buffer: optimize writing short strings

PR-URL: nodejs#54310

Author: ronag

benchmark/buffers/buffer-write-string.js

@@ -6,7 +6,7 @@ const bench = common.createBenchmark(main, {
     '', 'utf8', 'ascii', 'hex', 'utf16le', 'latin1',
   ],
   args: [ '', 'offset', 'offset+length' ],
-  len: [2048],
+  len: [1, 8, 16, 2048],
   n: [1e6],
 });
 

lib/buffer.js

@@ -1082,10 +1082,10 @@ function _fill(buf, value, offset, end, encoding) {
 Buffer.prototype.write = function write(string, offset, length, encoding) {
   // Buffer#write(string);
   if (offset === undefined) {
-    return this.utf8Write(string, 0, this.length);
-  }
+    offset = 0;
+    length = this.length;
   // Buffer#write(string, encoding)
-  if (length === undefined && typeof offset === 'string') {
+  } else if (length === undefined && typeof offset === 'string') {
     encoding = offset;
     length = this.length;
     offset = 0;
@@ -1108,6 +1108,29 @@ Buffer.prototype.write = function write(string, offset, length, encoding) {
     }
   }
 
+  const len = string?.length;
+  if (
+    len <= 16 &&
+    len <= length &&
+    (!encoding || encoding === 'ascii' || encoding === 'utf8') &&
+    typeof string === 'string'
+  ) {
+    let n = 0;
+    while (true) {
+      const code = StringPrototypeCharCodeAt(string, n);
+      if (code >= 128) {
+        break;
+      }
+
+      this[offset + n] = code;
+      n++;
+
+      if (n === len) {
+        return len;
+      }
+    }
+  }
+
   if (!encoding)
     return this.utf8Write(string, offset, length);