Re: Minimally Viable Plugins

[Noah Slater <ns...@apache.org>]

Aaaah, this looks so good! Thanks for sharing your work with the list!


On 31 July 2013 18:07, Jan Lehnardt <ja...@apache.org> wrote:

> Heya,
>
> I couldn’t help myself thinking about plugin stuff and ended up
> whipping up a proof of concept.
>
> Here’s a <1 minute demo video:
>
>   https://dl.dropboxusercontent.com/u/82149/couchdb-plugins-demo.mov
>
> Alternative encoding:
>
>   https://dl.dropboxusercontent.com/u/82149/couchdb-plugins-demo.m4v)
>
>
> In my head the whole plugin idea is a very wide area, but I was so
> intrigued by the idea of getting something running with a click on a
> button in Futon. So I looked for a minimally viable plugin system.
>
>
> ## Design principles
>
> It took me a day to put this all together and this was only possible
> because I took a lot of shortcuts. I believe they are all viable for a
> first iteration of a plugins system:
>
> 1. Install with one click on a button in Futon (or HTTP call)
> 2. Only pure Erlang plugins are allowed.
> 3. The plugin author must provide a binary package for each Erlang (and,
>    later, each CouchDB version).
> 4. Complete trust-based system. You trust me to not do any nasty things
>    when you click on the install button. No crypto, no nothing. Only
>    people who can commit to Futon can release new versions of plugins.
> 5. Minimal user-friendlyness: won’t install plugins that don’t match
>    the current Erlang version, gives semi-sensible error messages
>    (wrapped in a HTTP 500 response :)
> 6. Require a pretty strict format for binary releases.
>
>
> ## Roadmap
>
> Here’s a list of things this first iterations does and doesn’t do:
>
> - Pure Erlang plugins only. No C-dependencies, no JavaScript, no nothing.
> - No C-dependencies.
> - Install a plugin via Futon (or HTTP call). Admin only.
> - A hardcoded list of plugins in Futon.
> - Loads a pre-packaged, pre-compiled .tar.gz file from a URL.
> - Only installs if Erlang version matches.
> - No security checking of binaries.
> - No identity checking of binaries.
>
> Here are a few things I want to add before I call it MVP*:
>
> - Uninstall a plugin via Futon (or HTTP call). Admin only.
> - Only installs if CouchDB version matches.
> - Binaries must be published on *.apache.org.
> - Register installed plugins in the config system.
> - Make sure plugins start with the next restart of CouchDB.
> - Show when a particular plugin is installed.
>
> *MVP hopefully means you agree we can ship this with a few warnings
> so people can get a hang of it.
>
> Here is a rough list of features squared against future milestones:
>
> Milestone 2: Be creator friendly
>  - Make it easy to build a CouchDB plugin by providing one or more easy
>    to start templates.
>  - Make it easy to publish new plugins and new versions of existing
> plugins.
>  - Make it easy to supply packages for multiple Erlang & CouchDB versions.
>
> Milestone 3: Public registry
>  - Instead of hardcoding a list of plugins into Futon/Fauxton, we load
>    a list of applicable plugins from a central (and configurable)
>    plugins repository.
>  - This allows plugin authors to publish new plugins and new versions
>    of existing plugins independently.
>
> Milestone 4: Other Languages
>  - Figure out how to handle C-dependencies for Erlang plugins.
>  - Figure out how to allow other language plugins
>    (c.f. non-JS query servers)
>
> Milestone X: Later
>  - Add some account/identity/maybe crypto-web-of-trust system for
>    authors to publish “legit” plugins.
>  - Sign & verify individual releases.
>
> A few more things that can happen concurrently depending on what
> plugins require:
>  - Integrate Erlang/JS tests in the installation
>  - Integrate docs
>
>
> ## How it works
>
> This plugin system lives in `src/couch_plugins` and is a tiny CouchDB
> module.
>
> It exposes one new API endpoint `/_plugins` that an admin user can
> POST to.
>
> The additional Futon page lives at /_utils/plugins.html it is
> hardcoded.
>
> Futon (or you) post an object to `/_plugins` with four properties:
>
>     {
>       "name": "geocouch", // name of the plugin, must be unique
>       "url": "http://people.apache.org/~jan", // “base URL” for plugin
> releases (see below)
>       "version": "couchdb1.2.x_v0.3.0-11-gd83ba22", // whatever version
> internal to the plugin
>       "checksums": {
>         "R15B03": "ZetgdHj2bY2w37buulWVf3USOZs=" // base64’d sha hash over
> the binary
>       }
>     }
>
> `couch_plugins` then attempts to download a .tar.gz from this
> location:
>
>
> http://people.apache.org/~jan/geocouch-couchdb1.2.x_v0.3.0-12-g4ea0bea-R15B03.tar.gz
>
> It should be obvious how the URL is constructed from the POST data.
> (This url is live, feel free to play around with this tarball).
>
> Next it calculates the sha hash for the downloaded .tar.gz file and
> matches it against the correct version in the `checksums` parameter.
>
> If that succeeds, we unpack the .tar.gz file (currently in `/tmp`,
> need to find a better place for this) and adds the extracted directory
> to the Erlang code path
>
> (`code:add_path("/tmp/couchdb_plugins/geocouch-couchdb1.2.x_v0.3.0-12-g4ea0bea-R15B03/ebin")`)
> and loads the included application (`application:load(geocouch)`).
>
> Then it looks into the `./config` directory that lives next to `ebin/`
> in the plugin directory for a file `config.erlt` (“erl-terms”). with a
> list of configuration parameters to load. We parse the file and set
> the config directives one by one.
>
> If that all goes to plan, we report success back to the HTTP caller.
>
> That’s it! :)
>
> It’s deceptively simple, probably does a few things very wrong and
> leaves a few things open (see above).
>
> One open question I’d like an answer for is finding a good location to
> unpack & install the plugin files that isn’t `tmp`. If the answer is
> different for a pre-BigCouch/rcouch-merge and post-BigCouch/rcouch-
> merge world, I’d love to know :)
>
>
> ## Code
>
> The main branch for this is 1867-feature-plugins:
>
>      ASF:
> https://git-wip-us.apache.org/repos/asf?p=couchdb.git;a=log;h=refs/heads/1867-feature-plugins
>   GitHub: https://github.com/janl/couchdb/compare/1867-feature-plugins
>
> I created a branch on GeoCouch that adds a few lines to its `Makefile`
> that shows how a binary package is built:
>
>
> https://github.com/janl/geocouch/compare/couchbase:couchdb1.3.x...couchdb1.3.x-plugins
>
> * * *
>
> I hope you like this :) Please comment and improve heavily!
>
> Let me know if you have any questions :)
>
> If you have any criticism, please phrase it in a way that we can use
> to improve this, thanks!
>
> Best,
> Jan
> --
>
>


-- 
NS