notifications on request cancellation

include/mbgl/storage/base_request.hpp

@@ -1,6 +1,7 @@
 #ifndef MBGL_STORAGE_BASE_REQUEST
 #define MBGL_STORAGE_BASE_REQUEST
 
+#include <mbgl/storage/request_callback.hpp>
 #include <mbgl/util/ptr.hpp>
 
 #include <string>
@@ -15,8 +16,6 @@ namespace mbgl {
 
 class Response;
 class Request;
-using Callback = std::function<void(const Response &)>;
-
 
 class BaseRequest {
 private:
@@ -43,7 +42,6 @@ private:
     // This object may hold a shared_ptr to itself. It does this to prevent destruction of this object
     // while a request is in progress.
     util::ptr<BaseRequest> self;
-
     std::forward_list<std::unique_ptr<Callback>> callbacks;
 };
 

include/mbgl/storage/request.hpp

@@ -1,10 +1,10 @@
 #ifndef MBGL_STORAGE_REQUEST
 #define MBGL_STORAGE_REQUEST
 
+#include <mbgl/storage/request_callback.hpp>
 #include <mbgl/storage/response.hpp>
 #include <mbgl/util/ptr.hpp>
 
-#include <functional>
 #include <forward_list>
 
 typedef struct uv_loop_s uv_loop_t;
@@ -12,7 +12,6 @@ typedef struct uv_loop_s uv_loop_t;
 namespace mbgl {
 
 class BaseRequest;
-using Callback = std::function<void(const Response &)>;
 
 class Request {
 private:
@@ -25,7 +24,8 @@ public:
     Request(const util::ptr<BaseRequest> &base);
     ~Request();
 
-    void onload(Callback cb);
+    void onload(CompletedCallback cb);
+    void oncancel(AbortedCallback cb);
     void cancel();
 
 private:

include/mbgl/storage/request_callback.hpp

@@ -0,0 +1,22 @@
+#ifndef MBGL_STORAGE_REQUEST_CALLBACK
+#define MBGL_STORAGE_REQUEST_CALLBACK
+
+#include <mbgl/util/variant.hpp>
+
+#include <functional>
+
+namespace mbgl {
+
+class Response;
+
+using CompletedCallback = std::function<void(const Response &)>;
+using AbortedCallback = std::function<void()>;
+
+using Callback = mapbox::util::variant<
+    CompletedCallback,
+    AbortedCallback
+>;
+
+}
+
+#endif