Use evaluateJavascript for WebView postMessage, if available

[jordoh]

loadUrl's behavior on Android 4.4+ is to URL decode the input prior to evaluating it, so a %22 in the input will be decoded to ". Since it is not escaped, this quote introduces a syntax error into the javascript, preventing execution.

This changes postMessage to use evaluateJavascript on Android 4.4+ to fix #19611

Test Plan

Manual:

1. react-native init Test, cd Test, replace App.js with example from Including %22 in Android WebView postMessage payload results in SyntaxError #19611
2. yarn add github:jordoh/react-native#android-postMessage-evaluateJavascript and set up to build react-native from source
3. react-native run-android and verify that pressing the postMessage with %22 button changes the text in the WebView to "success".

Related PRs

There have been PRs to implement a similar change in injectedJavaScript, which appear to stall on the discussion of whether the inconsistency in behavior is acceptable:

• Using evaluateJavascript to fix #9749 #9945 (closed)
• injected javascript comments now work on android #12321 (open)

However, per this issue, my understanding is that Android before 4.4 did not URL decode the string passed to loadUrl, so calling loadURL would not suffer from #19611 - though there may be other differences in the behavior of evaluateJavascript and the pre-4.4 loadUrl that I am unaware of.

Release Notes

[ANDROID] [ BUGFIX] [WebView] - Fix "%22" in postMessage failing on Android 4.4+

[jordoh]

CC @shergin in case you have some spare cycles to take a look at this. It would be great to get this to master in time to be cherry-picked for 0.56.

[facebook-github-bot]

@jordoh I tried to find reviewers for this pull request and wanted to ping them to take another look. However, based on the blame information for the files in this pull request I couldn't find any reviewers. This sometimes happens when the files in the pull request are new or don't exist on master anymore. Is this pull request still relevant? If yes could you please rebase? In case you know who has context on this code feel free to mention them in a comment (one person is fine). Thanks for reading and hope you will continue contributing to the project.

[jordoh]

Hi @mdvacca - sorry to bother, but it looks like you've reviewed code touching the Android WebView recently - any chance you could take a look at this?

[LinusU]

@jordoh Would it be possible to fix the other invocation of root.loadUrl("javascript:", the one that handles injectedJavaScript, as well?

That would fix #20365 on Android 4.4+

[LinusU]

@jordoh Sent a PR to this PR here: jordoh#1

[LinusU]

I have a new PR up to React Native that fixes the problem for Android <4.4 as well. It also fixes the issues at the other invocations:

#20366

[jordoh]

Hi @LinusU - I like your approach, given the inclusion of the < 4.4 escaping. 👍

I left those other spots out here since the previous PR discussions (#9945 and #12321) stalled out on those updates, but it looks like your changes address the issues raised in those PRs.

I'll leave this PR open with the hope that something gets merged, but definitely recommend that #20366 gets merged instead to supersede this PR.

[hramos]

WebView PRs are on hold pending approval of the WebView proposal at react-native-community/discussions-and-proposals#3