Add support for Discount CT (#120)

Author: michael1011

src/transaction.d.ts

@@ -45,8 +45,8 @@ export declare class Transaction {
     addInput(hash: Buffer, index: number, sequence?: number, scriptSig?: Buffer, issuance?: Issuance): number;
     addOutput(scriptPubKey: Buffer, value: Buffer, asset: Buffer, nonce: Buffer, rangeProof?: Buffer, surjectionProof?: Buffer): number;
     hasWitnesses(): boolean;
-    weight(): number;
-    virtualSize(): number;
+    weight(discountCT?: boolean): number;
+    virtualSize(discountCT?: boolean): number;
     byteLength(_ALLOW_WITNESS?: boolean): number;
     clone(): Transaction;
     /**

src/transaction.js

@@ -280,14 +280,44 @@ class Transaction {
       })
     );
   }
-  weight() {
-    const base = this.__byteLength(false);
-    const total = this.__byteLength(true);
-    return base * (WITNESS_SCALE_FACTOR - 1) + total;
+  weight(discountCT = true) {
+    const base = this.__byteLength(false, false);
+    const total = this.__byteLength(true, false);
+    let weight = base * (WITNESS_SCALE_FACTOR - 1) + total;
+    if (!discountCT) {
+      return weight;
+    }
+    for (const txOut of this.outs) {
+      let witnessWeight = 0;
+      if (txOut.rangeProof !== undefined && txOut.rangeProof.length > 0) {
+        witnessWeight += txOut.rangeProof.length;
+        witnessWeight += bufferutils_1.varuint.encodingLength(
+          txOut.rangeProof.length,
+        );
+      }
+      if (
+        txOut.surjectionProof !== undefined &&
+        txOut.surjectionProof.length > 0
+      ) {
+        witnessWeight += txOut.surjectionProof.length;
+        witnessWeight += bufferutils_1.varuint.encodingLength(
+          txOut.surjectionProof.length,
+        );
+      }
+      // Explicit transactions have 1 byte for each empty proof
+      weight -= Math.max(witnessWeight - 2, 0);
+      // When the output has a range proof, it is safe to assume that the nonce and value are confidential
+      if (txOut.rangeProof !== undefined && txOut.rangeProof.length > 0) {
+        weight -= (33 - 9) * 4;
+        weight -= (33 - 1) * 4;
+      }
+    }
+    return weight;
   }
-  virtualSize() {
+  virtualSize(discountCT = true) {
     const vsize =
-      (this.weight() + WITNESS_SCALE_FACTOR - 1) / WITNESS_SCALE_FACTOR;
+      (this.weight(discountCT) + WITNESS_SCALE_FACTOR - 1) /
+      WITNESS_SCALE_FACTOR;
     return Math.floor(vsize);
   }
   byteLength(_ALLOW_WITNESS) {

test/fixtures/transaction.json

@@ -26,4 +26,22 @@ describe('Transaction', () => {
       });
     }
   });
+
+  describe('calculates weight and virtualSize', () => {
+    const fixtures = jsonFixture.discountCT;
+    for (const test of fixtures) {
+      it(test.description, () => {
+        const tx = Transaction.fromHex(test.txHex);
+        assert.strictEqual(tx.weight(false), test.weight);
+        assert.strictEqual(tx.virtualSize(false), test.vSize);
+
+        assert.strictEqual(tx.weight(true), test.discountWeight);
+        assert.strictEqual(tx.virtualSize(true), test.discountVSize);
+
+        // Check that the default behavior is discounted CT
+        assert.strictEqual(tx.weight(), test.discountWeight);
+        assert.strictEqual(tx.virtualSize(), test.discountVSize);
+      });
+    }
+  });
 });

test/transaction.spec.ts

@@ -314,15 +314,47 @@ export class Transaction {
     );
   }
 
-  weight(): number {
-    const base = this.__byteLength(false);
-    const total = this.__byteLength(true);
-    return base * (WITNESS_SCALE_FACTOR - 1) + total;
+  weight(discountCT = true): number {
+    const base = this.__byteLength(false, false);
+    const total = this.__byteLength(true, false);
+    let weight = base * (WITNESS_SCALE_FACTOR - 1) + total;
+
+    if (!discountCT) {
+      return weight;
+    }
+
+    for (const txOut of this.outs) {
+      let witnessWeight = 0;
+
+      if (txOut.rangeProof !== undefined && txOut.rangeProof.length > 0) {
+        witnessWeight += txOut.rangeProof.length;
+        witnessWeight += varuint.encodingLength(txOut.rangeProof.length);
+      }
+      if (
+        txOut.surjectionProof !== undefined &&
+        txOut.surjectionProof.length > 0
+      ) {
+        witnessWeight += txOut.surjectionProof.length;
+        witnessWeight += varuint.encodingLength(txOut.surjectionProof.length);
+      }
+
+      // Explicit transactions have 1 byte for each empty proof
+      weight -= Math.max(witnessWeight - 2, 0);
+
+      // When the output has a range proof, it is safe to assume that the nonce and value are confidential
+      if (txOut.rangeProof !== undefined && txOut.rangeProof.length > 0) {
+        weight -= (33 - 9) * 4;
+        weight -= (33 - 1) * 4;
+      }
+    }
+
+    return weight;
   }
 
-  virtualSize(): number {
+  virtualSize(discountCT = true): number {
     const vsize =
-      (this.weight() + WITNESS_SCALE_FACTOR - 1) / WITNESS_SCALE_FACTOR;
+      (this.weight(discountCT) + WITNESS_SCALE_FACTOR - 1) /
+      WITNESS_SCALE_FACTOR;
     return Math.floor(vsize);
   }