system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
#!/usr/bin/python3
# -*- coding: utf-8 -*-

import os
import json
from datetime import datetime
import yaml
from yaml import SafeLoader, BaseLoader
from jinja2 import Template, Environment, FileSystemLoader
from tag_ontology import *
from util import *
import sys
import logging

class AbsolutePathException(Exception):
    pass

class DirectoryException(Exception):
    pass

class Filepath(object):
    '''
    Represents a single filepath of a file relative to the current
    directory.
    '''
    def __init__(self, path):
        if type(path) is Filepath:
            self.path = path.path
        else:
            path = path.strip()
            if path[-1] in ["/"]:
                raise DirectoryException(
                    "path is a directory; must be a file"
                )
            self.path = path

    def __repr__(self):
        return self.path

    def filename(self):
        '''
        Return the base filename.

        >>> Filepath("pages/programming/hello.md").filename()
        'hello.md'
        '''
        return os.path.split(self.path)[1]

    def directory(self):
        '''
        Return the relative directory name.

        >>> Filepath("pages/programming/hello.md").directory()
        'pages/programming/'
        '''
        return os.path.split(self.path)[0] + "/"

    def path_lst(self):
        '''
        Return a list of the individual components of the filepath.

        >>> Filepath("pages/programming/hello.md").path_lst()
        ['pages', 'programming', 'hello.md']
        '''
        return split_path(self.path)

    def route_with(self, route):
        return route(self)

    def relative_to(self, other):
        '''
        >>> fp1 = Filepath("tags/python")
        >>> fp2 = Filepath("pages/programming/hello.md")
        >>> print(fp1.relative_to(fp2))
        ../../tags/python
        '''
        path1 = os.path.normpath(self.path)
        path2 = os.path.normpath(other.path)
        depth = len(Filepath(path2).path_lst()) - 1
        return Filepath("../" * depth + path1)

    def to_item(self):
        with open(self.path, 'r') as f:
            return Item(self, f.read())

class Route(object):
    '''
    Represents a route (Filepath -> Filepath)
    '''
    def __init__(self, route):
        self.route = route

    def __call__(self, filepath):
        if type(filepath) is not Filepath:
            raise TypeError("input is not a filepath")
        result = self.route(filepath)
        if type(result) is not Filepath:
            raise TypeError(
                "output is not a filepath; " +
                "this route object is an invalid route"
            )
        return result

class Tag(object):
    '''
    Represents a tag
    '''
    def __init__(self, name, pages=[]):
        self.name = name
        self.pages = pages

    def __repr__(self):
        return self.name

    def __eq__(self, other):
        return (slug(self.name) == slug(other.name))

class TagList(object):
    def __init__(self, data=[]):
        self.data = data

    def __repr__(self):
        return self.data.__repr__()

    def standardize_using(self, tag_synonyms):
        '''
        Take a dictionary of tag synonyms  and update the TagList
        instance's list of tags according to the synonyms.  For
        instance, if tag_synonyms contains the line
            "university-of-washington": ["uw", "uwashington"],
        and if tags contains "uw" or "uwashington", then this will be
        replaced by "university-of-washington".
        '''
        result = []
        for tag in self.data:
            canonical = []
            for key, value in tag_synonyms.items():
                slug_value = [slug(i) for i in value]
                if slug(tag) == slug(key) or slug(tag) in slug_value:
                    canonical.append(key)
            if not canonical:
                # So could not find a match in tag_synonyms
                canonical = [tag]
            result.extend(canonical)
        self.data = result

    def imply_using(self, tag_implications):
        '''
        Take an OrderedDict of tag implications and  update the TagList
        instance's list of tags with the implications applied.  Apply
        this after standardizing tags.
        '''
        for key in tag_implications:
            if key.lower() in self.data or key in self.data:
                self.data.extend(tag_implications.get(key))
        self.data = list(set(self.data))

    def organize_using(self, tag_synonyms, tag_implications):
        self.standardize_using(tag_synonyms)
        self.imply_using(tag_implications)

