Stream comunication between JavaScript and guest OS

[nwtgck]

Hi, thank you so much for the fantastic project!

I'd like to comunicate or stream data between JavaScript and guest OS. I know emulator.serial0_send() and "serial0-output-line" event, using in the Lua intepreter, but the output might have noises.

For example, when we have device files such as /dev/jsread and /dev/jswrite, we can compress in a guest OS and use in JavaScript by using cat /dev/jsread | gzip | /dev/jswrite. You can also do cat /dev/jsread | lua | /dev/jswrite.

Another my idea is to use named pipes (FIFO). I tried to use them, but unfortunelly they don't use FS.prototype.Read orFS.prototype.Write, so I could not give or obtain data to the named pipe from JavaScript.

Could you tell me how to comunicate between JavaScript and guest OS streamingly?

poor workaround

The script as follows create a large file/root/myjsread and emulator.fs9p.Read is modified to give arbitrary data to guest OS from JavaScript.

    var emulator = new V86Starter({...});

    const rootId = emulator.fs9p.SearchPath("/root").id;
    const filename = "myjsread";
    const parentid = rootId;
    const x = emulator.fs9p.CreateInode();
    x.uid = emulator.fs9p.inodes[parentid].uid;
    x.gid = emulator.fs9p.inodes[parentid].gid;
    x.qid.type = S_IFREG >> 8;
    x.mode = (emulator.fs9p.inodes[parentid].mode & 0x1B6) | S_IFREG;
    emulator.fs9p.PushInode(x, parentid, filename);
    emulator.fs9p.NotifyListeners(emulator.fs9p.inodes.length-1, 'newfile');
    var id = emulator.fs9p.inodes.length-1;
    x.size = Number.MAX_SAFE_INTEGER;

    const originalRead = emulator.fs9p.Read.bind(emulator.fs9p);

    console.log("ID", id);
    emulator.fs9p.Read = async function (nodeid, offset, count) {
        if (id === nodeid) {
            console.log("!! READ HOOK !! reading ", arguments);
            // You can return bytes what you want, but I just streams infinite "A"
            return new Uint8Array(Array(count).fill(65));
        }
        return originalRead(nodeid, offset, count);
    };

An example usage in a guest OS is as follows.

$ cat myjsread
AAAAAAAAAAAA...
AAAAAAAAAAAA...
...

In my experiment, reading the /root/myjsread stopped arround 2^32 bytes.

[nwtgck]

I finally made it, but it has a problem ! I specified uartN: true bellow, then we can read/write /dev/ttyS1 and/dev/ttyS2 in guest OS.

var emulator = new V86Starter({
        ...
        uart1: true,
        uart2: true,
        uart3: true,
        ...
});

JavaScript → guest OS

//  JavaScript → guest OS
setInterval(() => {
        console.log("send now!");
        emulator.bus.send("serial1-input", 65);
}, 1000);

stty raw < /dev/ttyS1
cat /dev/ttyS1

guest OS → JavaScript

stty raw < /dev/ttyS2
echo hello > /dev/ttyS2

    emulator.add_listener("serial2-output-char", function(char)
    {
        console.log("outchar2", char);
    });

The problem is the line buffer.

[ZXMushroom63]

I found this very, very useful. Thanks!

[nwtgck]

I'm glad to hear that!

[farhan-ct]

This is very helpful, thank you for sharing!

[coderofsalvation]

this is what I wanted.
I'm so happy somebody pointed me in #1140 to this issue.
Yesterday I gave up hacking on .Read() as I got weird javascript errors about incorrect size/offsets.
Seeing this example makes me realize I was unaware of multiple ttys, as well as using a real inode with a large size ❤

[SuperMaxusa]

Small update about the serial port method: the serialX-output-char event is deprecated (4928c91), so you need to use serialX-output-byte + String.fromCharCode/TextDecoder instead if you need to get a character:

    emulator.add_listener("serial2-output-byte", function(byte)
    {
        console.log("outchar2", String.fromCharCode(byte));
    });

---

Also you can use a virtio-console device (7660cbf), if you are using self-built Linux or Buildroot, you need to enable CONFIG_VIRTIO_CONSOLE in make menuconfig/linux-menuconfig (some Linux distributions have this module by default).

var emulator = new V86({
        ...
        virtio_console: true,
        ...
});

JavaScript → guest OS

//  JavaScript → guest OS
setInterval(() => {
    console.log("send now!");
    emulator.bus.send("virtio-console0-input-bytes", Uint8Array.from([65]));
}, 1000);

stty raw < /dev/hvc0
microcom /dev/hvc0

guest OS → JavaScript

// guest OS → JavaScript
emulator.add_listener("virtio-console1-output-bytes", function(bytes)
{
    console.log("out", new TextDecoder("utf-8").decode(bytes));
});

stty raw < /dev/hvc1
echo hello > /dev/hvc1

[Molnfront]

Could you have a node.js server in the guest OS listening for inputs from the external Javascript?

[SuperMaxusa]

Could you have a node.js server in the guest OS listening for inputs from the external Javascript?

Currently, no, there is some implementation on a custom network stack: #1048 (reply in thread)

UPD: Look at tcpip.js: #1197 and #1048 (comment)