[erlang-questions] Encode and decode binary data on port driver: undefined symbol ei_decode_version

[Brisa Jiménez]

Hi everyone!

I want to send and receive binary data through Erlang port, and use ei to encode and decode data, but when I try to test code below the next error occurs:

Erlang R14B03 (erts-5.8.4) [source] [rq:1] [async-threads:0] [kernel-poll:false]

Eshell V5.8.4  (abort with ^G)

1> erl_drv:start().

** exception exit: {error,"undefined symbol: ei_decode_version"}

     in function  erl_drv:start/0

Can anybody give me an example of how do it what I'm want?

I appreciate any advice.

Thanks.

===

-module(erl_drv).

-export([start/0, stop/0, init/1]).

-export([foz/1, baz/1]).

-define(C_LIBRARY, "library").

start() ->

    case erl_ddll:load_driver("priv", ?C_LIBRARY) of

ok -> ok;

{error, already_loaded} -> ok;

{error, Reason}-> exit({error, erl_ddll:format_error(Reason)})

    end,

    spawn(?MODULE, init, [?C_LIBRARY]).

init(?C_LIBRARY) ->

    register(erl_drv, self()),

    Port = open_port({spawn, ?C_LIBRARY}, [binary]),

    loop(Port).

stop() ->

    erl_drv ! stop.

foz(Arg)->

    call_port({foz, Arg}).

baz(Arg)->

    call_port({baz, Arg}).

call_port(Msg) ->

    erl_drv ! {call, self(), Msg},

    receive

        {erl_drv, Res} ->

   Res

    end.

loop(Port) ->

    receive

{call, Caller, {Command, Data}}->

   case Command of

foz-> port_control(Port, 3, encode(Data));

baz-> port_control(Port, 4, encode(Data))

   end,

   

   receive

       {Port, {data, Data}} ->

   Caller ! {erl_drv, decode(Data)}

       end,

   loop(Port);

    stop ->

   Port ! {self(), close},

   receive 

{Port, closed} ->

   exit(normal)

   end;

    {'EXIT', Port, Reason} ->

   io:format("~p ~n", [Reason]),

   exit(port_terminated)

    end.

encode(Msg)->

    term_to_binary(Msg).

decode(RetVal)->

    binary_to_term(RetVal).

===

/* port_driver.c*/

#include <stdio.h>

#include "erl_driver.h"

#include "ei.h"

#include "erl_interface.h"

double foz(double);

double baz(double);

typedef size_t ErlDrvSizeT;

typedef ssize_t ErlDrvSSizeT;

typedef struct {

    ErlDrvPort port;

} ptr_port;

static ErlDrvData start(ErlDrvPort port, char *buff)

{

    ptr_port* ptr_port1 = (ptr_port*)driver_alloc(sizeof(ptr_port));

    set_port_control_flags(port , PORT_CONTROL_FLAG_BINARY);

    ptr_port1->port = port;

    return (ErlDrvData)ptr_port1;

}

static void stop(ErlDrvData handle)

{

    driver_free((char*)handle);

}

static ErlDrvSSizeT control(ErlDrvData handle, unsigned int command,

                            char *buf, ErlDrvSizeT len,

char **rbuf, ErlDrvSizeT rlen)

{

ptr_port *ptr_port1 = (ptr_port*)handle;

    double arg, res;

    int version, index = 0;

    if (ei_decode_version(buf, &index, &version))

        return((ErlDrvSSizeT) ERL_DRV_ERROR_GENERAL);

    if (ei_decode_double(buf, &index, &arg))

        return((ErlDrvSSizeT) ERL_DRV_ERROR_BADARG);

    switch (command) {

        case 3:

            res = foz(arg);

            break;

        case 4:

            res = baz(arg);

            break;

        default:

            return((ErlDrvSSizeT) ERL_DRV_ERROR_BADARG);

    }

    index = 0;

    if (ei_encode_version(*rbuf, &index)

            || ei_encode_double(*rbuf, &index, res))

        return((ErlDrvSSizeT) ERL_DRV_ERROR_ERRNO);

    else

        return((ErlDrvSSizeT) index);

}

ErlDrvEntry driver_entry = {

    NULL, //* F_PTR init, N/A 

    start, //* L_PTR start, called when port is opened 

    stop, //* F_PTR stop, called when port is closed 

NULL, //* F_PTR output, called when erlang has sent 

    NULL, //* F_PTR ready_input, called when input descriptor ready 

    NULL, //* F_PTR ready_output, called when output descriptor ready 

    "library", //* char *driver_name, the argument to open_port 

    NULL, //* F_PTR finish, called when unloaded 

    control, //* F_PTR control, port_command callback 

    NULL, //* F_PTR timeout, reserved 

    NULL //* F_PTR outputv, reserved 

};

 

DRIVER_INIT(library) /* must match name in driver_entry */

{

return &driver_entry;

}

===

/*library.c*/

double foz(double x) {

return x/1.0;

}

double baz(double y) {

return y/2.0;

}

===

# Makefile

ERL_ROOT=/usr/local/lib/erlang

all: compile_c compile

compile_c:

@mkdir -p priv

gcc -o priv/library.so -I$(ERL_ROOT)/usr/include/ -I$(ERL_ROOT)/lib/erl_interface-3.7.4/include/ -fpic -shared c_src/*.c 

compile:

@mkdir -p ebin

erlc -o ebin/ src/erl_drv.erl

clean:

@rm -rf ebin priv

test:

erl -pa ebin/

.PHONY: c_src

[Jachym Holecek]

# Brisa Jim?nez 2012-11-22:

> I want to send and receive binary data through Erlang port, and use ei to
> encode and decode data, but when I try to test code below the next error
> occurs:
>
> Erlang R14B03 (erts-5.8.4) [source] [rq:1] [async-threads:0]
> [kernel-poll:false]
>
> Eshell V5.8.4 (abort with ^G)
> 1> erl_drv:start().
> ** exception exit: {error,"undefined symbol: ei_decode_version"}
> in function erl_drv:start/0
>

> [...]

>
> # Makefile
>
> ERL_ROOT=/usr/local/lib/erlang
>
> all: compile_c compile
>
> compile_c:
> @mkdir -p priv
> gcc -o priv/library.so -I$(ERL_ROOT)/usr/include/
> -I$(ERL_ROOT)/lib/erl_interface-3.7.4/include/ -fpic -shared c_src/*.c

You're not linking against ei so runtime linker complains about unresolved
symbols when you attempt to load your driver.

BTW Your Makefile doesn't look completely right either, I don't see why not
use filenames as source/target names allowing make to work as intended, but
even if there were a reason you should declare your targets as .PHONY (how
exactly is that done depends on make dialect at hand).

BR,
-- Jachym
_______________________________________________
erlang-questions mailing list
erlang-q...@erlang.org
http://erlang.org/mailman/listinfo/erlang-questions