`io.readLines` yield incomplete lines

Describe the bug

It seems io.readLines yield incomplete lines in some cases.

To Reproduce

Add gen.ts as

import { parse } from "https://deno.land/std@0.105.0/flags/mod.ts";

const opts = parse(Deno.args)
const size = opts.size || 128;
const v = "x".repeat(1024 * size);
const b = new TextEncoder().encode(`["${v}"]`);

await Deno.stdout.write(b);
console.log("");

And add test.ts as

import * as io from "https://deno.land/std@0.100.0/io/mod.ts";

for await (const line of io.readLines(Deno.stdin)) {
  console.log(`Recv ${line.length}`);
  if (!line) {
    continue;
  }
  JSON.parse(line);
}

When the buffer size is small enough, it process successfully.

deno run gen.ts --size=1 | deno run test.ts
Check file:///Users/alisue/ghq/github.com/lambdalisue/deno-io-test/gen.ts
Check file:///Users/alisue/ghq/github.com/lambdalisue/deno-io-test/test.ts
Recv 1028
Recv 0

But when the buffer size is big, io.readLines yield incomplete lines like

deno run gen.ts --size=100 | deno run test.ts
Check file:///Users/alisue/ghq/github.com/lambdalisue/deno-io-test/gen.ts
Check file:///Users/alisue/ghq/github.com/lambdalisue/deno-io-test/test.ts
Recv 16384
error: Uncaught (in promise) SyntaxError: Unexpected end of JSON input
  JSON.parse(line);
       ^
    at JSON.parse (<anonymous>)
    at file:///Users/alisue/ghq/github.com/lambdalisue/deno-io-test/test.ts:8:8

Expected behavior

io.readLines waits for a complete line.

Desktop (please complete the following information):

• OS: macOS 11.5
• Version

deno 1.13.0 (release, x86_64-apple-darwin)
v8 9.3.345.11
typescript 4.3.5

Additional context https://github.com/lambdalisue/deno-io-test

[mattn]

Sorry, I was cofused. This is not a cause of deno. Please close this,

[lambdalisue]

write() is a single syscall and it can write up to about 16Kb of data at once (with matches your Recv value). Use writeAll instead and the problem will go away.

Oops. I’ve forgotten about why there is the writeAll function… As you said, I could not find any issue with the following gen.ts

import { parse } from "https://deno.land/std@0.105.0/flags/mod.ts";
import * as io from "https://deno.land/std@0.100.0/io/mod.ts";

const opts = parse(Deno.args)
const size = opts.size || 128;
const v = "x".repeat(1024 * size);
const b = new TextEncoder().encode(`["${v}"]`);

await io.writeAll(Deno.stdout, b);
console.log("");

It can handle 1024 * 1024 data, so it seems it’s no longer an issue for me. Let wait for what @mattn can provide…