Fix #2459

[calzoneman]

The error reported in #2459 is caused by allowing junk UTF-16 strings to be passed to the utf8 module for encoding, which then throws an error (as documented in https://github.com/mathiasbynens/utf8.js#utf8encodestring).

This change avoids the issue by replacing such garbage values with U+FFFD 'REPLACEMENT CHARACTER' ("used to replace an incoming character whose value is unknown or unrepresentable in Unicode" -- http://www.fileformat.info/info/unicode/char/fffd/index.htm).

[nuclearace]

@rauchg @nkzawa Does this look good?

[darrachequesne]

Hi @calzoneman! Wouldn't it make sense to switch to wtf-8 (as you suggested here socketio/socket.io#2459), since there is currently no check for those lone surrogates for ws transport?

Maybe such sanitization should occur up-front?

[calzoneman]

Switching to wtf-8 may make sense. I didn't investigate what all had to change for that and implemented this as a stopgap for myself. Whichever solution would actually be merged I'm willing to take a look at, but with the way things are going I don't currently have confidence that anyone is paying attention to this issue.

[polarathene]

Perhaps @nuclearace being a Socket.IO member is able to help bring in a new maintainer for this repo? There has been an issue/PR for 5 months affecting React-Native developers that want to use socket.io for websockets that gets no attention from @rauchg or others that I and others have reached out to so far.

It would be great for a maintainer of this repo to step up and at least confirm they're no longer able to find time to maintain this repo and offer the role to another member of the community. It would seem that any new PR or issues raised will not be addressed for the foreseeable future :(