feat(flags): dynamic cohort matching in rust

rust/feature-flags/Cargo.toml

@@ -39,6 +39,8 @@ health = { path = "../common/health" }
 common-metrics = { path = "../common/metrics" }
 tower = { workspace = true }
 derive_builder = "0.20.1"
+petgraph = "0.6.5"
+moka = { version = "0.12.8", features = ["future"] }
 
 [lints]
 workspace = true

rust/feature-flags/src/api.rs

@@ -89,7 +89,7 @@ pub enum FlagError {
     #[error("Row not found in postgres")]
     RowNotFound,
     #[error("failed to parse redis cache data")]
-    DataParsingError,
+    RedisDataParsingError,
     #[error("failed to update redis cache")]
     CacheUpdateError,
     #[error("redis unavailable")]
@@ -102,6 +102,12 @@ pub enum FlagError {
     TimeoutError,
     #[error("No group type mappings")]
     NoGroupTypeMappings,
+    #[error("Cohort not found")]
+    CohortNotFound(String),
+    #[error("Failed to parse cohort filters")]
+    CohortFiltersParsingError,
+    #[error("Cohort dependency cycle")]
+    CohortDependencyCycle(String),
 }
 
 impl IntoResponse for FlagError {
@@ -138,7 +144,7 @@ impl IntoResponse for FlagError {
             FlagError::TokenValidationError => {
                 (StatusCode::UNAUTHORIZED, "The provided API key is invalid or has expired. Please check your API key and try again.".to_string())
             }
-            FlagError::DataParsingError => {
+            FlagError::RedisDataParsingError => {
                 tracing::error!("Data parsing error: {:?}", self);
                 (
                     StatusCode::SERVICE_UNAVAILABLE,
@@ -194,6 +200,18 @@ impl IntoResponse for FlagError {
                     "The requested row was not found in the database. Please try again later or contact support if the problem persists.".to_string(),
                 )
             }
+            FlagError::CohortNotFound(msg) => {
+                tracing::error!("Cohort not found: {}", msg);
+                (StatusCode::NOT_FOUND, msg)
+            }
+            FlagError::CohortFiltersParsingError => {
+                tracing::error!("Failed to parse cohort filters: {:?}", self);
+                (StatusCode::BAD_REQUEST, "Failed to parse cohort filters. Please try again later or contact support if the problem persists.".to_string())
+            }
+            FlagError::CohortDependencyCycle(msg) => {
+                tracing::error!("Cohort dependency cycle: {}", msg);
+                (StatusCode::BAD_REQUEST, msg)
+            }
         }
         .into_response()
     }
@@ -205,7 +223,7 @@ impl From<CustomRedisError> for FlagError {
             CustomRedisError::NotFound => FlagError::TokenValidationError,
             CustomRedisError::PickleError(e) => {
                 tracing::error!("failed to fetch data: {}", e);
-                FlagError::DataParsingError
+                FlagError::RedisDataParsingError
             }
             CustomRedisError::Timeout(_) => FlagError::TimeoutError,
             CustomRedisError::Other(e) => {

