Expose a close_queue and closed methods

If you have a consumer wrapping this one (FFI cases), the outer consumer must close
the queue and serve the events via Poll. Otherwise it will hang forever
as prior to calling close there's a rebalance & rdkafka awaits a
response before continuing.

Author: scanterog

src/consumer/base_consumer.rs

@@ -331,6 +331,27 @@ where
             PartitionQueue::new(self.clone(), queue)
         })
     }
+
+    /// Close the queue used by a consumer.
+    /// Only exposed for advanced usage of this API and should not be used under normal circumstances.
+    pub fn close_queue(&self) -> KafkaResult<()> {
+        let err = unsafe {
+            RDKafkaError::from_ptr(rdsys::rd_kafka_consumer_close_queue(
+                self.client.native_ptr(),
+                self.queue.ptr(),
+            ))
+        };
+        if err.is_error() {
+            Err(KafkaError::ConsumerQueueClose(err.code()))
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Returns true if the consumer is closed, else false.
+    pub fn closed(&self) -> bool {
+        unsafe { rdsys::rd_kafka_consumer_closed(self.client.native_ptr()) == 1 }
+    }
 }
 
 impl<C> Consumer<C> for BaseConsumer<C>

src/error.rs

@@ -147,6 +147,8 @@ pub enum KafkaError {
     ClientCreation(String),
     /// Consumer commit failed.
     ConsumerCommit(RDKafkaErrorCode),
+    /// Consumer queue close failed.
+    ConsumerQueueClose(RDKafkaErrorCode),
     /// Flushing failed
     Flush(RDKafkaErrorCode),
     /// Global error.
@@ -204,6 +206,9 @@ impl fmt::Debug for KafkaError {
             KafkaError::ConsumerCommit(err) => {
                 write!(f, "KafkaError (Consumer commit error: {})", err)
             }
+            KafkaError::ConsumerQueueClose(err) => {
+                write!(f, "KafkaError (Consumer queue close error: {})", err)
+            }
             KafkaError::Flush(err) => write!(f, "KafkaError (Flush error: {})", err),
             KafkaError::Global(err) => write!(f, "KafkaError (Global error: {})", err),
             KafkaError::GroupListFetch(err) => {
@@ -255,6 +260,7 @@ impl fmt::Display for KafkaError {
             }
             KafkaError::ClientCreation(ref err) => write!(f, "Client creation error: {}", err),
             KafkaError::ConsumerCommit(err) => write!(f, "Consumer commit error: {}", err),
+            KafkaError::ConsumerQueueClose(err) => write!(f, "Consumer queue close error: {}", err),
             KafkaError::Flush(err) => write!(f, "Flush error: {}", err),
             KafkaError::Global(err) => write!(f, "Global error: {}", err),
             KafkaError::GroupListFetch(err) => write!(f, "Group list fetch error: {}", err),
@@ -288,6 +294,7 @@ impl Error for KafkaError {
             KafkaError::ClientConfig(..) => None,
             KafkaError::ClientCreation(_) => None,
             KafkaError::ConsumerCommit(err) => Some(err),
+            KafkaError::ConsumerQueueClose(err) => Some(err),
             KafkaError::Flush(err) => Some(err),
             KafkaError::Global(err) => Some(err),
             KafkaError::GroupListFetch(err) => Some(err),
@@ -327,6 +334,7 @@ impl KafkaError {
             KafkaError::ClientConfig(..) => None,
             KafkaError::ClientCreation(_) => None,
             KafkaError::ConsumerCommit(err) => Some(*err),
+            KafkaError::ConsumerQueueClose(err) => Some(*err),
             KafkaError::Flush(err) => Some(*err),
             KafkaError::Global(err) => Some(*err),
             KafkaError::GroupListFetch(err) => Some(*err),