Use size_t instead of int in transfer functions

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The POSIX ​read and ​write functions let you specify the number of bytes to transfer as a ​size_t. These functions return a ssize_t indicating how much bytes were read or written. (The signed type is needed to allow negative error codes.)

As explained in the mailinglist ​thread, I would like to propose that the libusb transfer functions also use these size_t types instead of ints. Concretely I propose:

ssize_t libusb_control_transfer (...,size_t wLength,...)

int libusb_bulk_transfer (...,size_t length, size_t * transferred,...)

int libusb_interrupt_transfer (...,size_t length, size_t * transferred,...)

Note that the ​libusb_get_device_list function already returns a ssize_t to indicate the number of devices in the list or an error code.

I'm not familiar enough with the asynchronous API but I suppose that it can also use size_t types instead of ints.

[segher]

I still don't think it's worth making an ABI change for this, not until
a major version change anyway (that would be 2.0).

Is there ever a situation in practice where "int" isn't big enough?

[stuge]

libusb-1.1 is tentatively intended to change ABI and API, so this is on the right component. Anyway, it's all in the future.

[rogueresearch]

I would like to see this change too.

With the Mac OS X ABI, 'int' is always 32 bit, but 'size_t' is 32 bit for 32 bit apps and 64 bit for 64 bit apps. As a result, libusb is truncating 64 bit values to 32, which at best causes compiler warnings, and at worst results in actual truncation and incorrect behaviour.