doc: Fixed typo.
[ashd.git] / python / ashd / wsgidir.py
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1"""WSGI handler for serving chained WSGI modules from physical files
2
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3The WSGI handler in this module ensures that the SCRIPT_FILENAME
4variable is properly set in every request and points out a file that
5exists and is readable. It then dispatches the request in one of two
6ways: If the header X-Ash-Python-Handler is set in the request, its
7value is used as the name of a handler object to dispatch the request
8to; otherwise, the file extension of the SCRIPT_FILENAME is used to
9determine the handler object.
10
11The name of a handler object is specified as a string, which is split
12along its last constituent dot. The part left of the dot is the name
13of a module, which is imported; and the part right of the dot is the
14name of an object in that module, which should be a callable adhering
15to the WSGI specification. Alternatively, the module part may be
16omitted (such that the name is a string with no dots), in which case
17the handler object is looked up from this module.
18
19By default, this module will handle files with the extensions `.wsgi'
20or `.wsgi2' using the `chain' handler, which chainloads such files and
21runs them as independent WSGI applications. See its documentation for
22details.
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23
24This module itself contains both an `application' and a `wmain'
25object. If this module is used by ashd-wsgi(1) or scgi-wsgi(1) so that
26its wmain function is called, arguments can be specified to it to
27install handlers for other file extensions. Such arguments take the
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28form `.EXT=HANDLER', where EXT is the file extension to be handled,
29and HANDLER is a handler name, as described above. For example, the
30argument `.fpy=my.module.foohandler' can be given to pass requests for
31`.fpy' files to the function `foohandler' in the module `my.module'
32(which must, of course, be importable). When writing such handler
33functions, you may want to use the getmod() function in this module.
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34"""
35
c06db49a 36import os, threading, types
173e0e9e 37import wsgiutil
c06db49a 38
5c1a2105 39__all__ = ["application", "wmain", "getmod", "cachedmod", "chain"]
fc2aa563 40
f677567f 41class cachedmod(object):
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42 """Cache entry for modules loaded by getmod()
43
44 Instances of this class are returned by the getmod()
45 function. They contain three data attributes:
46 * mod - The loaded module
47 * lock - A threading.Lock object, which can be used for
48 manipulating this instance in a thread-safe manner
49 * mtime - The time the file was last modified
50
51 Additional data attributes can be arbitrarily added for recording
52 any meta-data about the module.
53 """
7fe08a6f 54 def __init__(self, mod = None, mtime = -1):
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55 self.lock = threading.Lock()
56 self.mod = mod
57 self.mtime = mtime
58
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59modcache = {}
60cachelock = threading.Lock()
61
62def mangle(path):
63 ret = ""
64 for c in path:
65 if c.isalnum():
66 ret += c
67 else:
68 ret += "_"
69 return ret
70
71def getmod(path):
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72 """Load the given file as a module, caching it appropriately
73
74 The given file is loaded and compiled into a Python module. The
75 compiled module is cached and returned upon subsequent requests
76 for the same file, unless the file has changed (as determined by
77 its mtime), in which case the cached module is discarded and the
78 new file contents are reloaded in its place.
79
80 The return value is an instance of the cachedmod class, which can
81 be used for locking purposes and for storing arbitrary meta-data
82 about the module. See its documentation for details.
83 """
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84 sb = os.stat(path)
85 cachelock.acquire()
86 try:
87 if path in modcache:
14ef1e0e 88 entry = modcache[path]
7fe08a6f 89 else:
b8d56e8f 90 entry = [threading.Lock(), None]
7fe08a6f 91 modcache[path] = entry
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92 finally:
93 cachelock.release()
b8d56e8f 94 entry[0].acquire()
7fe08a6f 95 try:
b8d56e8f 96 if entry[1] is None or sb.st_mtime > entry[1].mtime:
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97 f = open(path, "r")
98 try:
99 text = f.read()
100 finally:
101 f.close()
102 code = compile(text, path, "exec")
103 mod = types.ModuleType(mangle(path))
104 mod.__file__ = path
105 exec code in mod.__dict__
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106 entry[1] = cachedmod(mod, sb.st_mtime)
107 return entry[1]
7fe08a6f 108 finally:
b8d56e8f 109 entry[0].release()
c06db49a 110
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111class handler(object):
112 def __init__(self):
113 self.lock = threading.Lock()
114 self.handlers = {}
115 self.exts = {}
116 self.addext("wsgi", "chain")
117 self.addext("wsgi2", "chain")
118
119 def resolve(self, name):
120 self.lock.acquire()
121 try:
122 if name in self.handlers:
123 return self.handlers[name]
124 p = name.rfind('.')
