Store html content in a data-html attribute.

[dstein64]

This is a workaround for python-visualization/folium#812.

The prior approach of using a data URI for the src attribute can encounter a 2MB limit in Chrome, which is problematic for displaying folium maps with a lot of data (examples given in the aforementioned issue).

The approach proposed here is to use a data-html attribute containing the underlying html that will be used to populate the iframe. This requires javascript. It's not particularly elegant in my opinion, but it was the best I could think of given the trade offs.

An alternative approach, which I utilized to monkey patch folium/branca temporarily for a dashboard I created, is to use a srcdoc attribute in addition to the data URI in the src. srcdoc is not supported in IE/Edge, but utilizing the data URI in src combined with srcdoc works (the srcdoc is utilized by browsers that recognize it). However, this approach stores redundant data in src and srcdoc, and also requires special handling to escape the HTML stored under srcdoc (e.g., for quotes and ampersands).

[dstein64]

The test_rendering_utf8_iframe test failed after I opened this PR. However, that test is seemingly unrelated to my update.

Upon further inspection, it appeared the issue was related to firefox. The travis logs reveal the following error when the latest firefox is installed.

Installing Firefox latest
$ firefox --version
XPCOMGlueLoad error for file /home/travis/firefox-latest/firefox/libmozgtk.so:
libgtk-3.so.0: cannot open shared object file: No such file or directory
Couldn't load XPCOM.

I suppose this did not occur for whatever version of firefox installed when these tests were last run four months ago.

Adding libgtk-3-0 as a dependency to .travis.yml fixes the issue.

[dstein64]

Adding libgtk-3-0 dependency fixes the issue mentioned above, but travis_apt_get_update sometimes hangs, causing the tests to fail. There is no way to disable the apt updating, since it happens whenever there are apt packages listed:
https://github.com/travis-ci/travis-build/blob/master/lib/travis/build/addons/apt.rb#L85

[Conengmo]

I’m ready to merge this PR. I think it’s a good way to solve our issues with Jupyter on Chrome now. One question though, can you think of scenarios where this might break? You mentioned requiring JavaScript, but that’s required for Leaflet anyway. It seems according to specifications there’s no limit on data attributes. Anything else that might go wrong here?

[dstein64]

Hi @Conengmo,

Besides the Javascript scenario, I'm unable to think of any additional scenarios where this approach might break.

I've tested the approach on Chrome and Firefox. Additionally, I have not received any errors reported from the 10-20 users that are using an interface I built using this approach.

[Conengmo]

Thanks so much for your work on this @dstein64, and your useful comments. It’s appreciated. We’ll make sure to get this released soon.