diffs: limit the file context to ~1mln lines. Fixes #4184

Something more than 1mln lines is anyway not usable in web browser.

rhodecode/lib/diffs.py

@@ -1,877 +1,885 b''
 # -*- coding: utf-8 -*-
 
 # Copyright (C) 2011-2016  RhodeCode GmbH
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License, version 3
 # (only), as published by the Free Software Foundation.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 # This program is dual-licensed. If you wish to learn more about the
 # RhodeCode Enterprise Edition, including its added features, Support services,
 # and proprietary license terms, please see https://rhodecode.com/licenses/
 
 
 """
 Set of diffing helpers, previously part of vcs
 """
 
 import collections
 import re
 import difflib
 import logging
 
 from itertools import tee, imap
 
 from pylons.i18n.translation import _
 
 from rhodecode.lib.vcs.exceptions import VCSError
 from rhodecode.lib.vcs.nodes import FileNode, SubModuleNode
 from rhodecode.lib.vcs.backends.base import EmptyCommit
 from rhodecode.lib.helpers import escape
 from rhodecode.lib.utils2 import safe_unicode
 
 log = logging.getLogger(__name__)
 
+# define max context, a file with more than this numbers of lines is unusable
+# in browser anyway
+MAX_CONTEXT = 1024 * 1014
+
 
 class OPS(object):
     ADD = 'A'
     MOD = 'M'
     DEL = 'D'
 
 
 def wrap_to_table(str_):
     return '''<table class="code-difftable">
                 <tr class="line no-comment">
                 <td class="add-comment-line tooltip" title="%s"><span class="add-comment-content"></span></td>
                 <td class="lineno new"></td>
                 <td class="code no-comment"><pre>%s</pre></td>
                 </tr>
               </table>''' % (_('Click to comment'), str_)
 
 
 def wrapped_diff(filenode_old, filenode_new, diff_limit=None, file_limit=None,
                  show_full_diff=False, ignore_whitespace=True, line_context=3,
                  enable_comments=False):
     """
     returns a wrapped diff into a table, checks for cut_off_limit for file and
     whole diff and presents proper message
     """
 
     if filenode_old is None:
         filenode_old = FileNode(filenode_new.path, '', EmptyCommit())
 
     if filenode_old.is_binary or filenode_new.is_binary:
         diff = wrap_to_table(_('Binary file'))
         stats = None
         size = 0
         data = None
 
     elif diff_limit != -1 and (diff_limit is None or
         (filenode_old.size < diff_limit and filenode_new.size < diff_limit)):
 
         f_gitdiff = get_gitdiff(filenode_old, filenode_new,
                                 ignore_whitespace=ignore_whitespace,
                                 context=line_context)
         diff_processor = DiffProcessor(
             f_gitdiff, format='gitdiff', diff_limit=diff_limit,
             file_limit=file_limit, show_full_diff=show_full_diff)
         _parsed = diff_processor.prepare()
 
         diff = diff_processor.as_html(enable_comments=enable_comments)
         stats = _parsed[0]['stats'] if _parsed else None
         size = len(diff or '')
         data = _parsed[0] if _parsed else None
     else:
         diff = wrap_to_table(_('Changeset was too big and was cut off, use '
                                'diff menu to display this diff'))
         stats = None
         size = 0
         data = None
     if not diff:
         submodules = filter(lambda o: isinstance(o, SubModuleNode),
                             [filenode_new, filenode_old])
         if submodules:
             diff = wrap_to_table(escape('Submodule %r' % submodules[0]))
         else:
             diff = wrap_to_table(_('No changes detected'))
 
     cs1 = filenode_old.commit.raw_id
     cs2 = filenode_new.commit.raw_id
 
     return size, cs1, cs2, diff, stats, data
 
 
 def get_gitdiff(filenode_old, filenode_new, ignore_whitespace=True, context=3):
     """
     Returns git style diff between given ``filenode_old`` and ``filenode_new``.
 
