From 1e3ff9645282f3334a09565f8a78b6d2040d7b41 Mon Sep 17 00:00:00 2001
From: josibake <josibake@protonmail.com>
Date: Fri, 31 May 2024 13:10:39 +0200
Subject: [PATCH] keep same target ordering

previously, the silent payment outputs were being added at the end
of the target array, which changes the order from what the caller requested.

instead, keep track of the original index while creating silent payment
outputs and return the targets in the original order.
---
 src/index.ts | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index e52d06e..23fae51 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -23,7 +23,7 @@ export type Target = {
 
 export type SilentPaymentGroup = {
   Bscan: Buffer;
-  BmValues: Array<[Buffer, number | undefined]>;
+  BmValues: Array<[Buffer, number | undefined, number]>;
 };
 
 function taggedHash(tag: string, data: Buffer): Buffer {
@@ -45,12 +45,13 @@ export class SilentPayment {
    * Numeric values (if present) for targets are passed through.
    */
   createTransaction(utxos: UTXO[], targets: Target[]): Target[] {
-    const ret: Target[] = [];
+    const ret: Target[] = new Array(targets.length);
 
     const silentPaymentGroups: Array<SilentPaymentGroup> = [];
-    for (const target of targets) {
+    for (let i = 0; i < targets.length; i++) {
+      const target = targets[i];
       if (!target.address?.startsWith("sp1")) {
-        ret.push(target); // passthrough
+        ret[i] = target; // passthrough
         continue;
       }
 
@@ -66,11 +67,11 @@ export class SilentPayment {
       // Addresses with the same Bscan key all belong to the same recipient
       const recipient = silentPaymentGroups.find((group) => Buffer.compare(group.Bscan, Bscan) === 0);
       if (recipient) {
-        recipient.BmValues.push([Bm, target.value]);
+        recipient.BmValues.push([Bm, target.value, i]);
       } else {
         silentPaymentGroups.push({
           Bscan: Bscan,
-          BmValues: [[Bm, target.value]],
+          BmValues: [[Bm, target.value, i]],
         });
       }
     }
@@ -87,7 +88,7 @@ export class SilentPayment {
       const ecdh_shared_secret = Buffer.from(ecc.getSharedSecret(ecdh_shared_secret_step1, group.Bscan) as Uint8Array);
 
       let k = 0;
-      for (const [Bm, amount] of group.BmValues) {
+      for (const [Bm, amount, i] of group.BmValues) {
         const tk = taggedHash("BIP0352/SharedSecret", Buffer.concat([ecdh_shared_secret!, SilentPayment._ser32(k)]));
 
         // Let Pmk = tk·G + Bm
@@ -97,7 +98,7 @@ export class SilentPayment {
         const address = SilentPayment.pubkeyToAddress(Pmk.slice(1).toString("hex"));
         const newTarget: Target = { address };
         newTarget.value = amount;
-        ret.push(newTarget);
+        ret[i] = newTarget;
         k += 1;
       }
     }