Support offline signing coordination (#625)

README.md

@@ -10,7 +10,7 @@
     - [Using the Specter Desktop app](#using-the-specter-desktop-app)
     - [Installing Specter from Pip](#installing-specter-from-pip)
     - [Connect Specter to Bitcoin Core](#connect-specter-to-bitcoin-core)
-  - [Detailed instructions](#detailed-instructions)
+  - [Tips and tricks (detailed instructions)](#tips-and-tricks-detailed-instructions)
   - [Errors, doubts.. Read our FAQ!](#errors-doubts-read-our-faq)
   - [A few screenshots](#a-few-screenshots)
     - [Adding a new device](#adding-a-new-device)

src/cryptoadvance/specter/templates/wallet/send/sign/wallet_send_sign_psbt.jinja

@@ -115,6 +115,7 @@
 						{{ explorer_link('tx', input['txid'], input['txid'], specter.explorer) }}
 						(Output #{{ input['vout'] }})<br>
 						{% set tx = wallet.gettransaction(input['txid']) %}
+						{% if tx %}
 						<b>Address:</b>
 						{{ explorer_link('address', tx['details'][0]['address'], tx['details'][0]['address'], specter.explorer) }}
 						<br>
@@ -122,6 +123,7 @@
 							<b>Label:</b> {{ tx['details'][0]['label'] }}<br>
 						{% endif %}
 						<b>Amount:</b> {{ psbt['inputs'][loop.index0]['witness_utxo']['amount'] }} BTC
+						{% endif %}
 					</p>
 				{% endfor %}
 				<h2 class="tx_details_header">Outputs ({{psbt['tx']['vout']|length}})</h2>

src/cryptoadvance/specter/wallet.py

@@ -555,7 +555,10 @@ class Wallet:
         return sorted(result, key=lambda tx: tx["confirmations"])
 
     def gettransaction(self, txid, blockheight=None):
-        return self._transactions.gettransaction(txid, blockheight)
+        try:
+            return self._transactions.gettransaction(txid, blockheight)
+        except Exception as e:
+            logger.warning("Could not get transaction {}, error: {}".format(txid, e))
 
     def rescanutxo(self, explorer=None):
         t = threading.Thread(target=self._rescan_utxo_thread, args=(explorer,))
@@ -1184,12 +1187,14 @@ class Wallet:
                 txid = inp.prevout.hash.to_bytes(32, "big").hex()
                 try:
                     res = self.gettransaction(txid)
+                    stream = BytesIO(bytes.fromhex(res["hex"]))
+                    prevtx = CTransaction()
+                    prevtx.deserialize(stream)
+                    psbt.inputs[i].non_witness_utxo = prevtx
                 except:
-                    raise SpecterError("Can't find previous transaction in the wallet.")
-                stream = BytesIO(bytes.fromhex(res["hex"]))
-                prevtx = CTransaction()
-                prevtx.deserialize(stream)
-                psbt.inputs[i].non_witness_utxo = prevtx
+                    logger.error(
+                        "Can't find previous transaction in the wallet. Signing might not be possible for certain devices..."
+                    )
         else:
             # remove non_witness_utxo if we don't want them
             for inp in psbt.inputs: