There is the repository of groonga on GitHub. If you want to check-out groonga, type the below command:
% git clone git://github.com/groonga/groonga.git
There is the list of related projects of groonga (grntest, fluent-plugin-groonga and so on).
13.3. Groonga開発者向け情報
13.3.2. Groonga 通信アーキテクチャ
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