JezK
Edit File: handlers.py
"""Base classes for server/gateway implementations""" from types import StringType from util import FileWrapper, guess_scheme, is_hop_by_hop from headers import Headers import sys, os, time __all__ = ['BaseHandler', 'SimpleHandler', 'BaseCGIHandler', 'CGIHandler'] try: dict except NameError: def dict(items): d = {} for k,v in items: d[k] = v return d # Uncomment for 2.2 compatibility. #try: # True # False #except NameError: # True = not None # False = not True # Weekday and month names for HTTP date/time formatting; always English! _weekdayname = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"] _monthname = [None, # Dummy so we can use 1-based month numbers "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"] def format_date_time(timestamp): year, month, day, hh, mm, ss, wd, y, z = time.gmtime(timestamp) return "%s, %02d %3s %4d %02d:%02d:%02d GMT" % ( _weekdayname[wd], day, _monthname[month], year, hh, mm, ss ) class BaseHandler: """Manage the invocation of a WSGI application""" # Configuration parameters; can override per-subclass or per-instance wsgi_version = (1,0) wsgi_multithread = True wsgi_multiprocess = True wsgi_run_once = False origin_server = True # We are transmitting direct to client http_version = "1.0" # Version that should be used for response server_software = None # String name of server software, if any # os_environ is used to supply configuration from the OS environment: # by default it's a copy of 'os.environ' as of import time, but you can # override this in e.g. your __init__ method. os_environ = dict(os.environ.items()) # Collaborator classes wsgi_file_wrapper = FileWrapper # set to None to disable headers_class = Headers # must be a Headers-like class # Error handling (also per-subclass or per-instance) traceback_limit = None # Print entire traceback to self.get_stderr() error_status = "500 Internal Server Error" error_headers = [('Content-Type','text/plain')] error_body = "A server error occurred. Please contact the administrator." # State variables (don't mess with these) status = result = None headers_sent = False headers = None bytes_sent = 0 def run(self, application): """Invoke the application""" # Note to self: don't move the close()! Asynchronous servers shouldn't # call close() from finish_response(), so if you close() anywhere but # the double-error branch here, you'll break asynchronous servers by # prematurely closing. Async servers must return from 'run()' without # closing if there might still be output to iterate over. try: self.setup_environ() self.result = application(self.environ, self.start_response) self.finish_response() except: try: self.handle_error() except: # If we get an error handling an error, just give up already! self.close() raise # ...and let the actual server figure it out. def setup_environ(self): """Set up the environment for one request""" env = self.environ = self.os_environ.copy() self.add_cgi_vars() env['wsgi.input'] = self.get_stdin() env['wsgi.errors'] = self.get_stderr() env['wsgi.version'] = self.wsgi_version env['wsgi.run_once'] = self.wsgi_run_once env['wsgi.url_scheme'] = self.get_scheme() env['wsgi.multithread'] = self.wsgi_multithread env['wsgi.multiprocess'] = self.wsgi_multiprocess if self.wsgi_file_wrapper is not None: env['wsgi.file_wrapper'] = self.wsgi_file_wrapper if self.origin_server and self.server_software: env.setdefault('SERVER_SOFTWARE',self.server_software) def finish_response(self): """Send any iterable data, then close self and the iterable Subclasses intended for use in asynchronous servers will want to redefine this method, such that it sets up callbacks in the event loop to iterate over the data, and to call 'self.close()' once the response is finished. """ try: if not self.result_is_file() or not self.sendfile(): for data in self.result: self.write(data) self.finish_content() finally: self.close() def get_scheme(self): """Return the URL scheme being used""" return guess_scheme(self.environ) def set_content_length(self): """Compute Content-Length or switch to chunked encoding if possible""" try: blocks = len(self.result) except (TypeError,AttributeError,NotImplementedError): pass else: if blocks==1: self.headers['Content-Length'] = str(self.bytes_sent) return # XXX Try for chunked encoding if origin server and client is 1.1 def cleanup_headers(self): """Make any necessary