3 files changed, 77 insertions, 2 deletions
diff --git a/bytes/bytes.ts b/bytes/bytes.ts
index a79a9ed56..127dad1c2 100644
--- a/bytes/bytes.ts
+++ b/bytes/bytes.ts
@@ -1,4 +1,5 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { copyBytes } from "../io/util.ts";
 
 /** Find first index of binary pattern from a. If not found, then return -1 **/
 export function bytesFindIndex(a: Uint8Array, pat: Uint8Array): number {
@@ -60,3 +61,36 @@ export function bytesHasPrefix(a: Uint8Array, prefix: Uint8Array): boolean {
   }
   return true;
 }
+
+/**
+ * Repeat bytes. returns a new byte slice consisting of `count` copies of `b`.
+ * @param b The origin bytes
+ * @param count The count you want to repeat.
+ */
+export function bytesRepeat(b: Uint8Array, count: number): Uint8Array {
+  if (count === 0) {
+    return new Uint8Array();
+  }
+
+  if (count < 0) {
+    throw new Error("bytes: negative repeat count");
+  } else if ((b.length * count) / count !== b.length) {
+    throw new Error("bytes: repeat count causes overflow");
+  }
+
+  const int = Math.floor(count);
+
+  if (int !== count) {
+    throw new Error("bytes: repeat count must be an integer");
+  }
+
+  const nb = new Uint8Array(b.length * count);
+
+  let bp = copyBytes(nb, b);
+
+  for (; bp < nb.length; bp *= 2) {
+    copyBytes(nb, nb.slice(0, bp), bp);
+  }
+
+  return nb;
+}
diff --git a/bytes/bytes_test.ts b/bytes/bytes_test.ts
index 9d4754a39..8ca4cb386 100644
--- a/bytes/bytes_test.ts
+++ b/bytes/bytes_test.ts
@@ -1,11 +1,14 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
 import {
   bytesFindIndex,
   bytesFindLastIndex,
   bytesEqual,
-  bytesHasPrefix
+  bytesHasPrefix,
+  bytesRepeat
 } from "./bytes.ts";
 import { test } from "../testing/mod.ts";
-import { assertEquals } from "../testing/asserts.ts";
+import { assertEquals, assertThrows } from "../testing/asserts.ts";
 
 test(function bytesBytesFindIndex1(): void {
   const i = bytesFindIndex(
@@ -48,3 +51,39 @@ test(function bytesBytesHasPrefix(): void {
   const v = bytesHasPrefix(new Uint8Array([0, 1, 2]), new Uint8Array([0, 1]));
   assertEquals(v, true);
 });
+
+test(function bytesBytesRepeat(): void {
+  // input / output / count / error message
+  const repeatTestCase = [
+    ["", "", 0],
+    ["", "", 1],
+    ["", "", 1.1, "bytes: repeat count must be an integer"],
+    ["", "", 2],
+    ["", "", 0],
+    ["-", "", 0],
+    ["-", "-", -1, "bytes: negative repeat count"],
+    ["-", "----------", 10],
+    ["abc ", "abc abc abc ", 3]
+  ];
+  for (const [input, output, count, errMsg] of repeatTestCase) {
+    if (errMsg) {
+      assertThrows(
+        (): void => {
+          bytesRepeat(
+            new TextEncoder().encode(input as string),
+            count as number
+          );
+        },
+        Error,
+        errMsg as string
+      );
+    } else {
+      const newBytes = bytesRepeat(
+        new TextEncoder().encode(input as string),
+        count as number
+      );
+
+      assertEquals(new TextDecoder().decode(newBytes), output);
+    }
+  }
+});
diff --git a/bytes/test.ts b/bytes/test.ts
new file mode 100644
index 000000000..711bf62c4
--- /dev/null
+++ b/bytes/test.ts
@@ -0,0 +1,2 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import "./bytes_test.ts";