the Go "Callback" struct may have completely different size and
alignment than the C.Foo one expected by C.initialize_engine.
therefore you want to construct the C version when calling
C.initialize_engine, and the Go version for everything else. Your call
may look something like this:
initStruct := C.calloc(1, sizeof(C.Foo))
initStruct.key_value_cb = C.callOnMeGo_cgo
initStrudct.data: C.int(1)
C.initialize_engine(pattern_db, module_path,
(*C.Foo)(unsafe.Pointer(initStruct)))
the Go Callback struct is not required unless you expect the callbacks
to change or be settable by library clients, in which case you'll need
to construct a more elaborate struct that implements locking and (at
least what I do) a map between callback names and interface{} pointing
to the callbacks sent by the library clients.
On Wed, Jul 10, 2019 at 8:14 AM Nitish Saboo <nitish.sabo...@gmail.com> wrote:
>
> Hi Andrey,
>
> I am new to Go and cgo therefore did not exactly understand your point.
> Can you explain me in the context of the code that I had posted.It will
> really help me to get hold of the things much better.
>
> Thanks,
> Nitish
>
> On Wed, Jul 10, 2019 at 5:19 PM andrey mirtchovski <mirtchov...@gmail.com>
> wrote:
>>
>> what i do is have a similar struct in Go, and the original C one. here
>> 'callbacks' is the go one, and
>> "type Engine C.struct_cl_engine" is the opaque C one:
>>
>> https://github.com/mirtchovski/clamav/blob/master/callback.go#L63
>>
>> On Wed, Jul 10, 2019 at 5:25 AM Nitish Saboo <nitish.sabo...@gmail.com>
>> wrote:
>> >
>> > Hi Andrey,
>> >
>> > I understand the issue here but how can I pass a callback function in a
>> > struct to C code.I need a struct because I want to pass and an extra
>> > parameter 'userdata' as well that I would require back as part of callback.
>> >
>> > Thanks,
>> > Nitish
>> >
>> > On Wed, Jul 10, 2019 at 4:39 PM andrey mirtchovski <mirtchov...@gmail.com>
>> > wrote:
>> >>
>> >> i don't think you can use a go function directly in the callback. you
>> >> need a correctly-typed C helper to do it. at least that used to be the
>> >> case. see examples:
>> >>
>> >> https://github.com/mirtchovski/clamav/blob/master/cfuncs.go
>> >> https://github.com/mirtchovski/clamav/blob/master/callback.go
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