     :param ignore_whitespace: ignore whitespaces in diff
     """
     # make sure we pass in default context
     context = context or 3
+    # protect against IntOverflow when passing HUGE context
+    if context > MAX_CONTEXT:
+        context = MAX_CONTEXT
+
     submodules = filter(lambda o: isinstance(o, SubModuleNode),
                         [filenode_new, filenode_old])
     if submodules:
         return ''
 
     for filenode in (filenode_old, filenode_new):
         if not isinstance(filenode, FileNode):
             raise VCSError(
                 "Given object should be FileNode object, not %s"
                 % filenode.__class__)
 
     repo = filenode_new.commit.repository
     old_commit = filenode_old.commit or repo.EMPTY_COMMIT
     new_commit = filenode_new.commit
 
     vcs_gitdiff = repo.get_diff(
         old_commit, new_commit, filenode_new.path,
         ignore_whitespace, context, path1=filenode_old.path)
     return vcs_gitdiff
 
 NEW_FILENODE = 1
 DEL_FILENODE = 2
 MOD_FILENODE = 3
 RENAMED_FILENODE = 4
 COPIED_FILENODE = 5
 CHMOD_FILENODE = 6
 BIN_FILENODE = 7
 
 
 class LimitedDiffContainer(object):
 
     def __init__(self, diff_limit, cur_diff_size, diff):
         self.diff = diff
         self.diff_limit = diff_limit
         self.cur_diff_size = cur_diff_size
 
     def __getitem__(self, key):
         return self.diff.__getitem__(key)
 
     def __iter__(self):
         for l in self.diff:
             yield l
 
 
 class Action(object):
     """
     Contains constants for the action value of the lines in a parsed diff.
     """
 
     ADD = 'add'
     DELETE = 'del'
     UNMODIFIED = 'unmod'
 
     CONTEXT = 'context'
 
 
 class DiffProcessor(object):
     """
     Give it a unified or git diff and it returns a list of the files that were
     mentioned in the diff together with a dict of meta information that
     can be used to render it in a HTML template.
 
     .. note:: Unicode handling
 
        The original diffs are a byte sequence and can contain filenames
        in mixed encodings. This class generally returns `unicode` objects
        since the result is intended for presentation to the user.
 
     """
     _chunk_re = re.compile(r'^@@ -(\d+)(?:,(\d+))? \+(\d+)(?:,(\d+))? @@(.*)')
     _newline_marker = re.compile(r'^\\ No newline at end of file')
 
     # used for inline highlighter word split
     _token_re = re.compile(r'()(&gt;|&lt;|&amp;|\W+?)')
 
     def __init__(self, diff, format='gitdiff', diff_limit=None,
                  file_limit=None, show_full_diff=True):
         """
         :param diff: A `Diff` object representing a diff from a vcs backend
         :param format: format of diff passed, `udiff` or `gitdiff`
         :param diff_limit: define the size of diff that is considered "big"
             based on that parameter cut off will be triggered, set to None
             to show full diff
         """
         self._diff = diff
         self._format = format
         self.adds = 0
         self.removes = 0
         # calculate diff size
         self.diff_limit = diff_limit
         self.file_limit = file_limit
         self.show_full_diff = show_full_diff
         self.cur_diff_size = 0
         self.parsed = False
         self.parsed_diff = []
 
         if format == 'gitdiff':
             self.differ = self._highlight_line_difflib
             self._parser = self._parse_gitdiff
         else:
             self.differ = self._highlight_line_udiff
             self._parser = self._parse_udiff
 
     def _copy_iterator(self):
         """
         make a fresh copy of generator, we should not iterate thru
         an original as it's needed for repeating operations on
         this instance of DiffProcessor
         """
         self.__udiff, iterator_copy = tee(self.__udiff)
         return iterator_copy
 
     def _escaper(self, string):
         """
         Escaper for diff escapes special chars and checks the diff limit
 
