[rubygems/rubygems] Add "gem rebuild" command.

https://github.com/rubygems/rubygems/commit/6d661573f0

lib/rubygems/command_manager.rb

@@ -60,6 +60,7 @@ class Gem::CommandManager
     :push,
     :query,
     :rdoc,
+    :rebuild,
     :search,
     :server,
     :signin,

lib/rubygems/commands/rebuild_command.rb

@@ -0,0 +1,262 @@
+# frozen_string_literal: true
+
+require "date"
+require "digest"
+require "fileutils"
+require_relative "../package"
+
+class Gem::Commands::RebuildCommand < Gem::Command
+  DATE_FORMAT = "%Y-%m-%d %H:%M:%S.%N Z"
+
+  def initialize
+    super "rebuild", "Attempt to reproduce a build of a gem."
+
+    add_option "--force", "Skip validation of the spec." do |_value, options|
+      options[:force] = true
+    end
+
+    add_option "--strict", "Consider warnings as errors when validating the spec." do |_value, options|
+      options[:strict] = true
+    end
+
+    add_option "--source GEM_SOURCE", "Specify the source to download the gem from." do |value, options|
+      options[:source] = value
+    end
+
+    add_option "--original GEM_FILE", "Specify a local file to compare against (instead of downloading it)." do |value, options|
+      options[:original_gem_file] = value
+    end
+
+    add_option "--gemspec GEMSPEC_FILE", "Specify the name of the gemspec file." do |value, options|
+      options[:gemspec_file] = value
+    end
+
+    add_option "-C PATH", "Run as if gem build was started in <PATH> instead of the current working directory." do |value, options|
+      options[:build_path] = value
+    end
+  end
+
+  def arguments # :nodoc:
+    "GEM_NAME      gem name on gem server\n" \
+    "GEM_VERSION   gem version you are attempting to rebuild"
+  end
+
+  def description # :nodoc:
+    <<-EOF
+The rebuild command allows you to (attempt to) reproduce a build of a gem
+from a ruby gemspec.
+
+This command assumes the gemspec can be built with the `gem build` command.
+If you use either `gem build` or `rake build`/`rake release` to build/release
+a gem, it is a potential candidate.
+
+If the gem includes top-level files that change frequently (e.g. Gemfile.lock),
+it may require more effort to reproduce a build. For example, it might require
+more precisely matched versions of Ruby, RubyGems, or Bundler to be used.
+
+An example of reproducing a gem build:
+
+  $ pwd
+  /usr/home/puppy/test/rebuild
+  $ ls -a
+  ./  ../
+  $ git clone --branch v12.0.2 https://github.com/duckinator/okay.git
+  $ gem rebuild -C ./okay --gemspec okay.gemspec okay 12.0.2
+  Fetching okay-12.0.2.gem
+  Downloaded okay version 12.0.2 as /usr/home/puppy/test/rebuild/rebuild/old/okay-12.0.2.gem.
+    Successfully built RubyGem
+    Name: okay
+    Version: 12.0.2
+    File: okay-12.0.2.gem
+
+  Built at: 2023-08-31 21:39:02 EDT (1693532342)
+  Original build saved to:   /usr/home/puppy/test/rebuild/rebuild/old/okay-12.0.2.gem
+  Reproduced build saved to: /usr/home/puppy/test/rebuild/rebuild/new/okay-12.0.2.gem
+  Working directory: ./okay
+
+  Hash comparison:
+    38a8bd78ce10bc19189ead0b56fa490d03788a2f926a6481b2f1f5d5fa5ab75b      /usr/home/puppy/test/rebuild/rebuild/old/okay-12.0.2.gem
+    38a8bd78ce10bc19189ead0b56fa490d03788a2f926a6481b2f1f5d5fa5ab75b      /usr/home/puppy/test/rebuild/rebuild/new/okay-12.0.2.gem
+
+  SUCCESS - original and rebuild hashes matched
+    EOF
+  end
+
+  def usage # :nodoc:
+    "#{program_name} GEM_NAME GEM_VERSION"
+  end
+
+  def execute
+    gem_name, gem_version = get_gem_name_and_version
+
+    old_dir, new_dir = prep_dirs
+
+    gem_filename = "#{gem_name}-#{gem_version}.gem"
+    old_file = File.join(old_dir, gem_filename)
+    new_file = File.join(new_dir, gem_filename)
+
+    if options[:original_gem_file]
+      FileUtils.copy_file(options[:original_gem_file], old_file)
+    else
+      download_gem(gem_name, gem_version, old_file)
+    end
+
+    source_date_epoch = get_timestamp(old_file).to_s
+
+    if build_path = options[:build_path]
+      Dir.chdir(build_path) { build_gem(gem_name, source_date_epoch, new_file) }
+    else
