downloadCached: Return ETag

This allows fetchFlake() to return the Git revision of a GitHub
archive.

1 files changed, 10 insertions, 2 deletions

diff --git a/src/libstore/download.hh b/src/libstore/download.hh
index f0228f7d0..8acfe4e1a 100644
--- a/src/libstore/download.hh
+++ b/src/libstore/download.hh
@@ -41,6 +41,12 @@ struct DownloadResult
     uint64_t bodySize = 0;
 };
 
+struct CachedDownloadResult
+{
+    Path path;
+    std::optional<std::string> etag;
+};
+
 class Store;
 
 struct Downloader
@@ -64,8 +70,10 @@ struct Downloader
        and is more recent than ‘tarball-ttl’ seconds. Otherwise,
        use the recorded ETag to verify if the server has a more
        recent version, and if so, download it to the Nix store. */
-    Path downloadCached(ref<Store> store, const string & uri, bool unpack, string name = "",
-        const Hash & expectedHash = Hash(), string * effectiveUri = nullptr, int ttl = settings.tarballTtl);
+    CachedDownloadResult downloadCached(
+        ref<Store> store, const string & uri, bool unpack, string name = "",
+        const Hash & expectedHash = Hash(), string * effectiveUri = nullptr,
+        int ttl = settings.tarballTtl);
 
     enum Error { NotFound, Forbidden, Misc, Transient, Interrupted };
 };