OS compatibility functions

We’ve got a bunch of functions to wrap differences between various operating systems where we run.

The filesystem

We wrap the most important filesystem functions with load-file, save-file, and map-file abstractions declared in util.c or compat.c. If you’re messing about with file descriptors yourself, you might be doing things wrong. Most of the time, write_str_to_file() and read_str_from_file() are all you need.

Use the check_private_directory() function to create or verify the presence of directories, and tor_listdir() to list the files in a directory.

Those modules also have functions for manipulating paths a bit.


Nearly all the world is on a Berkeley sockets API, except for windows, whose version of the Berkeley API was corrupted by late-90s insistence on backward compatibility with the sort-of-berkeley-sort-of-not add-on thing that was WinSocks.

What’s more, everybody who implemented sockets realized that select() wasn’t a very good way to do nonblocking IO… and then the various implementations all decided to so something different.

You can forget about most of these differences, fortunately: We use libevent to hide most of the differences between the various networking backends, and we add a few of our own functions to hide the differences that Libevent doesn’t.

To create a network connection, the right level of abstraction to look at is probably the connection_t system in connection.c. Most of the lower level work has already been done for you. If you need to instantiate something that doesn’t fit well with connection_t, you should see whether you can instantiate it with connection_t anyway – or you might need to refactor connection.c a little.

Whenever possible, represent network addresses as tor_addr_t.

Process launch and monitoring

Launching and/or monitoring a process is tricky business. You can use the mechanisms in procmon.c and tor_spawn_background(), but they’re both a bit wonky. A refactoring would not be out of order.