Improve handling `Var`'s when passing them as `data` to `rx.download(...)`

[riebecj]

Related to #5954 and #5957.

When data is provided as a Var, strings could sometimes have formatting issues and bytes were ArrayVar's that were really not handled at all, as there is no such thing as byte-strings in JavaScript. They were correctly converted to byte arrays, but the resultant downloaded file was just a string representation of the byte array.

• Var[bytes]: The byte array is coerced into a Uint8Array and converted to a Blob using the specified mime_type. The object URL is then created from the Blob.
• Var[str]: The string data is left intact to preserve formatting.
• Var[Any]: Any other supplied state or non-state variable is stringify-ed.
• Base64 Encoded: To ensure correct data translation, the var data (except for bytes) is base64 encoded.

All of this is done within the variable ecosystem, as there seems to be some aversion to changing any of the Reflex embedded JS (not a gripe, just an observation).

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Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

New Feature Submission:

• [x] Does your submission pass the tests?
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[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #5961 will not alter performance

_{Comparing riebecj:main (ea9f14b) with main (3c3ddc2)}

Summary

✅ 8 untouched

[riebecj]

I don't think the failed test has anything to do with my code changes, but I can update if necessary.

[riebecj]

@masenf, I can work on that.

What about handling of Python bytes? Currently, nothing in the Var system is designed to ensure handling of Python byte strings to JS byte arrays. Since bytes are a Python primitive, I would suggest that it gets first class treatment before Blobs, urls, and base64 encoding. If the idea is to NOT handle bytes and require conversion to str, it should not be an accepted type anywhere.

[riebecj]

Converting to draft to use as a work space for BytesVar and BlobVar.

This will be abandoned and a new one created when the architecture and implementation of the referenced vars is agreed upon.

[riebecj]

@masenf , Take a look at BytesVar and BlobVar. Let me know where things should be changed/improved/etc.

I ran it through multiple example tests using direct State vars, computed vars, and even creating them directly. All seem to function correctly, download with proper formatting, and supports Unicode.

[riebecj]

All the type hinting seems to be there too.

I was a little wary about using encode and decode because of the underlying _decode for Vars, but it felt the most Pythonic given its implementation type.

[riebecj]

@masenf Made the changes you suggested.

[riebecj]

@masenf Any more suggestions?