1 files changed, 53 insertions, 0 deletions
diff --git a/std/io/_iotest.ts b/std/io/_iotest.ts
new file mode 100644
index 000000000..a309fb5e1
--- /dev/null
+++ b/std/io/_iotest.ts
@@ -0,0 +1,53 @@
+// Ported to Deno from
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+type Reader = Deno.Reader;
+
+/** OneByteReader returns a Reader that implements
+ * each non-empty Read by reading one byte from r.
+ */
+export class OneByteReader implements Reader {
+  constructor(readonly r: Reader) {}
+
+  read(p: Uint8Array): Promise<number | null> {
+    if (p.byteLength === 0) {
+      return Promise.resolve(0);
+    }
+    if (!(p instanceof Uint8Array)) {
+      throw Error("expected Uint8Array");
+    }
+    return Promise.resolve(this.r.read(p.subarray(0, 1)));
+  }
+}
+
+/** HalfReader returns a Reader that implements Read
+ * by reading half as many requested bytes from r.
+ */
+export class HalfReader implements Reader {
+  constructor(readonly r: Reader) {}
+
+  read(p: Uint8Array): Promise<number | null> {
+    if (!(p instanceof Uint8Array)) {
+      throw Error("expected Uint8Array");
+    }
+    const half = Math.floor((p.byteLength + 1) / 2);
+    return Promise.resolve(this.r.read(p.subarray(0, half)));
+  }
+}
+
+/** TimeoutReader returns `Deno.errors.TimedOut` on the second read
+ * with no data. Subsequent calls to read succeed.
+ */
+export class TimeoutReader implements Reader {
+  count = 0;
+  constructor(readonly r: Reader) {}
+
+  read(p: Uint8Array): Promise<number | null> {
+    this.count++;
+    if (this.count === 2) {
+      throw new Deno.errors.TimedOut();
+    }
+    return Promise.resolve(this.r.read(p));
+  }
+}