         :param string:
         """
 
         self.cur_diff_size += len(string)
 
         if not self.show_full_diff and (self.cur_diff_size > self.diff_limit):
             raise DiffLimitExceeded('Diff Limit Exceeded')
 
         return safe_unicode(string)\
             .replace('&', '&amp;')\
             .replace('<', '&lt;')\
             .replace('>', '&gt;')
 
     def _line_counter(self, l):
         """
         Checks each line and bumps total adds/removes for this diff
 
         :param l:
         """
         if l.startswith('+') and not l.startswith('+++'):
             self.adds += 1
         elif l.startswith('-') and not l.startswith('---'):
             self.removes += 1
         return safe_unicode(l)
 
     def _highlight_line_difflib(self, line, next_):
         """
         Highlight inline changes in both lines.
         """
 
         if line['action'] == Action.DELETE:
             old, new = line, next_
         else:
             old, new = next_, line
 
         oldwords = self._token_re.split(old['line'])
         newwords = self._token_re.split(new['line'])
         sequence = difflib.SequenceMatcher(None, oldwords, newwords)
 
         oldfragments, newfragments = [], []
         for tag, i1, i2, j1, j2 in sequence.get_opcodes():
             oldfrag = ''.join(oldwords[i1:i2])
             newfrag = ''.join(newwords[j1:j2])
             if tag != 'equal':
                 if oldfrag:
                     oldfrag = '<del>%s</del>' % oldfrag
                 if newfrag:
                     newfrag = '<ins>%s</ins>' % newfrag
             oldfragments.append(oldfrag)
             newfragments.append(newfrag)
 
         old['line'] = "".join(oldfragments)
         new['line'] = "".join(newfragments)
 
     def _highlight_line_udiff(self, line, next_):
         """
         Highlight inline changes in both lines.
         """
         start = 0
         limit = min(len(line['line']), len(next_['line']))
         while start < limit and line['line'][start] == next_['line'][start]:
             start += 1
         end = -1
         limit -= start
         while -end <= limit and line['line'][end] == next_['line'][end]:
             end -= 1
         end += 1
         if start or end:
             def do(l):
                 last = end + len(l['line'])
                 if l['action'] == Action.ADD:
                     tag = 'ins'
                 else:
                     tag = 'del'
                 l['line'] = '%s<%s>%s</%s>%s' % (
                     l['line'][:start],
                     tag,
                     l['line'][start:last],
                     tag,
                     l['line'][last:]
                 )
             do(line)
             do(next_)
 
     def _clean_line(self, line, command):
         if command in ['+', '-', ' ']:
             # only modify the line if it's actually a diff thing
             line = line[1:]
         return line
 
     def _parse_gitdiff(self, inline_diff=True):
         _files = []
         diff_container = lambda arg: arg
 
         for chunk in self._diff.chunks():
             head = chunk.header
 
             diff = imap(self._escaper, chunk.diff.splitlines(1))
             raw_diff = chunk.raw
             limited_diff = False
             exceeds_limit = False
 
             op = None
             stats = {
                 'added': 0,
                 'deleted': 0,
                 'binary': False,
                 'ops': {},
             }
 
             if head['deleted_file_mode']:
                 op = OPS.DEL
                 stats['binary'] = True
                 stats['ops'][DEL_FILENODE] = 'deleted file'
 
             elif head['new_file_mode']:
                 op = OPS.ADD
                 stats['binary'] = True
                 stats['ops'][NEW_FILENODE] = 'new file %s' % head['new_file_mode']
             else:  # modify operation, can be copy, rename or chmod
 
                 # CHMOD
                 if head['new_mode'] and head['old_mode']:
                     op = OPS.MOD
                     stats['binary'] = True
                     stats['ops'][CHMOD_FILENODE] = (
                         'modified file chmod %s => %s' % (
                             head['old_mode'], head['new_mode']))
                 # RENAME
                 if head['rename_from'] != head['rename_to']:
                     op = OPS.MOD
                     stats['binary'] = True
                     stats['ops'][RENAMED_FILENODE] = (
                         'file renamed from %s to %s' % (
                             head['rename_from'], head['rename_to']))
                 # COPY
                 if head.get('copy_from') and head.get('copy_to'):
                     op = OPS.MOD
                     stats['binary'] = True
                     stats['ops'][COPIED_FILENODE] = (
                         'file copied from %s to %s' % (
                             head['copy_from'], head['copy_to']))
 
