RemoteStore::addToStore(): Pass content-addressability assertion

... and use this in Downloader::downloadCached(). This fixes

  $ nix-build https://nixos.org/channels/nixos-16.09-small/nixexprs.tar.xz -A hello
  error: cannot import path ‘/nix/store/csfbp1s60dkgmk9f8g0zk0mwb7hzgabd-nixexprs.tar.xz’ because it lacks a valid signature

1 files changed, 6 insertions, 1 deletions

diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index d03e70849f..c344b9d66e 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -128,7 +128,7 @@ struct ValidPathInfo
        of an output path of a derivation were actually produced by
        that derivation. In the intensional model, we have to trust
        that a particular output path was produced by a derivation; the
-       path name then implies the contents.)
+       path then implies the contents.)
 
        Ideally, the content-addressability assertion would just be a
        Boolean, and the store path would be computed from
@@ -687,6 +687,11 @@ ValidPathInfo decodeValidPathInfo(std::istream & str,
     bool hashGiven = false);
 
 
+/* Compute the content-addressability assertion (ValidPathInfo::ca)
+   for paths created by makeFixedOutputPath() / addToStore(). */
+std::string makeFixedOutputCA(bool recursive, const Hash & hash);
+
+
 MakeError(SubstError, Error)
 MakeError(BuildError, Error) /* denotes a permanent build failure */
 MakeError(InvalidPath, Error)