1   概述

利用Erlang的 erl_interface ,我们可以构建自己的Erlang "Node",我们称为 "CNode ",erl_interface实现了基本的节点连接,以及消息发送接收,以及Erlang Term 的构建解析.

使用CNode,可以完成很多使用port完成的功能,区别是你的应用是一个c程序,而不需要 一个erlang应用.

CNode是hidden node,在erlang的 nodes() 结果中,无法看到CNode(可以通过nodes(connected)获取)

2   CNode 相关API

while (loop) {
    got = erl_receive_msg(fd, buf, BUFSIZE, &emsg);
     if (got == ERL_TICK) {
             /* ignore */
     } else if (got == ERL_ERROR) {
     loop = 0; /* exit while loop */
     } else {
         if (emsg.type == ERL_REG_SEND) {

fromp = erl_element(2, emsg.msg);
tuplep = erl_element(3, emsg.msg);
fnp = erl_element(1, tuplep);
argp = erl_element(2, tuplep);

if (strncmp(ERL_ATOM_PTR(fnp), "foo", 3) == 0) {
   res = foo(ERL_INT_VALUE(argp));
} else if (strncmp(ERL_ATOM_PTR(fnp), "bar", 3) == 0) {
   res = bar(ERL_INT_VALUE(argp));
}

erl_free_term(emsg.from); erl_free_term(emsg.msg);
erl_free_term(fromp); erl_free_term(tuplep);
erl_free_term(fnp); erl_free_term(argp);
erl_free_term(resp);

resp = erl_format("{cnode, ~i}", res);
erl_send(fd, fromp, resp);

-module(complex3).
-export([foo/1, bar/1]).

foo(X) ->
   call_cnode({foo, X}).
bar(Y) ->
   call_cnode({bar, Y}).

call_cnode(Msg) ->
   {any, c1@litao} ! {call, self(), Msg},
   receive
       {cnode, Result} ->
           Result
   end.

3   编译运行

编译C node:

$ gcc -o cserver -I/usr/local/lib/erlang/lib/erl_interface-3.6.2/include \
 -L/usr/local/lib/erlang/lib/erl_interface-3.6.2/lib \
 complex.c cnode_s.c -g -rdynamic -lerl_interface -lei  -lnsl -lpthread

启动epmd:

epmd -d -d #以debug方式启动

启动cserver:

./cserver 2342

至此C node启动完成，其绑定的本地端口为2342

启动client:

erl -sname t1

设置 c1@litao 的cookie，连接c1节点:

(t1@litao)6> erlang:set_cookie('c1@litao', 'secretcookie').
true
(t1@litao)7> net_kernel:connect_node('c1@litao').
true
(t1@litao)8> nodes(connected).
[c1@litao]

执行调用:

(t1@litao)12> complex3:foo(3).
4

4   完整代码

cnode_s.c:

/* cnode_s.c */

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#include "erl_interface.h"
#include "ei.h"

#define BUFSIZE 1000

int main(int argc, char **argv) {
 int port;                                /* Listen port number */
 int listen;                              /* Listen socket */
 int fd;                                  /* fd to Erlang node */
 ErlConnect conn;                         /* Connection data */

 int loop = 1;                            /* Loop flag */
 int got;                                 /* Result of receive */
 unsigned char buf[BUFSIZE];              /* Buffer for incoming message */
 ErlMessage emsg;                         /* Incoming message */

 ETERM *fromp, *tuplep, *fnp, *argp, *resp;
 int res;

 port = atoi(argv[1]);

 erl_init(NULL, 0);

 if (erl_connect_init(1, "secretcookie", 0) == -1)
   erl_err_quit("erl_connect_init");

 /* Make a listen socket */
 if ((listen = my_listen(port)) <= 0)
   erl_err_quit("my_listen");

 if (erl_publish(port) == -1)
   erl_err_quit("erl_publish");

 if ((fd = erl_accept(listen, &conn)) == ERL_ERROR)
   erl_err_quit("erl_accept");
 fprintf(stderr, "Connected to %s\n\r", conn.nodename);

 while (loop) {

   got = erl_receive_msg(fd, buf, BUFSIZE, &emsg);
   if (got == ERL_TICK) {
     /* ignore */
   } else if (got == ERL_ERROR) {
     loop = 0;
   } else {

     if (emsg.type == ERL_REG_SEND) {
       fromp = erl_element(2, emsg.msg);
       tuplep = erl_element(3, emsg.msg);
       fnp = erl_element(1, tuplep);
       argp = erl_element(2, tuplep);

       if (strncmp(ERL_ATOM_PTR(fnp), "foo", 3) == 0) {
         res = foo(ERL_INT_VALUE(argp));
       } else if (strncmp(ERL_ATOM_PTR(fnp), "bar", 3) == 0) {
         res = bar(ERL_INT_VALUE(argp));
       }

       resp = erl_format("{cnode, ~i}", res);
       erl_send(fd, fromp, resp);

       erl_free_term(emsg.from); erl_free_term(emsg.msg);
       erl_free_term(fromp); erl_free_term(tuplep);
       erl_free_term(fnp); erl_free_term(argp);
       erl_free_term(resp);
     }
   }
 } /* while */
}


int my_listen(int port) {
 int listen_fd;
 struct sockaddr_in addr;
 int on = 1;

 if ((listen_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
   return (-1);

 setsockopt(listen_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));

 memset((void*) &addr, 0, (size_t) sizeof(addr));
 addr.sin_family = AF_INET;
 addr.sin_port = htons(port);
 addr.sin_addr.s_addr = htonl(INADDR_ANY);

 if (bind(listen_fd, (struct sockaddr*) &addr, sizeof(addr)) < 0)
   return (-1);

 listen(listen_fd, 5);
 return listen_fd;
}

compex.c:

/* complex.c */

int foo(int x) {
 return x+1;
}

int bar(int y) {
 return y*2;
}