BLOCK_SIZE]));
         Transaction.verify(TESTNET.network(), tx);
     }
 
     @Test(expected = VerificationException.DuplicatedOutPoint.class)
     public void duplicateOutPoint() {
         Transaction tx = FakeTxBuilder.createFakeTx(TESTNET.network());
         TransactionInput input = tx.getInput(0);
-        input.setScriptBytes(new byte[1]);
+        input = input.withScriptBytes(new byte[1]);
         tx.addInput(input);
         Transaction.verify(TESTNET.network(), tx);
     }
@@ -336,7 +336,8 @@ public void testWitnessSignatureP2WPKH() {
                 ByteUtils.formatHex(txSig1.encodeToBitcoin()));
 
         assertFalse(correctlySpends(txIn0, scriptPubKey0, 0));
-        txIn0.setScriptSig(new ScriptBuilder().data(txSig0.encodeToBitcoin()).build());
+        txIn0 = txIn0.withScriptSig(new ScriptBuilder().data(txSig0.encodeToBitcoin()).build());
+	    tx.replaceInput(0, txIn0);
         assertTrue(correctlySpends(txIn0, scriptPubKey0, 0));
 
         assertFalse(correctlySpends(txIn1, scriptPubKey1, 1));
@@ -415,8 +416,8 @@ public void testWitnessSignatureP2SH_P2WPKH() {
 
         assertFalse(correctlySpends(txIn, scriptPubKey, 0));
         txIn = txIn.withWitness(TransactionWitness.redeemP2WPKH(txSig, key));
+        txIn = txIn.withScriptSig(new ScriptBuilder().data(redeemScript.program()).build());
         tx.replaceInput(0, txIn);
-        txIn.setScriptSig(new ScriptBuilder().data(redeemScript.program()).build());
         assertTrue(correctlySpends(txIn, scriptPubKey, 0));
 
         String signedTxHex = "01000000" // version
@@ -571,11 +572,11 @@ public void testPrioSizeCalc() {
         int size1 = tx1.messageSize();
         int size2 = tx1.getMessageSizeForPriorityCalc();
         assertEquals(113, size1 - size2);
-        tx1.getInput(0).setScriptSig(Script.parse(new byte[109]));
+        tx1.replaceInput(0, tx1.getInput(0).withScriptSig(Script.parse(new byte[109])));
         assertEquals(78, tx1.getMessageSizeForPriorityCalc());
-        tx1.getInput(0).setScriptSig(Script.parse(new byte[110]));
+        tx1.replaceInput(0, tx1.getInput(0).withScriptSig(Script.parse(new byte[110])));
         assertEquals(78, tx1.getMessageSizeForPriorityCalc());
-        tx1.getInput(0).setScriptSig(Script.parse(new byte[111]));
+        tx1.replaceInput(0, tx1.getInput(0).withScriptSig(Script.parse(new byte[111])));
         assertEquals(79, tx1.getMessageSizeForPriorityCalc());
     }