+      build_gem(gem_name, source_date_epoch, new_file)
+    end
+
+    compare(source_date_epoch, old_file, new_file)
+  end
+
+  private
+
+  def sha256(file)
+    Digest::SHA256.hexdigest(File.read(file))
+  end
+
+  def get_timestamp(file)
+    mtime = nil
+    Gem::Package::TarReader.new(File.open(file)) do |tar|
+      mtime = tar.seek("metadata.gz") {|f| f.header.mtime }
+    end
+
+    mtime
+  end
+
+  def compare(source_date_epoch, old_file, new_file)
+    date = Time.at(source_date_epoch.to_i).strftime("%F %T %Z")
+
+    old_hash = sha256(old_file)
+    new_hash = sha256(new_file)
+
+    say
+    say "Built at: #{date} (#{source_date_epoch})"
+    say "Original build saved to:   #{old_file}"
+    say "Reproduced build saved to: #{new_file}"
+    say "Working directory: #{options[:build_path] || Dir.pwd}"
+    say
+    say "Hash comparison:"
+    say "  #{old_hash}\t#{old_file}"
+    say "  #{new_hash}\t#{new_file}"
+    say
+
+    if old_hash == new_hash
+      say "SUCCESS - original and rebuild hashes matched"
+    else
+      say "FAILURE - original and rebuild hashes did not match"
+      terminate_interaction 1
+    end
+  end
+
+  def prep_dirs
+    rebuild_dir = File.expand_path("rebuild")
+    old_dir = File.join(rebuild_dir, "old")
+    new_dir = File.join(rebuild_dir, "new")
+
+    if File.directory?(rebuild_dir)
+      FileUtils.remove_dir(rebuild_dir)
+    end
+
+    FileUtils.mkdir_p(old_dir)
+    FileUtils.mkdir_p(new_dir)
+
+    [old_dir, new_dir]
+  end
+
+  def get_gem_name_and_version
+    args = options[:args] || []
+    if args.length == 2
+      gem_name, gem_version = args
+    elsif args.length > 2
+      raise Gem::CommandLineError, "Too many arguments"
+    else
+      raise Gem::CommandLineError, "Expected GEM_NAME and GEM_VERSION arguments (gem rebuild GEM_NAME GEM_VERSION)"
+    end
+
+    [gem_name, gem_version]
+  end
+
+  def build_gem(gem_name, source_date_epoch, output_file)
+    gemspec = options[:gemspec_file] || find_gemspec("#{gem_name}.gemspec")
+
+    if gemspec
+      build_package(gemspec, source_date_epoch, output_file)
+    else
+      alert_error error_message(gem_name)
+      terminate_interaction(1)
+    end
+  end
+
+  def build_package(gemspec, source_date_epoch, output_file)
+    with_source_date_epoch(source_date_epoch) do
+      spec = Gem::Specification.load(gemspec)
+      if spec
+        Gem::Package.build(
+          spec,
+          options[:force],
+          options[:strict],
+          output_file
+        )
+      else
+        alert_error "Error loading gemspec. Aborting."
+        terminate_interaction 1
+      end
+    end
+  end
+
+  def with_source_date_epoch(source_date_epoch)
+    old_sde = ENV["SOURCE_DATE_EPOCH"]
+    ENV["SOURCE_DATE_EPOCH"] = source_date_epoch.to_s
+
+    yield
+  ensure
+    ENV["SOURCE_DATE_EPOCH"] = old_sde
+  end
+
+  def find_gemspec(glob = "*.gemspec")
+    gemspecs = Dir.glob(glob).sort
+
+    if gemspecs.size > 1
+      alert_error "Multiple gemspecs found: #{gemspecs}, please specify one"
+      terminate_interaction(1)
+    end
+
+    gemspecs.first
+  end
+
+  def error_message(gem_name)
+    if gem_name
+      "Couldn't find a gemspec file matching '#{gem_name}' in #{Dir.pwd}"
+    else
+      "Couldn't find a gemspec file in #{Dir.pwd}"
+    end
+  end
+
+  def download_gem(gem_name, gem_version, old_file)
+    # This code was based loosely off the `gem fetch` command.
+    version = "= #{gem_version}"
+    dep = Gem::Dependency.new gem_name, version
+
+    specs_and_sources, errors =
+      Gem::SpecFetcher.fetcher.spec_for_dependency dep
+
+    # There should never be more than one item in specs_and_sources,
+    # since we search for an exact version.
+    spec, source = specs_and_sources[0]
+
+    if spec.nil?
+      show_lookup_failure gem_name, version, errors, options[:domain]
+      terminate_interaction 1
+    end
+
+    download_path = source.download spec
+
+    FileUtils.move(download_path, old_file)
+
+    say "Downloaded #{gem_name} version #{gem_version} as #{old_file}."
+  end
+end