rust/feature-flags/src/cohort_cache.rs

@@ -0,0 +1,217 @@
+use crate::api::FlagError;
+use crate::cohort_models::Cohort;
+use crate::flag_matching::{PostgresReader, TeamId};
+use moka::future::Cache;
+use std::time::Duration;
+
+/// CohortCache manages the in-memory cache of cohorts using `moka` for caching.
+///
+/// Features:
+/// - **TTL**: Each cache entry expires after 5 minutes.
+/// - **Size-based eviction**: The cache evicts least recently used entries when the maximum capacity is reached.
+///
+/// ```text
+/// CohortCache {
+///     postgres_reader: PostgresReader,
+///     per_team_cohorts: Cache<TeamId, Vec<Cohort>> {
+///         // Example:
+///         2: [
+///             Cohort { id: 1, name: "Power Users", filters: {...} },
+///             Cohort { id: 2, name: "Churned", filters: {...} }
+///         ],
+///         5: [
+///             Cohort { id: 3, name: "Beta Users", filters: {...} }
+///         ]
+///     }
+/// }
+/// ```
+///
+/// Caches only successful cohort lists to maintain cache integrity.
+#[derive(Clone)]
+pub struct CohortCache {
+    postgres_reader: PostgresReader,
+    per_team_cohorts: Cache<TeamId, Vec<Cohort>>,
+}
+
+impl CohortCache {
+    /// Creates a new `CohortCache` with configurable TTL and maximum capacity.
+    pub fn new(
+        postgres_reader: PostgresReader,
+        max_capacity: Option<u64>,
+        ttl_seconds: Option<u64>,
+    ) -> Self {
+        // We use the size of the cohort list as the weight of the entry
+        let weigher =
+            |_: &TeamId, value: &Vec<Cohort>| -> u32 { value.len().try_into().unwrap_or(u32::MAX) };
+
+        // Initialize the Moka cache with TTL and size-based eviction.
+        let cache = Cache::builder()
+            .time_to_live(Duration::from_secs(ttl_seconds.unwrap_or(300))) // Default to 5 minutes
+            .weigher(weigher)
+            .max_capacity(max_capacity.unwrap_or(10_000)) // Default to 10,000 cohorts
+            .build();
+
+        Self {
+            postgres_reader,
+            per_team_cohorts: cache,
+        }
+    }
+
+    /// Retrieves cohorts for a given team.
+    ///
+    /// If the cohorts are not present in the cache or have expired, it fetches them from the database,
+    /// caches the result upon successful retrieval, and then returns it.
+    pub async fn get_cohorts_for_team(&self, team_id: TeamId) -> Result<Vec<Cohort>, FlagError> {
+        if let Some(cached_cohorts) = self.per_team_cohorts.get(&team_id).await {
+            return Ok(cached_cohorts.clone());
+        }
+        let fetched_cohorts = Cohort::list_from_pg(self.postgres_reader.clone(), team_id).await?;
+        self.per_team_cohorts
+            .insert(team_id, fetched_cohorts.clone())
+            .await;
+
+        Ok(fetched_cohorts)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::cohort_models::Cohort;
+    use crate::test_utils::{
+        insert_cohort_for_team_in_pg, insert_new_team_in_pg, setup_pg_reader_client,
+        setup_pg_writer_client,
+    };
+    use std::sync::Arc;
+    use tokio::time::{sleep, Duration};
+
+    /// Helper function to setup a new team for testing.
+    async fn setup_test_team(
+        writer_client: Arc<dyn crate::database::Client + Send + Sync>,
+    ) -> Result<TeamId, anyhow::Error> {
+        let team = crate::test_utils::insert_new_team_in_pg(writer_client, None).await?;
+        Ok(team.id)
+    }
+
+    /// Helper function to insert a cohort for a team.
+    async fn setup_test_cohort(
+        writer_client: Arc<dyn crate::database::Client + Send + Sync>,
+        team_id: TeamId,
+        name: Option<String>,
+    ) -> Result<Cohort, anyhow::Error> {
+        let filters = serde_json::json!({"properties": {"type": "OR", "values": [{"type": "OR", "values": [{"key": "$active", "type": "person", "value": [true], "negation": false, "operator": "exact"}]}]}});
+        insert_cohort_for_team_in_pg(writer_client, team_id, name, filters, false).await
+    }
+
+    /// Tests that cache entries expire after the specified TTL.
+    #[tokio::test]
+    async fn test_cache_expiry() -> Result<(), anyhow::Error> {
+        let writer_client = setup_pg_writer_client(None).await;
+        let reader_client = setup_pg_reader_client(None).await;
+