                 # If our new parsed headers didn't match anything fallback to
                 # old style detection
                 if op is None:
                     if not head['a_file'] and head['b_file']:
                         op = OPS.ADD
                         stats['binary'] = True
                         stats['ops'][NEW_FILENODE] = 'new file'
 
                     elif head['a_file'] and not head['b_file']:
                         op = OPS.DEL
                         stats['binary'] = True
                         stats['ops'][DEL_FILENODE] = 'deleted file'
 
                 # it's not ADD not DELETE
                 if op is None:
                     op = OPS.MOD
                     stats['binary'] = True
                     stats['ops'][MOD_FILENODE] = 'modified file'
 
             # a real non-binary diff
             if head['a_file'] or head['b_file']:
                 try:
                     raw_diff, chunks, _stats = self._parse_lines(diff)
                     stats['binary'] = False
                     stats['added'] = _stats[0]
                     stats['deleted'] = _stats[1]
                     # explicit mark that it's a modified file
                     if op == OPS.MOD:
                         stats['ops'][MOD_FILENODE] = 'modified file'
                     exceeds_limit = len(raw_diff) > self.file_limit
 
                     # changed from _escaper function so we validate size of
                     # each file instead of the whole diff
                     # diff will hide big files but still show small ones
                     # from my tests, big files are fairly safe to be parsed
                     # but the browser is the bottleneck
                     if not self.show_full_diff and exceeds_limit:
                         raise DiffLimitExceeded('File Limit Exceeded')
 
                 except DiffLimitExceeded:
                     diff_container = lambda _diff: \
                         LimitedDiffContainer(
                             self.diff_limit, self.cur_diff_size, _diff)
 
                     exceeds_limit = len(raw_diff) > self.file_limit
                     limited_diff = True
                     chunks = []
 
             else:  # GIT format binary patch, or possibly empty diff
                 if head['bin_patch']:
                     # we have operation already extracted, but we mark simply
                     # it's a diff we wont show for binary files
                     stats['ops'][BIN_FILENODE] = 'binary diff hidden'
                 chunks = []
 
             if chunks and not self.show_full_diff and op == OPS.DEL:
                 # if not full diff mode show deleted file contents
                 # TODO: anderson: if the view is not too big, there is no way
                 # to see the content of the file
                 chunks = []
 
             chunks.insert(0, [{
                                   'old_lineno': '',
                                   'new_lineno': '',
                                   'action': Action.CONTEXT,
                                   'line': msg,
                               } for _op, msg in stats['ops'].iteritems()
                               if _op not in [MOD_FILENODE]])
 
             _files.append({
                 'filename': safe_unicode(head['b_path']),
                 'old_revision': head['a_blob_id'],
                 'new_revision': head['b_blob_id'],
                 'chunks': chunks,
                 'raw_diff': safe_unicode(raw_diff),
                 'operation': op,
                 'stats': stats,
                 'exceeds_limit': exceeds_limit,
                 'is_limited_diff': limited_diff,
             })
 
         sorter = lambda info: {OPS.ADD: 0, OPS.MOD: 1,
                                OPS.DEL: 2}.get(info['operation'])
 
         if not inline_diff:
             return diff_container(sorted(_files, key=sorter))
 
