Work on #300

-Update docs to specify that txindex is necessary for pre-v0.21 nodes
-Gracefully handle getindexinfo failures for old nodes
-Use graceful failure to fallback to assuming that txindex=1 (as docs indicate is necessary)

I'm open to other approaches for identifying absence of txindex, but this should keep older clients functioning at 100% for now.

README.md

@@ -45,7 +45,8 @@ See [CHANGELOG.md](/CHANGELOG.md).
 
 ### Note about pruning and indexing configurations
 
-This tool is designed to work best with full transaction indexing enabled (`txindex=1`) and pruning **disabled**. Running Bitcoin Core *without* `txindex` enabled and/or *with* `pruning` enabled works, but some data will be incomplete or missing. Also note that such Bitcoin Core configurations receive less thorough testing.
+This tool is designed to work best with full transaction indexing enabled (`txindex=1`) and pruning **disabled**. 
+However, if you're running Bitcoin Core v0.21+ you can run *without* `txindex` enabled and/or *with* `pruning` enabled and this tool will continue to function, but some data will be incomplete or missing. Also note that such Bitcoin Core configurations receive less thorough testing.
 
 In particular, with `pruning` enabled and/or `txindex` disabled, the following functionality is altered:
 

app.js

@@ -276,6 +276,11 @@ function onRpcConnectionVerified(getnetworkinfo, getblockchaininfo, getindexinfo
 
 	if (getindexinfo.txindex) {
 		global.txindexAvailable = true;
+
+	} else if (getindexinfo.minRpcVersionNeeded) {
+		// here we ASSUME that txindex is available because we're targeting pre-v0.21
+		// and docs specify that txindex is necessary for pre-v0.21 nodes
+		global.txindexAvailable = true;
 	}
 
 	if (getblockchaininfo.pruned) {

app/api/rpcApi.js

@@ -26,7 +26,10 @@ const rpcQueue = async.queue(function(task, callback) {
 
 }, config.rpcConcurrency);
 
-const minRpcVersions = {getblockstats:"0.17.0"};
+const minRpcVersions = {
+	getblockstats: "0.17.0",
+	getindexinfo: "0.21.0"
+};
 
 global.rpcStats = {};
 
@@ -64,7 +67,13 @@ function getMiningInfo() {
 }
 
 function getIndexInfo() {
-	return getRpcData("getindexinfo");
+	if (semver.gte(global.btcNodeSemver, minRpcVersions.getindexinfo)) {
+		return getRpcData("getindexinfo");
+
+	} else {
+		// unsupported
+		return unsupportedPromise(minRpcVersions.getindexinfo);
+	}
 }
 
 function getUptimeSeconds() {
@@ -282,7 +291,7 @@ async function noTxIndexTransactionLookup(txid, walletOnly) {
 			var blockhash = await electrumAddressApi.lookupTxBlockHash(txid);
 
 			return await getRawTransaction(txid, blockhash);
-			
+
 		} catch (err) {
 			debugLog(`Electrs blockhash lookup failed for ${txid}:`, err);
 		}