addrindexer: minor.

* allocate one buffer istead of concat.
* return results instead of mutating array.

lib/indexer/addrindexer.js

@@ -211,8 +211,6 @@ class AddrIndexer extends Indexer {
    */
 
   async getHashesByAddress(addr, options = {}) {
-    const txs = [];
-
     const {after, reverse} = options;
     let {limit} = options;
 
@@ -230,7 +228,7 @@ class AddrIndexer extends Indexer {
       reverse,
       parse: (key) => {
         const [,, height, index] = layout.A.decode(key);
-        txs.push([height, index]);
+        return [height, index];
       }
     };
 
@@ -265,8 +263,7 @@ class AddrIndexer extends Indexer {
       opts.lte = layout.A.max(prefix, hash);
     }
 
-    await this.db.keys(opts);
-
+    const txs = await this.db.keys(opts);
     const hashes = [];
 
     for (const [height, index] of txs)

lib/mempool/addrindexer.js

@@ -44,10 +44,15 @@ class AddrIndexer {
     if (prefix < 0)
       return null;
 
-    const raw = Buffer.allocUnsafe(1);
-    raw.writeUInt8(prefix);
+    const hash = addr.getHash();
+    const size = hash.length + 1;
+    const raw = Buffer.allocUnsafe(size);
 
-    return Buffer.concat([raw, addr.getHash()]);
+    let written = raw.writeUInt8(prefix);
+    written += hash.copy(raw, 1);
+    assert(written === size);
+
+    return raw;
   }
 
   /**