[Alan Kennedy]
3. If I had to pick one of the 3 you suggested, I'd pick the
last one, i.e. PJE's, because it fulfills exactly the criteria
I listed
[Robert Brewer]
I have to disagree (having examined/unraveled it quite a bit recently,
to remove modpython_gateway's dependency on it).
[Ian Bicking]
I think it also tries to enforce a lot of the details of WSGI, and thus
guide a WSGI implementor into creating a compliant server.
Well, I'm sure we all want our favourite server in the stdlib ;-)
But a few things have to happen first.
Priority #1: Make the requisite server a single standalone module.
Anticipating PJE's willingness to have WSGIRef included in the stdlib,
I've taken the liberty of putting it all into one big file. And I think
it looks pretty damn good: fully WSGI compliant, with code to represent
every single aspect of the spec. Take a look for yourself: the file is
attached. If the attachment doesn't make it to the list, I'll upload it
somewhere.
But that doesn't mean the decision's over. It means that the bar has
been raised. Anyone else who wants their module to be a contender has to
get it all into the one file, i.e. eliminating all framework
dependencies, etc.
Here's a few comments I put together about the three contenders that
have been proposed so far. They're just my own comments from reading the
code: feel free to treat them as the ravings of a madman if you so wish.
1. CherryPy server - 407 lines (non-code lines: ~80)
- Depends on cherrypy, cherryp._cputil, cherryp.lib.httptools
- Depends on cherrypy.config
- Implements HTTP header length limit checking
- Implements HTTP body length limit checking
- Uses own logging handler
- Subclasses SocketServer.BaseServer, not BaseHTTPServer.HTTPServer
- Therefore does low-level socket mucking-about
- Provides 2 server implementations
- CherryHTTPServer
- PooledThreadServer
- Explicitly checks for KeyboardInterrupt exceptions
- PooledThreadServer has clean shutdown through Queue.Queue messaging
- Does not detect hop-by-hop headers
- No demo application
My gut feeling: too complex, works to hard to be "production-ready", at
the expense of readability.
2. Paste Server - 450 lines
- Supports 100 continue responses
- No imports from outside stdlib
- Provides HTTPS/SSL server, with fallback if no SSL
- Supports socket timeout
- Demo application is (imported) paste.wsgilib.dump_environ
- Does not detect hop-by-hop headers
My gut feeling: Ignores many parts of the WSGI spec (sendfile, strict
error checking), supports unnecessary stuff for stdlib, i.e. Continue
support, HTTPS.
3. WSGIRef_onefile.py - 660 lines
- No imports from outside stdlib
- Detects hop-by-hop headers
- Has WSGI sendfile support
- Has dedicated class to manage WSGI headers list as dictionary
- Has builtin demo app
My gut feeling: WSGIRef is the sweetspot in terms of simplicity vs.
usability. Covers all aspects of WSGI (which is what it was designed
for, IIRC ;-)
The ball's in yizzir court now......
Alan.
"""BaseHTTPServer that implements the Python WSGI protocol (PEP 333, rev 1.21)
This is both an example of how WSGI can be implemented, and a basis for running
simple web applications on a local machine, such as might be done when testing
or debugging an application. It has not been reviewed for security issues,
however, and we strongly recommend that you use a "real" web server for
production use.
For example usage, see the 'if __name__=="__main__"' block at the end of the
module. See also the BaseHTTPServer module docs for other API information.
