lib/ghtorrent/retriever.rb
def retrieve_master_branch_diff(owner, repo, branch, parent_owner, parent_repo, parent_branch)
      branch   = retrieve_default_branch(owner, repo) if branch.nil?
      parent_branch = retrieve_default_branch(parent_owner, parent_repo) if parent_branch.nil?
      return nil if branch.nil? or parent_branch.nil?

      cmp_url = "https://api.github.com/repos/#{parent_owner}/#{parent_repo}/compare/#{parent_branch}...#{owner}:#{branch}"
      api_request(cmp_url)
    end
def retrieve_master_branch_diff(owner, repo, branch, parent_owner, parent_repo, parent_branch)
      branch   = retrieve_default_branch(owner, repo) if branch.nil?
      parent_branch = retrieve_default_branch(parent_owner, parent_repo) if parent_branch.nil?
      return nil if branch.nil? or parent_branch.nil?

      cmp_url = "https://api.github.com/repos/#{parent_owner}/#{parent_repo}/compare/#{parent_branch}...#{owner}:#{branch}"
      api_request(cmp_url)
    end
Retrieve diff between two branches. If either branch name is not provided
 the branch name is resolved to the corresponding default branch