feat(client): add observing events feature to client

Signed-off-by: Raphael Höser <[email protected]>

Author: Snapstromegon

README.md

@@ -11,6 +11,6 @@ Based on the [compliance criteria](https://docs.eventsourcingdb.io/client-sdks/c
 - 🚀 [Writing Events](https://docs.eventsourcingdb.io/client-sdks/compliance-criteria/#writing-events)
 - 🚀 [Reading Events](https://docs.eventsourcingdb.io/client-sdks/compliance-criteria/#reading-events)
 - ❌ [Using EventQL](https://docs.eventsourcingdb.io/client-sdks/compliance-criteria/#using-eventql)
-- ❌ [Observing Events](https://docs.eventsourcingdb.io/client-sdks/compliance-criteria/#observing-events)
+- 🚀 [Observing Events](https://docs.eventsourcingdb.io/client-sdks/compliance-criteria/#observing-events)
 - 🚀 [Metadata and Discovery](https://docs.eventsourcingdb.io/client-sdks/compliance-criteria/#metadata-and-discovery)
 - 🚀 [Testcontainers Support](https://docs.eventsourcingdb.io/client-sdks/compliance-criteria/#testcontainers-support)

src/client.rs

@@ -26,9 +26,7 @@ use crate::{
     event::{Event, EventCandidate, ManagementEvent},
 };
 use client_request::{
-    ClientRequest, ListEventTypesRequest, ListSubjectsRequest, OneShotRequest, PingRequest,
-    ReadEventsRequest, RegisterEventSchemaRequest, StreamingRequest, VerifyApiTokenRequest,
-    WriteEventsRequest, list_event_types::EventType,
+    list_event_types::EventType, ClientRequest, ListEventTypesRequest, ListSubjectsRequest, ObserveEventsRequest, OneShotRequest, PingRequest, ReadEventsRequest, RegisterEventSchemaRequest, StreamingRequest, VerifyApiTokenRequest, WriteEventsRequest
 };
 use futures::Stream;
 pub use precondition::Precondition;
@@ -210,6 +208,39 @@ impl Client {
         Ok(response)
     }
 
+    /// Observe events from the DB instance.
+    ///
+    /// ```
+    /// use eventsourcingdb_client_rust::event::EventCandidate;
+    /// use futures::StreamExt;
+    /// # use serde_json::json;
+    /// # tokio_test::block_on(async {
+    /// # let container = eventsourcingdb_client_rust::container::Container::start_default().await.unwrap();
+    /// let db_url = "http://localhost:3000/";
+    /// let api_token = "secrettoken";
+    /// # let db_url = container.get_base_url().await.unwrap();
+    /// # let api_token = container.get_api_token();
+    /// let client = eventsourcingdb_client_rust::client::Client::new(db_url, api_token);
+    /// let mut event_stream = client.observe_events("/", None).await.expect("Failed to observe events");
+    /// while let Some(event) = event_stream.next().await {
+    ///     println!("Found Type {:?}", event.expect("Error while reading event"));
+    /// }
+    /// # })
+    /// ```
+    ///
+    /// # Errors
+    /// This function will return an error if the request fails or if the URL is invalid.
+    pub async fn observe_events<'a>(
+        &self,
+        subject: &'a str,
+        options: Option<request_options::ObserveEventsRequestOptions<'a>>,
+    ) -> Result<impl Stream<Item = Result<Event, ClientError>>, ClientError> {
+        let response = self
+            .request_streaming(ObserveEventsRequest { subject, options })
+            .await?;
+        Ok(response)
+    }
+
     /// Verifies the API token by sending a request to the DB instance.
     ///
     /// ```

src/client/client_request.rs

@@ -2,6 +2,7 @@
 
 pub mod list_event_types;
 mod list_subjects;
+mod observe_events;
 mod ping;
 mod read_events;
 mod register_event_schema;
@@ -10,6 +11,7 @@ mod write_events;
 
 pub use list_event_types::ListEventTypesRequest;
 pub use list_subjects::ListSubjectsRequest;
+pub use observe_events::ObserveEventsRequest;
 pub use ping::PingRequest;
 pub use read_events::ReadEventsRequest;
 pub use register_event_schema::RegisterEventSchemaRequest;

src/client/client_request/observe_events.rs

@@ -0,0 +1,26 @@
+use reqwest::Method;
+use serde::Serialize;
+
+use crate::{client::request_options::ObserveEventsRequestOptions, error::ClientError, event::Event};
+
+use super::{ClientRequest, StreamingRequest};
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ObserveEventsRequest<'a> {
+    pub subject: &'a str,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub options: Option<ObserveEventsRequestOptions<'a>>,
+}
+
+impl<'a> ClientRequest for ObserveEventsRequest<'a> {
+    const URL_PATH: &'static str = "/api/v1/read-events";
+    const METHOD: Method = Method::POST;
+
+    fn body(&self) -> Option<Result<impl Serialize, ClientError>> {
+        Some(Ok(self))
+    }
+}
+
+impl<'a> StreamingRequest for ObserveEventsRequest<'a> {
+    type ItemType = Event;
+}

src/client/request_options.rs

@@ -22,6 +22,20 @@ pub struct ReadEventsRequestOptions<'a> {
     pub upper_bound: Option<Bound<'a>>,
 }
 
+/// Options for observing events from the database
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ObserveEventsRequestOptions<'a> {
+    /// Start reading events from this start event
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub from_latest_event: Option<FromLatestEventOptions<'a>>,
+    /// Lower bound of events to read
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub lower_bound: Option<Bound<'a>>,
+    /// Include recursive subject's events
+    pub recursive: bool,
+}
+
 /// Ordering of the responses of requests
 #[derive(Debug, Clone, Serialize)]
 #[serde(rename_all = "kebab-case")]