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django under apache / mod_fcgid

Author:
mike_45
Posted:
February 3, 2009
Language:
Python
Version:
1.0
Tags:
apache fastcgi cgi mod_fcgid
Score:
2 (after 2 ratings)

This recipe uses a modified version of Robin Dunn's fcgi.py module that adapts fcgi to wsgi and lets you run Django under mod_fcgid. One good thing about mod_fcgid is that it does all process management for you, which makes this setup quite straightforward.

Also, since Robin's module works both in a cgi and fcgi context, switching a django site between cgi and fastcgi is a one-liner in the apache config, without any changes to python code or django config. CGI may be handy for development, since it loads all code (including changed code) on every request, yet lets you work in an environment that resembles production.

Apache configuration examples are found in the comment at the beginning of the python module.

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#!/usr/bin/python
'''
FcgiWsgiAdapter.py

serves wsgi requests over fcgi. Basic usage in wsgi script:

from FcgiWsgiAdapter import serve
serve(myWsgiApp)

The fcgi part of this was adopted wholesale, with minor modifications, 
from Robin Dunn's fastcgi module; the original preamble of that module 
is further down.
---
To use with django and mod_fcgid, you need a cgi script, say django.cgi:

#!/usr/bin/python
from FcgiWsgiAdapter import list_environment, serve_wsgi

import os, sys
os.environ['DJANGO_SETTINGS_MODULE'] = 'settings'  # or whatever
from django.core.handlers.wsgi import WSGIHandler

# use this to test that fastcgi works and to inspect the environment
# serve_wsgi(list_environment)
# use this to serve django
serve_wsgi(WSGIHandler())
-----
Apache config example:

RewriteRule ^/(~[^/]+)/django/(.*)$ /$1/django/django.cgi/$2 [PT]
<Directory /home/*/public_html/django/>
    Options ExecCGI
    AddHandler fcgid-script .cgi
    # AddHandler cgi-script .cgi
</Directory>

This would invoke django for any "/~joe/django/joes_app" request.
This configuration example also works with suexec, which would be 
useful in a multi-user context. 

Commenting out fcgid-script and uncommenting cgi-script (and a 
server restart) will switch the execution mode from fastcgi 
to plain cgi, without any further changes being required 
anywhere else.

For simpler urls when serving a single site, you could do

RewriteRule ^/mysite/(.*)$ /~fakeuser/django/django.cgi/$1 [PT]
<Directory /home/fakeuser/public_html/django/>
    Options ExecCGI
    AddHandler fcgid-script .cgi
</Directory>

This config would still give you suexec in a typical apache 
install, since [PT] applies the output of mod_rewrite to 
suexec and ~fakeuser is a user directory, which suexec likes.
'''

#
#               Copyright (c) 1998 by Total Control Software
#                         All Rights Reserved
#
#
# Module Name:  fcgi.py
#
# Description:  Handles communication with the FastCGI module of the
#               web server without using the FastCGI developers kit, but
#               will also work in a non-FastCGI environment, (straight CGI.)
#               This module was originally fetched from someplace on the
#               Net (I don't remember where and I can't find it now...) and
#               has been significantly modified to fix several bugs, be more
#               readable, more robust at handling large CGI data and return
#               document sizes, and also to fit the model that we had previously
#               used for FastCGI.
#
#     WARNING:  If you don't know what you are doing, don't tinker with this
#               module!
#
# Creation Date:    1/30/98 2:59:04PM
#
# License:      This is free software.  You may use this software for any
#               purpose including modification/redistribution, so long as
#               this header remains intact and that you do not claim any
#               rights of ownership or authorship of this software.  This
#               software has been tested, but no warranty is expressed or
#               implied.
#
#

# minor modifications by Michael Palmer:
# - reduce string copying operations when writing output
# - some updates to more recent python syntax


import  os, sys, string, socket, errno, traceback
from    cStringIO   import StringIO

from wsgiref.handlers import BaseCGIHandler

#

# Set various FastCGI constants
# Maximum number of requests that can be handled
FCGI_MAX_REQS=1
FCGI_MAX_CONNS = 1

# Supported version of the FastCGI protocol
FCGI_VERSION_1 = 1

# Boolean: can this application multiplex connections?
FCGI_MPXS_CONNS=0

# Record types
FCGI_BEGIN_REQUEST = 1 ; FCGI_ABORT_REQUEST = 2 ; FCGI_END_REQUEST   = 3
FCGI_PARAMS        = 4 ; FCGI_STDIN         = 5 ; FCGI_STDOUT        = 6
FCGI_STDERR        = 7 ; FCGI_DATA          = 8 ; FCGI_GET_VALUES    = 9
FCGI_GET_VALUES_RESULT = 10
FCGI_UNKNOWN_TYPE = 11
FCGI_MAXTYPE = FCGI_UNKNOWN_TYPE

