Merge pull request #1401 from testn/remove-slice

Optimize string decoding by removing the use of slice()

Author: sidorares

lib/packets/column_definition.js

@@ -45,8 +45,10 @@ class ColumnDefinition {
     this.characterSet = packet.readInt16();
     this.encoding = CharsetToEncoding[this.characterSet];
     this.name = StringParser.decode(
-      this._buf.slice(_nameStart, _nameStart + _nameLength),
-      this.encoding === 'binary' ? this._clientEncoding : this.encoding
+      this._buf,
+      this.encoding === 'binary' ? this._clientEncoding : this.encoding,
+      _nameStart, 
+      _nameStart + _nameLength
     );
     this.columnLength = packet.readInt32();
     this.columnType = packet.readInt8();
@@ -113,8 +115,10 @@ const addString = function(name) {
       const start = this[`_${name}Start`];
       const end = start + this[`_${name}Length`];
       const val = StringParser.decode(
-        this._buf.slice(start, end),
-        this.encoding === 'binary' ? this._clientEncoding : this.encoding
+        this._buf,
+        this.encoding === 'binary' ? this._clientEncoding : this.encoding,
+        start, 
+        end
       );
 
       Object.defineProperty(this, name, {

lib/packets/packet.js

@@ -387,8 +387,10 @@ class Packet {
     // TODO: Use characterSetCode to get proper encoding
     // https://github.com/sidorares/node-mysql2/pull/374
     return StringParser.decode(
-      this.buffer.slice(this.offset - len, this.offset),
-      encoding
+      this.buffer,
+      encoding,
+      this.offset - len,
+      this.offset
     );
   }
 
@@ -407,7 +409,7 @@ class Packet {
       end = end + 1; // TODO: handle OOB check
     }
     this.offset = end + 1;
-    return StringParser.decode(this.buffer.slice(start, end), encoding);
+    return StringParser.decode(this.buffer, encoding, start, end);
   }
 
   // TODO reuse?
@@ -421,8 +423,10 @@ class Packet {
     }
     this.offset += len;
     return StringParser.decode(
-      this.buffer.slice(this.offset - len, this.offset),
-      encoding
+      this.buffer,
+      encoding,
+      this.offset - len, 
+      this.offset
     );
   }
 

lib/parsers/string.js

@@ -2,14 +2,14 @@
 
 const Iconv = require('iconv-lite');
 
-exports.decode = function(buffer, encoding, options) {
+exports.decode = function(buffer, encoding, start, end, options) {
   if (Buffer.isEncoding(encoding)) {
-    return buffer.toString(encoding);
+    return buffer.toString(encoding, start, end);
   }
 
   const decoder = Iconv.getDecoder(encoding, options || {});
 
-  const res = decoder.write(buffer);
+  const res = decoder.write(buffer.slice(start, end));
   const trail = decoder.end();
 
   return trail ? res + trail : res;