text: #!/usr/bin/env python3
  # Copyright (c) 2016-2017 Nobilitas Core Developers
  # Distributed under the MIT software license, see the accompanying
  # file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  # This script will locally construct a merge commit for a pull request on a
  # github repository, inspect it, sign it and optionally push it.
  
  # The following temporary branches are created/overwritten and deleted:
  # * pull/$PULL/base (the current master we're merging onto)
  # * pull/$PULL/head (the current state of the remote pull request)
  # * pull/$PULL/merge (github's merge)
  # * pull/$PULL/local-merge (our merge)
  
  # In case of a clean merge that is accepted by the user, the local branch with
  # name $BRANCH is overwritten with the merged result, and optionally pushed.
  import os
  from sys import stdin,stdout,stderr
  import argparse
  import hashlib
  import subprocess
  import sys
  import json
  import codecs
  from urllib.request import Request, urlopen
  from urllib.error import HTTPError
  
  # External tools (can be overridden using environment)
  GIT = os.getenv('GIT','git')
  BASH = os.getenv('BASH','bash')
  
  # OS specific configuration for terminal attributes
  ATTR_RESET = ''
  ATTR_PR = ''
  COMMIT_FORMAT = '%h %s (%an)%d'
  if os.name == 'posix': # if posix, assume we can use basic terminal escapes
      ATTR_RESET = '\033[0m'
      ATTR_PR = '\033[1;36m'
      COMMIT_FORMAT = '%C(bold blue)%h%Creset %s %C(cyan)(%an)%Creset%C(green)%d%Creset'
  
  def git_config_get(option, default=None):
      '''
      Get named configuration option from git repository.
      '''
      try:
          return subprocess.check_output([GIT,'config','--get',option]).rstrip().decode('utf-8')
      except subprocess.CalledProcessError:
          return default
  
  def get_response(req_url, ghtoken):
      req = Request(req_url)
      if ghtoken is not None:
          req.add_header('Authorization', 'token ' + ghtoken)
      return urlopen(req)
  
  def retrieve_json(req_url, ghtoken, use_pagination=False):
      '''
      Retrieve json from github.
      Return None if an error happens.
      '''
      try:
          reader = codecs.getreader('utf-8')
          if not use_pagination:
              return json.load(reader(get_response(req_url, ghtoken)))
  
          obj = []
          page_num = 1
          while True:
              req_url_page = '{}?page={}'.format(req_url, page_num)
              result = get_response(req_url_page, ghtoken)
              obj.extend(json.load(reader(result)))
  
              link = result.headers.get('link', None)
              if link is not None:
                  link_next = [l for l in link.split(',') if 'rel="next"' in l]
                  if len(link_next) > 0:
                      page_num = int(link_next[0][link_next[0].find("page=")+5:link_next[0].find(">")])
                      continue
              break
          return obj
      except HTTPError as e:
          error_message = e.read()
          print('Warning: unable to retrieve pull information from github: %s' % e)
          print('Detailed error: %s' % error_message)
          return None
      except Exception as e:
          print('Warning: unable to retrieve pull information from github: %s' % e)
          return None
  
  def retrieve_pr_info(repo,pull,ghtoken):
      req_url = "https://api.github.com/repos/"+repo+"/pulls/"+pull
      return retrieve_json(req_url,ghtoken)
  
  def retrieve_pr_comments(repo,pull,ghtoken):
      req_url = "https://api.github.com/repos/"+repo+"/issues/"+pull+"/comments"
      return retrieve_json(req_url,ghtoken,use_pagination=True)
  
  def retrieve_pr_reviews(repo,pull,ghtoken):
      req_url = "https://api.github.com/repos/"+repo+"/pulls/"+pull+"/reviews"
      return retrieve_json(req_url,ghtoken,use_pagination=True)
  
  def ask_prompt(text):
      print(text,end=" ",file=stderr)
      stderr.flush()
      reply = stdin.readline().rstrip()
      print("",file=stderr)
      return reply
  
  def get_symlink_files():
      files = sorted(subprocess.check_output([GIT, 'ls-tree', '--full-tree', '-r', 'HEAD']).splitlines())
      ret = []
      for f in files:
          if (int(f.decode('utf-8').split(" ")[0], 8) & 0o170000) == 0o120000:
              ret.append(f.decode('utf-8').split("\t")[1])
      return ret
  
