feat(std/node): Add Buffer.isEncoding (#6521)

std/node/_utils.ts

@@ -44,3 +44,67 @@ export function spliceOne(list: string[], index: number): void {
   for (; index + 1 < list.length; index++) list[index] = list[index + 1];
   list.pop();
 }
+
+// Taken from: https://github.com/nodejs/node/blob/ba684805b6c0eded76e5cd89ee00328ac7a59365/lib/internal/util.js#L125
+// Return undefined if there is no match.
+// Move the "slow cases" to a separate function to make sure this function gets
+// inlined properly. That prioritizes the common case.
+export function normalizeEncoding(enc: string | null): string | undefined {
+  if (enc == null || enc === "utf8" || enc === "utf-8") return "utf8";
+  return slowCases(enc);
+}
+
+// https://github.com/nodejs/node/blob/ba684805b6c0eded76e5cd89ee00328ac7a59365/lib/internal/util.js#L130
+function slowCases(enc: string): string | undefined {
+  switch (enc.length) {
+    case 4:
+      if (enc === "UTF8") return "utf8";
+      if (enc === "ucs2" || enc === "UCS2") return "utf16le";
+      enc = `${enc}`.toLowerCase();
+      if (enc === "utf8") return "utf8";
+      if (enc === "ucs2") return "utf16le";
+      break;
+    case 3:
+      if (enc === "hex" || enc === "HEX" || `${enc}`.toLowerCase() === "hex")
+        return "hex";
+      break;
+    case 5:
+      if (enc === "ascii") return "ascii";
+      if (enc === "ucs-2") return "utf16le";
+      if (enc === "UTF-8") return "utf8";
+      if (enc === "ASCII") return "ascii";
+      if (enc === "UCS-2") return "utf16le";
+      enc = `${enc}`.toLowerCase();
+      if (enc === "utf-8") return "utf8";
+      if (enc === "ascii") return "ascii";
+      if (enc === "ucs-2") return "utf16le";
+      break;
+    case 6:
+      if (enc === "base64") return "base64";
+      if (enc === "latin1" || enc === "binary") return "latin1";
+      if (enc === "BASE64") return "base64";
+      if (enc === "LATIN1" || enc === "BINARY") return "latin1";
+      enc = `${enc}`.toLowerCase();
+      if (enc === "base64") return "base64";
+      if (enc === "latin1" || enc === "binary") return "latin1";
+      break;
+    case 7:
+      if (
+        enc === "utf16le" ||
+        enc === "UTF16LE" ||
+        `${enc}`.toLowerCase() === "utf16le"
+      )
+        return "utf16le";
+      break;
+    case 8:
+      if (
+        enc === "utf-16le" ||
+        enc === "UTF-16LE" ||
+        `${enc}`.toLowerCase() === "utf-16le"
+      )
+        return "utf16le";
+      break;
+    default:
+      if (enc === "") return "utf8";
+  }
+}

std/node/buffer.ts

@@ -1,8 +1,7 @@
 import * as hex from "../encoding/hex.ts";
 import * as base64 from "../encoding/base64.ts";
-import { notImplemented } from "./_utils.ts";
+import { notImplemented, normalizeEncoding } from "./_utils.ts";
 
-const validEncodings = ["utf8", "hex", "base64"];
 const notImplementedEncodings = [
   "utf16le",
   "latin1",
@@ -17,20 +16,16 @@ function checkEncoding(encoding = "utf8", strict = true): string {
     throw new TypeError(`Unkown encoding: ${encoding}`);
   }
 
-  encoding = encoding.toLowerCase();
-  if (encoding === "utf-8" || encoding === "") {
-    return "utf8";
-  }
+  const normalized = normalizeEncoding(encoding);
+
+  if (normalized === undefined)
+    throw new TypeError(`Unkown encoding: ${encoding}`);
 
   if (notImplementedEncodings.includes(encoding)) {
     notImplemented(`"${encoding}" encoding`);
   }
 
-  if (!validEncodings.includes(encoding)) {
-    throw new TypeError(`Unkown encoding: ${encoding}`);
-  }
-
-  return encoding;
+  return normalized;
 }
 
 /**
@@ -181,6 +176,15 @@ export default class Buffer extends Uint8Array {
     return obj instanceof Buffer;
   }
 
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  static isEncoding(encoding: any): boolean {
+    return (
+      typeof encoding === "string" &&
+      encoding.length !== 0 &&
+      normalizeEncoding(encoding) !== undefined
+    );
+  }
+
   /**
    * Copies data from a region of buf to a region in target, even if the target
    * memory region overlaps with buf.

std/node/buffer_test.ts

@@ -471,3 +471,50 @@ Deno.test({
     assertEquals(slice.toString(), "deno");
   },
 });
+
+Deno.test({
+  name: "isEncoding returns true for valid encodings",
+  fn() {
+    [
+      "hex",
+      "HEX",
+      "HeX",
+      "utf8",
+      "utf-8",
+      "ascii",
+      "latin1",
+      "binary",
+      "base64",
+      "BASE64",
+      "BASe64",
+      "ucs2",
+      "ucs-2",
+      "utf16le",
+      "utf-16le",
+    ].forEach((enc) => {
+      assertEquals(Buffer.isEncoding(enc), true);
+    });
+  },
+});
+
+Deno.test({
+  name: "isEncoding returns false for invalid encodings",
+  fn() {
+    [
+      "utf9",
+      "utf-7",
+      "Unicode-FTW",
+      "new gnu gun",
+      false,
+      NaN,
+      {},
+      Infinity,
+      [],
+      1,
+      0,
+      -1,
+    ].forEach((enc) => {
+      assertEquals(Buffer.isEncoding(enc), false);
+    });
+  },
+});