CherryPy / cherrypy / _cpwsgi.py

"""WSGI interface (see PEP 333)."""

import sys as _sys

import cherrypy as _cherrypy
try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO
from cherrypy import _cperror
from cherrypy.lib import httputil


def downgrade_wsgi_ux_to_1x(environ):
    """Return a new environ dict for WSGI 1.x from the given WSGI u.x environ."""
    env1x = {}
    
    url_encoding = environ[u'wsgi.url_encoding']
    for k, v in environ.items():
        if k in [u'PATH_INFO', u'SCRIPT_NAME', u'QUERY_STRING']:
            v = v.encode(url_encoding)
        elif isinstance(v, unicode):
            v = v.encode('ISO-8859-1')
        env1x[k.encode('ISO-8859-1')] = v
    
    return env1x


class VirtualHost(object):
    """Select a different WSGI application based on the Host header.
    
    This can be useful when running multiple sites within one CP server.
    It allows several domains to point to different applications. For example::
    
        root = Root()
        RootApp = cherrypy.Application(root)
        Domain2App = cherrypy.Application(root)
        SecureApp = cherrypy.Application(Secure())
        
        vhost = cherrypy._cpwsgi.VirtualHost(RootApp,
            domains={'www.domain2.example': Domain2App,
                     'www.domain2.example:443': SecureApp,
                     })
        
        cherrypy.tree.graft(vhost)
    """
    default = None
    """Required. The default WSGI application."""
    
    use_x_forwarded_host = True
    """If True (the default), any "X-Forwarded-Host"
    request header will be used instead of the "Host" header. This
    is commonly added by HTTP servers (such as Apache) when proxying."""
    
    domains = {}
    """A dict of {host header value: application} pairs.
    The incoming "Host" request header is looked up in this dict,
    and, if a match is found, the corresponding WSGI application
    will be called instead of the default. Note that you often need
    separate entries for "example.com" and "www.example.com".
    In addition, "Host" headers may contain the port number.
    """
    
    def __init__(self, default, domains=None, use_x_forwarded_host=True):
        self.default = default
        self.domains = domains or {}
        self.use_x_forwarded_host = use_x_forwarded_host
    
    def __call__(self, environ, start_response):
        domain = environ.get('HTTP_HOST', '')
        if self.use_x_forwarded_host:
            domain = environ.get("HTTP_X_FORWARDED_HOST", domain)
        
        nextapp = self.domains.get(domain)
        if nextapp is None:
            nextapp = self.default
        return nextapp(environ, start_response)


class InternalRedirector(object):
    """WSGI middleware that handles raised cherrypy.InternalRedirect."""
    
    def __init__(self, nextapp, recursive=False):
        self.nextapp = nextapp
        self.recursive = recursive
    
    def __call__(self, environ, start_response):
        redirections = []
        while True:
            environ = environ.copy()
            try:
                return self.nextapp(environ, start_response)
            except _cherrypy.InternalRedirect, ir:
                sn = environ.get('SCRIPT_NAME', '')
                path = environ.get('PATH_INFO', '')
                qs = environ.get('QUERY_STRING', '')
                
                # Add the *previous* path_info + qs to redirections.
                old_uri = sn + path
                if qs:
                    old_uri += "?" + qs
                redirections.append(old_uri)
                
                if not self.recursive:
                    # Check to see if the new URI has been redirected to already
                    new_uri = sn + ir.path
                    if ir.query_string:
                        new_uri += "?" + ir.query_string
                    if new_uri in redirections:
                        ir.request.close()
                        raise RuntimeError("InternalRedirector visited the "
                                           "same URL twice: %r" % new_uri)
                
                # Munge the environment and try again.
                environ['REQUEST_METHOD'] = "GET"
                environ['PATH_INFO'] = ir.path
                environ['QUERY_STRING'] = ir.query_string
                environ['wsgi.input'] = StringIO()
                environ['CONTENT_LENGTH'] = "0"
                environ['cherrypy.previous_request'] = ir.request


class ExceptionTrapper(object):
    """WSGI middleware that traps exceptions."""
    
    def __init__(self, nextapp, throws=(KeyboardInterrupt, SystemExit)):
        self.nextapp = nextapp
        self.throws = throws
    
    def __call__(self, environ, start_response):
        return _TrappedResponse(self.nextapp, environ, start_response, self.throws)


class _TrappedResponse(object):
    
    response = iter([])
    
    def __init__(self, nextapp, environ, start_response, throws):
        self.nextapp = nextapp
        self.environ = environ
        self.start_response = start_response
        self.throws = throws
        self.started_response = False
        self.response = self.trap(self.nextapp, self.environ, self.start_response)
        self.iter_response = iter(self.response)
    
    def __iter__(self):
        self.started_response = True
        return self
    
    def next(self):
        return self.trap(self.iter_response.next)
    
    def close(self):
        if hasattr(self.response, 'close'):
            self.response.close()
    
    def trap(self, func, *args, **kwargs):
        try:
            return func(*args, **kwargs)
        except self.throws:
            raise
        except StopIteration:
            raise
        except:
            tb = _cperror.format_exc()
            #print('trapped (started %s):' % self.started_response, tb)
            _cherrypy.log(tb, severity=40)
            if not _cherrypy.request.show_tracebacks:
                tb = ""
            s, h, b = _cperror.bare_error(tb)
            if self.started_response:
                # Empty our iterable (so future calls raise StopIteration)
                self.iter_response = iter([])
            else:
                self.iter_response = iter(b)
            
            try:
                self.start_response(s, h, _sys.exc_info())
            except:
                # "The application must not trap any exceptions raised by
                # start_response, if it called start_response with exc_info.
                # Instead, it should allow such exceptions to propagate
                # back to the server or gateway."
                # But we still log and call close() to clean up ourselves.
                _cherrypy.log(traceback=True, severity=40)
                raise
            
            if self.started_response:
                return "".join(b)
            else:
                return b


