3 files changed, 47 insertions, 8 deletions
diff --git a/cli/js/buffer.ts b/cli/js/buffer.ts
index 3308a9a0c..4f88ff625 100644
--- a/cli/js/buffer.ts
+++ b/cli/js/buffer.ts
@@ -39,7 +39,8 @@ export class Buffer implements Reader, ReaderSync, Writer, WriterSync {
     this.#buf = new Uint8Array(ab);
   }
 
-  bytes(): Uint8Array {
+  bytes(options: { copy?: boolean } = { copy: true }): Uint8Array {
+    if (options.copy === false) return this.#buf.subarray(this.#off);
     return this.#buf.slice(this.#off);
   }
 
diff --git a/cli/js/lib.deno.ns.d.ts b/cli/js/lib.deno.ns.d.ts
index 32b9bb39b..373f3be2f 100644
--- a/cli/js/lib.deno.ns.d.ts
+++ b/cli/js/lib.deno.ns.d.ts
@@ -820,10 +820,12 @@ declare namespace Deno {
      *
      * The slice is valid for use only until the next buffer modification (that
      * is, only until the next call to a method like `read()`, `write()`,
-     * `reset()`, or `truncate()`). The slice aliases the buffer content at
+     * `reset()`, or `truncate()`). If `options.copy` is false the slice aliases the buffer content at
      * least until the next buffer modification, so immediate changes to the
-     * slice will affect the result of future reads. */
-    bytes(): Uint8Array;
+     * slice will affect the result of future reads.
+     * @param options Defaults to `{ copy: true }`
+     */
+    bytes(options?: { copy?: boolean }): Uint8Array;
     /** Returns whether the unread portion of the buffer is empty. */
     empty(): boolean;
     /** A read only number of bytes of the unread portion of the buffer. */
diff --git a/cli/tests/unit/buffer_test.ts b/cli/tests/unit/buffer_test.ts
index 440dd5495..320dddcc1 100644
--- a/cli/tests/unit/buffer_test.ts
+++ b/cli/tests/unit/buffer_test.ts
@@ -402,14 +402,50 @@ unitTest(function testWriteAllSync(): void {
 });
 
 unitTest(function testBufferBytesArrayBufferLength(): void {
-  const bytes = new TextEncoder().encode("a");
+  // defaults to copy
+  const args = [{}, { copy: undefined }, undefined, { copy: true }];
+  for (const arg of args) {
+    const bufSize = 64 * 1024;
+    const bytes = new TextEncoder().encode("a".repeat(bufSize));
+    const reader = new Deno.Buffer();
+    Deno.writeAllSync(reader, bytes);
+
+    const writer = new Deno.Buffer();
+    writer.readFromSync(reader);
+    const actualBytes = writer.bytes(arg);
+
+    assertEquals(actualBytes.byteLength, bufSize);
+    assert(actualBytes.buffer !== writer.bytes(arg).buffer);
+    assertEquals(actualBytes.byteLength, actualBytes.buffer.byteLength);
+  }
+});
+
+unitTest(function testBufferBytesCopyFalse(): void {
+  const bufSize = 64 * 1024;
+  const bytes = new TextEncoder().encode("a".repeat(bufSize));
   const reader = new Deno.Buffer();
   Deno.writeAllSync(reader, bytes);
 
   const writer = new Deno.Buffer();
   writer.readFromSync(reader);
-  const actualBytes = writer.bytes();
+  const actualBytes = writer.bytes({ copy: false });
+
+  assertEquals(actualBytes.byteLength, bufSize);
+  assertEquals(actualBytes.buffer, writer.bytes({ copy: false }).buffer);
+  assert(actualBytes.buffer.byteLength > actualBytes.byteLength);
+});
+
+unitTest(function testBufferBytesCopyFalseGrowExactBytes(): void {
+  const bufSize = 64 * 1024;
+  const bytes = new TextEncoder().encode("a".repeat(bufSize));
+  const reader = new Deno.Buffer();
+  Deno.writeAllSync(reader, bytes);
+
+  const writer = new Deno.Buffer();
+  writer.grow(bufSize);
+  writer.readFromSync(reader);
+  const actualBytes = writer.bytes({ copy: false });
 
-  assertEquals(bytes.byteLength, 1);
-  assertEquals(bytes.byteLength, actualBytes.buffer.byteLength);
+  assertEquals(actualBytes.byteLength, bufSize);
+  assertEquals(actualBytes.buffer.byteLength, actualBytes.byteLength);
 });