# Types of management records
ManagementTypes = [FCGI_GET_VALUES]

FCGI_NULL_REQUEST_ID=0

# Masks for flags component of FCGI_BEGIN_REQUEST
FCGI_KEEP_CONN = 1

# Values for role component of FCGI_BEGIN_REQUEST
FCGI_RESPONDER = 1 ; FCGI_AUTHORIZER = 2 ; FCGI_FILTER = 3

# Values for protocolStatus component of FCGI_END_REQUEST
FCGI_REQUEST_COMPLETE = 0               # Request completed nicely
FCGI_CANT_MPX_CONN    = 1               # This app can't multiplex
FCGI_OVERLOADED       = 2               # New request rejected; too busy
FCGI_UNKNOWN_ROLE     = 3               # Role value not known

# chunk size for writing data
CHUNK_SIZE = 2**13  # 8 kB - tried 64 kB but it fucks up. 8 kB is fast enough.

error = 'fcgi.error'

# The following function is used during debugging; it isn't called
# anywhere at the moment

def error(msg):
    "Append a string to /tmp/err"
    errf=open('/tmp/err', 'a+')
    errf.write(msg +'\n')
    errf.close()

class record:
    "Class representing FastCGI records"
    def __init__(self):
        self.version = FCGI_VERSION_1
        self.recType = FCGI_UNKNOWN_TYPE
        self.reqId   = FCGI_NULL_REQUEST_ID
        self.content = ""

    #
    def readRecord(self, sock):
        s = map(ord, sock.recv(8))
        self.version, self.recType, paddingLength = s[0], s[1], s[6]
        self.reqId, contentLength = (s[2]<<8)+s[3], (s[4]<<8)+s[5]
        self.content = ""
        while len(self.content) < contentLength:
            data = sock.recv(contentLength - len(self.content))
            self.content = self.content + data
        if paddingLength != 0:
            padding = sock.recv(paddingLength)

        # Parse the content information
        c = self.content
        if self.recType == FCGI_BEGIN_REQUEST:
            self.role = (ord(c[0])<<8) + ord(c[1])
            self.flags = ord(c[2])

        elif self.recType == FCGI_UNKNOWN_TYPE:
            self.unknownType = ord(c[0])

        elif self.recType == FCGI_GET_VALUES or self.recType == FCGI_PARAMS:
            self.values={}
            pos=0
            while pos < len(c):
                name, value, pos = readPair(c, pos)
                self.values[name] = value
        elif self.recType == FCGI_END_REQUEST:
            b = map(ord, c[0:4])
            self.appStatus = (b[0]<<24) + (b[1]<<16) + (b[2]<<8) + b[3]
            self.protocolStatus = ord(c[4])

    #
    def writeRecord(self, sock):
        content = self.content
        if self.recType == FCGI_BEGIN_REQUEST:
            content = chr(self.role>>8) + chr(self.role & 255) + chr(self.flags) + 5*'\000'

        elif self.recType == FCGI_UNKNOWN_TYPE:
            content = chr(self.unknownType) + 7*'\000'

        elif self.recType==FCGI_GET_VALUES or self.recType==FCGI_PARAMS:
            content = ""
            for i in self.values.keys():
                content = content + writePair(i, self.values[i])

        elif self.recType==FCGI_END_REQUEST:
            v = self.appStatus
            content = chr((v>>24)&255) + chr((v>>16)&255) + chr((v>>8)&255) + chr(v&255)
            content = content + chr(self.protocolStatus) + 3*'\000'

        cLen = len(content)
        eLen = (cLen + 7) & (0xFFFF - 7)    # align to an 8-byte boundary
        padLen = eLen - cLen

        hdr = [ self.version,
                self.recType,
                self.reqId >> 8,
                self.reqId & 255,
                cLen >> 8,
                cLen & 255,
                padLen,
                0]
        # hdr = string.joinfields(map(chr, hdr), '')
        hdr = ''.join([chr(h) for h in hdr])

        sock.send(hdr + content + padLen*'\000')