         # highlight inline changes
         for diff_data in _files:
             for chunk in diff_data['chunks']:
                 lineiter = iter(chunk)
                 try:
                     while 1:
                         line = lineiter.next()
                         if line['action'] not in (
                                 Action.UNMODIFIED, Action.CONTEXT):
                             nextline = lineiter.next()
                             if nextline['action'] in ['unmod', 'context'] or \
                                nextline['action'] == line['action']:
                                 continue
                             self.differ(line, nextline)
                 except StopIteration:
                     pass
 
         return diff_container(sorted(_files, key=sorter))
 
     def _parse_udiff(self, inline_diff=True):
         raise NotImplementedError()
 
     def _parse_lines(self, diff):
         """
         Parse the diff an return data for the template.
         """
 
         lineiter = iter(diff)
         stats = [0, 0]
         chunks = []
         raw_diff = []
 
         try:
             line = lineiter.next()
 
             while line:
                 raw_diff.append(line)
                 lines = []
                 chunks.append(lines)
 
                 match = self._chunk_re.match(line)
 
                 if not match:
                     break
 
                 gr = match.groups()
                 (old_line, old_end,
                  new_line, new_end) = [int(x or 1) for x in gr[:-1]]
                 old_line -= 1
                 new_line -= 1
 
                 context = len(gr) == 5
                 old_end += old_line
                 new_end += new_line
 
                 if context:
                     # skip context only if it's first line
                     if int(gr[0]) > 1:
                         lines.append({
                             'old_lineno': '...',
                             'new_lineno': '...',
                             'action':     Action.CONTEXT,
                             'line':       line,
                         })
 
                 line = lineiter.next()
 
                 while old_line < old_end or new_line < new_end:
                     command = ' '
                     if line:
                         command = line[0]
 
                     affects_old = affects_new = False
 
                     # ignore those if we don't expect them
                     if command in '#@':
                         continue
                     elif command == '+':
                         affects_new = True
                         action = Action.ADD
                         stats[0] += 1
                     elif command == '-':
                         affects_old = True
                         action = Action.DELETE
                         stats[1] += 1
                     else:
                         affects_old = affects_new = True
                         action = Action.UNMODIFIED
 
                     if not self._newline_marker.match(line):
                         old_line += affects_old
                         new_line += affects_new
                         lines.append({
                             'old_lineno':   affects_old and old_line or '',
                             'new_lineno':   affects_new and new_line or '',
                             'action':       action,
                             'line':         self._clean_line(line, command)
                         })
                         raw_diff.append(line)
 
                     line = lineiter.next()
 
                     if self._newline_marker.match(line):
                         # we need to append to lines, since this is not
                         # counted in the line specs of diff
                         lines.append({
                             'old_lineno':   '...',
                             'new_lineno':   '...',
                             'action':       Action.CONTEXT,
                             'line':         self._clean_line(line, command)
                         })
 
         except StopIteration:
             pass
         return ''.join(raw_diff), chunks, stats
 
     def _safe_id(self, idstring):
         """Make a string safe for including in an id attribute.
 
         The HTML spec says that id attributes 'must begin with
         a letter ([A-Za-z]) and may be followed by any number
         of letters, digits ([0-9]), hyphens ("-"), underscores
         ("_"), colons (":"), and periods (".")'. These regexps
         are slightly over-zealous, in that they remove colons
         and periods unnecessarily.
 
         Whitespace is transformed into underscores, and then
         anything which is not a hyphen or a character that
         matches \w (alphanumerics and underscore) is removed.
 
         """
         # Transform all whitespace to underscore
         idstring = re.sub(r'\s', "_", '%s' % idstring)
         # Remove everything that is not a hyphen or a member of \w
         idstring = re.sub(r'(?!-)\W', "", idstring).lower()
         return idstring
 
     def prepare(self, inline_diff=True):
         """
         Prepare the passed udiff for HTML rendering.
 
