JInterface question

Olivier Sambourg <>
Sun Jun 19 23:34:56 CEST 2005


Hi

I'm having another problem with erlang external format : an integer  
list in erlang is sometimes encoded as a string (when the integers  
all are in the 0..255 range).
That is :

binary_to_list(term_to_binary([1])).
[131,107,0,1,1]

When 107 is used to identify strings in the erlang external format  
(108 is for lists) :

  /** The tag used for strings and lists of small integers */
public static final int stringTag =      107;

The problem is that the JInterface library tries to make an  
OtpErlangString out of the byte sequence and comes out with "    
" (with special characters in the string). I've found no way to  
convert it to an OtpErlangList. All I can do in this particular case  
is get the last n bytes of the stream and cast them as integers  
(where n is the size of the original list).
For instance :

binary_to_list(term_to_binary([1])).
[131,107,0,1,1] -> last byte is 1
binary_to_list(term_to_binary([1,2,3,255])).
[131,107,0,4,1,2,3,255] -> last 4 bytes are 1,2,3, 255

When one integer is out of the 0..255 range, the list is not treated  
as a string and everything is fine.

Is there a cleaner way either on the server (erlang) or client (java)  
side ? I think I'll just add a dummy -1 integer to all the integer  
lists I want to transmit...

Thanks a lot,

--
Olivier

PS : I guess this is an old one, but are we gonna see a separate  
string type in erlang someday ? No troll intended please, just a  
question ;)


Le 15 juin 05 à 22:05, Vlad Dumitrescu a écrit :



> Hi,
>
> If your application permits, you could also send the binary as-is  
> (without any base64 encoding) and do the encoding where and when it  
> is needed. Or handle the encoded binary as a regular binary, send  
> it and decode it on the Erlang side.
>
> If you send "normal" Erlang objects, you don't need to use  
> OtpOutputStream at all, it is handled behind the scenes by for  
> example OtpMBox.send/receive.
>
>
>
>
>>  From the OtpOutputStream class documentation :
>> Provides a stream for encoding Erlang terms to external format,  
>> for transmission or storage.
>>
>>
>>
>
> Yes, for storage, you don't need any magic header, for transmission  
> you do.
>
> regards,
> Vlad
>
>
>






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