[ruby/rubygems] Remove verify_gz

This PR removes the `#verify_gz` method because it is redunant and
unnecessary.

Previously the `data.tar.gz` would get read twice for every file - once
in `verify_gz` and once in `extract_files`. The `extract_files` method
verifies the `data.tar.gz` when it reads it, and raises an error if
unzipping it fails.

The `verify_gz` code can be seen in some profiles as a hotspot -
although not major - as it accounts for between 9% and 17% of time, but
only when the installation thread doesn't have native extensions or
plugins.

ruby/rubygems@737c82986c

Author: eileencodes

lib/rubygems/package.rb

@@ -532,7 +532,7 @@ def normalize_path(pathname) # :nodoc:
   ##
   # Loads a Gem::Specification from the TarEntry +entry+
 
-  def load_spec(entry) # :nodoc:
+  def load_spec_from_metadata(entry) # :nodoc:
     limit = 10 * 1024 * 1024
     case entry.full_name
     when "metadata" then
@@ -678,12 +678,7 @@ def verify_entry(entry)
       digest entry
     end
 
-    case file_name
-    when "metadata", "metadata.gz" then
-      load_spec entry
-    when "data.tar.gz" then
-      verify_gz entry
-    end
+    load_spec_from_metadata entry
   rescue StandardError
     warn "Exception while verifying #{@gem.path}"
     raise
@@ -711,18 +706,6 @@ def verify_files(gem)
     end
   end
 
-  ##
-  # Verifies that +entry+ is a valid gzipped file.
-
-  def verify_gz(entry) # :nodoc:
-    Zlib::GzipReader.wrap entry do |gzio|
-      # TODO: read into a buffer once zlib supports it
-      gzio.read 16_384 until gzio.eof? # gzip checksum verification
-    end
-  rescue Zlib::GzipFile::Error => e
-    raise Gem::Package::FormatError.new(e.message, entry.full_name)
-  end
-
   if RUBY_ENGINE == "truffleruby"
     def copy_stream(src, dst, size) # :nodoc:
       dst.write src.read(size)

test/rubygems/test_gem_package.rb

@@ -858,15 +858,15 @@ def test_install_location_suffix
                  "#{@destination} is not allowed", e.message)
   end
 
-  def test_load_spec
+  def test_load_spec_from_metadata
     entry = StringIO.new Gem::Util.gzip @spec.to_yaml
     def entry.full_name
       "metadata.gz"
     end
 
     package = Gem::Package.new "nonexistent.gem"
 
-    spec = package.load_spec entry
+    spec = package.load_spec_from_metadata entry
 
     assert_equal @spec, spec
   end