Handle zip files containing symlinks

In streaming mode, libarchive doesn't handle symlinks in zip files
correctly. So write the entire file to disk so libarchive can access
it in random-access mode.

Fixes #10649. This was broken in cabee98152.

src/libfetchers/tarball.cc

@@ -145,9 +145,27 @@ DownloadTarballResult downloadTarball(
 
     // TODO: fall back to cached value if download fails.
 
+    AutoDelete cleanupTemp;
+
     /* Note: if the download is cached, `importTarball()` will receive
        no data, which causes it to import an empty tarball. */
-    TarArchive archive { *source };
+    auto archive =
+        hasSuffix(toLower(parseURL(url).path), ".zip")
+        ? ({
+                /* In streaming mode, libarchive doesn't handle
+                   symlinks in zip files correctly (#10649). So write
+                   the entire file to disk so libarchive can access it
+                   in random-access mode. */
+                auto [fdTemp, path] = createTempFile("nix-zipfile");
+                cleanupTemp.reset(path);
+                debug("downloading '%s' into '%s'...", url, path);
+                {
+                    FdSink sink(fdTemp.get());
+                    source->drainInto(sink);
+                }
+                TarArchive{path};
+          })
+        : TarArchive{*source};
     auto parseSink = getTarballCache()->getFileSystemObjectSink();
     auto lastModified = unpackTarfileToSink(archive, *parseSink);
 

tests/functional/flakes/prefetch.sh

@@ -0,0 +1,6 @@
+source common.sh
+
+# Test symlinks in zip files (#10649).
+path=$(nix flake prefetch --json file://$(pwd)/tree.zip | jq -r .storePath)
+[[ $(cat $path/foo) = foo ]]
+[[ $(readlink $path/bar) = foo ]]

tests/functional/local.mk

@@ -16,6 +16,7 @@ nix_tests = \
   flakes/absolute-attr-paths.sh \
   flakes/build-paths.sh \
   flakes/flake-in-submodule.sh \
+  flakes/prefetch.sh \
   gc.sh \
   nix-collect-garbage-d.sh \
   remote-store.sh \