5 files changed, 436 insertions, 11 deletions
diff --git a/std/node/_fs/_fs_common.ts b/std/node/_fs/_fs_common.ts
index 1f00bc481..bf7c0f675 100644
--- a/std/node/_fs/_fs_common.ts
+++ b/std/node/_fs/_fs_common.ts
@@ -35,6 +35,11 @@ export function getEncoding(
   const encoding =
     typeof optOrCallback === "string" ? optOrCallback : optOrCallback.encoding;
   if (!encoding) return null;
+  return encoding;
+}
+
+export function checkEncoding(encoding: string | null): string | null {
+  if (!encoding) return null;
   if (encoding === "utf8" || encoding === "utf-8") {
     return "utf8";
   }
diff --git a/std/node/_fs/_fs_readFile.ts b/std/node/_fs/_fs_readFile.ts
index ccea71cd6..448045fd2 100644
--- a/std/node/_fs/_fs_readFile.ts
+++ b/std/node/_fs/_fs_readFile.ts
@@ -3,23 +3,23 @@
 import { intoCallbackAPIWithIntercept, MaybeEmpty } from "../_utils.ts";
 
 import { getEncoding, FileOptions } from "./_fs_common.ts";
+import { Buffer } from "../buffer.ts";
 import { fromFileUrl } from "../path.ts";
 
 const { readFile: denoReadFile, readFileSync: denoReadFileSync } = Deno;
 
 type ReadFileCallback = (
   err: MaybeEmpty<Error>,
-  data: MaybeEmpty<string | Uint8Array>
+  data: MaybeEmpty<string | Buffer>
 ) => void;
 
 function maybeDecode(
   data: Uint8Array,
   encoding: string | null
-): string | Uint8Array {
-  if (encoding === "utf8") {
-    return new TextDecoder().decode(data);
-  }
-  return data;
+): string | Buffer {
+  const buffer = new Buffer(data.buffer, data.byteOffset, data.byteLength);
+  if (encoding) return buffer.toString(encoding);
+  return buffer;
 }
 
 export function readFile(
@@ -37,9 +37,9 @@ export function readFile(
 
   const encoding = getEncoding(optOrCallback);
 
-  intoCallbackAPIWithIntercept<Uint8Array, string | Uint8Array>(
+  intoCallbackAPIWithIntercept<Uint8Array, string | Buffer>(
     denoReadFile,
-    (data: Uint8Array): string | Uint8Array => maybeDecode(data, encoding),
+    (data: Uint8Array): string | Buffer => maybeDecode(data, encoding),
     cb,
     path
   );
@@ -48,7 +48,7 @@ export function readFile(
 export function readFileSync(
   path: string | URL,
   opt?: FileOptions | string
-): string | Uint8Array {
+): string | Buffer {
   path = path instanceof URL ? fromFileUrl(path) : path;
   return maybeDecode(denoReadFileSync(path), getEncoding(opt));
 }
diff --git a/std/node/_fs/_fs_writeFile.ts b/std/node/_fs/_fs_writeFile.ts
index 72e75c97a..4ede42638 100644
--- a/std/node/_fs/_fs_writeFile.ts
+++ b/std/node/_fs/_fs_writeFile.ts
@@ -7,6 +7,7 @@ import {
   CallbackWithError,
   isFileOptions,
   getEncoding,
+  checkEncoding,
   getOpenOptions,
 } from "./_fs_common.ts";
 
@@ -35,7 +36,7 @@ export function writeFile(
     ? options.mode
     : undefined;
 
-  const encoding = getEncoding(options) || "utf8";
+  const encoding = checkEncoding(getEncoding(options)) || "utf8";
   const openOptions = getOpenOptions(flag || "w");
 
   if (typeof data === "string" && encoding === "utf8")
@@ -82,7 +83,7 @@ export function writeFileSync(
     ? options.mode
     : undefined;
 
-  const encoding = getEncoding(options) || "utf8";
+  const encoding = checkEncoding(getEncoding(options)) || "utf8";
   const openOptions = getOpenOptions(flag || "w");
 
