Does html5_run() have limited return length? (SOLVED)

[decoded]

I am trying to get image data via user file ulpoad - from JavaScript into Defold using html5_run()
There seems to be a limit(around 2048) for data that is passed back on return.
Is this correct, or is something else going on?

For example, in Defold I use this:

local result = html5.run("upload_file();")

Which gets the image source through JavaScript:

<script type='text/javascript'>
function upload_file() {
	var output = document.getElementById('output_image');
	return output.src;
};
</script>

And gives me something like this (for a very small icon):

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAgAAAAICAYAAADED76LAAAABHNCSVQICAgIfAhkiAAAAAlwSFlzAAALEwAACxMBAJqcGAAAAC5JREFUGJVjZEAF/xlIBP+ZsAguYGBg4EI3Fh2vwmflfCQTCLrpPyO6ACEdGAAANaMM9wuhrTQAAAAASUVORK5CYII=

For larger images, the data gets truncated and corrupts the image.

[Mathias_Westerdahl]

No I don’t see that our code does any limitation per se. We use emscripten_run_script_string though, but that too seems to be dynamic (source)

What if you print the content+length in the upload_file() function, just after the “var output = …” statement, does it look ok then?

[decoded]

I think “upload file” probably confuses this a little. I’m technically trying to avoid actual uploading - but not sure if this will work.

There’s definitely some kind of limit in return from JavaScript with length > 2048 to html5_run()

Edit:
Repro case added below

[Mathias_Westerdahl]

Hmm, strange. Perhaps you can create a small repro case and I can take a look at it tomorrow?

[decoded]

Yes of course. Happy to have you take a look if you don’t mind.

Here’s a Defold project that reproduces the issue. decoded-html5-overflow.zip (4.2 KB)
(Build HTML5 and inspect console)

2034 seems to be the magic number, not 2048.
The repro case uses html5.run() with these:

<script type='text/javascript'>
function get_data_overflow() {
	return (Array(2034).join('x'));
};
function get_data_ok() {
	return (Array(2033).join('x'));
};
</script>

[decoded]

It’s OK to tell me, “just don’t use really long strings stupid!”
They seem to break a lot of things…

print() is apparently limited, and sometimes will not output if string length is too long.
Could be why this is happening.

The Defold editor itself will throw “java.lang.StackOverflowError: Unknown” if you type enough text in one line.

I think there is an issue for that already.

please don’t worry too much about this.
I believe the solution is for me to find a way that avoids long string data.

[Mathias_Westerdahl]

Well, it seems it was just the print that doesn’t support too long strings.

I changed the function like so:

function get_data_overflow() {
	var prefix = Array(8).join('a')
	var suffix = Array(8).join('b')
	var s = prefix + Array(4096).join('x') + suffix;
	console.log("LENGTH is " + s.length);
	return s;
};

And the printout like so:

print(string.sub(result, 0, 16), "...", string.sub(result, #result-15))

And I get:

LENGTH is 4109 // from javascript
DEBUG:SCRIPT: data is TOO BIG. len is	4109
DEBUG:SCRIPT: aaaaaaaxxxxxxxxx	...	xxxxxxxxxbbbbbbb

[decoded]

Thanks a ton @Mathias_Westerdahl - you inadvertently helped me with another question also.
How to strip the image headers from the base64 encoding.

All that fancy string manipulation, and no limits in the html5.run() return - it works!