#

def readPair(s, pos):
    nameLen = ord(s[pos])
    pos += 1

    if nameLen & 128:
        b = [ord(x) for x in s[pos:pos+3]]
        pos += 3
        nameLen = ((nameLen&127)<<24) + (b[0]<<16) + (b[1]<<8) + b[2]

    valueLen = ord(s[pos])
    pos += 1

    if valueLen & 128:
        b = [ord(x) for x in s[pos:pos+3]]
        pos += 3
        valueLen=((valueLen&127)<<24) + (b[0]<<16) + (b[1]<<8) + b[2]

    return ( s[pos:pos+nameLen], s[pos+nameLen:pos+nameLen+valueLen],
             pos+nameLen+valueLen )



def writePair(name, value):
    l=len(name)
    if l<128: s=chr(l)
    else:
        s=chr(128|(l>>24)&255) + chr((l>>16)&255) + chr((l>>8)&255) + chr(l&255)
    l=len(value)
    if l<128: s=s+chr(l)
    else:
        s=s+chr(128|(l>>24)&255) + chr((l>>16)&255) + chr((l>>8)&255) + chr(l&255)
    return s + name + value

#

def HandleManTypes(r, conn):
    if r.recType == FCGI_GET_VALUES:
        r.recType = FCGI_GET_VALUES_RESULT
        v={}
        vars={'FCGI_MAX_CONNS' : FCGI_MAX_CONNS,
              'FCGI_MAX_REQS'  : FCGI_MAX_REQS,
              'FCGI_MPXS_CONNS': FCGI_MPXS_CONNS}
        for i in r.values.keys():
            if vars.has_key(i): v[i]=vars[i]
        r.values=vars
        r.writeRecord(conn)

#
#


_isFCGI = 1         # assume it is until we find out for sure

def isFCGI():
    global _isFCGI
    return _isFCGI

#


fcgi_init = None
_sock = None

class FCGI:
    def __init__(self):
        self.haveFinished = 0
        if fcgi_init == None:
            _startup()
        if not isFCGI():
            self.haveFinished = 1
            self.inp, self.out, self.err, self.env = \
                                sys.stdin, sys.stdout, sys.stderr, os.environ
            return

        if os.environ.has_key('FCGI_WEB_SERVER_ADDRS'):
            good_addrs=string.split(os.environ['FCGI_WEB_SERVER_ADDRS'], ',')
            good_addrs=map(string.strip(good_addrs))        # Remove whitespace
        else:
            good_addrs=None

        self.conn, addr=_sock.accept()
        stdin, data="", ""
        self.env = {}
        self.requestId=0
        remaining=1

        # Check if the connection is from a legal address
        if good_addrs!=None and addr not in good_addrs:
            raise error, 'Connection from invalid server!'

        while remaining:
            r = record()
            r.readRecord(self.conn)

            if r.recType in ManagementTypes:
                HandleManTypes(r, self.conn)

            elif r.reqId==0:
                # Oh, poopy.  It's a management record of an unknown
                # type.  Signal the error.
                r2 = record()
                r2.recType = FCGI_UNKNOWN_TYPE ; r2.unknownType=r.recType
                r2.writeRecord(self.conn)
                continue                # Charge onwards

            # Ignore requests that aren't active
            elif r.reqId != self.requestId and r.recType != FCGI_BEGIN_REQUEST:
                continue

            # If we're already doing a request, ignore further BEGIN_REQUESTs
            elif r.recType == FCGI_BEGIN_REQUEST and self.requestId != 0:
                continue

            # Begin a new request
            if r.recType == FCGI_BEGIN_REQUEST:
                self.requestId = r.reqId
                if r.role == FCGI_AUTHORIZER:   remaining=1
                elif r.role == FCGI_RESPONDER:  remaining=2
                elif r.role == FCGI_FILTER:     remaining=3

            elif r.recType == FCGI_PARAMS:
                if r.content == "":
                    remaining=remaining-1
                else:
                    for i in r.values.keys():
                        self.env[i] = r.values[i]

            elif r.recType == FCGI_STDIN:
                if r.content == "":
                    remaining=remaining-1
                else:
                    stdin=stdin+r.content

            elif r.recType==FCGI_DATA:
                if r.content == "":
                    remaining=remaining-1
                else:
                    data=data+r.content
        # end of while remaining:

        self.inp = sys.stdin  = StringIO(stdin)
        self.err = sys.stderr = StringIO()
        self.out = sys.stdout = StringIO()
        #self.data = StringIO(data)

