1 files changed, 88 insertions, 0 deletions
diff --git a/lib/bundler/compact_index_client/updater.rb b/lib/bundler/compact_index_client/updater.rb
new file mode 100644
index 0000000000..5aa480fdcc
--- /dev/null
+++ b/lib/bundler/compact_index_client/updater.rb
@@ -0,0 +1,88 @@
+# frozen_string_literal: true
+require "fileutils"
+require "stringio"
+require "tmpdir"
+require "zlib"
+
+module Bundler
+  class CompactIndexClient
+    class Updater
+      class MisMatchedChecksumError < Error
+        def initialize(path, server_checksum, local_checksum)
+          @path = path
+          @server_checksum = server_checksum
+          @local_checksum = local_checksum
+        end
+
+        def message
+          "The checksum of /#{@path} does not match the checksum provided by the server! Something is wrong " \
+            "(local checksum is #{@local_checksum.inspect}, was expecting #{@server_checksum.inspect})."
+        end
+      end
+
+      def initialize(fetcher)
+        @fetcher = fetcher
+      end
+
+      def update(local_path, remote_path, retrying = nil)
+        headers = {}
+
+        Dir.mktmpdir("bundler-compact-index-") do |local_temp_dir|
+          local_temp_path = Pathname.new(local_temp_dir).join(local_path.basename)
+
+          # first try to fetch any new bytes on the existing file
+          if retrying.nil? && local_path.file?
+            FileUtils.cp local_path, local_temp_path
+            headers["If-None-Match"] = etag_for(local_temp_path)
+            headers["Range"] = "bytes=#{local_temp_path.size}-"
+          else
+            # Fastly ignores Range when Accept-Encoding: gzip is set
+            headers["Accept-Encoding"] = "gzip"
+          end
+
+          response = @fetcher.call(remote_path, headers)
+          return nil if response.is_a?(Net::HTTPNotModified)
+
+          content = response.body
+          if response["Content-Encoding"] == "gzip"
+            content = Zlib::GzipReader.new(StringIO.new(content)).read
+          end
+
+          mode = response.is_a?(Net::HTTPPartialContent) ? "a" : "w"
+          SharedHelpers.filesystem_access(local_temp_path) do
+            local_temp_path.open(mode) {|f| f << content }
+          end
+
+          response_etag = (response["ETag"] || "").gsub(%r{\AW/}, "")
+          if etag_for(local_temp_path) == response_etag
+            SharedHelpers.filesystem_access(local_path) do
+              FileUtils.mv(local_temp_path, local_path)
+            end
+            return nil
+          end
+
+          if retrying
+            raise MisMatchedChecksumError.new(remote_path, response_etag, etag_for(local_temp_path))
+          end
+
+          update(local_path, remote_path, :retrying)
+        end
+      end
+
+      def etag_for(path)
+        sum = checksum_for_file(path)
+        sum ? %("#{sum}") : nil
+      end
+
+      def checksum_for_file(path)
+        return nil unless path.file?
+        # This must use IO.read instead of Digest.file().hexdigest
+        # because we need to preserve \n line endings on windows when calculating
+        # the checksum
+        SharedHelpers.filesystem_access(path, :read) do
+          Digest::MD5.hexdigest(IO.read(path))
+        end
+      end
+    end
+  end
+end