   if (typeof data === "string" && encoding === "utf8")
diff --git a/std/node/buffer.ts b/std/node/buffer.ts
new file mode 100644
index 000000000..fa911ee6f
--- /dev/null
+++ b/std/node/buffer.ts
@@ -0,0 +1,417 @@
+/**
+ * See also https://nodejs.org/api/buffer.html
+ */
+export default class Buffer extends Uint8Array {
+  /**
+   * Allocates a new Buffer of size bytes.
+   */
+  static alloc(size: number): Buffer {
+    return new Buffer(size);
+  }
+
+  /**
+   * Returns the byte length of a string when encoded. This is not the same as
+   * String.prototype.length, which does not account for the encoding that is
+   * used to convert the string into bytes.
+   */
+  static byteLength(
+    string: string | Buffer | ArrayBufferView | ArrayBuffer | SharedArrayBuffer
+  ): number {
+    if (typeof string != "string") return string.byteLength;
+    return new TextEncoder().encode(string).length;
+  }
+
+  /**
+   * Returns a new Buffer which is the result of concatenating all the Buffer
+   * instances in the list together.
+   */
+  static concat(list: Buffer[] | Uint8Array[], totalLength?: number): Buffer {
+    if (totalLength == undefined) {
+      totalLength = 0;
+      for (const buf of list) {
+        totalLength += buf.length;
+      }
+    }
+
+    const buffer = new Buffer(totalLength);
+    let pos = 0;
+    for (const buf of list) {
+      buffer.set(buf, pos);
+      pos += buf.length;
+    }
+
+    return buffer;
+  }
+
+  /**
+   * Allocates a new Buffer using an array of bytes in the range 0 – 255. Array
+   * entries outside that range will be truncated to fit into it.
+   */
+  static from(array: number[]): Buffer;
+  /**
+   * This creates a view of the ArrayBuffer without copying the underlying
+   * memory. For example, when passed a reference to the .buffer property of a
+   * TypedArray instance, the newly created Buffer will share the same allocated
+   * memory as the TypedArray.
+   */
+  static from(
+    arrayBuffer: ArrayBuffer | SharedArrayBuffer,
+    byteOffset?: number,
+    length?: number
+  ): Buffer;
+  /**
+   * Copies the passed buffer data onto a new Buffer instance.
+   */
+  static from(buffer: Buffer | Uint8Array): Buffer;
+  /**
+   * Creates a new Buffer containing string.
+   */
+  static from(string: string): Buffer;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  static from(value: any, offset?: number, length?: number): Buffer {
+    if (typeof value == "string")
+      return new Buffer(new TextEncoder().encode(value).buffer);
+
+    // workaround for https://github.com/microsoft/TypeScript/issues/38446
+    return new Buffer(value, offset!, length);
+  }
+
+  /**
+   * Returns true if obj is a Buffer, false otherwise.
+   */
+  static isBuffer(obj: object): obj is Buffer {
+    return obj instanceof Buffer;
+  }
+
+  /**
+   * Copies data from a region of buf to a region in target, even if the target
+   * memory region overlaps with buf.
+   */
+  copy(
+    targetBuffer: Buffer | Uint8Array,
+    targetStart = 0,
+    sourceStart = 0,
+    sourceEnd = this.length
+  ): number {
+    const sourceBuffer = this.subarray(sourceStart, sourceEnd);
+    targetBuffer.set(sourceBuffer, targetStart);
+    return sourceBuffer.length;
+  }
+
+  readBigInt64BE(offset = 0): bigint {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getBigInt64(offset);
+  }
+  readBigInt64LE(offset = 0): bigint {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getBigInt64(offset, true);
+  }
+
+  readBigUInt64BE(offset = 0): bigint {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getBigUint64(offset);
+  }
+  readBigUInt64LE(offset = 0): bigint {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getBigUint64(offset, true);
+  }
+
+  readDoubleBE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getFloat64(offset);
+  }
+  readDoubleLE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getFloat64(offset, true);
+  }
+
+  readFloatBE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getFloat32(offset);
+  }
+  readFloatLE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getFloat32(offset, true);
+  }
+
+  readInt8(offset = 0): number {
+    return new DataView(this.buffer, this.byteOffset, this.byteLength).getInt8(
+      offset
+    );
+  }
+
+  readInt16BE(offset = 0): number {
+    return new DataView(this.buffer, this.byteOffset, this.byteLength).getInt16(
+      offset
+    );
+  }
+  readInt16LE(offset = 0): number {
+    return new DataView(this.buffer, this.byteOffset, this.byteLength).getInt16(
+      offset,
+      true
+    );
+  }
+
+  readInt32BE(offset = 0): number {
+    return new DataView(this.buffer, this.byteOffset, this.byteLength).getInt32(
+      offset
+    );
+  }
+  readInt32LE(offset = 0): number {
+    return new DataView(this.buffer, this.byteOffset, this.byteLength).getInt32(
+      offset,
+      true
+    );
+  }
+
+  readUInt8(offset = 0): number {
+    return new DataView(this.buffer, this.byteOffset, this.byteLength).getUint8(
+      offset
+    );
+  }
+
+  readUInt16BE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getUint16(offset);
+  }
+  readUInt16LE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getUint16(offset, true);
+  }
+
+  readUInt32BE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getUint32(offset);
+  }