    #def __del__(self): I really don't get what this is good for...
        #self.finish()

    def finish(self, status=0):
        if not self.haveFinished:
            self.haveFinished = 1

            self.err.seek(0,0)
            self.out.seek(0,0)

            r=record()
            r.recType = FCGI_STDERR
            r.reqId = self.requestId
            data = self.err.read()

            chunker = self.datachunker(data)
            for chunk in chunker:
                r.content = chunk
                r.writeRecord(self.conn)
            r.content="" ; r.writeRecord(self.conn)      # Terminate stream

            r.recType = FCGI_STDOUT
            data = self.out.read()

            chunker = self.datachunker(data)

            for chunk in chunker:
                r.content = chunk
                r.writeRecord(self.conn)
            r.content="" ; r.writeRecord(self.conn)      # Terminate stream

            r=record()
            r.recType=FCGI_END_REQUEST
            r.reqId=self.requestId
            r.appStatus=status
            r.protocolStatus=FCGI_REQUEST_COMPLETE
            r.writeRecord(self.conn)
            self.conn.close()
        elif not isFCGI():   # for some reason cgi repeats again and again if we don't do this.
            sys.exit()

    def datachunker(self, data):
        '''
        yield string in chunks for writing
        '''
        c = 0
        cs = CHUNK_SIZE
        d = data[c:c + cs]
        if d:
            c += cs
            yield d
        else:
            raise StopIteration


def _startup():
    global fcgi_init
    fcgi_init = 1
    try:
        s=socket.fromfd(sys.stdin.fileno(), socket.AF_INET,
                        socket.SOCK_STREAM)
        s.getpeername()
    except socket.error, (err, errmsg):
        if err != errno.ENOTCONN:       # must be a non-fastCGI environment
            global _isFCGI
            _isFCGI = 0
            return

    global _sock
    _sock = s


#--------------------------------------------------------------------
# the code below is not part of the original fcgi.py module; it builds
# on the fcgi.py code to run wsgi applications.

# show full traceback if request originated from any of these ips
SHOW_TRACEBACK_IPS = ['127.0.0.1']

class FCGIHandler(BaseCGIHandler):
    '''
    handle a single request received through fcgi
    '''
    wsgi_multithread = False    # the underlying fcgi module is not threaded
    wsgi_multiprocess = True    # might be wrong, depending on your config
    wsgi_run_once = False       # ... likewise
    origin_server = False       # We are not transmitting direct to client, so won't
                                # send http status line and protocol information

    def __init__(self, request):
        BaseCGIHandler.__init__(self, request.inp, request.out, request.err, request.env, \
                                      multithread=self.wsgi_multithread, \
                                      multiprocess=self.wsgi_multiprocess)

    # error handling. this is sent to the client by wsgiref.basehandler.

    def error_output(self, environ, start_response):
        '''
        show traceback if we are so entitled.
        '''
        start_response(self.error_status, self.error_headers[:], sys.exc_info())
        if self.environ.get('REMOTE_ADDR') in SHOW_TRACEBACK_IPS:
            err = traceback.format_exc()
        else:
            err = self.error_body
        return ['wsgi app execution error\n', '-' * 24, '\n', err]


    def run(self, application):
        '''
        Invoke the application
        '''
        self.setup_environ()
        self.result = application(self.environ, self.start_response)
        self.finish_response()


def serve_wsgi(app, handlerClass=FCGIHandler):
    '''
    run (wsgi) app on each incoming FCGI request.
    '''
    while True:
        req = FCGI()
        h = handlerClass(req)
        h.run(app)
        req.finish()
        del req

#------------------------------------------------
# test the thing...
def list_environment(environ, start_response):
    '''
    Simple WSGI test application - just display the wsgi environment.
    Kinda useful, too for debugging.
    '''
    status = '200 OK'
    response_headers = [('Content-type','text/plain')]
    start_response(status, response_headers)
    out = ['FcgiWsgiAdapter test output (just a listing of the WSGI environment)\n']
    out.append('-' * (len(out[0]) -1)  + '\n')

    for k,v in sorted(environ.items()):
        out.extend([k.ljust(25), ': ', str(v).strip(), '\n'])

    return out


def test():
    '''
    to run this, import and run in an actual cgi or fcgi script
    '''
    serve_wsgi(list_environment)

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Comments

dvd (on March 30, 2009):

The datachunker method emit only one chunk, I think it should be something like this:

def datachunker(self, data):
    '''
    yield string in chunks for writing
    '''
    c = 0
    cs = CHUNK_SIZE
    d = data[c:c + cs]
    while d:
        yield d
        c += cs
        d = data[c:c + cs]

#

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