Add BufReader.readFull (denoland/deno_std#24)

Original: https://github.com/denoland/deno_std/commit/abeb19890e5d6a0cd3461c4aefc920006ef284bd

bufio.ts

@@ -162,6 +162,30 @@ export class BufReader implements Reader {
     return rr;
   }
 
+  /** reads exactly len(p) bytes into p.
+   * Ported from https://golang.org/pkg/io/#ReadFull
+   * It returns the number of bytes copied and an error if fewer bytes were read.
+   * The error is EOF only if no bytes were read.
+   * If an EOF happens after reading some but not all the bytes,
+   * readFull returns ErrUnexpectedEOF. ("EOF" for current impl)
+   * On return, n == len(p) if and only if err == nil.
+   * If r returns an error having read at least len(buf) bytes,
+   * the error is dropped.
+   */
+  async readFull(p: Uint8Array): Promise<[number, BufState]> {
+    let rr = await this.read(p);
+    let nread = rr.nread;
+    if (rr.eof) {
+      return [nread, nread < p.length ? "EOF" : null];
+    }
+    while (!rr.eof && nread < p.length) {
+      rr = await this.read(p.subarray(nread));
+      nread += rr.nread;
+    }
+    return [nread, nread < p.length ? "EOF" : null];
+  }
+
+
   /** Returns the next byte [0, 255] or -1 if EOF. */
   async readByte(): Promise<number> {
     while (this.r === this.w) {

bufio_test.ts

@@ -321,3 +321,25 @@ test(async function bufioWriter() {
     }
   }
 });
+
+test(async function bufReaderReadFull() {
+  const enc = new TextEncoder();
+  const dec = new TextDecoder();
+  const text = "Hello World";
+  const data = new Buffer(enc.encode(text));
+  const bufr = new BufReader(data, 3);
+  {
+    const buf = new Uint8Array(6);
+    const [nread, err] = await bufr.readFull(buf);
+    assertEqual(nread, 6);
+    assert(!err);
+    assertEqual(dec.decode(buf), "Hello ");
+  }
+  {
+    const buf = new Uint8Array(6);
+    const [nread, err] = await bufr.readFull(buf);
+    assertEqual(nread, 5);
+    assertEqual(err, "EOF");
+    assertEqual(dec.decode(buf.subarray(0, 5)), "World");
+  }
+});

test.ts

@@ -10,7 +10,7 @@ const fileServer = run({
   args: ["deno", "--allow-net", "file_server.ts", "."]
 });
 // I am also too lazy to do this properly LOL
-runTests(new Promise(res => setTimeout(res, 1000)));
+runTests(new Promise(res => setTimeout(res, 5000)));
 (async () => {
   await completePromise;
   fileServer.close();