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//! # Nakadion //! //! A client for the [Nakadi](http://nakadi.io) Event Broker. //! //! ## Summary //! //! `Nakadion` is client that connects to the Nakadi Subscription API. It //! does all the cursor management so that users can concentrate on //! implementing their logic for processing events. The code implemented //! to process events by a user does not get in touch with the internals of Nakadi. //! //! `Nakadion` is almost completely configurable from environment variables. //! //! Please have a look at the documentation of [Nakadi](http://nakadi.io) //! first to become comfortable with the concepts of Nakadi. //! //! Currently `Nakadion` only works with the `tokio` runtime. Further execution //! environments might be added in the future. //! //! ## How to use //! //! To run this example the following environment variables need to be set: //! //! * `NAKADION_NAKADI_BASE_URL` //! * `NAKADION_SUBSCRIPTION_ID` //! * `NAKADION_ACCESS_TOKEN_FIXED` with a valid token or `NAKADION_ACCESS_TOKEN_ALLOW_NONE` set to `true` //! //! ```ignore //! use nakadion::api::ApiClient; //! use nakadion::consumer::*; //! //! #[tokio::main] //! async fn main() -> Result<(), Box<dyn std::error::Error>> { //! let client = ApiClient::builder().finish_from_env()?; //! //! let consumer = Consumer::builder_from_env()?.build_with( //! client, //! handler::MyHandlerFactory, //! StdOutLogger::default(), //! )?; //! //! let (_handle, consuming) = consumer.start(); //! //! let _ = consuming.await.into_result()?; //! //! Ok(()) //! } //! //! mod handler { //! use futures::future::{BoxFuture, FutureExt}; //! //! use nakadion::handler::*; //! //! pub struct MyHandler { //! events_received: usize, //! } //! //! impl EventsHandler for MyHandler { //! type Event = serde_json::Value; //! fn handle<'a>( //! &'a mut self, //! events: Vec<Self::Event>, //! _meta: BatchMeta<'a>, //! ) -> EventsHandlerFuture { //! async move { //! self.events_received += events.len(); //! EventsPostAction::Commit //! } //! .boxed() //! } //! } //! //! pub struct MyHandlerFactory; //! //! impl BatchHandlerFactory for MyHandlerFactory { //! fn handler( //! &self, //! _assignment: &HandlerAssignment, //! ) -> BoxFuture<Result<Box<dyn BatchHandler>, Error>> { //! async { Ok(Box::new(MyHandler { events_received: 0 }) as Box<_>) }.boxed() //! } //! } //! } //! ``` //! //! ## How Nakadion works //! //! ### Load balancing //! //! A started instance connects to the Nakadi Event Broker with one active connection. Due to //! Nakadi`s capability of automatically distributing partitions among clients Nakadion does //! not need to track concurrently consuming clients. In most use cases it does not make //! any sense to have more clients running than the number partitions assigned //! to an event type. //! //! ### Consuming events //! //! Nakadi delivers events in batches. Each batch contains the events of a single partition //! along with a cursor that is used for reporting progress to Nakadi. //! //! To consume events with `Nakadion` one has to implement a `BatchHandler`. This `BatchHandler` //! provides the processing logic and is passed the bytes containing the events of a batch. //! //! `Nakadion` itself does not do any deserialization of events. The `BatchHandler` is responsible //! for deserializing events. Nevertheless there is a `EventsHandler` for convenience //! that does the deserialization of events using `serde`. //! //! When `Nakadion` receives a batch it just extract the necessary data from //! the bytes received over the network and then delegates the batch //! to a dispatcher which spawns workers that are then passed the batch. //! This means `Nakadion` itself does not have any knowledge of the events contained in a batch. //! //! ### Buffering batches and maximizing throughput //! //! `Nakadion` has an unbounded buffer for events. When looking at how Nakadi works it turns //! out that a bounded buffer is not necessary. //! //! Nakadi has a timeout for committing the cursors of batches. This default timeout is 60 seconds. //! Furthermore Nakadi has a configuration parameter called `max_uncommitted_events`. //! With this parameter which can be configured for `Nakadion` one can steer how many //! events can be at most in `Nakadion`s buffers. In conjunction with a //! `CommitStrategy` one can optimize for maximum throughput and keep the amount //! of buffered events under control. //! //! ### Logging //! //! `Nakadion` does verbose logging when connecting to a stream and when a stream is closed. The //! reason is that this information can be quite important when problems arise. A reconnect //! happens roughly every full hour unless configured otherwise on Nakadi's side. //! //! `Nakadion` also logs a message each time a new worker is created and each time a worker is //! shut down. //! //! Otherwise `Nakadion` mostly only logs problems and errors. //! In the end your log files will not be flooded with messages from `Nakadion`. //! //! ### Metrics //! //! `Nakadion` provides an interface for attaching metrics libraries. Metrics are especially //! useful when optimizing for maximum throughput since one can see what //! effect (especially on cursors) the different possible settings have. //! //! ### Performance //! //! Nakadion is not meant to be used in a high performance scenario. It uses asynchronous IO. //! Nevertheless it is easily possible to consume tens of thousands events per second depending //! on the complexity of your processing logic. //! //! ## Recent Changes //! //! See CHANGELOG //! //! ## License //! //! Nakadion is distributed under the terms of both the MIT license and the Apache License (Version //! 2.0). //! //! See LICENSE-APACHE and LICENSE-MIT for details. //! //! License: Apache-2.0/MIT pub(crate) mod helpers; pub use nakadi_types; pub(crate) use nakadi_types::Error; pub mod api; pub mod auth; pub mod components; pub mod consumer; pub mod handler; pub mod instrumentation; pub mod publisher; pub(crate) mod tools; pub(crate) mod internals; pub(crate) mod logging;