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Re: Gio.InputStream (and friends)

this is gold, thank you!!!

do you know if MemoryInputStream is the only one usable? is there any list of available GJS streams one can use? I think memory is just fine though, thanks again a lot!

On Tue, Nov 7, 2017 at 6:46 PM, Sam Jansen <sam jansen starleaf com> wrote:
Hi Andrea,

I've come up with something that... almost does what you're looking at here. Perhaps it's useful as a guide of what one can do with the Gio interface.

I think you may hit some awkward problems with modelling Node-style streams with GLib ones. But perhaps it is possible and this helps. I don't really know the Node stream semantics so I have assumed various things in my Readable implementation as you'll see... Note that MemoryInputStream really is just a byte stream; so there is no guarantee you'll receive the exact block of bytes that was written -- for example, when I run this I get a first chunk of "12", followed by "3", "4", etc.


let Gio = imports.gi.Gio;
let byteArray = imports.byteArray;
let mainloop = imports.mainloop;

class Readable {
  constructor() {
    this._mio = Gio.MemoryInputStream.new();
    this._callbacks = {};
    this._startNext();
  }

  _startNext() {
    // Enqueue an async read; and re-enqueue when it finishes, so we're
    // always waiting for data...
    this._mio.read_bytes_async(4096, 1, null, (source, res) => { 
this._onData(this._mio.read_bytes_finish(res));
        this._startNext();
});
  }

  _onData(bytes) {
    if (this._callbacks['data']) {
      let ba = byteArray.fromGBytes(bytes);
      this._callbacks['data'](ba);
      this._read();
    }
  }

  push(bytes) {
    if (bytes == null) {
      mainloop.quit('main');
      return;
    }
    this._mio.add_bytes(bytes);
  }

  on(name, callback) {
    this._callbacks[name] = callback;
    if (name === 'data') {
      this._read();
    }
  }
}

class Counter extends Readable {
  constructor(opt) {
    super(opt);
    this._max = 1000;
    this._index = 1;
  }

  _read() {
    const i = this._index++;
    if (i > this._max)
      this.push(null);
    else {
      const str = '' + i;
      const buf = byteArray.fromString(str); // Buffer.from(str, 'ascii');
      this.push(buf);
    }
  }
}

(new Counter).on('data', (str) => { 
    print("data", str.toString());
});

mainloop.run('main');


On 7 November 2017 at 10:08, Andrea Giammarchi <andrea giammarchi gmail com> wrote:
I am trying to implement a stream module and apparently I have everything I need but practically I'm unable to use streams.

If I instantiate a `new Gio.InputStream` I have the following error:
cannot create instance of abstract (non-instantiatable) type 'GInputStream'

I cannot even extend it ... so I've though "ok, maybe it's like an interface, I implement it and that's it"

But then a JS class wouldn't work as base_stream for a Gio.BufferedInputStream, and if I extend the JS class to be a GObject.Object then:
Gjs-WARNING **: JS ERROR: TypeError: Object is of type GObject.Object - cannot convert to GInputStream

where GInputStream is the one I cannot use in the first place.

I've reached full circle then so ... I wonder if anyone has any idea how to use/create/extend streams in GJS (not talking about file streams but streams in general) or if it's even possible.

In node, as example, I could do this and it will work:

```js

const { Readable } = require('stream');

class Counter extends Readable {
constructor(opt) {
super(opt);
this._max = 1000;
this._index = 1;
}

_read() {
const i = this._index++;
if (i > this._max)
this.push(null);
else {
const str = '' + i;
const buf = Buffer.from(str, 'ascii');
this.push(buf);
}
}
}

(new Counter).on('data', console.log);

```

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