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