fix: auto retry once for connection closed

crates/router/src/routes/metrics.rs

@@ -106,6 +106,7 @@ counter_metric!(APPLE_PAY_MANUAL_FLOW_FAILED_PAYMENT, GLOBAL_METER);
 counter_metric!(APPLE_PAY_SIMPLIFIED_FLOW_FAILED_PAYMENT, GLOBAL_METER);
 
 // Metrics for Auto Retries
+counter_metric!(AUTO_RETRY_CONNECTION_CLOSED, GLOBAL_METER);
 counter_metric!(AUTO_RETRY_ELIGIBLE_REQUEST_COUNT, GLOBAL_METER);
 counter_metric!(AUTO_RETRY_GSM_MISS_COUNT, GLOBAL_METER);
 counter_metric!(AUTO_RETRY_GSM_FETCH_FAILURE_COUNT, GLOBAL_METER);

crates/router/src/services/api.rs

@@ -552,8 +552,7 @@ pub async fn send_request(
         key: consts::METRICS_HOST_TAG_NAME.into(),
         value: url.host_str().unwrap_or_default().to_string().into(),
     };
-
-    let send_request = async {
+    let request = {
         match request.method {
             Method::Get => client.get(url),
             Method::Post => {
@@ -607,32 +606,86 @@ pub async fn send_request(
         .timeout(Duration::from_secs(
             option_timeout_secs.unwrap_or(crate::consts::REQUEST_TIME_OUT),
         ))
-        .send()
-        .await
-        .map_err(|error| match error {
-            error if error.is_timeout() => {
-                metrics::REQUEST_BUILD_FAILURE.add(&metrics::CONTEXT, 1, &[]);
-                errors::ApiClientError::RequestTimeoutReceived
-            }
-            error if is_connection_closed(&error) => {
-                metrics::REQUEST_BUILD_FAILURE.add(&metrics::CONTEXT, 1, &[]);
-                errors::ApiClientError::ConnectionClosed
-            }
-            _ => errors::ApiClientError::RequestNotSent(error.to_string()),
-        })
-        .into_report()
-        .attach_printable("Unable to send request to connector")
     };
 
-    metrics_request::record_operation_time(
+    // We cannot clone the request type, because it has Form trait which is not clonable. So we are cloning the request builder here.
+    let cloned_send_request = request.try_clone().map(|cloned_request| async {
+        cloned_request
+            .send()
+            .await
+            .map_err(|error| match error {
+                error if error.is_timeout() => {
+                    metrics::REQUEST_BUILD_FAILURE.add(&metrics::CONTEXT, 1, &[]);
+                    errors::ApiClientError::RequestTimeoutReceived
+                }
+                error if is_connection_closed_before_message_could_complete(&error) => {
+                    metrics::REQUEST_BUILD_FAILURE.add(&metrics::CONTEXT, 1, &[]);
+                    errors::ApiClientError::ConnectionClosedIncompleteMessage
+                }
+                _ => errors::ApiClientError::RequestNotSent(error.to_string()),
+            })
+            .into_report()
+            .attach_printable("Unable to send request to connector")
+    });
+
+    let send_request = async {
+        request
+            .send()
+            .await
+            .map_err(|error| match error {
+                error if error.is_timeout() => {
+                    metrics::REQUEST_BUILD_FAILURE.add(&metrics::CONTEXT, 1, &[]);
+                    errors::ApiClientError::RequestTimeoutReceived
+                }
+                error if is_connection_closed_before_message_could_complete(&error) => {
+                    metrics::REQUEST_BUILD_FAILURE.add(&metrics::CONTEXT, 1, &[]);
+                    errors::ApiClientError::ConnectionClosedIncompleteMessage
+                }
+                _ => errors::ApiClientError::RequestNotSent(error.to_string()),
+            })
+            .into_report()
+            .attach_printable("Unable to send request to connector")
+    };
+
+    let response = metrics_request::record_operation_time(
         send_request,
         &metrics::EXTERNAL_REQUEST_TIME,
-        &[metrics_tag],
+        &[metrics_tag.clone()],
     )
-    .await
+    .await;
+    // Retry once if the response is connection closed.
+    //
+    // This is just due to the racy nature of networking.
+    // hyper has a connection pool of idle connections, and it selected one to send your request.
+    // Most of the time, hyper will receive the server’s FIN and drop the dead connection from its pool.
+    // But occasionally, a connection will be selected from the pool
+    // and written to at the same time the server is deciding to close the connection.
+    // Since hyper already wrote some of the request,
+    // it can’t really retry it automatically on a new connection, since the server may have acted already
+    match response {
+        Ok(response) => Ok(response),
+        Err(error)
+            if error.current_context()
+                == &errors::ApiClientError::ConnectionClosedIncompleteMessage =>
+        {
+            metrics::AUTO_RETRY_CONNECTION_CLOSED.add(&metrics::CONTEXT, 1, &[]);
+            match cloned_send_request {
+                Some(cloned_request) => {
+                    metrics_request::record_operation_time(
+                        cloned_request,
+                        &metrics::EXTERNAL_REQUEST_TIME,
+                        &[metrics_tag],
+                    )
+                    .await
+                }
+                None => Err(error),
+            }
+        }
+        err @ Err(_) => err,
+    }
 }
 
-fn is_connection_closed(error: &reqwest::Error) -> bool {
+fn is_connection_closed_before_message_could_complete(error: &reqwest::Error) -> bool {
     let mut source = error.source();
     while let Some(err) = source {
         if let Some(hyper_err) = err.downcast_ref::<hyper::Error>() {
@@ -1674,7 +1727,7 @@ pub fn build_redirection_form(
 
                     // Initialize the ThreeDSService
                     const threeDS = gateway.get3DSecure();
-            
+
                     const options = {{
                         customerVaultId: '{customer_vault_id}',
                         currency: '{currency}',

crates/storage_impl/src/errors.rs

@@ -267,7 +267,7 @@ pub enum ApiClientError {
     RequestTimeoutReceived,
 
     #[error("connection closed before a message could complete")]
-    ConnectionClosed,
+    ConnectionClosedIncompleteMessage,
 
     #[error("Server responded with Internal Server Error")]
     InternalServerErrorReceived,
@@ -285,8 +285,8 @@ impl ApiClientError {
     pub fn is_upstream_timeout(&self) -> bool {
         self == &Self::RequestTimeoutReceived
     }
-    pub fn is_connection_closed(&self) -> bool {
-        self == &Self::ConnectionClosed
+    pub fn is_connection_closed_before_message_could_complete(&self) -> bool {
+        self == &Self::ConnectionClosedIncompleteMessage
     }
 }