We have tools to "explore" the Cardano blockchain, which are useful when you know what you're looking for. We argue that there's a different, complementary use-case which is to "observe" the blockchain and react to particular event patterns.
Oura is a rust-native implementation of a pipeline that connects to the tip of a Cardano node through a combination of Ouroboros mini-protocol (using either a unix socket or tcp bearer), filters the events that match a particular pattern and then submits a succinct, self-contained payload to pluggable observers called "sinks".
The name of the tool is inspired by the
tail command available in unix-like systems which is used to display the tail end of a text file or piped data. Cardano's consensus protocol name, Ouroboros, is a reference to the ancient symbol depicting a serpent or dragon eating its own tail, which means "tail eating". "Oura" is the ancient greek word for "tail".
Under the Hood
All the heavy lifting required to communicate with the Cardano node is done by the Pallas library, which provides an implementation of the Ouroboros multiplexer and a few of the required mini-protocol state-machines (ChainSync and LocalState in particular).
The data pipeline makes heavy use (maybe a bit too much) of multi-threading and mpsc channels provided by Rust's
CLI to Watch Live Transactions
You can run
oura watch <socket> to print TX data into the terminal from the tip of a local or remote node. It can be useful as a debugging tool for developers or if you're just curious to see what's going on in the network (for example, to see airdrops as they happen or oracles posting new information).
As a Bridge to Other Persistence Mechanisms
Similar to the well-known db-sync tool provided by IOHK, Oura can be used as a daemon to follow a node and output the data into a different data storage technology more suited for your final use-case. The main difference with db-sync is that Oura was designed for easy integration with data-streaming pipelines instead of relational databases.
Given its small memory / cpu footprint, Oura can be deployed side-by-side with your Cardano node even in resource-constrained environments, such as Raspberry PIs.
As a Trigger of Custom Actions
Oura running in
daemon mode can be configured to use custom filters to pinpoint particular transaction patterns and trigger actions whenever it finds a match. For example: send an email when a particular policy / asset combination appears in a transaction; call an AWS Lambda function when a wallet delegates to a particular pool; send a http-call to a webhook each time a metadata key appears in the TX payload;
As a Library for Custom Scenarios
If the available out-of-the-box features don't satisfy your particular use-case, Oura can be used a library in your Rust project to set up tailor-made pipelines. Each component (sources, filters, sinks, etc) in Oura aims at being self-contained and reusable. For example, custom filters and sinks can be built while reusing the existing sources.
(Experimental) Windows Support
Oura Windows support is currently experimental, Windows build supports only Node-to-Node source with tcp socket bearer.