Lookup txid in external Electrum txindex

This only works with Electrs and requires enabling BTCEXP_ELECTRUM_TXINDEX.

See: romanz/electrs@a0a3d4f

.env-sample

@@ -44,6 +44,9 @@
 # used if BTCEXP_ADDRESS_API=electrumx
 #BTCEXP_ELECTRUMX_SERVERS=tls://electrumx.server.com:50002,tcp://127.0.0.1:50001,...
 
+# Use the Electrumx server as an external txindex. This is only available in Electrs.
+#BTCEXP_ELECTRUM_TXINDEX=true
+
 # Set number of concurrent RPC requests. Should be lower than your node's "rpcworkqueue" value.
 # Note that Bitcoin Core's default rpcworkqueue=16.
 # Default: 10

app/api/electrumAddressApi.js

@@ -323,6 +323,25 @@ function getAddressBalance(addrScripthash) {
 	});
 }
 
+// Lookup the confirming block hash of a given txid. This only works with Electrs.
+// https://github.com/romanz/electrs/commit/a0a3d4f9392e21f9e92fdc274c88fed6d0634794
+function lookupTxBlockHash(txid) {
+	if (electrumClients.length == 0) {
+		return Promise.reject({ error: "No ElectrumX Connection", userText: noConnectionsErrorText });
+	}
+
+	return runOnAllServers(function(electrumClient) {
+		return electrumClient.request('blockchain.transaction.get_confirmed_blockhash', [txid]);
+	}).then(function(results) {
+		var blockhash = results[0].result;
+		if (results.slice(1).every(({ result }) => result == blockhash)) {
+			return blockhash;
+		} else {
+			return Promise.reject({conflictedResults:results});
+		}
+	});
+}
+
 function logStats(cmd, dt, success) {
 	if (!global.electrumStats.rpc[cmd]) {
 		global.electrumStats.rpc[cmd] = {count:0, time:0, successes:0, failures:0};
@@ -341,6 +360,7 @@ function logStats(cmd, dt, success) {
 
 module.exports = {
 	connectToServers: connectToServers,
-	getAddressDetails: getAddressDetails
+	getAddressDetails: getAddressDetails,
+	lookupTxBlockHash: lookupTxBlockHash,
 };
 

app/api/rpcApi.js

@@ -268,6 +268,17 @@ function getRawTransaction(txid, blockhash) {
 }
 
 async function noTxIndexTransactionLookup(txid) {
+	// Try looking up with an external Electrum server, using 'get_confirmed_blockhash'.
+	// This is only available in Electrs and requires enabling BTCEXP_ELECTRUM_TXINDEX.
+	if (config.addressApi == "electrumx" && config.electrumTxIndex) {
+		try {
+			var blockhash = await electrumAddressApi.lookupTxBlockHash(txid);
+			return await getRawTransaction(txid, blockhash);
+		} catch (err) {
+			debugLog(`Electrs blockhash lookup failed for ${txid}:`, err);
+		}
+	}
+
 	// Try looking up in wallet transactions
 	for (var wallet of await listWallets()) {
 		try { return await getWalletTransaction(wallet, txid); }

app/config.js

@@ -49,7 +49,8 @@ for (var i = 0; i < electrumXServerUriStrings.length; i++) {
 	"BTCEXP_DEMO",
 	"BTCEXP_PRIVACY_MODE",
 	"BTCEXP_NO_INMEMORY_RPC_CACHE",
-	"BTCEXP_RPC_ALLOWALL"
+	"BTCEXP_RPC_ALLOWALL",
+	"BTCEXP_ELECTRUM_TXINDEX",
 
 ].forEach(function(item) {
 	if (process.env[item] === undefined) {
@@ -170,6 +171,7 @@ module.exports = {
 	],
 
 	addressApi:process.env.BTCEXP_ADDRESS_API,
+	electrumTxIndex:process.env.BTCEXP_ELECTRUM_TXINDEX != "false",
 	electrumXServers:electrumXServers,
 
 	redisUrl:process.env.BTCEXP_REDIS_URL,