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106 lines
3 KiB
Text
106 lines
3 KiB
Text
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Overview of the network subsystem
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Adrian Chadd <adrian@creative.net.au>
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$Id: network.txt 6 2005-09-10 01:02:21Z nenolod $
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This document is an overview of the new and hopefully improved network
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subsystem.
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The code is based loosely upon the network core found in the Squid web cache
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server, with some optimizations for ircd-specific IO patterns.
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Filedescriptor IO
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-----------------
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Filedescriptor IO is initiated using comm_setselect(). comm_setselect()
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registers interest in reading from or writing to a file descriptor.
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When a filedescriptor is ready for the required IO a callback is called
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from the IO loop.
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The comm_setselect() usage is:
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void
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comm_setselect(int fd, fdlist_t list, int type, PF *callback, void *cbdata,
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int timeout)
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where:
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fd filedescriptor
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list Which list the FD should be put on
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type IO type. Can currently include:
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COMM_SELECT_READ - register for read
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COMM_SELECT_WRITE - register for write
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callback Function to call when the FD is ready
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cbdata Data to be passed to above function
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timeout Update the timeout value. 0 is "don't update".
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A typical use is:
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..
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/* Register interest in the FD for a read event */
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comm_setselect(fd, FDLIST_SERVICE, COMM_SELECT_READ, read_callback, read_data,
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0);
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..
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(FD becomes ready for read in the IO loop)
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void
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read_callback(int fd, void *data)
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{
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/* called when the FD becomes ready for read */
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retval = read(fd, buf, len);
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..
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/* Ok, we need to read some more when its ready */
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comm_setselect(fd, FDLIST_SERVICE, COMM_SELECT_READ, read_callback, data,
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0);
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}
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Socket timeouts
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---------------
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A "socket timeout" is a callback registered to be called when a certain
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amount of time has elapsed. Think of it as an event, but against a FD.
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A good example of socket timeouts is in the comm_connect_tcp() code.
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When the connect() begins, comm_settimeout() is called to call
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comm_connect_timeout() if the timeout occurs. Once the connect() completes,
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comm_settimeout() is called with a timeout of 0 and callback of NULL
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to deregister the timeout. If the timeout occurs, comm_connect_timeout()
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is called and the connection attempt is aborted.
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Functions
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---------
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comm_open() - a socket() wrapper, enforcing fd limitations and tagging the
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file descriptor with a note
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comm_accept() - an accept() wrapper, enforcing fd limitations and tagging
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the file descriptor with a note
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comm_connect_tcp() - attempt an async connect(). Handles DNS lookups if
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required, and will call the given callback at completion or error
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comm_settimeout() - set a callback to be called after a given time period.
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This is good to implement things like PING checks and connect() timeouts.
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Notes:
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* All socket creation should go through comm_open() / comm_accept().
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* All socket closing should go through fd_close(). comm_close() isn't
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implemented yet.
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* comm_connect_tcp() is your best friend. :-)
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* *ALL* network sockets should be non-blocking. If your OS doesn't support
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non-blocking sockets, you shouldn't be here.
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