+        let team_id = setup_test_team(writer_client.clone()).await?;
+        let _cohort = setup_test_cohort(writer_client.clone(), team_id, None).await?;
+
+        // Initialize CohortCache with a short TTL for testing
+        let cohort_cache = CohortCache::new(
+            reader_client.clone(),
+            Some(100),
+            Some(1), // 1-second TTL
+        );
+
+        let cohorts = cohort_cache.get_cohorts_for_team(team_id).await?;
+        assert_eq!(cohorts.len(), 1);
+        assert_eq!(cohorts[0].team_id, team_id);
+
+        let cached_cohorts = cohort_cache.per_team_cohorts.get(&team_id).await;
+        assert!(cached_cohorts.is_some());
+
+        // Wait for TTL to expire
+        sleep(Duration::from_secs(2)).await;
+
+        // Attempt to retrieve from cache again
+        let cached_cohorts = cohort_cache.per_team_cohorts.get(&team_id).await;
+        assert!(cached_cohorts.is_none(), "Cache entry should have expired");
+
+        Ok(())
+    }
+
+    /// Tests that the cache correctly evicts least recently used entries based on the weigher.
+    #[tokio::test]
+    async fn test_cache_weigher() -> Result<(), anyhow::Error> {
+        let writer_client = setup_pg_writer_client(None).await;
+        let reader_client = setup_pg_reader_client(None).await;
+
+        // Define a smaller max_capacity for testing
+        let max_capacity: u64 = 3;
+
+        let cohort_cache = CohortCache::new(reader_client.clone(), Some(max_capacity), None);
+
+        let mut inserted_team_ids = Vec::new();
+
+        // Insert multiple teams and their cohorts
+        for _ in 0..max_capacity {
+            let team = insert_new_team_in_pg(writer_client.clone(), None).await?;
+            let team_id = team.id;
+            inserted_team_ids.push(team_id);
+            setup_test_cohort(writer_client.clone(), team_id, None).await?;
+            cohort_cache.get_cohorts_for_team(team_id).await?;
+        }
+
+        cohort_cache.per_team_cohorts.run_pending_tasks().await;
+        let cache_size = cohort_cache.per_team_cohorts.entry_count();
+        assert_eq!(
+            cache_size, max_capacity,
+            "Cache size should be equal to max_capacity"
+        );
+
+        let new_team = insert_new_team_in_pg(writer_client.clone(), None).await?;
+        let new_team_id = new_team.id;
+        setup_test_cohort(writer_client.clone(), new_team_id, None).await?;
+        cohort_cache.get_cohorts_for_team(new_team_id).await?;
+
+        cohort_cache.per_team_cohorts.run_pending_tasks().await;
+        let cache_size_after = cohort_cache.per_team_cohorts.entry_count();
+        assert_eq!(
+            cache_size_after, max_capacity,
+            "Cache size should remain equal to max_capacity after eviction"
+        );
+
+        let evicted_team_id = &inserted_team_ids[0];
+        let cached_cohorts = cohort_cache.per_team_cohorts.get(evicted_team_id).await;
+        assert!(
+            cached_cohorts.is_none(),
+            "Least recently used cache entry should have been evicted"
+        );
+
+        let cached_new_team = cohort_cache.per_team_cohorts.get(&new_team_id).await;
+        assert!(
+            cached_new_team.is_some(),
+            "Newly added cache entry should be present"
+        );
+
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn test_get_cohorts_for_team() -> Result<(), anyhow::Error> {
+        let writer_client = setup_pg_writer_client(None).await;
+        let reader_client = setup_pg_reader_client(None).await;
+        let team_id = setup_test_team(writer_client.clone()).await?;
+        let _cohort = setup_test_cohort(writer_client.clone(), team_id, None).await?;
+        let cohort_cache = CohortCache::new(reader_client.clone(), None, None);
+
+        let cached_cohorts = cohort_cache.per_team_cohorts.get(&team_id).await;
+        assert!(cached_cohorts.is_none(), "Cache should initially be empty");
+
+        let cohorts = cohort_cache.get_cohorts_for_team(team_id).await?;
+        assert_eq!(cohorts.len(), 1);
+        assert_eq!(cohorts[0].team_id, team_id);
+
+        let cached_cohorts = cohort_cache.per_team_cohorts.get(&team_id).await.unwrap();
+        assert_eq!(cached_cohorts.len(), 1);
+        assert_eq!(cached_cohorts[0].team_id, team_id);
+
+        Ok(())
+    }
+}