Gem::Format knows the guts of the RubyGem .gem file format and provides the capability to read gem files

Methods
F
N
Attributes
[RW] file_entries
[RW] gem_path
[RW] spec
Class Public methods
from_file_by_path(file_path, security_policy = nil)

Reads the gem file_path using security_policy and returns a Format representing the data in the gem

Source: show | on GitHub 

# File ../ruby/lib/rubygems/format.rb, line 30
def self.from_file_by_path(file_path, security_policy = nil)
  unless File.file?(file_path)
    raise Gem::Exception, "Cannot load gem at [#{file_path}] in #{Dir.pwd}"
  end

  start = File.read file_path, 20

  if start.nil? or start.length < 20 then
    nil
  elsif start.include?("MD5SUM =") # old version gems
    require 'rubygems/old_format'

    Gem::OldFormat.from_file_by_path file_path
  else
    begin
      open file_path, Gem.binary_mode do |io|
        from_io io, file_path, security_policy
      end
    rescue Gem::Package::TarInvalidError => e
      message = "corrupt gem (#{e.class}: #{e.message})"
      raise Gem::Package::FormatError.new(message, file_path)
    end
  end
end
from_io(io, gem_path="(io)", security_policy = nil)

Reads a gem from io at gem_path using security_policy and returns a Format representing the data from the gem

Source: show | on GitHub 

# File ../ruby/lib/rubygems/format.rb, line 59
def self.from_io(io, gem_path="(io)", security_policy = nil)
  format = new gem_path

  Gem::Package.open io, 'r', security_policy do |pkg|
    format.spec = pkg.metadata
    format.file_entries = []

    pkg.each do |entry|
      size = entry.header.size
      mode = entry.header.mode

      format.file_entries << [{
          "size" => size, "mode" => mode, "path" => entry.full_name,
        },
        entry.read
      ]
    end
  end

  format
end
new(gem_path)

Constructs a Format representing the gem's data which came from gem_path

Source: show | on GitHub 

# File ../ruby/lib/rubygems/format.rb, line 22
def initialize(gem_path)
  @gem_path = gem_path
end