         :return: A list of dicts with diff information.
         """
         parsed = self._parser(inline_diff=inline_diff)
         self.parsed = True
         self.parsed_diff = parsed
         return parsed
 
     def as_raw(self, diff_lines=None):
         """
         Returns raw diff as a byte string
         """
         return self._diff.raw
 
     def as_html(self, table_class='code-difftable', line_class='line',
                 old_lineno_class='lineno old', new_lineno_class='lineno new',
                 code_class='code', enable_comments=False, parsed_lines=None):
         """
         Return given diff as html table with customized css classes
         """
         def _link_to_if(condition, label, url):
             """
             Generates a link if condition is meet or just the label if not.
             """
 
             if condition:
                 return '''<a href="%(url)s" class="tooltip"
                 title="%(title)s">%(label)s</a>''' % {
                     'title': _('Click to select line'),
                     'url': url,
                     'label': label
                 }
             else:
                 return label
         if not self.parsed:
             self.prepare()
 
         diff_lines = self.parsed_diff
         if parsed_lines:
             diff_lines = parsed_lines
 
         _html_empty = True
         _html = []
         _html.append('''<table class="%(table_class)s">\n''' % {
             'table_class': table_class
         })
 
         for diff in diff_lines:
             for line in diff['chunks']:
                 _html_empty = False
                 for change in line:
                     _html.append('''<tr class="%(lc)s %(action)s">\n''' % {
                         'lc': line_class,
                         'action': change['action']
                     })
                     anchor_old_id = ''
                     anchor_new_id = ''
                     anchor_old = "%(filename)s_o%(oldline_no)s" % {
                         'filename': self._safe_id(diff['filename']),
                         'oldline_no': change['old_lineno']
                     }
                     anchor_new = "%(filename)s_n%(oldline_no)s" % {
                         'filename': self._safe_id(diff['filename']),
                         'oldline_no': change['new_lineno']
                     }
                     cond_old = (change['old_lineno'] != '...' and
                                 change['old_lineno'])
                     cond_new = (change['new_lineno'] != '...' and
                                 change['new_lineno'])
                     if cond_old:
                         anchor_old_id = 'id="%s"' % anchor_old
                     if cond_new:
                         anchor_new_id = 'id="%s"' % anchor_new
 
                     if change['action'] != Action.CONTEXT:
                         anchor_link = True
                     else:
                         anchor_link = False
 
                     ###########################################################
                     # COMMENT ICON
                     ###########################################################
                     _html.append('''\t<td class="add-comment-line"><span class="add-comment-content">''')
 
                     if enable_comments and change['action'] != Action.CONTEXT:
                         _html.append('''<a href="#"><span class="icon-comment-add"></span></a>''')
 
                     _html.append('''</span></td>\n''')
 
                     ###########################################################
                     # OLD LINE NUMBER
                     ###########################################################
                     _html.append('''\t<td %(a_id)s class="%(olc)s">''' % {
                         'a_id': anchor_old_id,
                         'olc': old_lineno_class
                     })
 
                     _html.append('''%(link)s''' % {
                         'link': _link_to_if(anchor_link, change['old_lineno'],
                                             '#%s' % anchor_old)
                     })
                     _html.append('''</td>\n''')
                     ###########################################################
                     # NEW LINE NUMBER
                     ###########################################################
 
                     _html.append('''\t<td %(a_id)s class="%(nlc)s">''' % {
                         'a_id': anchor_new_id,
                         'nlc': new_lineno_class
                     })
 
                     _html.append('''%(link)s''' % {
                         'link': _link_to_if(anchor_link, change['new_lineno'],
                                             '#%s' % anchor_new)
                     })
                     _html.append('''</td>\n''')
                     ###########################################################
                     # CODE
                     ###########################################################
                     code_classes = [code_class]
                     if (not enable_comments or
                             change['action'] == Action.CONTEXT):
                         code_classes.append('no-comment')
                     _html.append('\t<td class="%s">' % ' '.join(code_classes))
                     _html.append('''\n\t\t<pre>%(code)s</pre>\n''' % {
                         'code': change['line']
                     })
 
                     _html.append('''\t</td>''')
                     _html.append('''\n</tr>\n''')
         _html.append('''</table>''')
         if _html_empty:
             return None
         return ''.join(_html)
 
     def stat(self):
         """
         Returns tuple of added, and removed lines for this instance
         """
         return self.adds, self.removes
 
     def get_context_of_line(
             self, path, diff_line=None, context_before=3, context_after=3):
         """
         Returns the context lines for the specified diff line.
 
