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444 lines
16 KiB
Python
444 lines
16 KiB
Python
"""Base classes for server/gateway implementations"""
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from .util import FileWrapper, guess_scheme, is_hop_by_hop
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from .headers import Headers
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import sys, os, time
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__all__ = ['BaseHandler', 'SimpleHandler', 'BaseCGIHandler', 'CGIHandler']
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# Weekday and month names for HTTP date/time formatting; always English!
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_weekdayname = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
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_monthname = [None, # Dummy so we can use 1-based month numbers
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"Jan", "Feb", "Mar", "Apr", "May", "Jun",
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"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
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def format_date_time(timestamp):
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year, month, day, hh, mm, ss, wd, y, z = time.gmtime(timestamp)
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return "%s, %02d %3s %4d %02d:%02d:%02d GMT" % (
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_weekdayname[wd], day, _monthname[month], year, hh, mm, ss
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)
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class BaseHandler:
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"""Manage the invocation of a WSGI application"""
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# Configuration parameters; can override per-subclass or per-instance
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wsgi_version = (1,0)
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wsgi_multithread = True
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wsgi_multiprocess = True
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wsgi_run_once = False
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origin_server = True # We are transmitting direct to client
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http_version = "1.0" # Version that should be used for response
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server_software = None # String name of server software, if any
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# os_environ is used to supply configuration from the OS environment:
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# by default it's a copy of 'os.environ' as of import time, but you can
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# override this in e.g. your __init__ method.
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os_environ = dict(os.environ.items())
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# Collaborator classes
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wsgi_file_wrapper = FileWrapper # set to None to disable
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headers_class = Headers # must be a Headers-like class
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# Error handling (also per-subclass or per-instance)
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traceback_limit = None # Print entire traceback to self.get_stderr()
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error_status = "500 Internal Server Error"
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error_headers = [('Content-Type','text/plain')]
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error_body = "A server error occurred. Please contact the administrator."
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# State variables (don't mess with these)
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status = result = None
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headers_sent = False
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headers = None
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bytes_sent = 0
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def run(self, application):
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"""Invoke the application"""
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# Note to self: don't move the close()! Asynchronous servers shouldn't
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# call close() from finish_response(), so if you close() anywhere but
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# the double-error branch here, you'll break asynchronous servers by
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# prematurely closing. Async servers must return from 'run()' without
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# closing if there might still be output to iterate over.
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try:
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self.setup_environ()
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self.result = application(self.environ, self.start_response)
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self.finish_response()
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except:
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try:
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self.handle_error()
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except:
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# If we get an error handling an error, just give up already!
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self.close()
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raise # ...and let the actual server figure it out.
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def setup_environ(self):
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"""Set up the environment for one request"""
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env = self.environ = self.os_environ.copy()
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self.add_cgi_vars()
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env['wsgi.input'] = self.get_stdin()
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env['wsgi.errors'] = self.get_stderr()
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env['wsgi.version'] = self.wsgi_version
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env['wsgi.run_once'] = self.wsgi_run_once
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env['wsgi.url_scheme'] = self.get_scheme()
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env['wsgi.multithread'] = self.wsgi_multithread
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env['wsgi.multiprocess'] = self.wsgi_multiprocess
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if self.wsgi_file_wrapper is not None:
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env['wsgi.file_wrapper'] = self.wsgi_file_wrapper
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if self.origin_server and self.server_software:
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env.setdefault('SERVER_SOFTWARE',self.server_software)
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def finish_response(self):
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"""Send any iterable data, then close self and the iterable
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Subclasses intended for use in asynchronous servers will
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want to redefine this method, such that it sets up callbacks
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in the event loop to iterate over the data, and to call
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'self.close()' once the response is finished.
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"""
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if not self.result_is_file() or not self.sendfile():
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for data in self.result:
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self.write(data)
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self.finish_content()
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self.close()
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def get_scheme(self):
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"""Return the URL scheme being used"""
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return guess_scheme(self.environ)
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def set_content_length(self):
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"""Compute Content-Length or switch to chunked encoding if possible"""
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try:
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blocks = len(self.result)
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except (TypeError,AttributeError,NotImplementedError):
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pass
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else:
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if blocks==1:
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self.headers['Content-Length'] = str(self.bytes_sent)
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return
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# XXX Try for chunked encoding if origin server and client is 1.1
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def cleanup_headers(self):
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"""Make any necessary header changes or defaults
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Subclasses can extend this to add other defaults.
