appmap

• About
• Usage
• Development
  • Internal architecture
  • Running tests
  • Using fixture apps
    • test/fixtures
    • spec/fixtures

About

appmap-ruby is a Ruby Gem for recording AppMaps of your code. "AppMap" is a data format which records code structure (modules, classes, and methods), code execution events (function calls and returns), and code metadata (repo name, repo URL, commit SHA, labels, etc). It's more granular than a performance profile, but it's less granular than a full debug trace. It's designed to be optimal for understanding the design intent and structure of code and key data flows.

Usage

Visit the AppMap for Ruby reference page on AppLand.com for a complete reference guide.

Development

Internal architecture

Configuration

appmap.yml is loaded into an AppMap::Config.

Hooking

Once configuration is loaded, AppMap::Hook is enabled. "Hooking" refers to the process of replacing a method with a "hooked" version of the method. The hooked method checks to see if tracing is enabled. If so, it wraps the original method with calls that record the parameters and return value.

Builtins

Hook begins by iterating over builtin classes and modules defined in the Config. Builtins include code like openssl and net/http. This code is not dependent on any external libraries being present, and appmap cannot guarantee that it will be loaded before builtins. Therefore, it's necessary to require it and hook it by looking up the classes and modules as constants in the Object namespace.

User code and gems

After hooking builtins, Hook attaches a TracePoint to :begin events. This TracePoint is notified each time a new class or module is being evaluated. When this happens, Hook uses the Config to determine whether any code within the evaluated file is configured for hooking. If so, a TracePoint is attached to :end events. Each :end event is fired when a class or module definition is completed. When this happens, the Hook enumerates the public methods of the class or module, hooking the ones that are targeted by the Config. Once the :end TracePoint leaves the scope of the :begin, the :end TracePoint is disabled.

Running tests

Before running tests, configure local.appmap to point to your local appmap-ruby directory.

$ bundle config local.appmap $(pwd)

Run the tests via rake:

$ bundle exec rake test

The test target will build the native extension first, then run the tests. If you need to build the extension separately, run

$ bundle exec rake compile

Using fixture apps

test/fixtures

The fixture apps in test/fixtures are plain Ruby projects that exercise the basic functionality of the appmap gem. To develop in a fixture, simply enter the fixture directory and bundle.

spec/fixtures

The fixture apps in spec/fixtures are simple Rack, Rails5, and Rails6 apps. You can use them to interactively develop and test the recording features of the appmap gem. These fixture apps are more sophisticated than test/fixtures, because they include additional resources such as a PostgreSQL database.

To build the fixture container images, first run:

$ bundle exec rake build:fixtures:all

This will build the appmap.gem, along with a Docker image for each fixture app.

Then move to the directory of the fixture you want to use, and provision the environment. In this example, we use Ruby 2.6.

$ export RUBY_VERSION=2.6
$ docker-compose up -d pg
$ sleep 10s # Or some reasonable amount of time
$ docker-compose run --rm app ./create_app

Now you can start a development container.

$ docker-compose run --rm -v $PWD:/app -v $PWD/../../..:/src/appmap-ruby app bash
Starting rails_users_app_pg_1 ... done
root@6fab5f89125f:/app# cd /src/appmap-ruby
root@6fab5f89125f:/src/appmap-ruby# rm ext/appmap/*.so ext/appmap/*.o
root@6fab5f89125f:/src/appmap-ruby# bundle
root@6fab5f89125f:/src/appmap-ruby# bundle exec rake compile
root@6fab5f89125f:/src/appmap-ruby# cd /src/app
root@6fab5f89125f:/src/app# bundle config local.appmap /src/appmap-ruby
root@6fab5f89125f:/src/app# bundle

At this point, the bundle is built with the appmap gem located in /src/appmap, which is volume-mounted from the host. So you can edit the fixture code and the appmap code and run test commands such as rspec in the container. For example:

root@6fab5f89125f:/src/app# APPMAP=true bundle exec rspec
Configuring AppMap from path appmap.yml
....

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