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51 lines
2.0 KiB
Markdown
51 lines
2.0 KiB
Markdown
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## OS compatibility functions ##
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We've got a bunch of functions to wrap differences between various
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operating systems where we run.
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### The filesystem ###
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We wrap the most important filesystem functions with load-file,
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save-file, and map-file abstractions declared in util.c or compat.c. If
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you're messing about with file descriptors yourself, you might be doing
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things wrong. Most of the time, write_str_to_file() and
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read_str_from_file() are all you need.
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Use the check_private_directory() function to create or verify the
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presence of directories, and tor_listdir() to list the files in a
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directory.
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Those modules also have functions for manipulating paths a bit.
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### Networking ###
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Nearly all the world is on a Berkeley sockets API, except for
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windows, whose version of the Berkeley API was corrupted by late-90s
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insistence on backward compatibility with the
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sort-of-berkeley-sort-of-not add-on *thing* that was WinSocks.
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What's more, everybody who implemented sockets realized that select()
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wasn't a very good way to do nonblocking IO... and then the various
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implementations all decided to so something different.
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You can forget about most of these differences, fortunately: We use
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libevent to hide most of the differences between the various networking
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backends, and we add a few of our own functions to hide the differences
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that Libevent doesn't.
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To create a network connection, the right level of abstraction to look
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at is probably the connection_t system in connection.c. Most of the
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lower level work has already been done for you. If you need to
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instantiate something that doesn't fit well with connection_t, you
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should see whether you can instantiate it with connection_t anyway -- or
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you might need to refactor connection.c a little.
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Whenever possible, represent network addresses as tor_addr_t.
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### Process launch and monitoring ###
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Launching and/or monitoring a process is tricky business. You can use
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the mechanisms in procmon.c and tor_spawn_background(), but they're both
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a bit wonky. A refactoring would not be out of order.
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