Implement no copy memory

[Ardika Rommy Sanjaya]

Thanks for response, I really appreciate.

I want when every pcap_hander::fn callback function is called, buf::addr() returns the address of u_char *, after that I can use sun.misc.Unsafe to get the content data of u_char * based on that address.

Please refer below code:

This is libpcap api:

int     pcap_loop(pcap_t *, int, pcap_handler, u_char *);
typedef void (*pcap_handler)(u_char *, const struct pcap_pkthdr *,
                             const u_char *);


Below is java with part, generated by jextract with little changes:

@NativeHeader(
        libraries = {"pcap"}
)
public interface pcap_mapping {

        @NativeFunction("(u64:${pcap}i32u64:(u64:u8u64:${pcap_pkthdr}u64:u8)vu64:u8)i32")
        int pcap_loop(Pointer<pcap> p, int cnt, Callback<pcap_handler> callback, Pointer<Byte> usr);

        @FunctionalInterface
        @NativeCallback("(u64:u8u64:${pcap_pkthdr}u64:u8)v")
        public interface pcap_handler {
                void fn(Pointer<Byte> buf, Pointer<pcap_pkthdr> pkthdr, Pointer<Byte> arg) throws IllegalAccessException;
        }

}

Regards


> On 20 May 2019, at 20.30, Jorn Vernee <jbvernee at xs4all.nl> wrote:
> 
> Hi,
> 
>> It looks like pamana copy value from 'u_char *' into 'Pointer<Byte>
>> buf', correct or not?
> 
> Pointer<Byte> is just a wrapper for the native pointer value. Only the value of the pointer itself is copied, not the contents of the memory it points to.
> 
>> Because when I call buf.addr() it returns 0,
>> what zero mean?
> 
> Zero means NULL.
> 
>> How I can do with no copy? Just returns the address of 'u_char *' like
>> below in callback method?
> 
> Pointer::addr returns the value of the pointer, to get the address of the pointer value itself, à la:
> 
>   uchar_t **bufRef = &buf;
> 
> This is currently not possible.
> 
> Can you explain a bit more about your use case? We might be able to offer some suggestions.
> 
> Cheers,
> Jorn
> 
> Ardika Rommy Sanjaya schreef op 2019-05-20 01:33:
>> Hi,
>> There is native function in libpcap library: typedef void
>> (*pcap_handler)(u_char *, const struct pcap_pkthdr *, const u_char *);
>> When I use jextract it generate code like below:
>> @NativeHeader(...)
>> public interface pcap_h {
>>    ...
>>    @NativeLocation(...)
>> @NativeFunction("(u64:${pcap}i32u64:(u64:u8u64:${pcap_pkthdr}u64:u8)vu64:u8)i32")
>>    int pcap_loop(Pointer<pcap> p, int cnt, Callback<pcap_handler>
>> callback, Pointer<Byte> usr);
>>    @FunctionalInterface
>>    @NativeCallback("(u64:u8u64:${pcap_pkthdr}u64:u8)v")
>>    interface pcap_handler {
>>        void fn(Pointer<Byte> buf, Pointer<pcap_pkthdr> pkthdr,
>> Pointer<Byte> usr) throws IllegalAccessException;
>>    }
>>    ...
>> }
>> It looks like pamana copy value from 'u_char *' into 'Pointer<Byte>
>> buf', correct or not? Because when I call buf.addr() it returns 0,
>> what zero mean?
>> How I can do with no copy? Just returns the address of 'u_char *' like
>> below in callback method?
>> void fn(long memoryAddressOf_u_char_ptr, Pointer<pcap_pkthdr> pkthdr,
>> Pointer<Byte> usr) throws IllegalAccessException;
>> Thanks and Regards,
>> Ardika Rommy Sanjaya