feat: Add option to enable compression of event payloads

contract-tests/Cargo.toml

@@ -10,7 +10,7 @@ actix = "0.13.0"
 actix-web = "4.2.1"
 env_logger = "0.10.0"
 log = "0.4.14"
-launchdarkly-server-sdk = { path = "../launchdarkly-server-sdk/", default-features = false}
+launchdarkly-server-sdk = { path = "../launchdarkly-server-sdk/", default-features = false, features = ["event-compression"]}
 serde = { version = "1.0.132", features = ["derive"] }
 serde_json = "1.0.73"
 futures = "0.3.12"

contract-tests/src/client_entity.rs

@@ -113,6 +113,9 @@ impl ClientEntity {
                 processor_builder.capacity(capacity);
             }
             processor_builder.all_attributes_private(events.all_attributes_private);
+            if let Some(e) = events.enable_gzip {
+                processor_builder.compress_events(e);
+            }
 
             if let Some(interval) = events.flush_interval_ms {
                 processor_builder.flush_interval(Duration::from_millis(interval));

contract-tests/src/main.rs

@@ -41,6 +41,7 @@ pub struct EventParameters {
     pub enable_diagnostics: bool,
     #[serde(default = "bool::default")]
     pub all_attributes_private: bool,
+    pub enable_gzip: Option<bool>,
     pub global_private_attributes: Option<HashSet<Reference>>,
     pub flush_interval_ms: Option<u64>,
     #[serde(default = "bool::default")]
@@ -110,6 +111,8 @@ async fn status() -> impl Responder {
             "migrations".to_string(),
             "event-sampling".to_string(),
             "client-prereq-events".to_string(),
+            "event-gzip".to_string(),
+            "optional-event-gzip".to_string(),
         ],
     })
 }

launchdarkly-server-sdk/Cargo.toml

@@ -35,6 +35,7 @@ uuid = {version = "1.2.2", features = ["v4"] }
 hyper = { version = "0.14.19", features = ["client", "http1", "http2", "tcp"] }
 hyper-rustls = { version = "0.24.1" , optional = true}
 rand = "0.8"
+flate2 = { version = "1.0.35", optional = true }
 
 [dev-dependencies]
 maplit = "1.0.1"
@@ -50,6 +51,7 @@ reqwest = { version = "0.12.4", features = ["json"] }
 [features]
 default = ["rustls"]
 rustls = ["hyper-rustls/http1", "hyper-rustls/http2", "eventsource-client/rustls"]
+event-compression = ["flate2"]
 
 [[example]]
 name = "print_flags"

launchdarkly-server-sdk/src/data_source_builders.rs

@@ -345,7 +345,7 @@ impl DataSourceFactory for MockDataSourceBuilder {
         _sdk_key: &str,
         _tags: Option<String>,
     ) -> Result<Arc<dyn DataSource>, BuildError> {
-        return Ok(self.data_source.as_ref().unwrap().clone());
+        Ok(self.data_source.as_ref().unwrap().clone())
     }
 
     fn to_owned(&self) -> Box<dyn DataSourceFactory> {

launchdarkly-server-sdk/src/events/processor_builders.rs

@@ -84,6 +84,7 @@ pub struct EventProcessorBuilder<C> {
     private_attributes: HashSet<Reference>,
     connector: Option<C>,
     omit_anonymous_contexts: bool,
+    compress_events: bool,
     // diagnostic_recording_interval: Duration
 }
 
@@ -109,6 +110,7 @@ where
         }
 
         let event_sender_result: Result<Arc<dyn EventSender>, BuildError> =
+            // NOTE: This would only be possible under unit testing conditions.
             if let Some(event_sender) = &self.event_sender {
                 Ok(event_sender.clone())
             } else if let Some(connector) = &self.connector {
@@ -117,6 +119,7 @@ where
                     hyper::Uri::from_str(url_string.as_str()).unwrap(),
                     sdk_key,
                     default_headers,
+                    self.compress_events,
                 )))
             } else {
                 #[cfg(feature = "rustls")]
@@ -133,6 +136,7 @@ where
                         hyper::Uri::from_str(url_string.as_str()).unwrap(),
                         sdk_key,
                         default_headers,
+                        self.compress_events,
                     )))
                 }
                 #[cfg(not(feature = "rustls"))]
@@ -178,6 +182,7 @@ impl<C> EventProcessorBuilder<C> {
             private_attributes: HashSet::new(),
             omit_anonymous_contexts: false,
             connector: None,
+            compress_events: false,
         }
     }
 