         :type diff_line: :class:`DiffLineNumber`
         """
         assert self.parsed, "DiffProcessor is not initialized."
 
         if None not in diff_line:
             raise ValueError(
                 "Cannot specify both line numbers: {}".format(diff_line))
 
         file_diff = self._get_file_diff(path)
         chunk, idx = self._find_chunk_line_index(file_diff, diff_line)
 
         first_line_to_include = max(idx - context_before, 0)
         first_line_after_context = idx + context_after + 1
         context_lines = chunk[first_line_to_include:first_line_after_context]
 
         line_contents = [
             _context_line(line) for line in context_lines
             if _is_diff_content(line)]
         # TODO: johbo: Interim fixup, the diff chunks drop the final newline.
         # Once they are fixed, we can drop this line here.
         if line_contents:
             line_contents[-1] = (
                 line_contents[-1][0], line_contents[-1][1].rstrip('\n') + '\n')
         return line_contents
 
     def find_context(self, path, context, offset=0):
         """
         Finds the given `context` inside of the diff.
 
         Use the parameter `offset` to specify which offset the target line has
         inside of the given `context`. This way the correct diff line will be
         returned.
 
         :param offset: Shall be used to specify the offset of the main line
             within the given `context`.
         """
         if offset < 0 or offset >= len(context):
             raise ValueError(
                 "Only positive values up to the length of the context "
                 "minus one are allowed.")
 
         matches = []
         file_diff = self._get_file_diff(path)
 
         for chunk in file_diff['chunks']:
             context_iter = iter(context)
             for line_idx, line in enumerate(chunk):
                 try:
                     if _context_line(line) == context_iter.next():
                         continue
                 except StopIteration:
                     matches.append((line_idx, chunk))
                 context_iter = iter(context)
 
         # Increment position and triger StopIteration
         # if we had a match at the end
         line_idx += 1
         try:
             context_iter.next()
         except StopIteration:
             matches.append((line_idx, chunk))
 
         effective_offset = len(context) - offset
         found_at_diff_lines = [
             _line_to_diff_line_number(chunk[idx - effective_offset])
             for idx, chunk in matches]
 
         return found_at_diff_lines
 
     def _get_file_diff(self, path):
         for file_diff in self.parsed_diff:
             if file_diff['filename'] == path:
                 break
         else:
             raise FileNotInDiffException("File {} not in diff".format(path))
         return file_diff
 
     def _find_chunk_line_index(self, file_diff, diff_line):
         for chunk in file_diff['chunks']:
             for idx, line in enumerate(chunk):
                 if line['old_lineno'] == diff_line.old:
                     return chunk, idx
                 if line['new_lineno'] == diff_line.new:
                     return chunk, idx
         raise LineNotInDiffException(
             "The line {} is not part of the diff.".format(diff_line))
 
 
 def _is_diff_content(line):
     return line['action'] in (
         Action.UNMODIFIED, Action.ADD, Action.DELETE)
 
 
 def _context_line(line):
     return (line['action'], line['line'])
 
 
 DiffLineNumber = collections.namedtuple('DiffLineNumber', ['old', 'new'])
 
 
 def _line_to_diff_line_number(line):
     new_line_no = line['new_lineno'] or None
     old_line_no = line['old_lineno'] or None
     return DiffLineNumber(old=old_line_no, new=new_line_no)
 
 
 class FileNotInDiffException(Exception):
     """
     Raised when the context for a missing file is requested.
 
     If you request the context for a line in a file which is not part of the
     given diff, then this exception is raised.
     """
 
 
 class LineNotInDiffException(Exception):
     """
     Raised when the context for a missing line is requested.
 
     If you request the context for a line in a file and this line is not
     part of the given diff, then this exception is raised.
     """
 
 
 class DiffLimitExceeded(Exception):
     pass