+  readUInt32LE(offset = 0): number {
+    return new DataView(
+      this.buffer,
+      this.byteOffset,
+      this.byteLength
+    ).getUint32(offset, true);
+  }
+
+  /**
+   * Returns a new Buffer that references the same memory as the original, but
+   * offset and cropped by the start and end indices.
+   */
+  slice(begin = 0, end = this.length): Buffer {
+    // workaround for https://github.com/microsoft/TypeScript/issues/38665
+    return this.subarray(begin, end) as Buffer;
+  }
+
+  /**
+   * Returns a JSON representation of buf. JSON.stringify() implicitly calls
+   * this function when stringifying a Buffer instance.
+   */
+  toJSON(): object {
+    return { type: "Buffer", data: Array.from(this) };
+  }
+
+  /**
+   * Decodes buf to a string according to the specified character encoding in
+   * encoding. start and end may be passed to decode only a subset of buf.
+   */
+  toString(encoding = "utf8", start = 0, end = this.length): string {
+    return new TextDecoder(encoding).decode(this.subarray(start, end));
+  }
+
+  /**
+   * Writes string to buf at offset according to the character encoding in
+   * encoding. The length parameter is the number of bytes to write. If buf did
+   * not contain enough space to fit the entire string, only part of string will
+   * be written. However, partially encoded characters will not be written.
+   */
+  write(string: string, offset = 0, length = this.length): number {
+    return new TextEncoder().encodeInto(
+      string,
+      this.subarray(offset, offset + length)
+    ).written;
+  }
+
+  writeBigInt64BE(value: bigint, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setBigInt64(
+      offset,
+      value
+    );
+    return offset + 4;
+  }
+  writeBigInt64LE(value: bigint, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setBigInt64(
+      offset,
+      value,
+      true
+    );
+    return offset + 4;
+  }
+
+  writeBigUInt64BE(value: bigint, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setBigUint64(
+      offset,
+      value
+    );
+    return offset + 4;
+  }
+  writeBigUInt64LE(value: bigint, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setBigUint64(
+      offset,
+      value,
+      true
+    );
+    return offset + 4;
+  }
+
+  writeDoubleBE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setFloat64(
+      offset,
+      value
+    );
+    return offset + 8;
+  }
+  writeDoubleLE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setFloat64(
+      offset,
+      value,
+      true
+    );
+    return offset + 8;
+  }
+
+  writeFloatBE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setFloat32(
+      offset,
+      value
+    );
+    return offset + 4;
+  }
+  writeFloatLE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setFloat32(
+      offset,
+      value,
+      true
+    );
+    return offset + 4;
+  }
+
+  writeInt8(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setInt8(
+      offset,
+      value
+    );
+    return offset + 1;
+  }
+
+  writeInt16BE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setInt16(
+      offset,
+      value
+    );
+    return offset + 2;
+  }
+  writeInt16LE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setInt16(
+      offset,
+      value,
+      true
+    );
+    return offset + 2;
+  }
+
+  writeInt32BE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setUint32(
+      offset,
+      value
+    );
+    return offset + 4;
+  }
+  writeInt32LE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setInt32(
+      offset,
+      value,
+      true
+    );
+    return offset + 4;
+  }
+
+  writeUInt8(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setUint8(
+      offset,
+      value
+    );
+    return offset + 1;
+  }
+
+  writeUInt16BE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setUint16(
+      offset,
+      value
+    );
+    return offset + 2;
+  }
+  writeUInt16LE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setUint16(
+      offset,
+      value,
+      true
+    );
+    return offset + 2;
+  }
+
+  writeUInt32BE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setUint32(
+      offset,
+      value
+    );
+    return offset + 4;
+  }
+  writeUInt32LE(value: number, offset = 0): number {
+    new DataView(this.buffer, this.byteOffset, this.byteLength).setUint32(
+      offset,
+      value,
+      true
+    );
+    return offset + 4;
+  }
+}
+
+export { Buffer };
+
+Object.defineProperty(globalThis, "Buffer", {
+  value: Buffer,
+  enumerable: false,
+  writable: true,
+  configurable: true,
+});
diff --git a/std/node/module.ts b/std/node/module.ts
index 13b2ac325..8d0160f78 100644
--- a/std/node/module.ts
+++ b/std/node/module.ts
@@ -21,6 +21,7 @@
 
 import "./global.ts";
 
+import * as nodeBuffer from "./buffer.ts";
 import * as nodeFS from "./fs.ts";
 import * as nodeUtil from "./util.ts";
 import * as nodePath from "./path.ts";
@@ -595,6 +596,7 @@ function createNativeModule(id: string, exports: any): Module {
   return mod;
 }
 
+nativeModulePolyfill.set("buffer", createNativeModule("buffer", nodeBuffer));
 nativeModulePolyfill.set("fs", createNativeModule("fs", nodeFS));
 nativeModulePolyfill.set("events", createNativeModule("events", nodeEvents));
 nativeModulePolyfill.set("os", createNativeModule("os", nodeOs));