Containerized Cordova App Building for Android

Why

https://developer.chrome.com/apps/chrome_apps_on_mobile describes using Apache Cordoba to turn Chrome Apps into Mobile apps for Android (and iOS, but this won't actually help you with that.)

Sounds great - but once you dig in to the instructions you find a lot of downloading and a lot of java installation and unpacking, all of which is tedious and in the longer term, prone to version skew problems - and since none of this plays well with your operating system's packaging tools, there's reason to be a bit fearful of the install.

There are two ways to reduce this fear. The traditional way would be to actually package all of the components; this works ok up until you hit the underlying android sdk tool, which is itself an application-specific package manager. The "modern" way is to take a huge shortcut - instead of caring about how messy the install is, just do it inside a docker container, which you can just throw away when you're done or need to upgrade.

How

The problem is broken into two parts: creating a docker image with the complete build environment, and using it for your own development.

Building the image

The "zeroeth" step is to create a docker image you can use at all (since public docker images are Just Wrong - not only is the documented provenance of an image usually unclear, but the tools themselves don't validate that the downloads match the manifests, so you don't have any confidence that you even got the intended-but-unverified packages.) On Debian, at least, the make basedeb step uses mkimage.sh to produce one locally with debootstrap which will get packages using your sources.list and already-configured package-signing mechanisms to assure that you're building something out of Debian packages which you actually got from Debian itself - there is of course room for more concern beyond that, but it seems like a reasonable standard to start from.

For the first step, simply make image which took about an hour over DSL, and will probably be faster for you... two things you should know in advance:

the Dockerfile just types y at all license prompts for you, so be sure to read through them afterwards.
all of the explicit downloads (and as far as I can tell all of the implicit ones) are done with https - this is good and correct, but means there is no useful caching you can do to save time iterating over the configuration if anything goes wrong. (It is possible to force some of the tools to use http, but there's no alternate way to verify them, so don't do that.) Ultimately you're going to use the Docker Image as your cache anyway.

The build step runs cca checkenv to perform installation self-tests at the end; running make check will repeat the test.

Using the image

If you're starting from scratch like I am, after the image is built, simply make sample which will create and build a sample app - it displays the Chrome logo and a little text, producing a 20M apk to do so. The output will show you where to find the apk files, pick the relevant one (which is probably android-armv7-debug.apk) and copy it to your phone, and you should be able to launch it from there. On a 2014 model Intel NUC with SSD, this applications build takes about four minutes.

Doing your own development

This is where you want to go back to the chrome apps page, step 3 "develop" for help. You can take basic baby steps simply by exploring the code directory that make sample created; in particular, the app itself is just rendering code/sample/www/index.html, so if you just edit that (and add other content there, look at the existing layout for images and javascript assets) and re-run the cca build in that directory (make rebuild will do this directly) you should be able to copy the new apk over to your phone and see the results.

You will likely want to copy the lines in the Makefile to fit your app as you develop it - or even just run a shell inside the docker image (make shell) and then run cca and other dev-kit commands directly. (Bonus points for coming up with an inotify/cca build loop that you can just leave running.) Also you'll very quickly want to actually set up an android emulator, or have it push directly to your phone; see the develop step linked above.

Updates

In theory, you could take new updates to the Android and Chrome SDKs by setting up a dockerfile that based a new image on the one generated here, run the update inside that, then re-run cca build. (Since /code is outside the image, that survives the upgrade.) This mostly suggests the need for docker rebase, though it might turn out that just re-tagging the new image with the old name is enough.

Alternatively, you can just discard (docker rmi) the image and recreate it when there's a new upstream release that you actually want; this avoids having to care about whether the "update" process actually works.

What Next

If you find this prep work useful, drop me a note describing your app; if it doesn't work out, please open issues about the problems (I haven't gotten my own apps beyond the hello world step here.)

eichin / cca-sdk-nocache