feat(std/io): add LimitedReader (#6026)

1 files changed, 26 insertions, 1 deletions

diff --git a/std/io/readers_test.ts b/std/io/readers_test.ts
index b0810f9e0..04e9b7488 100644
--- a/std/io/readers_test.ts
+++ b/std/io/readers_test.ts
@@ -1,6 +1,6 @@
 const { copy, test } = Deno;
 import { assertEquals } from "../testing/asserts.ts";
-import { MultiReader, StringReader } from "./readers.ts";
+import { LimitedReader, MultiReader, StringReader } from "./readers.ts";
 import { StringWriter } from "./writers.ts";
 import { copyN } from "./ioutil.ts";
 import { decode } from "../encoding/utf8.ts";
@@ -36,3 +36,28 @@ test("ioMultiReader", async function (): Promise<void> {
   await copy(r, w);
   assertEquals(w.toString(), "abcdef");
 });
+
+test("ioLimitedReader", async function (): Promise<void> {
+  let sr = new StringReader("abc");
+  let r = new LimitedReader(sr, 2);
+  let buffer = await Deno.readAll(r);
+  assertEquals(decode(buffer), "ab");
+  assertEquals(decode(await Deno.readAll(sr)), "c");
+  sr = new StringReader("abc");
+  r = new LimitedReader(sr, 3);
+  buffer = await Deno.readAll(r);
+  assertEquals(decode(buffer), "abc");
+  assertEquals((await Deno.readAll(r)).length, 0);
+  sr = new StringReader("abc");
+  r = new LimitedReader(sr, 4);
+  buffer = await Deno.readAll(r);
+  assertEquals(decode(buffer), "abc");
+  assertEquals((await Deno.readAll(r)).length, 0);
+});
+
+test("ioLimitedReader", async function (): Promise<void> {
+  const rb = new StringReader("abc");
+  const wb = new StringWriter();
+  await Deno.copy(new LimitedReader(rb, -1), wb);
+  assertEquals(wb.toString(), "");
+});