From c7300714c57652e68fcadcdbcfcce3df8dd7d37b Mon Sep 17 00:00:00 2001
From: Adam Soltys <adam@coinos.io>
Date: Mon, 2 Mar 2026 22:50:58 -0800
Subject: fee bumping

---
 lib/cpfp.ts | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 lib/cpfp.ts

(limited to 'lib/cpfp.ts')

diff --git a/lib/cpfp.ts b/lib/cpfp.ts
new file mode 100644
index 00000000..6f0eb948
--- /dev/null
+++ b/lib/cpfp.ts
@@ -0,0 +1,107 @@
+import config from "$config";
+import { s } from "$lib/db";
+import { l } from "$lib/logging";
+import { CHILD_VSIZE } from "$lib/p2a";
+import { fail, sats } from "$lib/utils";
+import rpc from "@coinos/rpc";
+
+const bc = rpc(config.bitcoin);
+
+export function estimateBumpCost(
+  parentFee: number,
+  parentVsize: number,
+  targetFeeRate: number,
+): number {
+  const packageVsize = parentVsize + CHILD_VSIZE;
+  const requiredPackageFee = Math.ceil(targetFeeRate * packageVsize);
+  return Math.max(0, requiredPackageFee - parentFee);
+}
+
+export async function createCpfpChild(payment: any, targetFeeRate: number) {
+  const { hash: parentTxid, p2aVout, parentVsize, fee: parentFee, bumpReserve } = payment;
+
+  if (p2aVout < 0) fail("no P2A output on this transaction");
+
+  const childFee = estimateBumpCost(parentFee, parentVsize, targetFeeRate);
+  if (childFee <= 0) fail("transaction already meets target fee rate");
+  if (childFee > bumpReserve) fail("bump cost exceeds reserve");
+
+  // Get a confirmed wallet UTXO to fund the child
+  const utxos = await bc.listUnspent(1);
+  if (!utxos.length) fail("no confirmed wallet UTXOs available for bump");
+
+  const walletUtxo = utxos[0];
+  const walletUtxoValue = sats(walletUtxo.amount);
+  const p2aValue = 240;
+
+  const changeValue = walletUtxoValue + p2aValue - childFee;
+  if (changeValue < 0) fail("wallet UTXO too small for bump");
+
+  // Get a change address from the wallet
+  const changeAddress = await bc.getRawChangeAddress();
+
+  // Build child tx inputs
+  const inputs = [
+    { txid: parentTxid, vout: p2aVout },
+    { txid: walletUtxo.txid, vout: walletUtxo.vout },
+  ];
+
+  // Build child tx outputs
+  const outputs = [{ [changeAddress]: parseFloat((changeValue / 1e8).toFixed(8)) }];
+
+  // Create raw transaction with nVersion=3 (TRUC child must also be v3)
+  let raw = await bc.createRawTransaction(inputs, outputs);
+  raw = "03000000" + raw.substring(8);
+
+  // Sign — wallet signs the wallet input, P2A input needs no signature (keyless anchor)
+  if ((config.bitcoin as any).walletpass) await bc.walletPassphrase((config.bitcoin as any).walletpass, 300);
+  const { hex } = await bc.signRawTransactionWithWallet(raw);
+
+  // Verify child vsize ≤ 1000 (TRUC child limit)
+  const decoded = await bc.decodeRawTransaction(hex);
+  if (decoded.vsize > 1000) fail("child transaction exceeds TRUC 1kvB limit");
+
+  // Try mempool accept, fall back to package submission
+  let childTxid: string;
+  try {
+    const r = await bc.testMempoolAccept([hex]);
+    if (r[0].allowed) {
+      childTxid = await bc.sendRawTransaction(hex);
+    } else {
+      // Parent might not be in mempool — try package submission
+      const parentHex = await bc.getRawTransaction(parentTxid);
+      const pkg = await bc.submitPackage([parentHex, hex]);
+      if (pkg["tx-results"]) {
+        const results = Object.values(pkg["tx-results"]) as any[];
+        const childResult = results[results.length - 1];
+        childTxid = childResult?.txid || decoded.txid;
+      } else {
+        fail("package submission failed");
+      }
+    }
+  } catch (e) {
+    // Try package submission as fallback
+    try {
+      const parentHex = await bc.getRawTransaction(parentTxid);
+      const pkg = await bc.submitPackage([parentHex, hex]);
+      if (pkg["tx-results"]) {
+        const results = Object.values(pkg["tx-results"]) as any[];
+        const childResult = results[results.length - 1];
+        childTxid = childResult?.txid || decoded.txid;
+      } else {
+        fail("package submission failed");
+      }
+    } catch (e2) {
+      fail(`bump failed: ${e2.message}`);
+    }
+  }
+
+  // Update payment
+  payment.childTxid = childTxid;
+  payment.bumpedFee = childFee;
+  await s(`payment:${payment.id}`, payment);
+
+  l("CPFP bump", parentTxid, "->", childTxid, "fee:", childFee);
+
+  return { txid: childTxid, childFee };
+}
-- 
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