chore: Enhance HttpClient5 Retry-Strategy for 429 and 503 responses

cloudplatform/connectivity-apache-httpclient5/src/main/java/com/sap/cloud/sdk/cloudplatform/connectivity/DefaultApacheHttpClient5Factory.java

@@ -14,6 +14,7 @@
 import org.apache.hc.client5.http.classic.HttpClient;
 import org.apache.hc.client5.http.config.ConnectionConfig;
 import org.apache.hc.client5.http.config.RequestConfig;
+import org.apache.hc.client5.http.impl.DefaultHttpRequestRetryStrategy;
 import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
 import org.apache.hc.client5.http.impl.classic.HttpClientBuilder;
 import org.apache.hc.client5.http.impl.classic.HttpClients;
@@ -24,8 +25,11 @@
 import org.apache.hc.client5.http.ssl.NoopHostnameVerifier;
 import org.apache.hc.client5.http.ssl.TlsSocketStrategy;
 import org.apache.hc.core5.http.HttpHost;
+import org.apache.hc.core5.http.HttpRequest;
 import org.apache.hc.core5.http.HttpRequestInterceptor;
+import org.apache.hc.core5.http.HttpResponse;
 import org.apache.hc.core5.http.io.SocketConfig;
+import org.apache.hc.core5.http.protocol.HttpContext;
 import org.apache.hc.core5.util.Timeout;
 
 import com.sap.cloud.sdk.cloudplatform.connectivity.exception.DestinationAccessException;
@@ -92,6 +96,7 @@ private CloseableHttpClient buildHttpClient(
                 .custom()
                 .setConnectionManager(getConnectionManager(destination))
                 .setDefaultRequestConfig(requestConfig)
+                .setRetryStrategy(new LoggingHttpRequestRetryStrategy(destination))
                 .setProxy(getProxy(destination));
 
         if( requestInterceptor != null ) {
@@ -233,4 +238,42 @@ private boolean isValidProxyConfigurationUriInDestination( @Nullable final HttpD
         }
         return true;
     }
+
+    private static class LoggingHttpRequestRetryStrategy extends DefaultHttpRequestRetryStrategy
+    {
+        final @Nullable HttpDestinationProperties destination;
+
+        public LoggingHttpRequestRetryStrategy( final @Nullable HttpDestinationProperties destination )
+        {
+            super();
+            this.destination = destination;
+        }
+
+        @Override
+        public boolean retryRequest( final HttpResponse response, final int execCount, final HttpContext context )
+        {
+            final boolean retry = super.retryRequest(response, execCount, context);
+            if( retry ) {
+                final String msg = "Retrying request for destination {} due to response {}. Retry attempt #{}.";
+                log.debug(msg, destination, response.getCode(), execCount);
+            }
+            return retry;
+        }
+
+        @Override
+        public boolean retryRequest(
+            final HttpRequest req,
+            final IOException exception,
+            final int execCount,
+            final HttpContext context )
+        {
+            final boolean retry = super.retryRequest(req, exception, execCount, context);
+            if( retry ) {
+                final String msg =
+                    "Retrying {} request for destination {} to {} due to exception \"{}\". Retry attempt #{}.";
+                log.debug(msg, req.getMethod(), destination, req.getRequestUri(), exception.getMessage(), execCount);
+            }
+            return retry;
+        }
+    }
 }