@@ -258,7 +263,20 @@ impl<C> EventProcessorBuilder<C> {
         self
     }
 
+    #[cfg(feature = "event-compression")]
+    /// Should the event payload sent to LaunchDarkly use gzip compression. By
+    /// default this is false to prevent backward breaking compatibility issues with
+    /// older versions of the relay proxy.
+    //
+    /// Customers not using the relay proxy are strongly encouraged to enable this
+    /// feature to reduce egress bandwidth cost.
+    pub fn compress_events(&mut self, enabled: bool) -> &mut Self {
+        self.compress_events = enabled;
+        self
+    }
+
     #[cfg(test)]
+    /// Test only functionality that allows us to override the event sender.
     pub fn event_sender(&mut self, event_sender: Arc<dyn EventSender>) -> &mut Self {
         self.event_sender = Some(event_sender);
         self

launchdarkly-server-sdk/src/events/sender.rs

@@ -2,10 +2,17 @@ use crate::{
     reqwest::is_http_error_recoverable, LAUNCHDARKLY_EVENT_SCHEMA_HEADER,
     LAUNCHDARKLY_PAYLOAD_ID_HEADER,
 };
-use std::collections::HashMap;
-
 use chrono::DateTime;
 use crossbeam_channel::Sender;
+use std::collections::HashMap;
+
+#[cfg(feature = "event-compression")]
+use flate2::write::GzEncoder;
+#[cfg(feature = "event-compression")]
+use flate2::Compression;
+#[cfg(feature = "event-compression")]
+use std::io::Write;
+
 use futures::future::BoxFuture;
 use hyper::{client::connect::Connection, service::Service, Uri};
 use tokio::{
@@ -36,6 +43,10 @@ pub struct HyperEventSender<C> {
     sdk_key: String,
     http: hyper::Client<C>,
     default_headers: HashMap<&'static str, String>,
+
+    // used with event-compression feature
+    #[allow(dead_code)]
+    compress_events: bool,
 }
 
 impl<C> HyperEventSender<C>
@@ -50,12 +61,14 @@ where
         url: hyper::Uri,
         sdk_key: &str,
         default_headers: HashMap<&'static str, String>,
+        compress_events: bool,
     ) -> Self {
         Self {
             url,
             sdk_key: sdk_key.to_owned(),
             http: hyper::Client::builder().build(connector),
             default_headers,
+            compress_events,
         }
     }
 
@@ -96,7 +109,9 @@ where
                 serde_json::to_string_pretty(&events).unwrap_or_else(|e| e.to_string())
             );
 
-            let json = match serde_json::to_vec(&events) {
+            // mut is needed for event-compression feature
+            #[allow(unused_mut)]
+            let mut payload = match serde_json::to_vec(&events) {
                 Ok(json) => json,
                 Err(e) => {
                     error!(
@@ -107,6 +122,21 @@ where
                 }
             };
 
+            // mut is needed for event-compression feature
+            #[allow(unused_mut)]
+            let mut additional_headers = self.default_headers.clone();
+
+            #[cfg(feature = "event-compression")]
+            if self.compress_events {
+                let mut e = GzEncoder::new(Vec::new(), Compression::default());
+                if e.write_all(payload.as_slice()).is_ok() {
+                    if let Ok(compressed) = e.finish() {
+                        payload = compressed;
+                        additional_headers.insert("Content-Encoding", "gzip".into());
+                    }
+                }
+            }
+
             for attempt in 1..=2 {
                 if attempt == 2 {
                     sleep(Duration::from_secs(1)).await;
@@ -124,11 +154,12 @@ where
                     )
                     .header(LAUNCHDARKLY_PAYLOAD_ID_HEADER, uuid.to_string());
 
-                for default_header in &self.default_headers {
+                for default_header in &additional_headers {
+                    error!("Adding header: {} = {}", default_header.0, default_header.1);
                     request_builder =
                         request_builder.header(*default_header.0, default_header.1.as_str());
                 }
-                let request = request_builder.body(hyper::Body::from(json.clone()));
+                let request = request_builder.body(hyper::Body::from(payload.clone()));
 
                 let result = self.http.request(request.unwrap()).await;
 
@@ -334,6 +365,7 @@ mod tests {
             url,
             "sdk-key",
             HashMap::<&str, String>::new(),
+            false,
         )
     }
 }

launchdarkly-server-sdk/src/test_common.rs

@@ -7,7 +7,7 @@ use crate::Stage;
 pub const FLOAT_TO_INT_MAX: i64 = 9007199254740991;
 
 pub fn basic_flag(key: &str) -> Flag {
-    return basic_flag_with_visibility(key, false);
+    basic_flag_with_visibility(key, false)
 }
 
 pub fn basic_flag_with_visibility(key: &str, visible_to_environment_id: bool) -> Flag {