createEvent broken by mutating strings

[ThaUnknown]

adding an event with createEvent

{
Duration: 4880,
Effect: "",
Layer: 0,
MarginL: 0,
MarginR: 0,
MarginV: 0,
Name: "",
ReadOrder: 0,
Start: 7870,
Style: 1,
Text: "Text."
}

for some reason creates an event that looks like:

{
Duration: 4880,
Effect: "Text.",
Layer: 0,
MarginL: 0,
MarginR: 0,
MarginV: 0,
Name: "Text.",
ReadOrder: 0,
Start: 7870,
Style: 1,
Text: "Text."
}

breaking the entire renderer, adding more subtitles with the createEvent function overwrites the text, effect and name values of the previous events

[ThaUnknown]

are there any fixes for this? its becoming a serious issues for very well typesetted subs like [μtw-Kaleido] releases, which can be shown here: 60a5523d6380ed07ff63648b76324c6ca8192faf, i currently work around this issue by building the sub file and passing it via octopusInstance.setTrack() but for videos with a few thousand subtitles it kills the service worker thread, even on high-end hardware!

[TheOneric]

Can confirm this still happens with current master. And even worse, if you add another event all strings in the previously created events change to the newly added string. This appears to be an issue with improperly passing memory/pointers from JS to WASM.

On a side note though, you should not create events with a non-unique ReadOrder value. Your example sets ReadOrder: 0 which would be valid if the track was empty before, but otherwise this has the potential to mess things up.

[TheOneric]

@TFSThiagoBR98: Seems like you added this in ec21ec3, do you know what the "best practce"-way of passing strings from JS to WASM is? This likely affects more than just createEvent.
EDIT: Probably affected are createEvent, setEvent, createStyle and getStyle. Furthermore setEvent, setStyle, removEvent and removeStyle are hard to use right as such direct modifications aren't always allowed by libass.

[TFSThiagoBR98]

WebIDL uses this 2 generated functions:

void EMSCRIPTEN_KEEPALIVE emscripten_bind_ASS_Event_set_Text_1(ASS_Event* self, char* arg0) {
  self->Text = arg0;
}

and its JS counterpart:

ASS_Event.prototype['set_Text'] = ASS_Event.prototype.set_Text = /** @suppress {undefinedVars, duplicate} */function(arg0) {
  var self = this.ptr;
  ensureCache.prepare();
  if (arg0 && typeof arg0 === 'object') arg0 = arg0.ptr;
  else arg0 = ensureString(arg0);
  _emscripten_bind_ASS_Event_set_Text_1(self, arg0);
};

Also the ensureString function:

function ensureString(value) {
  if (typeof value === 'string') {
    var intArray = intArrayFromString(value);
    var offset = ensureCache.alloc(intArray, HEAP8);
    ensureCache.copy(intArray, HEAP8, offset);
    return offset;
  }
  return value;
}

This uses the intArrayFromString function but Emscripten also have the stringToUTF8, see here

[ThaUnknown]

WebIDL uses this 2 generated functions:

void EMSCRIPTEN_KEEPALIVE emscripten_bind_ASS_Event_set_Text_1(ASS_Event* self, char* arg0) {
  self->Text = arg0;
}

and its JS counterpart:

ASS_Event.prototype['set_Text'] = ASS_Event.prototype.set_Text = /** @suppress {undefinedVars, duplicate} */function(arg0) {
  var self = this.ptr;
  ensureCache.prepare();
  if (arg0 && typeof arg0 === 'object') arg0 = arg0.ptr;
  else arg0 = ensureString(arg0);
  _emscripten_bind_ASS_Event_set_Text_1(self, arg0);
};

Also the ensureString function:

function ensureString(value) {
  if (typeof value === 'string') {
    var intArray = intArrayFromString(value);
    var offset = ensureCache.alloc(intArray, HEAP8);
    ensureCache.copy(intArray, HEAP8, offset);
    return offset;
  }
  return value;
}

This uses the intArrayFromString function but Emscripten also have the stringToUTF8, see here

so any chance this will get fixed?