  def tree_sha512sum(commit='HEAD'):
      # request metadata for entire tree, recursively
      files = []
      blob_by_name = {}
      for line in subprocess.check_output([GIT, 'ls-tree', '--full-tree', '-r', commit]).splitlines():
          name_sep = line.index(b'\t')
          metadata = line[:name_sep].split() # perms, 'blob', blobid
          assert(metadata[1] == b'blob')
          name = line[name_sep+1:]
          files.append(name)
          blob_by_name[name] = metadata[2]
  
      files.sort()
      # open connection to git-cat-file in batch mode to request data for all blobs
      # this is much faster than launching it per file
      p = subprocess.Popen([GIT, 'cat-file', '--batch'], stdout=subprocess.PIPE, stdin=subprocess.PIPE)
      overall = hashlib.sha512()
      for f in files:
          blob = blob_by_name[f]
          # request blob
          p.stdin.write(blob + b'\n')
          p.stdin.flush()
          # read header: blob, "blob", size
          reply = p.stdout.readline().split()
          assert(reply[0] == blob and reply[1] == b'blob')
          size = int(reply[2])
          # hash the blob data
          intern = hashlib.sha512()
          ptr = 0
          while ptr < size:
              bs = min(65536, size - ptr)
              piece = p.stdout.read(bs)
              if len(piece) == bs:
                  intern.update(piece)
              else:
                  raise IOError('Premature EOF reading git cat-file output')
              ptr += bs
          dig = intern.hexdigest()
          assert(p.stdout.read(1) == b'\n') # ignore LF that follows blob data
          # update overall hash with file hash
          overall.update(dig.encode("utf-8"))
          overall.update("  ".encode("utf-8"))
          overall.update(f)
          overall.update("\n".encode("utf-8"))
      p.stdin.close()
      if p.wait():
          raise IOError('Non-zero return value executing git cat-file')
      return overall.hexdigest()
  
  def get_acks_from_comments(head_commit, comments):
      assert len(head_commit) == 6
      ack_str ='\n\nACKs for commit {}:\n'.format(head_commit)
      for c in comments:
          review = [l for l in c['body'].split('\r\n') if 'ACK' in l and head_commit in l]
          if review:
              ack_str += '  {}:\n'.format(c['user']['login'])
              ack_str += '    {}\n'.format(review[0])
      return ack_str
  
  def print_merge_details(pull, title, branch, base_branch, head_branch):
      print('%s#%s%s %s %sinto %s%s' % (ATTR_RESET+ATTR_PR,pull,ATTR_RESET,title,ATTR_RESET+ATTR_PR,branch,ATTR_RESET))
      subprocess.check_call([GIT,'log','--graph','--topo-order','--pretty=format:'+COMMIT_FORMAT,base_branch+'..'+head_branch])
  
  def parse_arguments():
      epilog = '''
          In addition, you can set the following git configuration variables:
          githubmerge.repository (mandatory),
          user.signingkey (mandatory),
          user.ghtoken (default: none).
          githubmerge.host (default: git@github.com),
          githubmerge.branch (no default),
          githubmerge.testcmd (default: none).
      '''
      parser = argparse.ArgumentParser(description='Utility to merge, sign and push github pull requests',
              epilog=epilog)
      parser.add_argument('pull', metavar='PULL', type=int, nargs=1,
          help='Pull request ID to merge')
      parser.add_argument('branch', metavar='BRANCH', type=str, nargs='?',
          default=None, help='Branch to merge against (default: githubmerge.branch setting, or base branch for pull, or \'master\')')
      return parser.parse_args()
  
  def main():
      # Extract settings from git repo
      repo = git_config_get('githubmerge.repository')
      host = git_config_get('githubmerge.host','git@github.com')
      opt_branch = git_config_get('githubmerge.branch',None)
      testcmd = git_config_get('githubmerge.testcmd')
      ghtoken = git_config_get('user.ghtoken')
      signingkey = git_config_get('user.signingkey')
      if repo is None:
          print("ERROR: No repository configured. Use this command to set:", file=stderr)
          print("git config githubmerge.repository <owner>/<repo>", file=stderr)
          sys.exit(1)
      if signingkey is None:
          print("ERROR: No GPG signing key set. Set one using:",file=stderr)
          print("git config --global user.signingkey <key>",file=stderr)
          sys.exit(1)
  
      if host.startswith(('https:','http:')):
          host_repo = host+"/"+repo+".git"
      else:
          host_repo = host+":"+repo
  
