Sort substituters by priority

Fixes #1438.

3 files changed, 11 insertions, 0 deletions

diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index bf5a56ab4d..f9c1c2cbe8 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -123,6 +123,8 @@ public:
 
     std::shared_ptr<std::string> getBuildLog(const Path & path) override;
 
+    int getPriority() override { return priority; }
+
 };
 
 }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index db2e023ab0..108e2d4ce9 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -812,6 +812,10 @@ std::list<ref<Store>> getDefaultSubstituters()
         for (auto uri : settings.extraSubstituters.get())
             addStore(uri);
 
+        stores.sort([](ref<Store> & a, ref<Store> & b) {
+            return a->getPriority() < b->getPriority();
+        });
+
         return stores;
     } ());
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index c625a36303..cada37653e 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -590,6 +590,11 @@ public:
        a notion of connection. Otherwise this is a no-op. */
     virtual void connect() { };
 
+    /* Get the priority of the store, used to order substituters. In
+       particular, binary caches can specify a priority field in their
+       "nix-cache-info" file. Lower value means higher priority. */
+    virtual int getPriority() { return 0; }
+
 protected:
 
     Stats stats;