2 files changed, 91 insertions, 3 deletions
diff --git a/std/node/buffer.ts b/std/node/buffer.ts
index 0fc8be6f1..dae04a66e 100644
--- a/std/node/buffer.ts
+++ b/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);
   }
 
   /**
diff --git a/std/node/buffer_test.ts b/std/node/buffer_test.ts
index 2e0a8c176..f96fa8e4b 100644
--- a/std/node/buffer_test.ts
+++ b/std/node/buffer_test.ts
@@ -195,10 +195,55 @@ Deno.test({
   },
 });
 
+// tests from:
+// https://github.com/nodejs/node/blob/56dbe466fdbc598baea3bfce289bf52b97b8b8f7/test/parallel/test-buffer-bytelength.js#L70
 Deno.test({
   name: "Byte length is the expected for strings",
   fn() {
-    assertEquals(Buffer.byteLength("test"), 4, "Byte lenght differs on string");
+    // Special case: zero length string
+    assertEquals(Buffer.byteLength("", "ascii"), 0);
+    assertEquals(Buffer.byteLength("", "HeX"), 0);
+
+    // utf8
+    assertEquals(Buffer.byteLength("∑éllö wørl∂!", "utf-8"), 19);
+    assertEquals(Buffer.byteLength("κλμνξο", "utf8"), 12);
+    assertEquals(Buffer.byteLength("挵挶挷挸挹", "utf-8"), 15);
+    assertEquals(Buffer.byteLength("𠝹𠱓𠱸", "UTF8"), 12);
+    // Without an encoding, utf8 should be assumed
+    assertEquals(Buffer.byteLength("hey there"), 9);
+    assertEquals(Buffer.byteLength("𠱸挶νξ#xx :)"), 17);
+    assertEquals(Buffer.byteLength("hello world", ""), 11);
+    // It should also be assumed with unrecognized encoding
+    assertEquals(Buffer.byteLength("hello world", "abc"), 11);
+    assertEquals(Buffer.byteLength("ßœ∑≈", "unkn0wn enc0ding"), 10);
+
+    // base64
+    assertEquals(Buffer.byteLength("aGVsbG8gd29ybGQ=", "base64"), 11);
+    assertEquals(Buffer.byteLength("aGVsbG8gd29ybGQ=", "BASE64"), 11);
+    assertEquals(Buffer.byteLength("bm9kZS5qcyByb2NrcyE=", "base64"), 14);
+    assertEquals(Buffer.byteLength("aGkk", "base64"), 3);
+    assertEquals(
+      Buffer.byteLength("bHNrZGZsa3NqZmtsc2xrZmFqc2RsZmtqcw==", "base64"),
+      25
+    );
+    // special padding
+    assertEquals(Buffer.byteLength("aaa=", "base64"), 2);
+    assertEquals(Buffer.byteLength("aaaa==", "base64"), 3);
+
+    assertEquals(Buffer.byteLength("Il était tué"), 14);
+    assertEquals(Buffer.byteLength("Il était tué", "utf8"), 14);
+
+    ["ascii", "latin1", "binary"]
+      .reduce((es: string[], e: string) => es.concat(e, e.toUpperCase()), [])
+      .forEach((encoding: string) => {
+        assertEquals(Buffer.byteLength("Il était tué", encoding), 12);
+      });
+
+    ["ucs2", "ucs-2", "utf16le", "utf-16le"]
+      .reduce((es: string[], e: string) => es.concat(e, e.toUpperCase()), [])
+      .forEach((encoding: string) => {
+        assertEquals(Buffer.byteLength("Il était tué", encoding), 24);
+      });
   },
 });