def process_metadata(metadata, **kwargs):
    '''
    Take a dict and optional keywords, and return a sane dict for use as
    metadata to a page.  The input dict is unmodified.
    '''
    metadata = dict(metadata)
    # Combine kwargs; kwargs overrides
    metadata.update(kwargs)
    aliases = []
    if "aliases" in metadata:
        metadata["aliases"] = list(map(slug,
            parse_as_list(metadata["aliases"])))
    else:
        metadata["aliases"] = []
    if "author" not in metadata:
        metadata["author"] = []
    #if "belief" in metadata:
        #if metadata["belief"] in ["possible", "unlikely",
            #"very unlikely", "remote", "impossible", "emotional"]:
            #metadata["belief"] = "log"
    if "feed_description" not in metadata:
        metadata["feed_description"] = ""
    if "language" not in metadata:
        metadata["language"] = "English"
    license = "UNKNOWN"
    if "license" in metadata:
        license = metadata['license']
        # Clean up license string
        for char in ' -':
            license = license.replace(char, '')
        license = license.upper()
        if license in ["CC0", "PUBLICDOMAIN", "PD"]:
            license = "CC0"
        elif license in ["CCBY", "BY", "ATTRIBUTION"]:
            license = "CC-BY"
        elif license in ["CCBYSA", "CCSA", "SHAREALIKE"]:
            license = "CC-BY-SA"
        else:
            # Set default license to unknown (i.e., copyrighted)
            license = "UNKNOWN"
    metadata['license'] = license
    # Change possible bool to str
    metadata["math"] = str(metadata['math']) if "math" in metadata\
        else "False"
    #if "status" in metadata:
        #status = metadata["status"]
        #if status in ["notes", "draft", "in progress"]:
            #status = "draft"
        #else:
            #status = "finished"
        #metadata["status"] = status
    tags = ["untagged"]
    if "tags" in metadata:
        tag_list = TagList(parse_as_list(metadata['tags']))
        tag_list.organize_using(TAG_SYNONYMS, TAG_IMPLICATIONS)
        tags = tag_list.data
    metadata['tags'] = tags
    if "title" not in metadata:
        metadata["title"] = ""
    return metadata

class Page(object):
    """
    Represents a page.
    """
    def __init__(self, origin=None, metadata={}):
        """
        Initialize Page object.

        Args:
            origin: A string containing the location of the source file for the
                page. This is converted to a Filepath object for better routing.
            metadata: A dictionary containing the metadata for the page. This is
                most likely a dictionary produced from a YAML header. Each
                key-value pair can then be used in templates when producing the
                page.
        """
        self.origin = Filepath(origin)
        self.metadata = metadata

    @classmethod
    def from_filename(cls, filename):
        with open(filename, "r") as f:
            meta_str = ""
            initial = f.readline()
            # Check if file starts with valid YAML delimiter
            if initial == '---\n':
                curr = f.readline()
                while curr not in ['---\n', '...\n', '']:
                    meta_str += curr
                    curr = f.readline()
        meta_dict = yaml.load(meta_str, Loader=BaseLoader)
        return cls(origin=filename, metadata=meta_dict)

    pandoc_options = ("-f json -t html --toc --toc-depth=4 " +
            # FIXME make sure this exists somehow
            #"--template=templates/toc.html " +
            "--smart --mathjax " +
            "--base-header-level=2 --filter ./url_filter.py")

    def pandoc_compiled(self, options=pandoc_options):
        """
        Compile page with Pandoc and return the string of the output.

        Args:
            options: A string containing Pandoc flags for use in compiling the
                page.

        Returns:
            A string containing the output given by Pandoc.
        """
        command = "pandoc --smart -f markdown -t json " + self.origin.path
        # Parse to JSON first
        proc_parse = subprocess.Popen(shlex.split(command),
            stdout=subprocess.PIPE)
        stdout, _ = proc_parse.communicate()
        ast = json.dumps(json.loads(str(stdout, encoding="utf-8")),
            separators=(",",":"))
        # Now compile to HTML
        command = "pandoc " + options
        proc_html = subprocess.Popen(shlex.split(command),
            stdout=subprocess.PIPE, stdin=subprocess.PIPE)
        stdout, _ = proc_html.communicate(input=bytes(ast, 'utf-8'))
        return str(stdout, encoding="utf-8")


    def compiled(self, tags_dir, permalink=""):
        """
        Compile page all the way and return the string of the output.
        """
        env = Environment(loader=FileSystemLoader("."))
        skeleton = env.get_template("templates/skeleton.html")
        # Make tags list
        tags = []
        for tag in metadata["tags"]:
            path = Filepath(slug(tag)).route_with(to_dir(tags_dir)).path
            tags.append({"name": tag, "path": path})
        tags.sort(key=lambda t: t["name"].lower())
        final = skeleton.render(body=self.pandoc_compiled(), page=self.metadata,
            tags=tags, source=self.origin.path,
            base=self.origin.route_with(set_extension("")).route_with(
                drop_one_parent_dir_route
            ), path="./")
        return final

    def base(self):
        return self.origin.route_with(set_extension("")).route_with(
            drop_one_parent_dir_route).path

    def __repr__(self):
        return "Page({})".format(self.origin.path.__repr__())

    def revision_date(self, fmt=None):
        '''
        Return the last major revision date of the page. Takes format
        fmt, which accepts None (return as object), "rfc822" (RSS 2.0),
        "rfc3339" (Atom), or any valid strftime format. Return None if
        no last major revision date is set.
        '''
        rev_date = self.metadata.get('last_major_revision_date', '')
        if rev_date:
            date_obj = datetime.strptime(rev_date, '%Y-%m-%d')
            return get_date(date_obj, fmt=fmt)