"""
from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer
import urllib, sys, os, mimetools, types, time
__version__ = "0.1"
__all__ = ['WSGIServer','WSGIRequestHandler','demo_app']
server_version = "WSGIServer/" + __version__
sys_version = "Python/" + sys.version.split()[0]
software_version = server_version + ' ' + sys_version
hop_by_hop_headers = {
'connection':1,
'keep-alive':1,
'proxy-authenticate':1,
'proxy-authorization':1,
'te':1,
'trailers':1,
'transfer-encoding':1,
'upgrade':1
}
def is_hop_by_hop(header_name):
"""Return true if 'header_name' is an HTTP/1.1 "Hop-by-Hop" header"""
return hop_by_hop_headers.has_key(header_name.lower())
class FileWrapper:
"""Wrapper to convert file-like objects to iterables"""
def __init__(self, filelike, blocksize=8192):
self.filelike = filelike
self.blocksize = blocksize
if hasattr(filelike,'close'):
self.close = filelike.close
def __getitem__(self,key):
data = self.filelike.read(self.blocksize)
if data:
return data
raise IndexError
def __iter__(self):
return self
def next(self):
data = self.filelike.read(self.blocksize)
if data:
return data
raise StopIteration
class Headers:
"""Manage a collection of HTTP response headers"""
def __init__(self,headers):
if type(headers) is not types.ListType:
raise TypeError("Headers must be a list of name/value tuples")
self._headers = headers
def __len__(self):
"""Return the total number of headers, including duplicates."""
return len(self._headers)
def __setitem__(self, name, val):
"""Set the value of a header."""
del self[name]
self._headers.append((name, val))
def __delitem__(self,name):
"""Delete all occurrences of a header, if present.
Does *not* raise an exception if the header is missing.
"""
name = name.lower()
self._headers[:] = [kv for kv in self._headers if kv[0].lower()<>name]
def __getitem__(self,name):
"""Get the first header value for 'name'
Return None if the header is missing instead of raising an exception.
Note that if the header appeared multiple times, the first exactly which
occurrance gets returned is undefined. Use getall() to get all
the values matching a header field name.
"""
return self.get(name)
def has_key(self, name):
"""Return true if the message contains the header."""
return self.get(name) is not None
__contains__ = has_key
def get_all(self, name):
"""Return a list of all the values for the named field.
These will be sorted in the order they appeared in the original header
list or were added to this instance, and may contain duplicates. Any
fields deleted and re-inserted are always appended to the header list.
If no fields exist with the given name, returns an empty list.
"""
name = name.lower()
return [kv[1] for kv in self._headers if kv[0].lower()==name]
def get(self,name,default=None):
"""Get the first header value for 'name', or return 'default'"""
name = name.lower()
for k,v in self._headers:
if k.lower()==name:
return v
return default
def keys(self):
"""Return a list of all the header field names.
These will be sorted in the order they appeared in the original header
list, or were added to this instance, and may contain duplicates.
Any fields deleted and re-inserted are always appended to the header
list.
"""
return [k for k, v in self._headers]
def values(self):
"""Return a list of all header values.
These will be sorted in the order they appeared in the original header
list, or were added to this instance, and may contain duplicates.
Any fields deleted and re-inserted are always appended to the header
list.
"""
return [v for k, v in self._headers]
def items(self):
"""Get all the header fields and values.
These will be sorted in the order they were in the original header
list, or were added to this instance, and may contain duplicates.
Any fields deleted and re-inserted are always appended to the header
list.
"""
return self._headers[:]
def __repr__(self):
return "Headers(%s)" % `self._headers`
def __str__(self):
"""str() returns the formatted headers, complete with end line,
suitable for direct HTTP transmission."""
return '\r\n'.join(["%s: %s" % kv for kv in self._headers]+['',''])
def setdefault(self,name,value):
"""Return first matching header value for 'name', or 'value'
If there is no header named 'name', add a new header with name 'name'
and value 'value'."""
result = self.get(name)
if result is None:
self._headers.append((name,value))
return value
else:
return result
def add_header(self, _name, _value, **_params):
"""Extended header setting.
_name is the header field to add. keyword arguments can be used to set
additional parameters for the header field, with underscores converted
to dashes. Normally the parameter will be added as key="value" unless
value is None, in which case only the key will be added.
Example:
h.add_header('content-disposition', 'attachment', filename='bud.gif')
Note that unlike the corresponding 'email.Message' method, this does
*not* handle '(charset, language, value)' tuples: all values must be
strings or None.
"""
parts = []
if _value is not None:
parts.append(_value)
for k, v in _params.items():
if v is None:
parts.append(k.replace('_', '-'))
else:
parts.append(_formatparam(k.replace('_', '-'), v))
self._headers.append((_name, "; ".join(parts)))
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 Dude, this is whack!"
