1 files changed, 42 insertions, 0 deletions
diff --git a/std/io/readers.ts b/std/io/readers.ts
new file mode 100644
index 000000000..0208de413
--- /dev/null
+++ b/std/io/readers.ts
@@ -0,0 +1,42 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+type Reader = Deno.Reader;
+import { encode } from "../strings/mod.ts";
+
+/** Reader utility for strings */
+export class StringReader implements Reader {
+  private offs = 0;
+  private buf = new Uint8Array(encode(this.s));
+
+  constructor(private readonly s: string) {}
+
+  async read(p: Uint8Array): Promise<number | Deno.EOF> {
+    const n = Math.min(p.byteLength, this.buf.byteLength - this.offs);
+    p.set(this.buf.slice(this.offs, this.offs + n));
+    this.offs += n;
+    if (n === 0) {
+      return Deno.EOF;
+    }
+    return n;
+  }
+}
+
+/** Reader utility for combining multiple readers */
+export class MultiReader implements Reader {
+  private readonly readers: Reader[];
+  private currentIndex = 0;
+
+  constructor(...readers: Reader[]) {
+    this.readers = readers;
+  }
+
+  async read(p: Uint8Array): Promise<number | Deno.EOF> {
+    const r = this.readers[this.currentIndex];
+    if (!r) return Deno.EOF;
+    const result = await r.read(p);
+    if (result === Deno.EOF) {
+      this.currentIndex++;
+      return 0;
+    }
+    return result;
+  }
+}