fix(std/node): add encoding argument to Buffer.byteLength (#6639)

std/node/buffer.ts

@@ -28,6 +28,46 @@ function checkEncoding(encoding = "utf8", strict = true): string {
   return normalized;
 }
 
+interface EncodingOp {
+  byteLength(string: string): number;
+}
+
+// https://github.com/nodejs/node/blob/56dbe466fdbc598baea3bfce289bf52b97b8b8f7/lib/buffer.js#L598
+const encodingOps: { [key: string]: EncodingOp } = {
+  utf8: {
+    byteLength: (string: string): number =>
+      new TextEncoder().encode(string).byteLength,
+  },
+  ucs2: {
+    byteLength: (string: string): number => string.length * 2,
+  },
+  utf16le: {
+    byteLength: (string: string): number => string.length * 2,
+  },
+  latin1: {
+    byteLength: (string: string): number => string.length,
+  },
+  ascii: {
+    byteLength: (string: string): number => string.length,
+  },
+  base64: {
+    byteLength: (string: string): number =>
+      base64ByteLength(string, string.length),
+  },
+  hex: {
+    byteLength: (string: string): number => string.length >>> 1,
+  },
+};
+
+function base64ByteLength(str: string, bytes: number): number {
+  // Handle padding
+  if (str.charCodeAt(bytes - 1) === 0x3d) bytes--;
+  if (bytes > 1 && str.charCodeAt(bytes - 1) === 0x3d) bytes--;
+
+  // Base64 ratio: 3/4
+  return (bytes * 3) >>> 2;
+}
+
 /**
  * See also https://nodejs.org/api/buffer.html
  */
@@ -95,10 +135,13 @@ export default class Buffer extends Uint8Array {
    * used to convert the string into bytes.
    */
   static byteLength(
-    string: string | Buffer | ArrayBufferView | ArrayBuffer | SharedArrayBuffer
+    string: string | Buffer | ArrayBufferView | ArrayBuffer | SharedArrayBuffer,
+    encoding = "utf8"
   ): number {
     if (typeof string != "string") return string.byteLength;
-    return new TextEncoder().encode(string).length;
+
+    encoding = normalizeEncoding(encoding) || "utf8";
+    return encodingOps[encoding].byteLength(string);
   }
 
   /**