<amp-iframe> Proper base64 encoding of srcdoc

[aghassemi]

Closes #6098

[jridgewell]

This seems like it belongs in the base64 library, and used with our other encoding.

[jridgewell]

Whoot, this function can replace utf8Encode and the stringToBytes stuff in bytes, and the base64 encode decode!

[aghassemi]

Thanks, will send out a separate refactor CL.

[muxin]

This might look prettier for encoding unicode?
@jridgewell Why can this replace base64 encode decode? base64Encode is simply btoa that encode ascii string (not unicode).

[aghassemi]

@muxin @jridgewell Here is what I am thinking to do:

1- Change the iframe to use utf8Encode from bytes.js and then pass it to base64EncodeFromBytes from base64.js. This should be the fastest way to do this specially for browsers that have native TextEncoder support.

2- Remove base64Encode and base64Decode from base64.js They are not used anywhere and are confusing (same way btoa is confusing) in terms of what input string are valid.

thoughts?

[muxin]

utf8Encode is async indeed. How about we change base64Encode to support unicode encoding:

export function base64Encode(str) {
  return btoa(unescape(encodeURIComponent(str)));
}
export function base64Decode(str) {
  return decodeURIComponent(escape(atob(str)));
}

And base64Encode can be called in amp-iframe.

[aghassemi]

unescape is deprecated and that inner function simply does what unescape does. Otherwise both solutions are the same.

I wonder why utf8Encode in bytes wasn't polyfilled with this approach when TextEncoder is not available. That would have kept it sync. @lannka Do you know?

[jridgewell]

Likely didn't know about it.

[lannka]

Yep, I reviewed that code but honestly I didn't know this better approach here. we can do a refactoring.

[aghassemi]

I tried a few designs and decided mixing base64 encoding and string encoding does not make sense since they are completely different concepts. I will send a PR soon with the code and the reasoning behind the design.

[jridgewell]

This function can be hoisted out.