4.3 Acessing Socket Methods
Keywords: pyOpenSSL

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4.3 Acessing Socket Methods

We quickly saw the benefit of wrapping socket methods in the `SSL.Connection` class, for an easy transition into using SSL. The problem here is that the `socket` module lacks a C API, and all the methods are declared static. One approach would be to have `OpenSSL` as a submodule to the `socket` module, placing all the code in socketmodule.c, but this is obviously not a good solution, since you might not want to import tonnes of extra stuff you're not going to use when importing the `socket` module. The other approach is to somehow get a pointer to the method to be called, either the C function, or a callable Python object. This is not really a good solution either, since there's a lot of lookups involved.

The way it works is that you have to supply a ```socket`-like'' transport object to the `SSL.Connection`. The only requirement of this object is that it has a `fileno()` method that returns a file descriptor that's valid at the C level (i.e. you can use the system calls read and write). If you want to use the `connect()` or `accept()` methods of the `SSL.Connection` object, the transport object has to supply such methods too. Apart from them, any method lookups in the `SSL.Connection` object that fail are passed on to the underlying transport object.

Future changes might be to allow Python-level transport objects, that instead of having `fileno()` methods, have `read()` and `write()` methods, so more advanced features of Python can be used. This would probably entail some sort of OpenSSL ``BIOs'', but converting Python strings back and forth is expensive, so this shouldn't be used unless necessary. Other nice things would be to be able to pass in different transport objects for reading and writing, but then the `fileno()` method of `SSL.Connection` becomes virtually useless. Also, should the method resolution be used on the read-transport or the write-transport?