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EDIT :: NoGemActivationDuringRubyLoaderInitialization.md

# No gem activation during Ruby loader initialization ## Context Passenger loads a Ruby app using loader scripts (rack-loader.rb and rack-preloader.rb). These scripts perform these steps: 1. Initialization, e.g., to setup communication with the Passenger Core. 2. Activate Bundler. 3. Load the application (config.ru). If step 1 activates any gems, then that may conflict with Bundler activation because Gemfile could specify a different gem version. ## Decision All code callable by the Ruby loaders' initialization steps, must not activate any gems. ## Consequences Any needed functionality that's typically provided by gems, must be reimplemented within the `PhusionPassenger` module. For example, the initialization step needs to parse JSON. Instead of activating the JSON gem, we reimplement a JSON parser in `PhusionPassenger::Utils::JSON`. ### Caveat: standard library gems More and more parts of the Ruby standard library are becoming [gemified](https://stdgems.org/). This increases the chances of the initialization step activating a standard library gem. In principle, our strategy remains the same: we reimplement those libraries. For example, we reimplemented StringScanner (needed by our JSON implementation) in `PhusionPassenger::Utils::StringScanner`, but we limited its scope to just the functionality needed by the JSON implementation. If the standard library in question is a native extension (e.g., `etc`), then the strategy is to reimplement it in C++ as part of the [Passenger Agent binary](../../src/agent/README.md), as a separately callable tool. The Ruby code then spawns the written-in-C++ tool and parses its output.

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