Implement no copy memory

[Ardika Rommy Sanjaya]

> how are you calling the function? From the pcap doc, I see this:
> 
> 	void got_packet(u_char *args, const struct pcap_pkthdr *header,
> 	    const u_char *packet);
Sorry, my mistake, fixed.

I'm using sun.misc.Unsafe to get the content data and it's deprecated on java 9+ also jdk.intenal.misc.Unsafe not exported.
If using panama should I cast the Pointer<Byte> before get the content data? 

For example if I want to get 2 byte and then 4 byte with Unsafe I can do like below:

Unsafe UNSAFE = ...

UNSAFE.getShort(..)
UNSAFE.getInt(...)

Thanks and Regards




> On 20 May 2019, at 21.21, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
> 
> Hi,
> how are you calling the function? From the pcap doc, I see this:
> 
> 	void got_packet(u_char *args, const struct pcap_pkthdr *header,
> 	    const u_char *packet);
> Let's examine this in more detail. First, you'll notice that the function has a void return type. This is logical, because pcap_loop() wouldn't know how to handle a return value anyway. The first argument corresponds to the last argument of pcap_loop(). 
> 
> So, if you see that buf.addr() == 0, that probably means you passed NULL as last parameter of the pcap_loop call?
> 
> Maurizio
> 
> On 20/05/2019 14:56, Ardika Rommy Sanjaya wrote:
>> 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:${pcap_pkthdr}u64:u8)v")
>>         public interface pcap_handler {
>>                 void fn(Pointer<Byte> buf, Pointer<pcap_pkthdr> pkthdr, Pointer<Byte> arg) throws IllegalAccessException;
>>         }
>> 
>> }
>> 
>> Regards
>> 
>> 
>>> On 20 May 2019, at 20.30, Jorn Vernee <jbvernee at xs4all.nl> <mailto:jbvernee at xs4all.nl> wrote:
>>> 
>>> Hi,
>>> 
>>>> It looks like pamana copy value from 'u_char *' into 'Pointer<Byte>
>>>> buf', correct or not?
>>> Pointer<Byte> is just a wrapper for the native pointer value. Only the value of the pointer itself is copied, not the contents of the memory it points to.
>>> 
>>>> Because when I call buf.addr() it returns 0,
>>>> what zero mean?
>>> Zero means NULL.
>>> 
>>>> How I can do with no copy? Just returns the address of 'u_char *' like
>>>> below in callback method?
>>> Pointer::addr returns the value of the pointer, to get the address of the pointer value itself, à la:
>>> 
>>>   uchar_t **bufRef = &buf;
>>> 
>>> This is currently not possible.
>>> 
>>> Can you explain a bit more about your use case? We might be able to offer some suggestions.
>>> 
>>> Cheers,
>>> Jorn
>>> 
>>> Ardika Rommy Sanjaya schreef op 2019-05-20 01:33:
>>>> Hi,
>>>> There is native function in libpcap library: typedef void
>>>> (*pcap_handler)(u_char *, const struct pcap_pkthdr *, const u_char *);
>>>> When I use jextract it generate code like below:
>>>> @NativeHeader(...)
>>>> public interface pcap_h {
>>>>    ...
>>>>    @NativeLocation(...)
>>>> @NativeFunction("(u64:${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