Replaced termination callback with throwing exception

include/cppkafka/utils/backoff_performer.h

@@ -34,6 +34,7 @@
 #include <functional>
 #include <thread>
 #include "../consumer.h"
+#include "../exceptions.h"
 
 namespace cppkafka {
 
@@ -47,6 +48,14 @@ public:
     static const TimeUnit DEFAULT_BACKOFF_STEP;
     static const TimeUnit DEFAULT_MAXIMUM_BACKOFF;
     static const size_t DEFAULT_MAXIMUM_RETRIES;
+    
+    /**
+     * @brief Type which any functor must return.
+     */
+    struct ReturnType {
+        bool    abort_{true};
+        Error   error_;
+    };
 
     /**
      * The backoff policy to use
@@ -119,11 +128,16 @@ public:
     void perform(const Functor& callback) {
         TimeUnit backoff = initial_backoff_;
         size_t retries = maximum_retries_;
+        ReturnType rt;
         while (retries--) {
             auto start = std::chrono::steady_clock::now();
             // If the callback returns true, we're done
-            if (callback()) {
-                return;
+            rt = callback();
+            if (rt.abort_) {
+                if (rt.error_) {
+                    break; //terminal error
+                }
+                return; //success
             }
             auto end = std::chrono::steady_clock::now();
             auto time_elapsed = end - start;
@@ -134,6 +148,8 @@ public:
             // Increase out backoff depending on the policy being used
             backoff = increase_backoff(backoff);
         }
+        // No more retries left or we have a terminal error.
+        throw ConsumerException(rt.error_);
     }
 private:
     TimeUnit increase_backoff(TimeUnit backoff);