Consider whether to encode SPACE as "%20" instead of "+"

[mgiuca]

Due to the recent spec changes by @ericwilligers (re-using the application/x-www-form-urlencoded serializer), we are now using that encoder instead of the hand-coded one I previously had in the spec (which was equivalent to calling ECMAScript encodeURIComponent).

The major difference is that the application/x-www-form-urlencoded serializer encodes U+0020 (SPACE) as U+002B (+) instead of "%20". This is compatible with how HTML forms work, so isn't that unusual on the web. However, it is fairly unusual for any URL encoding other than directly-submitted HTML forms. Most other URL encoding/decoding encodes SPACE as "%20" and does not expect "+" to represent space in a URL being decoded.

The major issue with this is that we anticipate client-side decoding of Web Share Targets, and JavaScript's decodeURIComponent DOES NOT decode + (it just leaves it as +). This means that every client-side decoder needs to specially replace U+002B (+) with U+0020 (SPACE) before running decodeURIComponent. Remember that part of the reason we went with this URL encoding approach is for compatibility with existing share target endpoints.

As a (single) data point, Twitter does handle + characters as spaces: https://twitter.com/intent/tweet?text=Can+share+targets+handle+plus%3F

Should we deviate from the application/x-www-form-urlencoded serializer, and encode spaces as %20? This is tricky now that we're explicitly using the string "application/x-www-form-urlencoded" in the "enctype" member of the "share_target" dictionary.

[mgiuca]

@ericwilligers Do you have thoughts on this? Could you have a look at a bunch of sites like Facebook and other targets found in existing share sheets on the web, to see if they handle + correctly?

[YosokaHosting]

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