Server-Sent Events (SSE) support (#36)

* WIP realtime features repo

* add SSE config to existing GBFeaturesRepository

* interceptor notes

* fix real networking test

* WIP: event stream connection

* add error for SSE

* add constructor w/o okHttpClient

* no timeout for SSE connections

* add test server to test SSE refreshing

* implement retry functionality

* fallback to SWR refresh strategy

* refactor: separate method to process response JSON string

* update features json from SSE payload

* remove custom http client from the builder class

* rm log statements

* bump version to 0.9.0

lib/build.gradle

@@ -38,7 +38,9 @@ dependencies {
     implementation 'com.google.code.gson:gson:2.9.1'
 
     // https://square.github.io/okhttp
-    implementation 'com.squareup.okhttp3:okhttp:4.10.0'
+    implementation 'com.squareup.okhttp3:okhttp:4.11.0'
+    // https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp-sse
+    implementation 'com.squareup.okhttp3:okhttp-sse:4.11.0'
 
     // Adds getter, setter and builder boilerplate
     // https://projectlombok.org/

lib/src/main/java/growthbook/sdk/java/FeatureFetchException.java

@@ -38,6 +38,11 @@ public enum FeatureFetchErrorCode {
          */
         NO_RESPONSE_ERROR,
 
+        /**
+         * - could not establish a connection to the events (server-sent events) for feature updates
+         */
+        SSE_CONNECTION_ERROR,
+
         /**
          *   - there was an unknown error that occurred when attempting to make the request.
          */

lib/src/main/java/growthbook/sdk/java/FeatureRefreshStrategy.java

@@ -0,0 +1,6 @@
+package growthbook.sdk.java;
+
+public enum FeatureRefreshStrategy {
+    STALE_WHILE_REVALIDATE,
+    SERVER_SENT_EVENTS
+}