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"""
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if 'Content-Length' not in self.headers:
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self.set_content_length()
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def start_response(self, status, headers,exc_info=None):
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"""'start_response()' callable as specified by PEP 333"""
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if exc_info:
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try:
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if self.headers_sent:
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# Re-raise original exception if headers sent
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raise exc_info[0](exc_info[1]).with_traceback(exc_info[2])
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finally:
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exc_info = None # avoid dangling circular ref
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elif self.headers is not None:
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raise AssertionError("Headers already set!")
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status = self._convert_string_type(status, "Status")
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assert len(status)>=4,"Status must be at least 4 characters"
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assert int(status[:3]),"Status message must begin w/3-digit code"
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assert status[3]==" ", "Status message must have a space after code"
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str_headers = []
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for name,val in headers:
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name = self._convert_string_type(name, "Header name")
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val = self._convert_string_type(val, "Header value")
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str_headers.append((name, val))
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assert not is_hop_by_hop(name),"Hop-by-hop headers not allowed"
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self.status = status
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self.headers = self.headers_class(str_headers)
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return self.write
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def _convert_string_type(self, value, title):
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"""Convert/check value type."""
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if isinstance(value, str):
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return value
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assert isinstance(value, bytes), \
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"{0} must be a string or bytes object (not {1})".format(title, value)
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return str(value, "iso-8859-1")
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def send_preamble(self):
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"""Transmit version/status/date/server, via self._write()"""
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if self.origin_server:
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if self.client_is_modern():
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self._write('HTTP/%s %s\r\n' % (self.http_version,self.status))
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if 'Date' not in self.headers:
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self._write(
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'Date: %s\r\n' % format_date_time(time.time())
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)
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if self.server_software and 'Server' not in self.headers:
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self._write('Server: %s\r\n' % self.server_software)
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else:
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self._write('Status: %s\r\n' % self.status)
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def write(self, data):
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"""'write()' callable as specified by PEP 333"""
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assert isinstance(data, (str, bytes)), \
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"write() argument must be a string or bytes"
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if not self.status:
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raise AssertionError("write() before start_response()")
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elif not self.headers_sent:
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# Before the first output, send the stored headers
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self.bytes_sent = len(data) # make sure we know content-length
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self.send_headers()
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else:
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self.bytes_sent += len(data)
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# XXX check Content-Length and truncate if too many bytes written?
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self._write(data)
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self._flush()
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def sendfile(self):
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"""Platform-specific file transmission
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Override this method in subclasses to support platform-specific
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file transmission. It is only called if the application's
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return iterable ('self.result') is an instance of
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'self.wsgi_file_wrapper'.
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This method should return a true value if it was able to actually
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transmit the wrapped file-like object using a platform-specific
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approach. It should return a false value if normal iteration
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should be used instead. An exception can be raised to indicate
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that transmission was attempted, but failed.
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NOTE: this method should call 'self.send_headers()' if
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'self.headers_sent' is false and it is going to attempt direct
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transmission of the file.
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"""
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return False # No platform-specific transmission by default
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def finish_content(self):
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"""Ensure headers and content have both been sent"""
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if not self.headers_sent:
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self.headers['Content-Length'] = "0"
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self.send_headers()
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else:
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pass # XXX check if content-length was too short?
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def close(self):
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"""Close the iterable (if needed) and reset all instance vars
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Subclasses may want to also drop the client connection.
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"""
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try:
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if hasattr(self.result,'close'):
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self.result.close()
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finally:
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self.result = self.headers = self.status = self.environ = None
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self.bytes_sent = 0; self.headers_sent = False
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def send_headers(self):
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"""Transmit headers to the client, via self._write()"""
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self.cleanup_headers()
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self.headers_sent = True
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if not self.origin_server or self.client_is_modern():
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self.send_preamble()
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self._write(str(self.headers))
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def result_is_file(self):
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"""True if 'self.result' is an instance of 'self.wsgi_file_wrapper'"""
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wrapper = self.wsgi_file_wrapper
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return wrapper is not None and isinstance(self.result,wrapper)
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def client_is_modern(self):
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"""True if client can accept status and headers"""
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return self.environ['SERVER_PROTOCOL'].upper() != 'HTTP/0.9'
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def log_exception(self,exc_info):
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"""Log the 'exc_info' tuple in the server log
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Subclasses may override to retarget the output or change its format.
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"""
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try:
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from traceback import print_exception
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stderr = self.get_stderr()
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print_exception(
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exc_info[0], exc_info[1], exc_info[2],
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self.traceback_limit, stderr
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)
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stderr.flush()
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finally:
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exc_info = None
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def handle_error(self):
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"""Log current error, and send error output to client if possible"""
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self.log_exception(sys.exc_info())
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if not self.headers_sent:
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self.result = self.error_output(self.environ, self.start_response)
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self.finish_response()
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# XXX else: attempt advanced recovery techniques for HTML or text?
