Given a file, this will return all potenial APT source URIs.

def FindPotentialURIs(self, file_obj):
    """Given a file, this will return all potenial APT source URIs."""
    rfc822_format = ""  # will contain all lines not in legacy format
    uris_to_parse = []

    for line in utils.ReadFileBytesAsUnicode(file_obj).splitlines(True):
      # check if legacy style line - if it is then extract URL
      m = re.search(r"^\s*deb(?:-\S+)?(?:\s+\[[^\]]*\])*\s+(\S+)(?:\s|$)", line)
      if m:
        uris_to_parse.append(m.group(1))
      else:
        rfc822_format += line

    uris_to_parse.extend(self.ParseURIFromKeyValues(rfc822_format, ":", "uri"))
    return uris_to_parse