Fix: allow reading into a 0-length array (denoland#3329)

cli/js/files.ts

@@ -50,6 +50,9 @@ export async function open(
  *
  */
 export function readSync(rid: number, p: Uint8Array): number | EOF {
+ if (p.length == 0) {
+ return 0;
+ }
  const nread = sendSyncMinimal(dispatch.OP_READ, rid, p);
  if (nread < 0) {
  throw new Error("read error");
@@ -70,6 +73,9 @@ export function readSync(rid: number, p: Uint8Array): number | EOF {
  * const text = new TextDecoder().decode(buf);
  */
 export async function read(rid: number, p: Uint8Array): Promise<number | EOF> {
+ if (p.length == 0) {
+ return 0;
+ }
  const nread = await sendAsyncMinimal(dispatch.OP_READ, rid, p);
  if (nread < 0) {
  throw new Error("read error");

cli/js/files_test.ts

@@ -118,6 +118,10 @@ testPerm(
  const filename = tempDir + "hello.txt";
  const file = await Deno.open(filename, "w+");
 
+ // reading into an empty buffer should return 0 immediately
+ const bytesRead = await file.read(new Uint8Array(0));
+ assert(bytesRead === 0);
+
  // reading file into null buffer should throw an error
  let err;
  try {

cli/js/io.ts

@@ -18,12 +18,14 @@ export enum SeekMode {
 // https://golang.org/pkg/io/#Reader
 export interface Reader {
  /** Reads up to p.byteLength bytes into `p`. It resolves to the number
- * of bytes read (`0` < `n` <= `p.byteLength`) and rejects if any error encountered.
+ * of bytes read (`0` <= `n` <= `p.byteLength`) and rejects if any error encountered.
  * Even if `read()` returns `n` < `p.byteLength`, it may use all of `p` as
  * scratch space during the call. If some data is available but not
  * `p.byteLength` bytes, `read()` conventionally returns what is available
  * instead of waiting for more.
  *
+ * When `p.byteLength` == `0`, `read()` returns `0` and has no other effects.
+ *
  * When `read()` encounters end-of-file condition, it returns EOF symbol.
  *
  * When `read()` encounters an error, it rejects with an error.