Safely store concurrent compact index downloads

When bundler is run concurrently using the same bundle dir in $HOME,
the versions file can be updated from two processes at once. The
download has been changed to a temporary file, which is securely moved
into place over the original.

If retrying the update operation, the original file is no longer
immediately deleted and instead a full download is performed, later
overwriting the original file if successful.

If two processes are updating in parallel, this should ensure the
original file isn't corrupted and that both processes succeed.

- Fixes #4519

1 files changed, 18 insertions, 0 deletions

diff --git a/spec/install/gems/compact_index_spec.rb b/spec/install/gems/compact_index_spec.rb
index ef3bc5aedc..e96936f01d 100644
--- a/spec/install/gems/compact_index_spec.rb
+++ b/spec/install/gems/compact_index_spec.rb
@@ -656,4 +656,22 @@ The checksum of /versions does not match the checksum provided by the server! So
       bundle! :install, :artifice => "compact_index_forbidden"
     end
   end
+
+  it "performs partial update while local cache is updated by another process" do
+    gemfile <<-G
+      source "#{source_uri}"
+      gem 'rack'
+    G
+
+    # Create an empty file to trigger a partial download
+    versions = File.join(Bundler.rubygems.user_home, ".bundle", "cache", "compact_index",
+      "localgemserver.test.80.dd34752a738ee965a2a4298dc16db6c5", "versions")
+    FileUtils.mkdir_p(File.dirname(versions))
+    FileUtils.touch(versions)
+
+    bundle! :install, :artifice => "compact_index_concurrent_download"
+
+    expect(File.read(versions)).to start_with("created_at")
+    should_be_installed "rack 1.0.0"
+  end
 end