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.guess_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.
"""
if not self.result_is_file() and not self.sendfile():
for data in self.result:
self.write(data)
self.finish_content()
self.close()
def guess_scheme(self):
"""Return a guess for whether 'wsgi.url_scheme' should be 'http' or 'https' """
if self.environ.get("HTTPS") in ('yes','on','1'):
return 'https'
else:
return 'http'
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 not self.headers.has_key('Content-Length'):
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 types.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 types.StringType,"Header names must be strings"
assert type(val) is types.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 not self.headers.has_key('Date'):
self._write(
'Date: %s\r\n' % time.asctime(time.gmtime(time.time()))
)
if self.server_software and not self.headers.has_key('Server'):
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 types.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 file1.
"""
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:
self.headers['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 ServerHandler(SimpleHandler):
server_software = software_version
def close(self):
try:
self.request_handler.log_request(
self.status.split(' ',1)[0], self.bytes_sent
)
finally:
SimpleHandler.close(self)
class WSGIServer(HTTPServer):
"""BaseHTTPServer that implements the Python WSGI protocol"""
application = None
def server_bind(self):
"""Override server_bind to store the server name."""
HTTPServer.server_bind(self)
self.setup_environ()
def setup_environ(self):
# Set up base environment
env = self.base_environ = {}
env['SERVER_NAME'] = self.server_name
env['GATEWAY_INTERFACE'] = 'CGI/1.1'
env['SERVER_PORT'] = str(self.server_port)
env['REMOTE_HOST']=''
env['CONTENT_LENGTH']=''
env['SCRIPT_NAME'] = ''
def get_app(self):
return self.application
def set_app(self,application):
self.application = application
class WSGIRequestHandler(BaseHTTPRequestHandler):
server_version = "WSGIServer/" + __version__
def get_environ(self):
env = self.server.base_environ.copy()
env['SERVER_PROTOCOL'] = self.request_version
env['REQUEST_METHOD'] = self.command
if '?' in self.path:
path,query = self.path.split('?',1)
else:
path,query = self.path,''
env['PATH_INFO'] = urllib.unquote(path)
env['QUERY_STRING'] = query
host = self.address_string()
if host != self.client_address[0]:
env['REMOTE_HOST'] = host
env['REMOTE_ADDR'] = self.client_address[0]
if self.headers.typeheader is None:
env['CONTENT_TYPE'] = self.headers.type
else:
env['CONTENT_TYPE'] = self.headers.typeheader
length = self.headers.getheader('content-length')
if length:
env['CONTENT_LENGTH'] = length
for h in self.headers.headers:
k,v = h.split(':',1)
k=k.replace('-','_').upper(); v=v.strip()
if k in env:
continue # skip content length, type,etc.
if 'HTTP_'+k in env:
env['HTTP_'+k] += ','+v # comma-separate multiple headers
else:
env['HTTP_'+k] = v
return env
def get_stderr(self):
return sys.stderr
def handle(self):
"""Handle a single HTTP request"""
self.raw_requestline = self.rfile.readline()
if not self.parse_request(): # An error code has been sent, just exit
return
handler = ServerHandler(
self.rfile, self.wfile, self.get_stderr(), self.get_environ()
)
handler.request_handler = self # backpointer for logging
handler.run(self.server.get_app())
def demo_app(environ,start_response):
from StringIO import StringIO
stdout = StringIO()
print >>stdout, "Hello world!"
print >>stdout
h = environ.items(); h.sort()
for k,v in h:
print >>stdout, k,'=',`v`
start_response("200 OK", [('Content-Type','text/plain')])
return [stdout.getvalue()]
if __name__ == '__main__':
server_address = ('', 8000)
httpd = WSGIServer(server_address, WSGIRequestHandler)
httpd.set_app(demo_app)
sa = httpd.socket.getsockname()
print "Serving HTTP on", sa[0], "port", sa[1], "..."
import webbrowser
webbrowser.open('http://localhost:8000/xyz?abc')
httpd.handle_request() # serve one request, then exit
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