eventsourcingdb

The official Rust client SDK for EventSourcingDB – a purpose-built database for event sourcing.

EventSourcingDB enables you to build and operate event-driven applications with native support for writing, reading, and observing events. This client SDK provides convenient access to its capabilities in Rust.

For more information on EventSourcingDB, see its official documentation.

This client SDK includes support for Testcontainers to spin up EventSourcingDB instances in integration tests. For details, see Using Testcontainers.

Getting Started

Install the client SDK:

cargo add eventsourcingdb

Import the package and create an instance by providing the URL of your EventSourcingDB instance and the API token to use:

use eventsourcingdb::client::Client;

// ...

let base_url: Url = "localhost:3000".parse().unwrap();
let api_token = "secret";
let client = Client::new(base_url, api_token);

Then call the ping function to check whether the instance is reachable. If it is not, the function will return an error:

let result = client.ping().await;
if let Err(err) = result {
  // handle error...
}

Note that ping does not require authentication, so the call may succeed even if the API token is invalid.

If you want to verify the API token, call verify_api_token. If the token is invalid, the function will return an error:

let result = client.verify_api_token().await;
if let Err(err) = result {
  // handle error...
}

Writing Events

Call the write_events function and hand over a vector with one or more events. You do not have to provide all event fields – some are automatically added by the server.

Specify source, subject, type (using ty), and data according to the CloudEvents format.

For data provide a JSON object using a serde_json:Value.

The function returns the written events, including the fields added by the server:

let event = EventCandidate::builder()
  .source("https://library.eventsourcingdb.io".to_string())
  .subject("/books/42".to_string())
  .ty("io.eventsourcingdb.library.book-acquired")
  .data(json!({
    "title": "2001 - A Space Odyssey",
    "author": "Arthur C. Clarke",
    "isbn": "978-0756906788",
  }))
  .build();

let result = client.write_events(vec![event.clone()], vec![]).await;
match result {
  Ok(written_events) => // ...
  Err(err) => // ...
}

Using the IsSubjectPristine precondition

If you only want to write events in case a subject (such as /books/42) does not yet have any events, use the IsSubjectPristine precondition to create a precondition and pass it in a vector as the second argument:

let result = client.write_events(
  vec![event.clone()],
  vec![Precondition::IsSubjectPristine {
    subject: "/books/42".to_string(),
  }],
).await;
match result {
  Ok(written_events) => // ...
  Err(err) => // ...
}

Using the IsSubjectOnEventId precondition

If you only want to write events in case the last event of a subject (such as /books/42) has a specific ID (e.g., 0), use the IsSubjectOnEventId precondition to create a precondition and pass it in a vector as the second argument:

let result = client.write_events(
  vec![event.clone()],
  vec![Precondition::IsSubjectOnEventId {
    subject: "/books/42".to_string(),
    event_id: "0".to_string(),
  }],
).await;
match result {
  Ok(written_events) => // ...
  Err(err) => // ...
}

Note that according to the CloudEvents standard, event IDs must be of type string.

Reading Events

To read all events of a subject, call the read_events function with the subject and an options object. Set the recursive option to false. This ensures that only events of the given subject are returned, not events of nested subjects.

The function returns a stream from which you can retrieve one event at a time:

let result = client
  .read_events("/books/42", Some(
    ReadEventsOptions {
      recursive: false,
      ...Default::default(),
    }
  ))
  .await;

match result {
  Err(err) => // ...
  Ok(mut stream) => {
    while let Some(event) = stream.next().await {
      // ...
    }
  }
}

Reading From Subjects Recursively

If you want to read not only all the events of a subject, but also the events of all nested subjects, set the recursive option to true:

let result = client
  .read_events("/books/42", Some(
    ReadEventsOptions {
      recursive: true,
      ..Default::default(),
    }
  ))
  .await;

This also allows you to read all events ever written. To do so, provide / as the subject and set recursive to true, since all subjects are nested under the root subject.

Reading in Anti-Chronological Order

By default, events are read in chronological order. To read in anti-chronological order, provide the order option and set it using the Antichronological ordering:

let result = client
  .read_events("/books/42", Some(
    ReadEventsOptions {
      recursive: false,
      order: Some(Ordering::Antichronological)
      ..Default::default(),
    }
  ))
  .await;

Note that you can also use the Chronological ordering to explicitly enforce the default order.

Specifying Bounds

Sometimes you do not want to read all events, but only a range of events. For that, you can specify the lower_bound and upper_bound options – either one of them or even both at the same time.

Specify the ID and whether to include or exclude it, for both the lower and upper bound:

let result = client
  .read_events("/books/42", Some(
    ReadEventsOptions {
      recursive: false,
      lower_bound: Some(Bound {
        bound_type: BoundType::Inclusive,
        id: "100",
      }),
      upper_bound: Some(Bound {
        bound_type: BoundType::Exclusive,
        id: "200",
      }),
      ..Default::default(),
    }
  ))
  .await;

Starting From the Latest Event of a Given Type

To read starting from the latest event of a given type, provide the from_latest_event option and specify the subject, the type, and how to proceed if no such event exists.

