feat(blockapis): add fetchPrevTxBuffers

This is a helper function that fetches the previous transaction buffers.

We are reusing Buffer references

modules/blockapis/src/UtxoApi.ts

@@ -42,32 +42,60 @@ export interface UtxoApi extends TransactionApi {
   getUnspentsForAddresses(address: string[]): Promise<utxolib.bitgo.Unspent[]>;
 }
 
+function toOutPoints(arr: utxolib.TxInput[] | utxolib.bitgo.TxOutPoint[]): utxolib.bitgo.TxOutPoint[] {
+  return arr.map((i) => {
+    if ('txid' in i) {
+      return i;
+    }
+    return utxolib.bitgo.getOutputIdForInput(i);
+  });
+}
+
 /**
- * Helper to efficiently fetch output data.
- * Typical we can query output data for all outputs of a transaction, so we first fetch all
- * the output list via `f` and then pick the output data from the result.
+ * Helper to efficiently fetch output data. Deduplicates transaction ids and only does one lookup per txid.
  * @param outpoints
- * @param f - maps txid to a list of outputs with type TOut
- * @return list of TOut corresponding to outputs
+ * @param f - lookup function for txid
+ * @return list of T corresponding to outpoints
  */
-async function mapInputs<TOut>(
-  outpoints: utxolib.bitgo.TxOutPoint[],
-  f: (txid: string) => Promise<TOut[]>
-): Promise<TOut[]> {
+async function mapInputs<T>(outpoints: utxolib.bitgo.TxOutPoint[], f: (txid: string) => Promise<T>): Promise<T[]> {
   const txids = [...new Set(outpoints.map((i) => i.txid))];
   const txMap = new Map(await mapSeries(txids, async (txid) => [txid, await f(txid)]));
   return outpoints.map((i) => {
-    const arr = txMap.get(i.txid);
-    if (arr) {
-      if (i.vout in arr) {
-        return arr[i.vout];
-      }
-      throw new Error(`could not find output ${i.vout}`);
+    const v = txMap.get(i.txid);
+    if (!v) {
+      throw new Error(`could not find tx ${i.txid}`);
     }
-    throw new Error(`could not find tx ${i.txid}`);
+    return v;
   });
 }
 
+/**
+ * @param outpoints
+ * @param f - maps txid to a list of TOut.
+ * @return list of TOut corresponding to outpoints
+ */
+async function mapInputsVOut<TOut>(
+  outpoints: utxolib.bitgo.TxOutPoint[],
+  f: (txid: string) => Promise<TOut[]>
+): Promise<TOut[]> {
+  const allOutputs = await mapInputs(outpoints, f);
+  return outpoints.map((p, i) => {
+    const arr = allOutputs[i];
+    if (p.vout in arr) {
+      return allOutputs[i][p.vout];
+    }
+    throw new Error(`could not find output ${p.vout}`);
+  });
+}
+
+export async function fetchPrevTxBuffers(
+  ins: utxolib.TxInput[] | utxolib.bitgo.TxOutPoint[],
+  api: UtxoApi,
+  _network: utxolib.Network
+): Promise<Buffer[]> {
+  return mapInputs(toOutPoints(ins), async (txid) => Buffer.from(await api.getTransactionHex(txid), 'hex'));
+}
+
 /**
  * Fetch transaction inputs from transaction input list
  * @param ins
@@ -79,13 +107,8 @@ export async function fetchInputs(
   api: UtxoApi,
   network: utxolib.Network
 ): Promise<utxolib.TxOutput[]> {
-  return mapInputs(
-    ins.map((i: utxolib.TxInput | utxolib.bitgo.TxOutPoint) => {
-      if ('txid' in i) {
-        return i;
-      }
-      return utxolib.bitgo.getOutputIdForInput(i);
-    }),
+  return mapInputsVOut(
+    toOutPoints(ins),
     async (txid) => utxolib.bitgo.createTransactionFromHex(await api.getTransactionHex(txid), network).outs
   );
 }
@@ -97,5 +120,5 @@ export async function fetchTransactionSpends(
   outpoints: utxolib.bitgo.TxOutPoint[],
   api: UtxoApi
 ): Promise<OutputSpend[]> {
-  return mapInputs(outpoints, async (txid) => await api.getTransactionSpends(txid));
+  return mapInputsVOut(outpoints, async (txid) => await api.getTransactionSpends(txid));
 }