cache deserialized form of txs in history method

Prior to this commit, while the result of the gettransaction rpc call
was being cached so as to not have to repeat these rpc calls, the
deserialized form of the transaction created by a call to
CMutableTransaction.deserialize, was not, and since this call is rather
expensive, the history method was running more slowly than needed.
After this commit, we cache the deserialized form also, resulting in a
speedup to the wallet_utils.wallet_fetch_history method.

src/jmclient/wallet_utils.py

@@ -9,6 +9,7 @@ from optparse import OptionParser
 from numbers import Integral
 from collections import Counter, defaultdict
 from itertools import islice, chain
+from typing import Optional, Tuple
 from jmclient import (get_network, WALLET_IMPLEMENTATIONS, Storage, podle,
     jm_single, WalletError, BaseWallet, VolatileStorage,
     StoragePasswordError, is_segwit_mode, SegwitLegacyWallet, LegacyWallet,
@@ -364,7 +365,8 @@ class WalletView(WalletViewBase):
         json_serialized.update(self.get_fmt_balance_json())
         return json_serialized
 
-def get_tx_info(txid, tx_cache=None):
+def get_tx_info(txid: str, tx_cache: Optional[dict] = None) -> Tuple[
+    bool, int, int, dict, int, btc.CTransaction]:
     """
     Retrieve some basic information about the given transaction.
 
@@ -379,14 +381,14 @@ def get_tx_info(txid, tx_cache=None):
         txd: deserialized transaction object (hex-encoded data)
     """
     if tx_cache is not None and txid in tx_cache:
-        rpctx = tx_cache[txid]
+        rpctx, rpctx_deser = tx_cache[txid]
     else:
         rpctx = jm_single().bc_interface.get_transaction(txid)
+        txhex = str(rpctx['hex'])
+        rpctx_deser = btc.CMutableTransaction.deserialize(hextobin(txhex))
         if tx_cache is not None:
-            tx_cache[txid] = rpctx
-    txhex = str(rpctx['hex'])
-    tx = btc.CMutableTransaction.deserialize(hextobin(txhex))
-    output_script_values = {x.scriptPubKey: x.nValue for x in tx.vout}
+            tx_cache[txid] = (rpctx, rpctx_deser)
+    output_script_values = {x.scriptPubKey: x.nValue for x in rpctx_deser.vout}
     value_freq_list = sorted(
         Counter(output_script_values.values()).most_common(),
         key=lambda x: -x[1])
@@ -398,7 +400,7 @@ def get_tx_info(txid, tx_cache=None):
     cj_amount = value_freq_list[0][0]
     cj_n = value_freq_list[0][1]
     return is_coinjoin, cj_amount, cj_n, output_script_values,\
-        rpctx.get('blocktime', 0), tx
+        rpctx.get('blocktime', 0), rpctx_deser
 
 
 def get_imported_privkey_branch(wallet_service, m, showprivkey):
@@ -846,7 +848,6 @@ def wallet_fetch_history(wallet, options):
                 'blocktme' not in tx)
         tx_db.executemany('INSERT INTO transactions VALUES(?, ?, ?, ?);',
                 uc_tx_data)
-
     txes = tx_db.execute(
         'SELECT DISTINCT txid, blockhash, blocktime '
         'FROM transactions '
@@ -903,22 +904,23 @@ def wallet_fetch_history(wallet, options):
 
         our_output_scripts = wallet_script_set.intersection(
             output_script_values.keys())
-
         rpc_inputs = []
         for ins in txd.vin:
             if ins.prevout.hash[::-1] in tx_cache:
-                wallet_tx = tx_cache[ins.prevout.hash[::-1]]
+                wallet_tx, wallet_tx_deser = tx_cache[ins.prevout.hash[::-1]]
             else:
                 wallet_tx = jm_single().bc_interface.get_transaction(
                     ins.prevout.hash[::-1])
-                tx_cache[ins.prevout.hash[::-1]] = wallet_tx
+                if wallet_tx:
+                    wallet_tx_deser = btc.CMutableTransaction.deserialize(
+                        hextobin(wallet_tx['hex']))
+                    tx_cache[ins.prevout.hash[::-1]] = (wallet_tx,
+                                                        wallet_tx_deser)
             if wallet_tx is None:
                 continue
-            inp = btc.CMutableTransaction.deserialize(hextobin(
-                wallet_tx['hex'])).vout[ins.prevout.n]
+            inp = wallet_tx_deser.vout[ins.prevout.n]
             input_dict = {"script": inp.scriptPubKey, "value": inp.nValue}
             rpc_inputs.append(input_dict)
-
         rpc_input_scripts = set(ind['script'] for ind in rpc_inputs)
         our_input_scripts = wallet_script_set.intersection(rpc_input_scripts)
         our_input_values = [