test/rubygems/test_gem_commands_rebuild_command.rb

@@ -0,0 +1,145 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+require "rubygems/commands/build_command"
+require "rubygems/commands/rebuild_command"
+require "rubygems/package"
+
+class TestGemCommandsRebuildCommand < Gem::TestCase
+  def setup
+    super
+
+    readme_file = File.join(@tempdir, "README.md")
+
+    begin
+      umask_orig = File.umask(2)
+      File.open readme_file, "w" do |f|
+        f.write "My awesome gem"
+      end
+    ensure
+      File.umask(umask_orig)
+    end
+
+    @gem_name = "rebuild_test_gem"
+    @gem_version = "1.0.0"
+    @gem = util_spec @gem_name do |s|
+      s.version = @gem_version
+      s.license = "AGPL-3.0"
+      s.files = ["README.md"]
+    end
+  end
+
+  def util_test_build_gem(gem, args)
+    @ui = Gem::MockGemUi.new
+
+    cmd = Gem::Commands::BuildCommand.new
+
+    cmd.options[:args] = args
+    cmd.options[:build_path] = @tempdir
+    use_ui @ui do
+      cmd.execute
+    end
+    gem_file = "#{@gem_name}-#{@gem_version}.gem"
+    output = @ui.output.split "\n"
+    assert_equal "  Successfully built RubyGem", output.shift
+    assert_equal "  Name: #{@gem_name}", output.shift
+    assert_equal "  Version: #{@gem_version}", output.shift
+    assert_equal "  File: #{gem_file}", output.shift
+    assert_equal [], output
+
+    gem_file = File.join(@tempdir, gem_file)
+    assert File.exist?(gem_file)
+
+    spec = Gem::Package.new(gem_file).spec
+
+    assert_equal @gem_name, spec.name
+    assert_equal "this is a summary", spec.summary
+    gem_file
+  end
+
+  def util_test_rebuild_gem(gem, args, original_gem_file, gemspec_file, timestamp)
+    @ui = Gem::MockGemUi.new
+
+    cmd = Gem::Commands::RebuildCommand.new
+
+    cmd.options[:args] = args
+    cmd.options[:original_gem_file] = original_gem_file
+    cmd.options[:build_path] = @tempdir
+    cmd.options[:gemspec_file] = gemspec_file
+    use_ui @ui do
+      cmd.execute
+    end
+    gem_file = "#{@gem_name}-#{@gem_version}.gem"
+    output = @ui.output.split "\n"
+
+    assert_equal "  Successfully built RubyGem", output.shift
+    assert_equal "  Name: #{@gem_name}", output.shift
+    assert_equal "  Version: #{@gem_version}", output.shift
+    assert_equal "  File: #{gem_file}", output.shift
+    assert_empty output.shift
+    assert_match(/^Built at: .+ \(#{timestamp}\)/, output.shift)
+    original_line = output.shift
+    original = original_line.split(" ")[-1]
+    assert_match(/^Original build saved to:   /, original_line)
+    reproduced_line = output.shift
+    reproduced = reproduced_line.split(" ")[-1]
+    assert_match(/^Reproduced build saved to: /, reproduced_line)
+    assert_equal "Working directory: #{@tempdir}", output.shift
+    assert_equal "", output.shift
+    assert_equal "Hash comparison:", output.shift
+    output.shift # "  #{old_hash}\t#{old_file}"
+    output.shift # "  #{new_hash}\t#{new_file}"
+    assert_empty output.shift
+    assert_equal "SUCCESS - original and rebuild hashes matched", output.shift
+    assert_equal [], output
+
+    assert File.exist?(original)
+    assert File.exist?(reproduced)
+
+    old_spec = Gem::Package.new(original).spec
+    new_spec = Gem::Package.new(reproduced).spec
+
+    assert_equal @gem_name, old_spec.name
+    assert_equal "this is a summary", old_spec.summary
+
+    assert_equal old_spec.name, new_spec.name
+    assert_equal old_spec.summary, new_spec.summary
+
+    reproduced
+  end
+
+  def test_build_is_reproducible
+    # Back up SOURCE_DATE_EPOCH to restore later.
+    epoch = ENV["SOURCE_DATE_EPOCH"]
+
+    gemspec_file = File.join(@tempdir, @gem.spec_name)
+
+    # Initial Build
+
+    # Set SOURCE_DATE_EPOCH to 2001-02-03 04:05:06 -0500.
+    ENV["SOURCE_DATE_EPOCH"] = timestamp = Time.new(2001, 2, 3, 4, 5, 6).to_i.to_s
+    File.write(gemspec_file, @gem.to_ruby)
+    gem_file = util_test_build_gem @gem, [gemspec_file]
+
+    build_contents = File.read(gem_file)
+
+    gem_file_dir = File.dirname(gem_file)
+    gem_file_name = File.basename(gem_file)
+    original_gem_file = File.join(gem_file_dir, "original-" + gem_file_name)
+    File.rename(gem_file, original_gem_file)
+
+    # Rebuild
+
+    # Set SOURCE_DATE_EPOCH to a different value, meaning we are
+    # also testing that `gem rebuild` overrides the value.
+    ENV["SOURCE_DATE_EPOCH"] = Time.new(2007, 8, 9, 10, 11, 12).to_s
+
+    rebuild_gem_file = util_test_rebuild_gem(@gem, [@gem_name, @gem_version], original_gem_file, gemspec_file, timestamp)
+
+    rebuild_contents = File.read(rebuild_gem_file)
+
+    assert_equal build_contents, rebuild_contents
+  ensure
+    ENV["SOURCE_DATE_EPOCH"] = epoch
+  end
+end