      # Extract settings from command line
      args = parse_arguments()
      pull = str(args.pull[0])
  
      # Receive pull information from github
      info = retrieve_pr_info(repo,pull,ghtoken)
      if info is None:
          sys.exit(1)
      comments = retrieve_pr_comments(repo,pull,ghtoken) + retrieve_pr_reviews(repo,pull,ghtoken)
      if comments is None:
          sys.exit(1)
      title = info['title'].strip()
      body = info['body'].strip()
      # precedence order for destination branch argument:
      #   - command line argument
      #   - githubmerge.branch setting
      #   - base branch for pull (as retrieved from github)
      #   - 'master'
      branch = args.branch or opt_branch or info['base']['ref'] or 'master'
  
      # Initialize source branches
      head_branch = 'pull/'+pull+'/head'
      base_branch = 'pull/'+pull+'/base'
      merge_branch = 'pull/'+pull+'/merge'
      local_merge_branch = 'pull/'+pull+'/local-merge'
  
      devnull = open(os.devnull, 'w', encoding="utf8")
      try:
          subprocess.check_call([GIT,'checkout','-q',branch])
      except subprocess.CalledProcessError:
          print("ERROR: Cannot check out branch %s." % (branch), file=stderr)
          sys.exit(3)
      try:
          subprocess.check_call([GIT,'fetch','-q',host_repo,'+refs/pull/'+pull+'/*:refs/heads/pull/'+pull+'/*',
                                                            '+refs/heads/'+branch+':refs/heads/'+base_branch])
      except subprocess.CalledProcessError:
          print("ERROR: Cannot find pull request #%s or branch %s on %s." % (pull,branch,host_repo), file=stderr)
          sys.exit(3)
      try:
          subprocess.check_call([GIT,'log','-q','-1','refs/heads/'+head_branch], stdout=devnull, stderr=stdout)
      except subprocess.CalledProcessError:
          print("ERROR: Cannot find head of pull request #%s on %s." % (pull,host_repo), file=stderr)
          sys.exit(3)
      try:
          subprocess.check_call([GIT,'log','-q','-1','refs/heads/'+merge_branch], stdout=devnull, stderr=stdout)
      except subprocess.CalledProcessError:
          print("ERROR: Cannot find merge of pull request #%s on %s." % (pull,host_repo), file=stderr)
          sys.exit(3)
      subprocess.check_call([GIT,'checkout','-q',base_branch])
      subprocess.call([GIT,'branch','-q','-D',local_merge_branch], stderr=devnull)
      subprocess.check_call([GIT,'checkout','-q','-b',local_merge_branch])
  
      try:
          # Go up to the repository's root.
          toplevel = subprocess.check_output([GIT,'rev-parse','--show-toplevel']).strip()
          os.chdir(toplevel)
          # Create unsigned merge commit.
          if title:
              firstline = 'Merge #%s: %s' % (pull,title)
          else:
              firstline = 'Merge #%s' % (pull,)
          message = firstline + '\n\n'
          message += subprocess.check_output([GIT,'log','--no-merges','--topo-order','--pretty=format:%h %s (%an)',base_branch+'..'+head_branch]).decode('utf-8')
          message += '\n\nPull request description:\n\n  ' + body.replace('\n', '\n  ') + '\n'
          message += get_acks_from_comments(head_commit=subprocess.check_output([GIT,'log','-1','--pretty=format:%H',head_branch]).decode('utf-8')[:6], comments=comments)
          try:
              subprocess.check_call([GIT,'merge','-q','--commit','--no-edit','--no-ff','-m',message.encode('utf-8'),head_branch])
          except subprocess.CalledProcessError:
              print("ERROR: Cannot be merged cleanly.",file=stderr)
              subprocess.check_call([GIT,'merge','--abort'])
              sys.exit(4)
          logmsg = subprocess.check_output([GIT,'log','--pretty=format:%s','-n','1']).decode('utf-8')
          if logmsg.rstrip() != firstline.rstrip():
              print("ERROR: Creating merge failed (already merged?).",file=stderr)
              sys.exit(4)
  
          symlink_files = get_symlink_files()
          for f in symlink_files:
              print("ERROR: File %s was a symlink" % f)
          if len(symlink_files) > 0:
              sys.exit(4)
  
