[erlang-questions] Decoding Erlang Messages Sent Over TCP With EI

[Alexey Romanov]

Use ei_decode_version first (I ran into the same problem first time I used EI).

Yours, Alexey Romanov



On Sun, Jan 2, 2011 at 11:05 PM, John Koenig <koenigjm@REDACTED> wrote:
> Code is attached.
>
> What you have said so far has brought me close of identifying the problem.  Up until now I have assumed that ei_decode_tuple_header would scan me ahead to the proper location, but I starting to think I was wrong to do so.  Especially after looking at the received data more closely in gdb.
>
> How does one know the proper offset from which to start decoding the actual message?
>
> John
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> On Jan 2, 2011, at 1:48 PM, Steve Vinoski wrote:
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>> On Sun, Jan 2, 2011 at 2:29 PM, John Koenig <koenigjm@REDACTED> wrote:
>>> I am currently porting a server process (written in C) to ei, which used to interact with an
>>> erlang process via the older erl_interface.  I am able to get the the two sides talking over a
>>> localhost TCP socket, but I am having trouble decoding the tuples sent to the C based server.
>>>
>>> Tuples are being sent from an interactive erlang session as follows:
>>>
>>> {any, mynode@REDACTED} ! {tuple1, typle2, []}
>>>
>>> When the message is received in the C based server via ei_receive,  however,
>>> ei_decode_tuple_header returns non-zero and I am unable to proceed further.  Calling
>>> ei_get_type on the buffer results in 'p' which, according to ei.h, corresponds to
>>> ERL_NEW_FUN_EXT.  Why is this failing and why is this tuple being reported as an
>>> ERL_NEW_FUN_EXT?
>>>
>>> The only example I have seen thus far
>>> (http://www.trapexit.org/How_to_use_ei_to_marshal_binary_terms_in_port_programs) uses ei
>>> stdin/stdout, can ei be used over a TCP socket at all?
>>
>> Ei most definitely works over TCP. Can you post more of your decoding
>> code? Hard to tell what's going on from what you've told us so far,
>> but p is value 112 and there are a couple instances of that value in
>> the encoded form of your tuple above, so you're likely just decoding
>> at the wrong offset.
>>
>> --steve
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