python: Added some actual documentation(!).
[ashd.git] / python / ashd / proto.py
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1"""Low-level protocol module for ashd(7)
2
3This module provides primitive functions that speak the raw ashd(7)
4protocol. Primarily, it implements the `req' class that is used to
5represent ashd requests. The functions it provides can also be used to
6create ashd handlers, but unless you require very precise control, the
7ashd.util module provides an easier-to-use interface.
8"""
9
10import os, socket
11import htlib
12
13class protoerr(Exception):
14 pass
15
16class req(object):
17 """Represents a single ashd request. Normally, you would not
18 create instances of this class manually, but receive them from the
19 recvreq function.
20
21 For the abstract structure of ashd requests, please see the
22 ashd(7) manual page. This class provides access to the HTTP
23 method, raw URL, HTTP version and rest string via the `method',
24 `url', `ver' and `rest' variables respectively. It also implements
25 a dict-like interface for case-independent access to the HTTP
26 headers. The raw headers are available as a list of (name, value)
27 tuples in the `headers' variable.
28
29 For responding, the response socket is available as a standard
30 Python stream object in the `sk' variable. Again, see the ashd(7)
31 manpage for what to receive and transmit on the response socket.
32
33 Note that instances of this class contain a reference to the live
34 socket used for responding to requests, which should be closed
35 when you are done with the request. The socket can be closed
36 manually by calling the close() method on this
37 object. Alternatively, this class implements the resource-manager
38 interface, so that it can be used in `with' statements.
39 """
40
41 def __init__(self, method, url, ver, rest, headers, fd):
42 self.method = method
43 self.url = url
44 self.ver = ver
45 self.rest = rest
46 self.headers = headers
47 self.sk = socket.fromfd(fd, socket.AF_UNIX, socket.SOCK_STREAM).makefile('r+')
48 os.close(fd)
49
50 def close(self):
51 "Close this request's response socket."
52 self.sk.close()
53
54 def __getitem__(self, header):
55 """Find a HTTP header case-insensitively. For example,
56 req["Content-Type"] returns the value of the content-type
57 header regardlessly of whether the client specified it as
58 "Content-Type", "content-type" or "Content-type".
59 """
60 header = header.lower()
61 for key, val in self.headers:
62 if key.lower() == header:
63 return val
64 raise KeyError(header)
65
66 def __contains__(self, header):
67 """Works analogously to the __getitem__ method for checking
68 header presence case-insensitively.
69 """
70 header = header.lower()
71 for key, val in self.headers:
72 if key.lower() == header:
73 return True
74 return False
75
76 def dup(self):
77 """Creates a duplicate of this request, referring to a
78 duplicate of the response socket.
79 """
80 return req(self.method, self.url, self.ver, self.rest, self.headers, os.dup(self.sk.fileno()))
81
82 def match(self, match):
83 """If the `match' argument matches exactly the leading part of
84 the rest string, this method strips that part of the rest
85 string off and returns True. Otherwise, it returns False
86 without doing anything.
87
88 This can be used for simple dispatching. For example:
89 if req.match("foo/"):
90 handle(req)
91 elif req.match("bar/"):
92 handle_otherwise(req)
93 else:
94 util.respond(req, "Not found", status = "404 Not Found", ctype = "text/plain")
95 """
96 if self.rest[:len(match)] == match:
97 self.rest = self.rest[len(match):]
98 return True
99 return False
100
101 def __str__(self):
102 return "\"%s %s %s\"" % (self.method, self.url, self.ver)
103
104 def __enter__(self):
105 return self
106
107 def __exit__(self, *excinfo):
108 self.sk.close()
109 return False
110
111def recvreq(sock = 0):
112 """Receive a single ashd request on the specified socket file
113 descriptor (or standard input if unspecified).
114
115 The returned value is an instance of the `req' class. As per its
116 description, care should be taken to close() the request when
117 done, to avoid leaking response sockets.
118
119 This function may either raise on OSError if an error occurs on
120 the socket, or a ashd.proto.protoerr if the incoming request is
121 invalidly encoded.
122 """
123 data, fd = htlib.recvfd(sock)
124 if fd is None:
125 return None
126 try:
127 parts = data.split('\0')[:-1]
128 if len(parts) < 5:
129 raise protoerr("Truncated request")
130 method, url, ver, rest = parts[:4]
131 headers = []
132 i = 4
133 while True:
134 if parts[i] == "": break
135 if len(parts) - i < 3:
136 raise protoerr("Truncated request")
137 headers.append((parts[i], parts[i + 1]))
138 i += 2
139 return req(method, url, ver, rest, headers, os.dup(fd))
140 finally:
141 os.close(fd)
142
143def sendreq(sock, req):
144 """Encode and send a single request to the specified socket file
145 descriptor using the ashd protocol. The request should be an
146 instance of the `req' class.
147
148 This function may raise an OSError if an error occurs on the
149 socket.
150 """
151 data = ""
152 data += req.method + '\0'
153 data += req.url + '\0'
154 data += req.ver + '\0'
155 data += req.rest + '\0'
156 for key, val in req.headers:
157 data += key + '\0'
158 data += val + '\0'
159 data += '\0'
160 htlib.sendfd(sock, req.sk.fileno(), data)