          # Put tree SHA512 into the message
          try:
              first_sha512 = tree_sha512sum()
              message += '\n\nTree-SHA512: ' + first_sha512
          except subprocess.CalledProcessError:
              print("ERROR: Unable to compute tree hash")
              sys.exit(4)
          try:
              subprocess.check_call([GIT,'commit','--amend','-m',message.encode('utf-8')])
          except subprocess.CalledProcessError:
              print("ERROR: Cannot update message.", file=stderr)
              sys.exit(4)
  
          print_merge_details(pull, title, branch, base_branch, head_branch)
          print()
  
          # Run test command if configured.
          if testcmd:
              if subprocess.call(testcmd,shell=True):
                  print("ERROR: Running %s failed." % testcmd,file=stderr)
                  sys.exit(5)
  
              # Show the created merge.
              diff = subprocess.check_output([GIT,'diff',merge_branch+'..'+local_merge_branch])
              subprocess.check_call([GIT,'diff',base_branch+'..'+local_merge_branch])
              if diff:
                  print("WARNING: merge differs from github!",file=stderr)
                  reply = ask_prompt("Type 'ignore' to continue.")
                  if reply.lower() == 'ignore':
                      print("Difference with github ignored.",file=stderr)
                  else:
                      sys.exit(6)
          else:
              # Verify the result manually.
              print("Dropping you on a shell so you can try building/testing the merged source.",file=stderr)
              print("Run 'git diff HEAD~' to show the changes being merged.",file=stderr)
              print("Type 'exit' when done.",file=stderr)
              if os.path.isfile('/etc/debian_version'): # Show pull number on Debian default prompt
                  os.putenv('debian_chroot',pull)
              subprocess.call([BASH,'-i'])
  
          second_sha512 = tree_sha512sum()
          if first_sha512 != second_sha512:
              print("ERROR: Tree hash changed unexpectedly",file=stderr)
              sys.exit(8)
  
          # Sign the merge commit.
          print_merge_details(pull, title, branch, base_branch, head_branch)
          while True:
              reply = ask_prompt("Type 's' to sign off on the above merge, or 'x' to reject and exit.").lower()
              if reply == 's':
                  try:
                      subprocess.check_call([GIT,'commit','-q','--gpg-sign','--amend','--no-edit'])
                      break
                  except subprocess.CalledProcessError:
                      print("Error while signing, asking again.",file=stderr)
              elif reply == 'x':
                  print("Not signing off on merge, exiting.",file=stderr)
                  sys.exit(1)
  
          # Put the result in branch.
          subprocess.check_call([GIT,'checkout','-q',branch])
          subprocess.check_call([GIT,'reset','-q','--hard',local_merge_branch])
      finally:
          # Clean up temporary branches.
          subprocess.call([GIT,'checkout','-q',branch])
          subprocess.call([GIT,'branch','-q','-D',head_branch],stderr=devnull)
          subprocess.call([GIT,'branch','-q','-D',base_branch],stderr=devnull)
          subprocess.call([GIT,'branch','-q','-D',merge_branch],stderr=devnull)
          subprocess.call([GIT,'branch','-q','-D',local_merge_branch],stderr=devnull)
  
      # Push the result.
      while True:
          reply = ask_prompt("Type 'push' to push the result to %s, branch %s, or 'x' to exit without pushing." % (host_repo,branch)).lower()
          if reply == 'push':
              subprocess.check_call([GIT,'push',host_repo,'refs/heads/'+branch])
              break
          elif reply == 'x':
              sys.exit(1)
  
  if __name__ == '__main__':
      main()
  
  