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def error_output(self, environ, start_response):
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"""WSGI mini-app to create error output
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By default, this just uses the 'error_status', 'error_headers',
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and 'error_body' attributes to generate an output page. It can
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be overridden in a subclass to dynamically generate diagnostics,
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choose an appropriate message for the user's preferred language, etc.
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Note, however, that it's not recommended from a security perspective to
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spit out diagnostics to any old user; ideally, you should have to do
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something special to enable diagnostic output, which is why we don't
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include any here!
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"""
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start_response(self.error_status,self.error_headers[:],sys.exc_info())
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return [self.error_body]
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# Pure abstract methods; *must* be overridden in subclasses
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def _write(self,data):
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"""Override in subclass to buffer data for send to client
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It's okay if this method actually transmits the data; BaseHandler
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just separates write and flush operations for greater efficiency
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when the underlying system actually has such a distinction.
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"""
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raise NotImplementedError
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def _flush(self):
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"""Override in subclass to force sending of recent '_write()' calls
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It's okay if this method is a no-op (i.e., if '_write()' actually
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sends the data.
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"""
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raise NotImplementedError
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def get_stdin(self):
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"""Override in subclass to return suitable 'wsgi.input'"""
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raise NotImplementedError
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def get_stderr(self):
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"""Override in subclass to return suitable 'wsgi.errors'"""
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raise NotImplementedError
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def add_cgi_vars(self):
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"""Override in subclass to insert CGI variables in 'self.environ'"""
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raise NotImplementedError
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class SimpleHandler(BaseHandler):
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"""Handler that's just initialized with streams, environment, etc.
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This handler subclass is intended for synchronous HTTP/1.0 origin servers,
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and handles sending the entire response output, given the correct inputs.
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Usage::
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handler = SimpleHandler(
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inp,out,err,env, multithread=False, multiprocess=True
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)
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handler.run(app)"""
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def __init__(self,stdin,stdout,stderr,environ,
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multithread=True, multiprocess=False
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):
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self.stdin = stdin
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self.stdout = stdout
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self.stderr = stderr
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self.base_env = environ
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self.wsgi_multithread = multithread
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self.wsgi_multiprocess = multiprocess
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def get_stdin(self):
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return self.stdin
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def get_stderr(self):
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return self.stderr
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def add_cgi_vars(self):
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self.environ.update(self.base_env)
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def _write(self,data):
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if isinstance(data, str):
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try:
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data = data.encode("iso-8859-1")
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except UnicodeEncodeError:
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raise ValueError("Unicode data must contain only code points"
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" representable in ISO-8859-1 encoding")
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self.stdout.write(data)
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def _flush(self):
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self.stdout.flush()
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self._flush = self.stdout.flush
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class BaseCGIHandler(SimpleHandler):
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"""CGI-like systems using input/output/error streams and environ mapping
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Usage::
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handler = BaseCGIHandler(inp,out,err,env)
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handler.run(app)
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This handler class is useful for gateway protocols like ReadyExec and
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FastCGI, that have usable input/output/error streams and an environment
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mapping. It's also the base class for CGIHandler, which just uses
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sys.stdin, os.environ, and so on.
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The constructor also takes keyword arguments 'multithread' and
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'multiprocess' (defaulting to 'True' and 'False' respectively) to control
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the configuration sent to the application. It sets 'origin_server' to
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False (to enable CGI-like output), and assumes that 'wsgi.run_once' is
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False.
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"""
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origin_server = False
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class CGIHandler(BaseCGIHandler):
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"""CGI-based invocation via sys.stdin/stdout/stderr and os.environ
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Usage::
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CGIHandler().run(app)
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The difference between this class and BaseCGIHandler is that it always
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uses 'wsgi.run_once' of 'True', 'wsgi.multithread' of 'False', and
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'wsgi.multiprocess' of 'True'. It does not take any initialization
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parameters, but always uses 'sys.stdin', 'os.environ', and friends.
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If you need to override any of these parameters, use BaseCGIHandler
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instead.
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"""
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wsgi_run_once = True
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# Do not allow os.environ to leak between requests in Google App Engine
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# and other multi-run CGI use cases. This is not easily testable.
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# See http://bugs.python.org/issue7250
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os_environ = {}
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def __init__(self):
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BaseCGIHandler.__init__(
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self, sys.stdin, sys.stdout, sys.stderr, dict(os.environ.items()),
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multithread=False, multiprocess=True
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)
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