125 if p < 0:
126 return globals()[name]
127 mname = name[:p]
128 hname = name[p + 1:]
129 mod = __import__(mname, fromlist = ["dummy"])
130 ret = getattr(mod, hname)
131 self.handlers[name] = ret
132 return ret
133 finally:
134 self.lock.release()
135
136 def addext(self, ext, handler):
137 self.exts[ext] = self.resolve(handler)
138
139 def handle(self, env, startreq):
140 if not "SCRIPT_FILENAME" in env:
141 return wsgiutil.simpleerror(env, startreq, 500, "Internal Error", "The server is erroneously configured.")
142 path = env["SCRIPT_FILENAME"]
7ed9b82b 143 if not os.access(path, os.R_OK):
e9817fee 144 return wsgiutil.simpleerror(env, startreq, 500, "Internal Error", "The server is erroneously configured.")
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145 if "HTTP_X_ASH_PYTHON_HANDLER" in env:
146 handler = self.resolve(env["HTTP_X_ASH_PYTHON_HANDLER"])
147 else:
148 base = os.path.basename(path)
149 p = base.rfind('.')
150 if p < 0:
151 return wsgiutil.simpleerror(env, startreq, 500, "Internal Error", "The server is erroneously configured.")
152 ext = base[p + 1:]
153 if not ext in self.exts:
154 return wsgiutil.simpleerror(env, startreq, 500, "Internal Error", "The server is erroneously configured.")
155 handler = self.exts[ext]
156 return handler(env, startreq)
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157
158def wmain(*argv):
159 """Main function for ashd(7)-compatible WSGI handlers
160
161 Returns the `application' function. If any arguments are given,
162 they are parsed according to the module documentation.
163 """
164 ret = handler()
165 for arg in argv:
166 if arg[0] == '.':
167 p = arg.index('=')
168 ret.addext(arg[1:p], arg[p + 1:])
169 return ret.handle
170
9b417336 171def chain(env, startreq):
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172 """Chain-loading WSGI handler
173
174 This handler loads requested files, compiles them and loads them
175 into their own modules. The compiled modules are cached and reused
176 until the file is modified, in which case the previous module is
177 discarded and the new file contents are loaded into a new module
178 in its place. When chaining such modules, an object named `wmain'
179 is first looked for and called with no arguments if found. The
180 object it returns is then used as the WSGI application object for
181 that module, which is reused until the module is reloaded. If
182 `wmain' is not found, an object named `application' is looked for
183 instead. If found, it is used directly as the WSGI application
184 object.
185 """
9b417336 186 path = env["SCRIPT_FILENAME"]
c06db49a 187 mod = getmod(path)
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188 entry = None
189 if mod is not None:
190 mod.lock.acquire()
191 try:
192 if hasattr(mod, "entry"):
193 entry = mod.entry
194 else:
195 if hasattr(mod.mod, "wmain"):
adb11d5f 196 entry = mod.mod.wmain()
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197 elif hasattr(mod.mod, "application"):
198 entry = mod.mod.application
199 mod.entry = entry
200 finally:
201 mod.lock.release()
202 if entry is not None:
203 return entry(env, startreq)
36ea06a6 204 return wsgiutil.simpleerror(env, startreq, 500, "Internal Error", "Invalid WSGI handler.")
c06db49a 205
e9817fee 206application = handler().handle