refactor(abstract-utxo): accept better arguments for explainTx and explainPsbt

Move decoding step to callsite

Issue: BTC-1450

Author: OttoAllmendinger

modules/abstract-utxo/src/abstractUtxoCoin.ts

@@ -1503,7 +1503,11 @@ export abstract class AbstractUtxoCoin extends BaseCoin {
     if (typeof txHex !== 'string' || !txHex.match(/^([a-f0-9]{2})+$/i)) {
       throw new Error('invalid transaction hex, must be a valid hex string');
     }
-    return utxolib.bitgo.isPsbt(txHex) ? explainPsbt(params, this.network) : explainTx(params, this);
+    if (utxolib.bitgo.isPsbt(txHex)) {
+      return explainPsbt(utxolib.bitgo.createPsbtFromHex(txHex, this.network), params, this.network);
+    } else {
+      return explainTx(this.createTransactionFromHex<TNumber>(txHex), params, this.network);
+    }
   }
 
   /**

modules/abstract-utxo/src/transaction.ts

@@ -258,17 +258,11 @@ function getTxInputSignaturesCount<TNumber extends number | bigint>(
  * Decompose a raw psbt into useful information, such as the total amounts,
  * change amounts, and transaction outputs.
  */
-export function explainPsbt<TNumber extends number | bigint>(
+export function explainPsbt<TNumber extends number | bigint, Tx extends bitgo.UtxoTransaction<bigint>>(
+  psbt: bitgo.UtxoPsbt<Tx>,
   params: ExplainTransactionOptions<TNumber>,
   network: utxolib.Network
 ): TransactionExplanation {
-  const { txHex } = params;
-  let psbt: bitgo.UtxoPsbt;
-  try {
-    psbt = bitgo.createPsbtFromHex(txHex, network);
-  } catch (e) {
-    throw new Error('failed to parse psbt hex');
-  }
   const txOutputs = psbt.txOutputs;
 
   function getChainAndIndexFromBip32Derivations(output: bitgo.PsbtOutput) {
@@ -346,18 +340,12 @@ export function explainPsbt<TNumber extends number | bigint>(
  * change amounts, and transaction outputs.
  */
 export function explainTx<TNumber extends number | bigint>(
+  tx: bitgo.UtxoTransaction<TNumber>,
   params: ExplainTransactionOptions<TNumber>,
-  coin: AbstractUtxoCoin
+  network: utxolib.Network
 ): TransactionExplanation {
-  const { txHex } = params;
-  let tx;
-  try {
-    tx = coin.createTransactionFromHex(txHex);
-  } catch (e) {
-    throw new Error('failed to parse transaction hex');
-  }
-  const common = explainCommon(tx, params, coin.network);
-  const inputSignaturesCount = getTxInputSignaturesCount(tx, params, coin.network);
+  const common = explainCommon(tx, params, network);
+  const inputSignaturesCount = getTxInputSignaturesCount(tx, params, network);
   return {
     ...common,
     inputSignatures: inputSignaturesCount,