fix: allow for specification of initial reconnect delay in streaming data source (#229)

The public API was already available, but we didn't have the plumbing
required to get it into the SSE client.

Author: cwaldren-ld

contract-tests/sdk-contract-tests/src/entity_manager.cpp

@@ -48,15 +48,20 @@ std::optional<std::string> EntityManager::create(ConfigParams const& in) {
             endpoints.EventsBaseUrl(*in.serviceEndpoints->events);
         }
     }
+    auto& datasource = config_builder.DataSource();
 
     if (in.streaming) {
         if (in.streaming->baseUri) {
             endpoints.StreamingBaseUrl(*in.streaming->baseUri);
         }
+        if (in.streaming->initialRetryDelayMs) {
+            auto streaming = DataSourceBuilder::Streaming();
+            streaming.InitialReconnectDelay(
+                std::chrono::milliseconds(*in.streaming->initialRetryDelayMs));
+            datasource.Method(std::move(streaming));
+        }
     }
 
-    auto& datasource = config_builder.DataSource();
-
     if (in.polling) {
         if (in.polling->baseUri) {
             endpoints.PollingBaseUrl(*in.polling->baseUri);

libs/client-sdk/src/data_sources/streaming_data_source.cpp

@@ -91,7 +91,6 @@ void StreamingDataSource::Start() {
         return;
     }
 
-    // TODO: Initial reconnect delay. sc-204393
     boost::urls::url url = uri_components.value();
 
     if (data_source_config_.with_reasons) {
@@ -117,6 +116,9 @@ void StreamingDataSource::Start() {
 
     client_builder.connect_timeout(http_config_.ConnectTimeout());
 
+    client_builder.initial_reconnect_delay(
+        streaming_config.initial_reconnect_delay);
+
     for (auto const& header : http_config_.BaseHeaders()) {
         client_builder.header(header.first, header.second);
     }

libs/server-sent-events/include/launchdarkly/sse/client.hpp

@@ -90,6 +90,14 @@ class Builder {
      */
     Builder& write_timeout(std::chrono::milliseconds timeout);
 
+    /**
+     * Specifies the initial delay before reconnection when backoff takes place
+     * due to an error on the connection.
+     * @param timeout
+     * @return Reference to this builder.
+     */
+    Builder& initial_reconnect_delay(std::chrono::milliseconds delay);
+
     /**
      * Specify the method for the initial request. The default method is GET.
      * @param verb The HTTP method.
@@ -138,6 +146,7 @@ class Builder {
     std::optional<std::chrono::milliseconds> read_timeout_;
     std::optional<std::chrono::milliseconds> write_timeout_;
     std::optional<std::chrono::milliseconds> connect_timeout_;
+    std::optional<std::chrono::milliseconds> initial_reconnect_delay_;
     LogCallback logging_cb_;
     EventReceiver receiver_;
     ErrorCallback error_cb_;

libs/server-sent-events/src/client.cpp

@@ -37,6 +37,13 @@ auto const kDefaultUserAgent = BOOST_BEAST_VERSION_STRING;
 // Time duration used when no timeout is specified (1 year).
 auto const kNoTimeout = std::chrono::hours(8760);
 
+// Time duration that the backoff algorithm uses before initiating a new
+// connection, the first time a failure is detected.
+auto const kDefaultInitialReconnectDelay = std::chrono::seconds(1);
+
+// Maximum duration between backoff attempts.
+auto const kDefaultMaxBackoffDelay = std::chrono::seconds(30);
+
 static boost::optional<net::ssl::context&> ToOptRef(
     std::optional<net::ssl::context>& maybe_val) {
     if (maybe_val) {
@@ -60,6 +67,7 @@ class FoxyClient : public Client,
                std::optional<std::chrono::milliseconds> connect_timeout,
                std::optional<std::chrono::milliseconds> read_timeout,
                std::optional<std::chrono::milliseconds> write_timeout,
+               std::optional<std::chrono::milliseconds> initial_reconnect_delay,
                Builder::EventReceiver receiver,
                Builder::LogCallback logger,
                Builder::ErrorCallback errors,
@@ -75,7 +83,9 @@ class FoxyClient : public Client,
                    launchdarkly::foxy::session_opts{
                        ToOptRef(ssl_context_),
                        connect_timeout.value_or(kNoTimeout)}),
-          backoff_(std::chrono::seconds(1), std::chrono::seconds(30)),
+          backoff_(
+              initial_reconnect_delay.value_or(kDefaultInitialReconnectDelay),
+              kDefaultMaxBackoffDelay),
           last_event_id_(std::nullopt),
           backoff_timer_(session_.get_executor()),
           event_receiver_(std::move(receiver)),
@@ -347,6 +357,7 @@ Builder::Builder(net::any_io_executor ctx, std::string url)
       read_timeout_{std::nullopt},
       write_timeout_{std::nullopt},
       connect_timeout_{std::nullopt},
+      initial_reconnect_delay_{std::nullopt},
       logging_cb_([](auto msg) {}),
       receiver_([](launchdarkly::sse::Event const&) {}),
       error_cb_([](auto err) {}) {
@@ -382,6 +393,11 @@ Builder& Builder::write_timeout(std::chrono::milliseconds timeout) {
     return *this;
 }
 
+Builder& Builder::initial_reconnect_delay(std::chrono::milliseconds delay) {
+    initial_reconnect_delay_ = delay;
+    return *this;
+}
+
 Builder& Builder::method(http::verb verb) {
     request_.method(verb);
     return *this;
@@ -441,8 +457,8 @@ std::shared_ptr<Client> Builder::build() {
 
     return std::make_shared<FoxyClient>(
         net::make_strand(executor_), request, host, service, connect_timeout_,
-        read_timeout_, write_timeout_, receiver_, logging_cb_, error_cb_,
-        std::move(ssl));
+        read_timeout_, write_timeout_, initial_reconnect_delay_, receiver_,
+        logging_cb_, error_cb_, std::move(ssl));
 }
 
 }  // namespace launchdarkly::sse