From c16db7bbb205607d01b76b4dc9cbbd4f20377106 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A2u=20Cao?= <raucao@kosmos.org>
Date: Fri, 2 May 2025 17:35:25 +0400
Subject: [PATCH] Add fuzzing for amounts

* +- 0 to 1%, or +- 1 sat for tiny amounts
* Ensure balance cannot go negative
---
 generate-stats.ts | 54 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 42 insertions(+), 12 deletions(-)

diff --git a/generate-stats.ts b/generate-stats.ts
index 96a5a10..9259a68 100644
--- a/generate-stats.ts
+++ b/generate-stats.ts
@@ -17,7 +17,7 @@ for (const key of ["DB_USER", "DB_PASSWORD", "DB_NAME", "ANONYMIZATION_KEY"]) {
 // Adjust based on database capacity
 const BATCH_SIZE = parseInt(env.BATCH_SIZE) || 10;
 // Maximum number of invoices to process per user
-// Skip user if exceeded (likely the case for streaming payments e.g.)
+// Skip user if exceeded (likely the case for streaming payments)
 const MAX_INVOICES = parseInt(env.MAX_INVOICES) || 21000;
 
 // Database connection configuration from .env or environment variables
@@ -72,7 +72,7 @@ const csvHeaders = [
 // Write headers to CSV (create file or overwrite if it exists)
 await Deno.writeTextFile(csvFilePath, csvHeaders.join(",") + "\n");
 
-// Function to compute HMAC-SHA256 hash of user_id, truncated to 48 bits (12 hex chars)
+// Compute HMAC-SHA256 hash of user_id, truncated to 48 bits (12 hex chars)
 async function anonymizeUserId(userId) {
   const keyData = new TextEncoder().encode(env.ANONYMIZATION_KEY);
   const data = new TextEncoder().encode(userId.toString());
@@ -88,7 +88,19 @@ async function anonymizeUserId(userId) {
   return hashArray.map((b) => b.toString(16).padStart(2, "0")).join("");
 }
 
-// Function to process a single user and return CSV rows
+// Generate a random fuzzing factor
+function getFuzzFactor(amount) {
+  const bytes = new Uint8Array(4);
+  crypto.getRandomValues(bytes);
+  const randomValue = new Uint32Array(bytes.buffer)[0];
+  const normalized = randomValue / 0xFFFFFFFF;
+  if (amount < 100) {
+    return normalized < 0.5 ? -1 : 1; // ±1 satoshi for small amounts
+  }
+  return normalized * 0.02 - 0.01; // -1% to +1% for larger amounts
+}
+
+// Process a single user and return CSV rows
 async function processUser(userId, client) {
   // Check the number of settled invoices for the user
   const countResult = await client.queryObject(
@@ -123,16 +135,34 @@ async function processUser(userId, client) {
 
   for (const invoice of invoices) {
     const day = invoice.settled_at.toISOString().split("T")[0]; // YYYY-MM-DD
-    // Convert amounts to BigInt, handling NULL fees
-    const amount = BigInt(invoice.amount);
-    const serviceFee = invoice.service_fee ? BigInt(invoice.service_fee) : BigInt(0);
-    const routingFee = invoice.routing_fee ? BigInt(invoice.routing_fee) : BigInt(0);
 
-    // Calculate effective amount: include fees for outgoing, not for incoming
-    const effectiveAmount = invoice.type === "incoming"
-      ? amount
-      : amount + serviceFee + routingFee; // Add fees for outgoing
-    const signedAmount = invoice.type === "incoming" ? effectiveAmount : -effectiveAmount;
+    // Get fuzzing factor for this invoice
+    const fuzzFactor = getFuzzFactor(Number(invoice.amount));
+
+    // Convert amounts to BigInt
+    const amount = BigInt(invoice.amount);
+    const serviceFee = BigInt(invoice.service_fee);
+    const routingFee = BigInt(invoice.routing_fee);
+
+    // Apply fuzzing: value * (1 + fuzzFactor) or ±1 sat, rounded to nearest integer
+    let fuzzedAmount = amount < 100
+      ? amount + BigInt(fuzzFactor)
+      : BigInt(Math.round(Number(amount) * (1 + fuzzFactor)));
+
+    // Calculate effective amount: include fees for outgoing
+    let effectiveAmount = invoice.type === "incoming"
+      ? fuzzedAmount
+      : fuzzedAmount + serviceFee + routingFee; // Add fees for outgoing
+    let signedAmount = invoice.type === "incoming" ? effectiveAmount : -effectiveAmount;
+
+    // Prevent negative running balance for outgoing invoices
+    if (invoice.type === "outgoing" && runningBalance + signedAmount < 0) {
+      // Adjust fuzzed amount to spend only up to available balance
+      const maxSpend = runningBalance;
+      fuzzedAmount = maxSpend - serviceFee - routingFee;
+      effectiveAmount = fuzzedAmount + serviceFee + routingFee;
+      signedAmount = -effectiveAmount;
+    }
 
     if (!dailyData[day]) {
       dailyData[day] = {