path: root/python/werkzeug/middleware/lint.py

"""
WSGI Protocol Linter
====================

This module provides a middleware that performs sanity checks on the
behavior of the WSGI server and application. It checks that the
:pep:`3333` WSGI spec is properly implemented. It also warns on some
common HTTP errors such as non-empty responses for 304 status codes.

.. autoclass:: LintMiddleware

:copyright: 2007 Pallets
:license: BSD-3-Clause
"""
from warnings import warn

from .._compat import implements_iterator
from .._compat import PY2
from .._compat import string_types
from ..datastructures import Headers
from ..http import is_entity_header
from ..wsgi import FileWrapper

try:
    from urllib.parse import urlparse
except ImportError:
    from urlparse import urlparse


class WSGIWarning(Warning):
    """Warning class for WSGI warnings."""


class HTTPWarning(Warning):
    """Warning class for HTTP warnings."""


def check_string(context, obj, stacklevel=3):
    if type(obj) is not str:
        warn(
            "'%s' requires strings, got '%s'" % (context, type(obj).__name__),
            WSGIWarning,
        )


class InputStream(object):
    def __init__(self, stream):
        self._stream = stream

    def read(self, *args):
        if len(args) == 0:
            warn(
                "WSGI does not guarantee an EOF marker on the input stream, thus making"
                " calls to 'wsgi.input.read()' unsafe. Conforming servers may never"
                " return from this call.",
                WSGIWarning,
                stacklevel=2,
            )
        elif len(args) != 1:
            warn(
                "Too many parameters passed to 'wsgi.input.read()'.",
                WSGIWarning,
                stacklevel=2,
            )
        return self._stream.read(*args)

    def readline(self, *args):
        if len(args) == 0:
            warn(
                "Calls to 'wsgi.input.readline()' without arguments are unsafe. Use"
                " 'wsgi.input.read()' instead.",
                WSGIWarning,
                stacklevel=2,
            )
        elif len(args) == 1:
            warn(
                "'wsgi.input.readline()' was called with a size hint. WSGI does not"
                " support this, although it's available on all major servers.",
                WSGIWarning,
                stacklevel=2,
            )
        else:
            raise TypeError("Too many arguments passed to 'wsgi.input.readline()'.")
        return self._stream.readline(*args)

    def __iter__(self):
        try:
            return iter(self._stream)
        except TypeError:
            warn("'wsgi.input' is not iterable.", WSGIWarning, stacklevel=2)
            return iter(())

    def close(self):
        warn("The application closed the input stream!", WSGIWarning, stacklevel=2)
        self._stream.close()


class ErrorStream(object):
    def __init__(self, stream):
        self._stream = stream

    def write(self, s):
        check_string("wsgi.error.write()", s)
        self._stream.write(s)

    def flush(self):
        self._stream.flush()

    def writelines(self, seq):
        for line in seq:
            self.write(line)

    def close(self):
        warn("The application closed the error stream!", WSGIWarning, stacklevel=2)
        self._stream.close()


class GuardedWrite(object):
    def __init__(self, write, chunks):
        self._write = write
        self._chunks = chunks

    def __call__(self, s):
        check_string("write()", s)
        self._write.write(s)
        self._chunks.append(len(s))


@implements_iterator
class GuardedIterator(object):
    def __init__(self, iterator, headers_set, chunks):
        self._iterator = iterator
        if PY2:
            self._next = iter(iterator).next
        else:
            self._next = iter(iterator).__next__
        self.closed = False
        self.headers_set = headers_set
        self.chunks = chunks

    def __iter__(self):
        return self

    def __next__(self):
        if self.closed:
            warn("Iterated over closed 'app_iter'.", WSGIWarning, stacklevel=2)

        rv = self._next()

        if not self.headers_set:
            warn(
                "The application returned before it started the response.",
                WSGIWarning,
                stacklevel=2,
            )

        check_string("application iterator items", rv)
        self.chunks.append(len(rv))
        return rv

    def close(self):
        self.closed = True

        if hasattr(self._iterator, "close"):
            self._iterator.close()

        if self.headers_set:
            status_code, headers = self.headers_set
            bytes_sent = sum(self.chunks)
            content_length = headers.get("content-length", type=int)

            if status_code == 304:
                for key, _value in headers:
                    key = key.lower()
                    if key not in ("expires", "content-location") and is_entity_header(
                        key
                    ):
                        warn(
                            "Entity header %r found in 304 response." % key, HTTPWarning
                        )
                if bytes_sent:
                    warn("304 responses must not have a body.", HTTPWarning)
            elif 100 <= status_code < 200 or status_code == 204:
                if content_length != 0:
                    warn(
                        "%r responses must have an empty content length." % status_code,
                        HTTPWarning,
                    )
                if bytes_sent:
                    warn(
                        "%r responses must not have a body." % status_code, HTTPWarning
                    )
            elif content_length is not None and content_length != bytes_sent:
                warn(
                    "Content-Length and the number of bytes sent to the client do not"
                    " match.",
                    WSGIWarning,
                )

    def __del__(self):
        if not self.closed:
            try:
                warn(
                    "Iterator was garbage collected before it was closed.", WSGIWarning
                )
            except Exception:
                pass


class LintMiddleware(object):
    """Warns about common errors in the WSGI and HTTP behavior of the
    server and wrapped application. Some of the issues it check are:

    -   invalid status codes
    -   non-bytestrings sent to the WSGI server
    -   strings returned from the WSGI application
    -   non-empty conditional responses
    -   unquoted etags
    -   relative URLs in the Location header
    -   unsafe calls to wsgi.input
    -   unclosed iterators

    Error information is emitted using the :mod:`warnings` module.