header changes or defaults Subclasses can extend this to add other defaults. """ if 'Content-Length' not in self.headers: self.set_content_length() def start_response(self, status, headers,exc_info=None): """'start_response()' callable as specified by PEP 333""" if exc_info: try: if self.headers_sent: # Re-raise original exception if headers sent raise exc_info[0], exc_info[1], exc_info[2] finally: exc_info = None # avoid dangling circular ref elif self.headers is not None: raise AssertionError("Headers already set!") assert type(status) is StringType,"Status must be a string" assert len(status)>=4,"Status must be at least 4 characters" assert int(status[:3]),"Status message must begin w/3-digit code" assert status[3]==" ", "Status message must have a space after code" if __debug__: for name,val in headers: assert type(name) is StringType,"Header names must be strings" assert type(val) is StringType,"Header values must be strings" assert not is_hop_by_hop(name),"Hop-by-hop headers not allowed" self.status = status self.headers = self.headers_class(headers) return self.write def send_preamble(self): """Transmit version/status/date/server, via self._write()""" if self.origin_server: if self.client_is_modern(): self._write('HTTP/%s %s\r\n' % (self.http_version,self.status)) if 'Date' not in self.headers: self._write( 'Date: %s\r\n' % format_date_time(time.time()) ) if self.server_software and 'Server' not in self.headers: self._write('Server: %s\r\n' % self.server_software) else: self._write('Status: %s\r\n' % self.status) def write(self, data): """'write()' callable as specified by PEP 333""" assert type(data) is StringType,"write() argument must be string" if not self.status: raise AssertionError("write() before start_response()") elif not self.headers_sent: # Before the first output, send the stored headers self.bytes_sent = len(data) # make sure we know content-length self.send_headers() else: self.bytes_sent += len(data) # XXX check Content-Length and truncate if too many bytes written? self._write(data) self._flush() def sendfile(self): """Platform-specific file transmission Override this method in subclasses to support platform-specific file transmission. It is only called if the application's return iterable ('self.result') is an instance of 'self.wsgi_file_wrapper'. This method should return a true value if it was able to actually transmit the wrapped file-like object using a platform-specific approach. It should return a false value if normal iteration should be used instead. An exception can be raised to indicate that transmission was attempted, but failed. NOTE: this method should call 'self.send_headers()' if 'self.headers_sent' is false and it is going to attempt direct transmission of the file. """ return False # No platform-specific transmission by default def finish_content(self): """Ensure headers and content have both been sent""" if not self.headers_sent: # Only zero Content-Length if not set by the application (so # that HEAD requests can be satisfied properly, see #3839) self.headers.setdefault('Content-Length', "0") self.send_headers() else: pass # XXX check if content-length was too short? def close(self): """Close the iterable (if needed) and reset all instance vars Subclasses may want to also drop the client connection. """ try: if hasattr(self.result,'close'): self.result.close() finally: self.result = self.headers = self.status = self.environ = None self.bytes_sent = 0; self.headers_sent = False def send_headers(self): """Transmit headers to the client, via self._write()""" self.cleanup_headers() self.headers_sent = True if not self.origin_server or self.client_is_modern(): self.send_preamble() self._write(str(self.headers)) def result_is_file(self): """True if 'self.result' is an instance of 'self.wsgi_file_wrapper'""" wrapper = self.wsgi_file_wrapper return wrapper is not None and isinstance(self.result,wrapper) def client_is_modern(self): """True if client can accept status and headers""" return self.environ['SERVER_PROTOCOL'].upper() != 'HTTP/0.9' def log_exception(self,exc_info): """Log the 'exc_info' tuple in the server log Subclasses may override to retarget the output or change its format. """ try: from traceback import print_exception stderr = self.get_stderr() print_exception( exc_info[0], exc_info[1], exc_info[2], self.traceback_limit, stderr ) stderr.flush() finally: exc_info = None def handle_error(self): """Log current error, and send error output to client if possible""" self.log_exception(sys.exc_info()) if not self.headers_sent: self.result = self.error_output(self.environ, self.start_response) self.finish_response() # XXX else: attempt advanced recovery techniques for HTML or text? def error_output(self, environ, start_response): """WSGI mini-app to create error output By default, this just uses the 'error_status', 'error_headers', and 'error_body' attributes to generate an output page. It can be overridden in a subclass to dynamically generate diagnostics, choose an appropriate message for the user's preferred language, etc. Note, however, that it's not recommended from a security perspective to spit out diagnostics to any old user; ideally, you should have to do something special to enable diagnostic output, which is why we don't include any here! """ start_response(self.error_status,self.error_headers[:],sys.exc_info()) return [self.error_body] # Pure abstract methods; *must* be overridden in subclasses def _write(self,data): """Override in subclass to buffer data for send to client It's okay if this method actually transmits the data; BaseHandler just separates write and flush operations for greater efficiency when the underlying system actually has such a distinction. """ raise NotImplementedError def _flush(self): """Override in subclass to force sending of recent '_write()' calls It's okay if this method is a no-op (i.e., if '_write()' actually sends the data. """ raise NotImplementedError def get_stdin(self): """Override in subclass to return suitable 'wsgi.input'""" raise NotImplementedError def get_stderr(self): """Override in subclass to return suitable 'wsgi.errors'""" raise NotImplementedError def add_cgi_vars(self): """Override in subclass to insert CGI variables in 'self.environ'""" raise NotImplementedError class SimpleHandler(BaseHandler): """Handler that's just initialized with streams, environment, etc. This handler subclass is intended for synchronous HTTP/1.0 origin servers, and handles sending the entire response output, given the correct inputs. Usage:: handler = SimpleHandler( inp,out,err,env, multithread=False, multiprocess=True ) handler.run(app)""" def __init__(self,stdin,stdout,stderr,environ, multithread=True, multiprocess=False ): self.stdin = stdin self.stdout = stdout self.stderr = stderr self.base_env = environ self.wsgi_multithread = multithread self.wsgi_multiprocess = multiprocess def get_stdin(self): return self.stdin def get_stderr(self): return self.stderr def add_cgi_vars(self): self.environ.update(self.base_env) def _write(self,data): self.stdout.write(data) self._write = self.stdout.write def _flush(self): self.stdout.flush() self._flush = self.stdout.flush class BaseCGIHandler(SimpleHandler): """CGI-like systems using input/output/error streams and environ mapping Usage:: handler = BaseCGIHandler(inp,out,err,env) handler.run(app) This handler class is useful for gateway protocols like ReadyExec and FastCGI, that have usable input/output/error streams and an environment mapping. It's also the base class for CGIHandler, which just uses sys.stdin, os.environ, and so on. The constructor also takes keyword arguments 'multithread' and 'multiprocess' (defaulting to 'True' and 'False' respectively) to control the configuration sent to the application. It sets 'origin_server' to False (to enable CGI-like output), and assumes that 'wsgi.run_once' is False. """ origin_server = False class CGIHandler(BaseCGIHandler): """CGI-based invocation via sys.stdin/stdout/stderr and os.environ Usage:: CGIHandler().run(app) The difference between this class and BaseCGIHandler is that it always uses 'wsgi.run_once' of 'True', 'wsgi.multithread' of 'False', and 'wsgi.multiprocess' of 'True'. It does not take any initialization parameters, but always uses 'sys.stdin', 'os.environ', and friends. If you need to override any of these parameters, use BaseCGIHandler instead. """ wsgi_run_once = True # Do not allow os.environ to leak between requests in Google App Engine # and other multi-run CGI use cases. This is not easily testable. # See http://bugs.python.org/issue7250 os_environ = {} def __init__(self): BaseCGIHandler.__init__( self, sys.stdin, sys.stdout, sys.stderr, dict(os.environ.items()), multithread=False, multiprocess=True )