#                           WSGI-to-CP Adapter                           #


class AppResponse(object):
    """WSGI response iterable for CherryPy applications."""
    
    def __init__(self, environ, start_response, cpapp):
        if environ.get(u'wsgi.version') == (u'u', 0):
            environ = downgrade_wsgi_ux_to_1x(environ)
        self.environ = environ
        self.cpapp = cpapp
        try:
            self.run()
        except:
            self.close()
            raise
        r = _cherrypy.serving.response
        self.iter_response = iter(r.body)
        self.write = start_response(r.output_status, r.header_list)
    
    def __iter__(self):
        return self
    
    def next(self):
        return self.iter_response.next()
    
    def close(self):
        """Close and de-reference the current request and response. (Core)"""
        self.cpapp.release_serving()
    
    def run(self):
        """Create a Request object using environ."""
        env = self.environ.get
        
        local = httputil.Host('', int(env('SERVER_PORT', 80)),
                           env('SERVER_NAME', ''))
        remote = httputil.Host(env('REMOTE_ADDR', ''),
                               int(env('REMOTE_PORT', -1) or -1),
                               env('REMOTE_HOST', ''))
        scheme = env('wsgi.url_scheme')
        sproto = env('ACTUAL_SERVER_PROTOCOL', "HTTP/1.1")
        request, resp = self.cpapp.get_serving(local, remote, scheme, sproto)
        
        # LOGON_USER is served by IIS, and is the name of the
        # user after having been mapped to a local account.
        # Both IIS and Apache set REMOTE_USER, when possible.
        request.login = env('LOGON_USER') or env('REMOTE_USER') or None
        request.multithread = self.environ['wsgi.multithread']
        request.multiprocess = self.environ['wsgi.multiprocess']
        request.wsgi_environ = self.environ
        request.prev = env('cherrypy.previous_request', None)
        
        meth = self.environ['REQUEST_METHOD']
        
        path = httputil.urljoin(self.environ.get('SCRIPT_NAME', ''),
                                self.environ.get('PATH_INFO', ''))
        qs = self.environ.get('QUERY_STRING', '')
        rproto = self.environ.get('SERVER_PROTOCOL')
        headers = self.translate_headers(self.environ)
        rfile = self.environ['wsgi.input']
        request.run(meth, path, qs, rproto, headers, rfile)
    
    headerNames = {'HTTP_CGI_AUTHORIZATION': 'Authorization',
                   'CONTENT_LENGTH': 'Content-Length',
                   'CONTENT_TYPE': 'Content-Type',
                   'REMOTE_HOST': 'Remote-Host',
                   'REMOTE_ADDR': 'Remote-Addr',
                   }
    
    def translate_headers(self, environ):
        """Translate CGI-environ header names to HTTP header names."""
        for cgiName in environ:
            # We assume all incoming header keys are uppercase already.
            if cgiName in self.headerNames:
                yield self.headerNames[cgiName], environ[cgiName]
            elif cgiName[:5] == "HTTP_":
                # Hackish attempt at recovering original header names.
                translatedHeader = cgiName[5:].replace("_", "-")
                yield translatedHeader, environ[cgiName]


class CPWSGIApp(object):
    """A WSGI application object for a CherryPy Application."""
    
    pipeline = [('ExceptionTrapper', ExceptionTrapper),
                ('InternalRedirector', InternalRedirector),
                ]
    """A list of (name, wsgiapp) pairs. Each 'wsgiapp' MUST be a
    constructor that takes an initial, positional 'nextapp' argument,
    plus optional keyword arguments, and returns a WSGI application
    (that takes environ and start_response arguments). The 'name' can
    be any you choose, and will correspond to keys in self.config."""
    
    head = None
    """Rather than nest all apps in the pipeline on each call, it's only
    done the first time, and the result is memoized into self.head. Set
    this to None again if you change self.pipeline after calling self."""
    
    config = {}
    """A dict whose keys match names listed in the pipeline. Each
    value is a further dict which will be passed to the corresponding
    named WSGI callable (from the pipeline) as keyword arguments."""
    
    response_class = AppResponse
    """The class to instantiate and return as the next app in the WSGI chain."""
    
    def __init__(self, cpapp, pipeline=None):
        self.cpapp = cpapp
        self.pipeline = self.pipeline[:]
        if pipeline:
            self.pipeline.extend(pipeline)
        self.config = self.config.copy()
    
    def tail(self, environ, start_response):
        """WSGI application callable for the actual CherryPy application.
        
        You probably shouldn't call this; call self.__call__ instead,
        so that any WSGI middleware in self.pipeline can run first.
        """
        return self.response_class(environ, start_response, self.cpapp)
    
    def __call__(self, environ, start_response):
        head = self.head
        if head is None:
            # Create and nest the WSGI apps in our pipeline (in reverse order).
            # Then memoize the result in self.head.
            head = self.tail
            for name, callable in self.pipeline[::-1]:
                conf = self.config.get(name, {})
                head = callable(head, **conf)
            self.head = head
        return head(environ, start_response)
    
    def namespace_handler(self, k, v):
        """Config handler for the 'wsgi' namespace."""
        if k == "pipeline":
            # Note this allows multiple 'wsgi.pipeline' config entries
            # (but each entry will be processed in a 'random' order).
            # It should also allow developers to set default middleware
            # in code (passed to self.__init__) that deployers can add to
            # (but not remove) via config.
            self.pipeline.extend(v)
        elif k == "response_class":
            self.response_class = v
        else:
            name, arg = k.split(".", 1)
            bucket = self.config.setdefault(name, {})
            bucket[arg] = v
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