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212380e3 | 1 | Overview of the network subsystem |
2 | Adrian Chadd <adrian@creative.net.au> | |
3 | ||
4 | $Id: network.txt 6 2005-09-10 01:02:21Z nenolod $ | |
5 | ||
6 | ||
7 | This document is an overview of the new and hopefully improved network | |
8 | subsystem. | |
9 | ||
10 | The code is based loosely upon the network core found in the Squid web cache | |
11 | server, with some optimizations for ircd-specific IO patterns. | |
12 | ||
13 | ||
14 | ||
15 | Filedescriptor IO | |
16 | ----------------- | |
17 | ||
18 | Filedescriptor IO is initiated using comm_setselect(). comm_setselect() | |
19 | registers interest in reading from or writing to a file descriptor. | |
20 | When a filedescriptor is ready for the required IO a callback is called | |
21 | from the IO loop. | |
22 | ||
23 | The comm_setselect() usage is: | |
24 | ||
25 | void | |
26 | comm_setselect(int fd, fdlist_t list, int type, PF *callback, void *cbdata, | |
27 | int timeout) | |
28 | ||
29 | where: | |
30 | fd filedescriptor | |
31 | list Which list the FD should be put on | |
32 | type IO type. Can currently include: | |
33 | COMM_SELECT_READ - register for read | |
34 | COMM_SELECT_WRITE - register for write | |
35 | callback Function to call when the FD is ready | |
36 | cbdata Data to be passed to above function | |
37 | timeout Update the timeout value. 0 is "don't update". | |
38 | ||
39 | ||
40 | A typical use is: | |
41 | ||
42 | .. | |
43 | ||
44 | /* Register interest in the FD for a read event */ | |
45 | comm_setselect(fd, FDLIST_SERVICE, COMM_SELECT_READ, read_callback, read_data, | |
46 | 0); | |
47 | ||
48 | .. | |
49 | ||
50 | (FD becomes ready for read in the IO loop) | |
51 | ||
52 | void | |
53 | read_callback(int fd, void *data) | |
54 | { | |
55 | /* called when the FD becomes ready for read */ | |
56 | retval = read(fd, buf, len); | |
57 | ||
58 | .. | |
59 | /* Ok, we need to read some more when its ready */ | |
60 | comm_setselect(fd, FDLIST_SERVICE, COMM_SELECT_READ, read_callback, data, | |
61 | 0); | |
62 | } | |
63 | ||
64 | ||
65 | ||
66 | ||
67 | Socket timeouts | |
68 | --------------- | |
69 | ||
70 | A "socket timeout" is a callback registered to be called when a certain | |
71 | amount of time has elapsed. Think of it as an event, but against a FD. | |
72 | ||
73 | A good example of socket timeouts is in the comm_connect_tcp() code. | |
74 | When the connect() begins, comm_settimeout() is called to call | |
75 | comm_connect_timeout() if the timeout occurs. Once the connect() completes, | |
76 | comm_settimeout() is called with a timeout of 0 and callback of NULL | |
77 | to deregister the timeout. If the timeout occurs, comm_connect_timeout() | |
78 | is called and the connection attempt is aborted. | |
79 | ||
80 | ||
81 | ||
82 | ||
83 | Functions | |
84 | --------- | |
85 | ||
86 | comm_open() - a socket() wrapper, enforcing fd limitations and tagging the | |
87 | file descriptor with a note | |
88 | ||
89 | comm_accept() - an accept() wrapper, enforcing fd limitations and tagging | |
90 | the file descriptor with a note | |
91 | ||
92 | comm_connect_tcp() - attempt an async connect(). Handles DNS lookups if | |
93 | required, and will call the given callback at completion or error | |
94 | ||
95 | comm_settimeout() - set a callback to be called after a given time period. | |
96 | This is good to implement things like PING checks and connect() timeouts. | |
97 | ||
98 | Notes: | |
99 | ||
100 | * All socket creation should go through comm_open() / comm_accept(). | |
101 | * All socket closing should go through fd_close(). comm_close() isn't | |
102 | implemented yet. | |
103 | * comm_connect_tcp() is your best friend. :-) | |
104 | * *ALL* network sockets should be non-blocking. If your OS doesn't support | |
105 | non-blocking sockets, you shouldn't be here. |