fix(std/io): StringReader implementation (#6148)

6 files changed, 37 insertions, 39 deletions

diff --git a/std/examples/tests/xeval_test.ts b/std/examples/tests/xeval_test.ts
index 3db1459a9..f86e27866 100644
--- a/std/examples/tests/xeval_test.ts
+++ b/std/examples/tests/xeval_test.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
 import { xeval } from "../xeval.ts";
-import { stringsReader } from "../../io/util.ts";
+import { StringReader } from "../../io/readers.ts";
 import { decode, encode } from "../../encoding/utf8.ts";
 import {
   assertEquals,
@@ -11,15 +11,19 @@ const { execPath, run } = Deno;
 
 Deno.test("xevalSuccess", async function (): Promise<void> {
   const chunks: string[] = [];
-  await xeval(stringsReader("a\nb\nc"), ($): number => chunks.push($));
+  await xeval(new StringReader("a\nb\nc"), ($): number => chunks.push($));
   assertEquals(chunks, ["a", "b", "c"]);
 });
 
 Deno.test("xevalDelimiter", async function (): Promise<void> {
   const chunks: string[] = [];
-  await xeval(stringsReader("!MADMADAMADAM!"), ($): number => chunks.push($), {
-    delimiter: "MADAM",
-  });
+  await xeval(
+    new StringReader("!MADMADAMADAM!"),
+    ($): number => chunks.push($),
+    {
+      delimiter: "MADAM",
+    }
+  );
   assertEquals(chunks, ["!MAD", "ADAM!"]);
 });
 
diff --git a/std/io/bufio_test.ts b/std/io/bufio_test.ts
index 671ed2115..b03640d52 100644
--- a/std/io/bufio_test.ts
+++ b/std/io/bufio_test.ts
@@ -17,7 +17,8 @@ import {
   readLines,
 } from "./bufio.ts";
 import * as iotest from "./_iotest.ts";
-import { charCode, copyBytes, stringsReader } from "./util.ts";
+import { StringReader } from "./readers.ts";
+import { charCode, copyBytes } from "./util.ts";
 
 const encoder = new TextEncoder();
 
@@ -38,7 +39,7 @@ async function readBytes(buf: BufReader): Promise<string> {
 
 Deno.test("bufioReaderSimple", async function (): Promise<void> {
   const data = "hello world";
-  const b = new BufReader(stringsReader(data));
+  const b = new BufReader(new StringReader(data));
   const s = await readBytes(b);
   assertEquals(s, data);
 });
@@ -119,7 +120,7 @@ Deno.test("bufioBufReader", async function (): Promise<void> {
     for (const readmaker of readMakers) {
       for (const bufreader of bufreaders) {
         for (const bufsize of bufsizes) {
-          const read = readmaker.fn(stringsReader(text));
+          const read = readmaker.fn(new StringReader(text));
           const buf = new BufReader(read, bufsize);
           const s = await bufreader.fn(buf);
           const debugStr =
@@ -136,7 +137,7 @@ Deno.test("bufioBufferFull", async function (): Promise<void> {
   const longString =
     "And now, hello, world! It is the time for all good men to come to the" +
     " aid of their party";
-  const buf = new BufReader(stringsReader(longString), MIN_READ_BUFFER_SIZE);
+  const buf = new BufReader(new StringReader(longString), MIN_READ_BUFFER_SIZE);
   const decoder = new TextDecoder();
 
   try {
@@ -156,7 +157,7 @@ Deno.test("bufioBufferFull", async function (): Promise<void> {
 
 Deno.test("bufioReadString", async function (): Promise<void> {
   const string = "And now, hello world!";
-  const buf = new BufReader(stringsReader(string), MIN_READ_BUFFER_SIZE);
+  const buf = new BufReader(new StringReader(string), MIN_READ_BUFFER_SIZE);
 
   const line = await buf.readString(",");
   assert(line !== null);
@@ -248,7 +249,7 @@ Deno.test("bufioPeek", async function (): Promise<void> {
   const p = new Uint8Array(10);
   // string is 16 (minReadBufferSize) long.
   const buf = new BufReader(
-    stringsReader("abcdefghijklmnop"),
+    new StringReader("abcdefghijklmnop"),
     MIN_READ_BUFFER_SIZE
   );
 
@@ -453,7 +454,7 @@ Deno.test(
     const decoder = new TextDecoder();
     const data = "abcdefghijklmnopqrstuvwxyz";
     const bufSize = 25;
-    const b = new BufReader(stringsReader(data), bufSize);
+    const b = new BufReader(new StringReader(data), bufSize);
 
     const r1 = (await b.readLine()) as ReadLineResult;
     assert(r1 !== null);
diff --git a/std/io/ioutil_test.ts b/std/io/ioutil_test.ts
index cf8eaf437..977c7022c 100644
--- a/std/io/ioutil_test.ts
+++ b/std/io/ioutil_test.ts
@@ -9,8 +9,9 @@ import {
   readShort,
   sliceLongToBytes,
 } from "./ioutil.ts";
+import { StringReader } from "./readers.ts";
 import { BufReader } from "./bufio.ts";
-import { stringsReader, tempFile } from "./util.ts";
+import { tempFile } from "./util.ts";
 import * as path from "../path/mod.ts";
 
 class BinaryReader implements Reader {
@@ -73,7 +74,7 @@ Deno.test("testSliceLongToBytes2", function (): void {
 
