optimize requests sent by RemoteImporter with batch rpc calls

lib/remote-importer/remote-importer.js

@@ -260,19 +260,21 @@ class RemoteImporter {
 
       Logger.info(` Got ${scanTx.length} transactions`)
 
-      await util.seriesCall(scanTx, async txid => {
-        try {
-          const tx = await rpcTxns.getTransaction(txid, false)
-          if (tx == null) {
-            Logger.info(`   got null for ${txid}`)
-            return null
+      // Retrieve the transactions by batches of 100 transactions
+      const txsChunks = util.splitList(scanTx, 100)
+      try {
+        for (let txsChunk of txsChunks) {
+          const txs = await rpcTxns.getTransactions(txsChunk, false)
+          for (let tx of txs) {
+            if (tx != null) {
+              ret.transactions.push(tx)
+              txids[tx.txid] = true
+            }
           }
-          ret.transactions.push(tx)
-          txids[tx.txid] = true
-        } catch(e) {
-          Logger.error(e, `RemoteImporter.xpubScan() : rawTransaction error, txid ${txid}`)
         }
-      })
+      } catch(e) {
+        Logger.error(e, `RemoteImporter.xpubScan() : getTransactions error`)
+      }
 
       if (gotTransactions) {
         // We must go deeper
@@ -335,15 +337,14 @@ class RemoteImporter {
 
       Logger.info(` Got ${scanTx.length} transactions`)
 
-      // Get transaction s data from bitcoind
-      await util.seriesCall(scanTx, async txid => {
-        const tx = await rpcTxns.getTransaction(txid, false)
-        if (tx == null) {
-          Logger.info(`   got null for ${txid}`)
-          return null
-        }
-        txns.push(tx)
-      })
+      // Retrieve the transactions by batches of 100 transactions
+      const txsChunks = util.splitList(scanTx, 100)
+      for (let txsChunk of txsChunks) {
+        const txs = await rpcTxns.getTransactions(txsChunk, false)
+        for (let tx of txs)
+          if (tx != null)
+            txns.push(tx)
+      }
 
       // Import addresses and transactions into the database
       await db.addAddresses(imported)