class PageOld(object):
    '''
    Represents a page.  Typical pages are initialized with just an
    origin, and the metadata is read from the file, and the destination
    is computed using routes.  On the other hand, special pages (i.e.
    those that are generated by the program, like the page of all tags)
    are initialized with metadata, data, and a destination.
    '''
    def __init__(self, origin=None, metadata={}, data=None,
        destination=None):
        if origin is not None:
            self.origin = Filepath(origin)
        self.metadata = process_metadata(metadata)
        self.data = data
        self.destination = destination

    def load_metadata(self):
        with open(self.origin.path, 'r') as f:
            metadata = ""
            first = f.readline()
            if first == '---\n':
                then = f.readline()
                while then not in ['---\n', '...\n', '']:
                    metadata += then
                    then = f.readline()
            self.metadata = process_metadata(yaml.load(metadata,
                Loader=BaseLoader))

    def write(self):
        if self.destination is None:
            print("No destination is set; cannot write to file.", file=sys.stderr)
        else:
            directory = Filepath(self.destination).directory()
            if not os.path.exists(directory):
                os.makedirs(directory)
            with open(self.destination, "w", encoding="utf-8") as f:
                f.write(self.data)

    def pandoc_compiled(self):
        '''
        Compile page with Pandoc and return the string of the output.
        '''
        output = run_command(
            "pandoc --smart -f markdown -t json {page}".format(
            page=self.origin.path))
        ast = json.loads(output)
        return to_unicode(
            run_command(
                "pandoc -f json -t html --toc --toc-depth=4 " +
                "--template=templates/toc.html --smart --mathjax " +
                "--base-header-level=2 --filter generator/url_filter.py",
                pipe_in=json.dumps(ast, separators=(',',':'))
            )
        )

    def compiled(self, tags_dir, commit_ps=""):
        '''
        Compile page all the way and return the string of the output.
        '''
        if not self.metadata:
            self.load_metadata()
        if "description" in self.metadata:
            self.metadata["description"] = escape(self.metadata["description"])
        env = Environment(loader=FileSystemLoader('.'))
        if self.metadata['language'].lower() in [u"ja", u"japanese",
            u"にほんご", u"日本語"]:
            skeleton = env.get_template('templates/ja/skeleton.html')
        else:
            skeleton = env.get_template('templates/skeleton.html')
        self.metadata["commit_ps"] = commit_ps
        final = skeleton.render(
            body = self.pandoc_compiled(),
            # In templates, we use page.field to access metadata fields
            page = self.metadata,
            tags = sorted(
                [
                    {
                        'name': tag,
                        'path': to_unicode(
                            Filepath(to_string(slug(tag))).\
                            route_with(to_dir(tags_dir)).path,
                        ),
                    }
                    for tag in self.metadata["tags"]
                ],
                key = lambda t: t['name'].lower(),
            ),
            source = to_unicode(self.origin.path),
            base=self.origin.route_with(set_extension("")).route_with(drop_one_parent_dir_route),
            path = "./",
        )
        return final

    def base(self):
        return self.origin.route_with(set_extension("")).route_with(
            drop_one_parent_dir_route).path

    def __repr__(self):
        return "Page({})".format(self.origin.path.__repr__())

    def revision_date(self, fmt=None):
        '''
        Return the last major revision date of the page. Takes format
        fmt, which accepts None (return as object), "rfc822" (RSS 2.0),
        "rfc3339" (Atom), or any valid strftime format. Return None if
        no last major revision date is set.
        '''
        rev_date = self.metadata.get('last_major_revision_date', '')
        if rev_date:
            date_obj = datetime.strptime(rev_date, '%Y-%m-%d')
            return get_date(date_obj, fmt=fmt)

@Route
def drop_one_parent_dir_route(filepath):
    path = filepath.path
    dirs = split_path(path)
    if len(dirs) < 2:
        raise ValueError(
            "The path {} is too short; cannot drop directory".format(path))
    dirs = dirs[1:]
    return Filepath('/'.join(dirs))

def to_dir(dirname):
    '''
    dirname(str) -> (Filepath -> Filepath)
    '''
    @Route
    def f(filepath):
        return Filepath(dirname + filepath.path)
    return f

def set_extension(extension):
    '''
    Extension(str) -> Filepath -> Filepath
    '''
    @Route
    def f(filepath):
        '''
        Filepath -> Filepath
        '''
        return Filepath(os.path.splitext(filepath.path)[0] + extension)
    return f

site_dir = "_site/"
site_dir_route = to_dir(site_dir)

@Route
def my_route(filepath):
    return filepath.route_with(set_extension("")).route_with(drop_one_parent_dir_route).route_with(site_dir_route)


```

Which of the following functions or classes contains a `CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')` vulnerability?

  A) Route
  B) process_metadata
  C) compiled
  D) from_filename
Answer: C