update cache checksums to decrease string allocations

bundler/lib/bundler/compact_index_client/cache.rb

@@ -55,14 +55,9 @@ def versions_etag_path
       end
 
       def checksums
-        checksums = {}
-
-        lines(versions_path).each do |line|
-          name, _, checksum = line.split(" ", 3)
-          checksums[name] = checksum
+        lines(versions_path).each_with_object({}) do |line, checksums|
+          parse_version_checksum(line, checksums)
         end
-
-        checksums
       end
 
       def dependencies(name)
@@ -106,6 +101,20 @@ def parse_gem(line)
         @dependency_parser.parse(line)
       end
 
+      # This is mostly the same as `split(" ", 3)` but it avoids allocating extra objects.
+      # This method gets called at least once for every gem when parsing versions.
+      def parse_version_checksum(line, checksums)
+        line.freeze # allows slicing into the string to not allocate a copy of the line
+        name_end = line.index(" ")
+        checksum_start = line.index(" ", name_end + 1) + 1
+        checksum_end = line.size - checksum_start
+        # freeze name since it is used as a hash key
+        # pre-freezing means a frozen copy isn't created
+        name = line[0, name_end].freeze
+        checksum = line[checksum_start, checksum_end]
+        checksums[name] = checksum
+      end
+
       def info_roots
         [
           directory.join("info"),