Re: Gio.InputStream (and friends)

[Sam Jansen <sam jansen starleaf com>]

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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