From 7348653ff4fc4e9b2dc24943aabdb57179b1c75a Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 3 Sep 2019 12:51:35 +0200
Subject: Ensure that Callback is called only once

Also, make Callback movable but uncopyable.
---
 src/libstore/http-binary-cache-store.cc | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

(limited to 'src/libstore/http-binary-cache-store.cc')

diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index df2fb93320fc..e631d95f0fd1 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -137,17 +137,19 @@ protected:
 
         auto request(makeRequest(path));
 
+        auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
+
         getDownloader()->enqueueDownload(request,
-            {[callback, this](std::future<DownloadResult> result) {
+            {[callbackPtr, this](std::future<DownloadResult> result) {
                 try {
-                    callback(result.get().data);
+                    (*callbackPtr)(result.get().data);
                 } catch (DownloadError & e) {
                     if (e.error == Downloader::NotFound || e.error == Downloader::Forbidden)
-                        return callback(std::shared_ptr<std::string>());
+                        return (*callbackPtr)(std::shared_ptr<std::string>());
                     maybeDisable();
-                    callback.rethrow();
+                    callbackPtr->rethrow();
                 } catch (...) {
-                    callback.rethrow();
+                    callbackPtr->rethrow();
                 }
             }});
     }
-- 
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