Feature Request: Allow reading into a 0-length array

[qexk]

Hello! I got this error while working with sockets implementing a low-level protocol:

error: Uncaught InvalidInput: no buffer specified
► $deno$/dispatch_minimal.ts:64:11
    at DenoError ($deno$/errors.ts:20:5)
    at unwrapResponse ($deno$/dispatch_minimal.ts:64:11)
    at sendAsyncMinimal ($deno$/dispatch_minimal.ts:106:10)

Turns out core’s implementation of Deno.Conn.read seems to have undefined behaviour when the buffer has no size.
Here’s an example to reproduce the error:

const PORT = 62394;

const server = new Promise(async resolve => {
  const listener = Deno.listen({ hostname: "127.0.0.1", port: PORT });
  const sock = await listener.accept();
  const rdbuf = new Uint8Array(12);
  await sock.read(rdbuf);
  console.log("SERVER", rdbuf);
  await sock.write(rdbuf);
  resolve();
});

const client = new Promise(async resolve => {
  await new Promise(resolve => setTimeout(resolve, 500));
  const sock = await Deno.dial({ hostname: "127.0.0.1", port: PORT });
  await sock.write(new Uint8Array(12).fill(12));
  const rdbuf = new Uint8Array(0);
  await sock.read(rdbuf);
  sock.close();
  resolve();
});

Giving a size other than 0 to the client’s rdbuf makes this piece of code work as expected.

Some solutions:

• Make it explicit in the JSDoc that p.length must be greater than 0.
• Mimic POSIX read behaviour: In the absence of any errors, or if read() does not check for errors, a read() with a count of 0 returns zero and has no other effects. (from the manpage). This requires adding a check to the following function (and readSync), and writing tests.

  deno/cli/js/files.ts

  Lines 76 to 85 in 6c5a981

  	export async function read(rid: number, p: Uint8Array): Promise<number | EOF> {
  	const nread = await sendAsyncMinimal(dispatch.OP_READ, rid, p);
  	if (nread < 0) {
  	throw new Error("read error");
  	} else if (nread == 0) {
  	return EOF;
  	} else {
  	return nread;
  	}
  	}

If you’re ok with the second solution, I can do the PR :)
I’m using Deno v0.22.0.

[zekth]

Second solution looks like a good one for me