 Deno.test("testCopyN1", async function (): Promise<void> {
   const w = new Buffer();
-  const r = stringsReader("abcdefghij");
+  const r = new StringReader("abcdefghij");
   const n = await copyN(r, w, 3);
   assertEquals(n, 3);
   assertEquals(new TextDecoder().decode(w.bytes()), "abc");
@@ -81,7 +82,7 @@ Deno.test("testCopyN1", async function (): Promise<void> {
 
 Deno.test("testCopyN2", async function (): Promise<void> {
   const w = new Buffer();
-  const r = stringsReader("abcdefghij");
+  const r = new StringReader("abcdefghij");
   const n = await copyN(r, w, 11);
   assertEquals(n, 10);
   assertEquals(new TextDecoder().decode(w.bytes()), "abcdefghij");
@@ -91,10 +92,17 @@ Deno.test("copyNWriteAllData", async function (): Promise<void> {
   const { filepath, file } = await tempFile(path.resolve("io"));
   const size = 16 * 1024 + 1;
   const data = "a".repeat(32 * 1024);
-  const r = stringsReader(data);
+  const r = new StringReader(data);
   const n = await copyN(r, file, size); // Over max file possible buffer
   file.close();
   await Deno.remove(filepath);
 
   assertEquals(n, size);
 });
+
+Deno.test("testStringReaderEof", async function (): Promise<void> {
+  const r = new StringReader("abc");
+  assertEquals(await r.read(new Uint8Array()), 0);
+  assertEquals(await r.read(new Uint8Array(4)), 3);
+  assertEquals(await r.read(new Uint8Array(1)), null);
+});
diff --git a/std/io/readers.ts b/std/io/readers.ts
index 201b87cd8..d43655263 100644
--- a/std/io/readers.ts
+++ b/std/io/readers.ts
@@ -7,22 +7,12 @@
 
 type Reader = Deno.Reader;
 import { encode } from "../encoding/utf8.ts";
+const { Buffer } = Deno;
 
 /** Reader utility for strings */
-export class StringReader implements Reader {
-  private offs = 0;
-  private buf = new Uint8Array(encode(this.s));
-
-  constructor(private readonly s: string) {}
-
-  read(p: Uint8Array): Promise<number | null> {
-    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 Promise.resolve(null);
-    }
-    return Promise.resolve(n);
+export class StringReader extends Buffer {
+  constructor(private readonly s: string) {
+    super(encode(s).buffer);
   }
 }
 
diff --git a/std/io/util.ts b/std/io/util.ts
index 237747a89..47e48a981 100644
--- a/std/io/util.ts
+++ b/std/io/util.ts
@@ -1,9 +1,8 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-const { Buffer, mkdir, open } = Deno;
+const { mkdir, open } = Deno;
 type File = Deno.File;
 type Reader = Deno.Reader;
 import * as path from "../path/mod.ts";
-import { encode } from "../encoding/utf8.ts";
 
 /**
  * Copy bytes from one Uint8Array to another.  Bytes from `src` which don't fit
@@ -28,10 +27,6 @@ export function charCode(s: string): number {
   return s.charCodeAt(0);
 }
 
-export function stringsReader(s: string): Reader {
-  return new Buffer(encode(s).buffer);
-}
-
 /** Create or open a temporal file at specified directory with prefix and
  *  postfix
  * */
diff --git a/std/textproto/test.ts b/std/textproto/test.ts
index ec66bfd8c..7539e9779 100644
--- a/std/textproto/test.ts
+++ b/std/textproto/test.ts
@@ -5,12 +5,12 @@
 
 import { BufReader } from "../io/bufio.ts";
 import { TextProtoReader } from "./mod.ts";
-import { stringsReader } from "../io/util.ts";
+import { StringReader } from "../io/readers.ts";
 import { assert, assertEquals, assertThrows } from "../testing/asserts.ts";
 const { test } = Deno;
 
 function reader(s: string): TextProtoReader {
-  return new TextProtoReader(new BufReader(stringsReader(s)));
+  return new TextProtoReader(new BufReader(new StringReader(s)));
 }
 
 test({
@@ -187,7 +187,7 @@ test({
     const input = "abcdefghijklmnopqrstuvwxyz";
     const bufSize = 25;
     const tp = new TextProtoReader(
-      new BufReader(stringsReader(input), bufSize)
+      new BufReader(new StringReader(input), bufSize)
     );
     const line = await tp.readLine();
     assertEquals(line, input);