I strongly believe that's not possible, but let me ask it anyway:
There's any way to make an asynchronous WebRequest with no DLLs use at all?
I need to grab some large data from a website but can't afford losing ticks in the meanwhile.
What if you ran the synchronous WebRequest() MQL5 function in a second EA on a different chart?
If the first EA needs to know when the file is there, it could use FileIsExist(), or monitor the file size. Or, you could probably fashion some sort of signaling from EA #2 to EA #1 using terminal global variables.
My advice is using an indicator for grabbing the data, process it and save it locally or in a global variable. Then the EA can read the file if needed or get the result from a global variable.
Impossible. Indicators are not allowed to use WebRequest.