    :param app: The WSGI application to wrap.

    .. code-block:: python

        from werkzeug.middleware.lint import LintMiddleware
        app = LintMiddleware(app)
    """

    def __init__(self, app):
        self.app = app

    def check_environ(self, environ):
        if type(environ) is not dict:
            warn(
                "WSGI environment is not a standard Python dict.",
                WSGIWarning,
                stacklevel=4,
            )
        for key in (
            "REQUEST_METHOD",
            "SERVER_NAME",
            "SERVER_PORT",
            "wsgi.version",
            "wsgi.input",
            "wsgi.errors",
            "wsgi.multithread",
            "wsgi.multiprocess",
            "wsgi.run_once",
        ):
            if key not in environ:
                warn(
                    "Required environment key %r not found" % key,
                    WSGIWarning,
                    stacklevel=3,
                )
        if environ["wsgi.version"] != (1, 0):
            warn("Environ is not a WSGI 1.0 environ.", WSGIWarning, stacklevel=3)

        script_name = environ.get("SCRIPT_NAME", "")
        path_info = environ.get("PATH_INFO", "")

        if script_name and script_name[0] != "/":
            warn(
                "'SCRIPT_NAME' does not start with a slash: %r" % script_name,
                WSGIWarning,
                stacklevel=3,
            )

        if path_info and path_info[0] != "/":
            warn(
                "'PATH_INFO' does not start with a slash: %r" % path_info,
                WSGIWarning,
                stacklevel=3,
            )

    def check_start_response(self, status, headers, exc_info):
        check_string("status", status)
        status_code = status.split(None, 1)[0]

        if len(status_code) != 3 or not status_code.isdigit():
            warn(WSGIWarning("Status code must be three digits"), stacklevel=3)

        if len(status) < 4 or status[3] != " ":
            warn(
                WSGIWarning(
                    "Invalid value for status %r.  Valid "
                    "status strings are three digits, a space "
                    "and a status explanation"
                ),
                stacklevel=3,
            )

        status_code = int(status_code)

        if status_code < 100:
            warn(WSGIWarning("status code < 100 detected"), stacklevel=3)

        if type(headers) is not list:
            warn(WSGIWarning("header list is not a list"), stacklevel=3)

        for item in headers:
            if type(item) is not tuple or len(item) != 2:
                warn(WSGIWarning("Headers must tuple 2-item tuples"), stacklevel=3)
            name, value = item
            if type(name) is not str or type(value) is not str:
                warn(WSGIWarning("header items must be strings"), stacklevel=3)
            if name.lower() == "status":
                warn(
                    WSGIWarning(
                        "The status header is not supported due to "
                        "conflicts with the CGI spec."
                    ),
                    stacklevel=3,
                )

        if exc_info is not None and not isinstance(exc_info, tuple):
            warn(WSGIWarning("invalid value for exc_info"), stacklevel=3)

        headers = Headers(headers)
        self.check_headers(headers)

        return status_code, headers

    def check_headers(self, headers):
        etag = headers.get("etag")

        if etag is not None:
            if etag.startswith(("W/", "w/")):
                if etag.startswith("w/"):
                    warn(
                        HTTPWarning("weak etag indicator should be upcase."),
                        stacklevel=4,
                    )

                etag = etag[2:]

            if not (etag[:1] == etag[-1:] == '"'):
                warn(HTTPWarning("unquoted etag emitted."), stacklevel=4)

        location = headers.get("location")

        if location is not None:
            if not urlparse(location).netloc:
                warn(
                    HTTPWarning("absolute URLs required for location header"),
                    stacklevel=4,
                )

    def check_iterator(self, app_iter):
        if isinstance(app_iter, string_types):
            warn(
                "The application returned astring. The response will send one character"
                " at a time to the client, which will kill performance. Return a list"
                " or iterable instead.",
                WSGIWarning,
                stacklevel=3,
            )

    def __call__(self, *args, **kwargs):
        if len(args) != 2:
            warn("A WSGI app takes two arguments.", WSGIWarning, stacklevel=2)

        if kwargs:
            warn(
                "A WSGI app does not take keyword arguments.", WSGIWarning, stacklevel=2
            )

        environ, start_response = args

        self.check_environ(environ)
        environ["wsgi.input"] = InputStream(environ["wsgi.input"])
        environ["wsgi.errors"] = ErrorStream(environ["wsgi.errors"])

        # Hook our own file wrapper in so that applications will always
        # iterate to the end and we can check the content length.
        environ["wsgi.file_wrapper"] = FileWrapper

        headers_set = []
        chunks = []

        def checking_start_response(*args, **kwargs):
            if len(args) not in (2, 3):
                warn(
                    "Invalid number of arguments: %s, expected 2 or 3." % len(args),
                    WSGIWarning,
                    stacklevel=2,
                )

            if kwargs:
                warn("'start_response' does not take keyword arguments.", WSGIWarning)

            status, headers = args[:2]

            if len(args) == 3:
                exc_info = args[2]
            else:
                exc_info = None

            headers_set[:] = self.check_start_response(status, headers, exc_info)
            return GuardedWrite(start_response(status, headers, exc_info), chunks)

        app_iter = self.app(environ, checking_start_response)
        self.check_iterator(app_iter)
        return GuardedIterator(app_iter, headers_set, chunks)