Possible options are ReadNothing, which skips reading entirely, or ReadEverything, which effectively behaves as if from_latest_event was not specified:

let result = client
  .read_events("/books/42", Some(
    ReadEventsOptions {
      recursive: false,
      from_latest_event: Some(
        FromLatestEventOptions {
          subject: "/books/42",
          ty: "io.eventsourcingdb.library.book-borrowed",
          if_event_is_missing: ReadEventMissingStrategy::ReadEverything,
        }
      )
      ..Default::default(),
    }
  ))
  .await;

Note that from_latest_event and lower_bound can not be provided at the same time.

Running EventQL Queries

To run an EventQL query, call the run_eventql_query function and provide the query as argument. The function returns a stream.

let result = client
  .run_eventql_query("FROM e IN events PROJECT INTO e")
  .await;

match result {
  Err(err) => // ...
  Ok(mut stream) => {
    while let Some(row) = stream.next().await {
      // ...
    }
  }
}

Note that each row returned by the stream is of type serde_json::Value and matches the projection specified in your query.

Observing Events

To observe all events of a subject, call the observe_events function with the subject and an options object. Set the recursive option to false. This ensures that only events of the given subject are returned, not events of nested subjects.

The function returns a stream from which you can retrieve one event at a time:

let result = client
  .observe_events("/books/42", Some(
    ObserveEventsOptions {
      recursive: false,
      from_latest_event: None,
      lower_bound: None,
    }
  ))
  .await;

match result {
  Err(err) => // ...
  Ok(mut stream) => {
    while let Some(event) = stream.next().await {
      // ...
    }
  }
}

Observing From Subjects Recursively

If you want to observe not only all the events of a subject, but also the events of all nested subjects, set the recursive option to true:

let result = client
  .observe_events("/books/42", Some(
    ObserveEventsOptions {
      recursive: true,
      ..Default::default(),
    }
  ))
  .await

This also allows you to observe all events ever written. To do so, provide / as the subject and set recursive to true, since all subjects are nested under the root subject.

Specifying Bounds

Sometimes you do not want to observe all events, but only a range of events. For that, you can specify the lower_bound option.

Specify the ID and whether to include or exclude it:

let result = client
  .observe_events("/books/42", Some(
    ObserveEventsOptions {
      recursive: false,
      lower_bound: Some(Bound {
        bound_type: BoundType::Inclusive,
        id: "100",
      }),
      ..Default::default(),
    }
  ))
  .await

Starting From the Latest Event of a Given Type

To observe starting from the latest event of a given type, provide the from_latest_event option and specify the subject, the type, and how to proceed if no such event exists.

Possible options are WaitForEvent, which waits for an event of the given type to happen, or ObserveEverything, which effectively behaves as if from_latest_event was not specified:

let result = client
  .observe_events("/books/42", Some(
    ObserveEventsOptions {
      recursive: false,
      from_latest_event: Some(
        ObserveFromLatestEventOptions {
          subject: "/books/42",
          ty: "io.eventsourcingdb.library.book-borrowed",
          if_event_is_missing: ObserveEventMissingStrategy::ObserveEverything,
        }
      )
      ..Default::default(),
    }
  ))
  .await

Note that from_latest_event and lower_bound can not be provided at the same time.

Aborting Observing

The observe will automatically be canceled if the stream is dropped from scope.

Registering an Event Schema

To register an event schema, call the register_event_schema function and hand over an event type and the desired schema:

client.register_event_schema(
  "io.eventsourcingdb.library.book-acquired",
  &json!({
    "type": "object",
    "properties": {
      "title":  { "type": "string" },
      "author": { "type": "string" },
      "isbn":   { "type": "string" },
    },
    "required": [
      "title",
      "author",
      "isbn",
    ],
    "additionalProperties": false,
  }).await;,
)

Listing Subjects

To list all subjects, call the list_subjects function with / as the base subject. The function returns a stream from which you can retrieve one subject at a time:

let result = client.list_subjects(Some("/")).await;
match result {
  Ok(subjects) => // ...
  Err(err) => // ...
}

If you only want to list subjects within a specific branch, provide the desired base subject instead:

let result := client.list_subjects("/books");

Listing Event Types

To list all event types, call the list_event_types function. The function returns a stream from which you can retrieve one event type at a time:

let result := client.list_event_types().await;
match result {
  Ok(event_types) => // ...
  Err(err) => // ...
}

Using Testcontainers

Call the Container::start_default() function, get a client, and run your test code:

let container  = Container::start_default().await.unwrap();
let client = container.get_client().await.unwrap();

Configuring the Container Instance

By default, Container uses the latest tag of the official EventSourcingDB Docker image. To change that use the provided builder and call the with_image_tag function.

let container = Container::builder()
  .with_image_tag("1.0.0")
  .build()
  .await.unwrap()

Similarly, you can configure the port to use and the API token. Call the with_port or the with_api_token function respectively:

let container = Container::builder()
  .with_port(4000)
  .with_api_token("secret")
  .build()
  .await.unwrap()

Configuring the Client Manually

In case you need to set up the client yourself, use the following functions to get details on the container:

• get_host() returns the host name
• get_mapped_port() returns the port
• get_base_url() returns the full URL of the container
• get_api_token() returns the API token