erlang nif小结

一、nif获取string参数的两种方式

1、eif_get_string

实例如下：

 static ERL_NIF_TERM erl_sm4_encrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {

     unsigned int input_len = 0;
     unsigned int key_len   = 1024;
     char key_string[1024]   = {0};

     int output_len = sizeof(buff);
     enif_get_list_length(env, argv[0],&input_len);

     char *input_string = NULL;
     if (input_len <= 1)
         input_len = 2018;
     else
         input_len = input_len +1;

     input_string = (char*)malloc(input_len);
     memset(input_string,0x00,input_len);

     enif_get_string(env,argv[0],input_string,input_len, ERL_NIF_LATIN1);
     enif_get_string(env,argv[1],key_string,key_len, ERL_NIF_LATIN1);
     printf("input_string=%s,input_len=%d,key_string=%s,key_len=%d\n", input_string,input_len,key_string,key_len);
     SM4_KEY iKey;
     sm4_SetKey(&iKey, (unsigned char *)key_string, 1);
     printf("ERK=%s,DRK=%s,MK=%s\n", iKey.ERK,iKey.DRK,iKey.MK);
     enin_sm4((unsigned char*)input_string,input_len,buff,&output_len, &iKey, 1);
     memset(buff+output_len,0x00,sizeof(buff)-output_len);

     free(input_string);
     input_string = NULL;
     return enif_make_string_len(env, (const char *)buff, output_len,ERL_NIF_LATIN1);
 }

2、enif_inspect_iolist_as_binary

 static ERL_NIF_TERM erl_sm4_encrypt(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
 {
     ErlNifBinary ebinary_input,ebinary_key;

     if (!enif_inspect_iolist_as_binary(env, argv[0], &ebinary_input) ||
         !enif_inspect_iolist_as_binary(env, argv[1], &ebinary_key)){

         return enif_make_badarg(env);
     }

     int key_len   = ebinary_key.size;
     int input_len = ebinary_input.size;
     int output_len = sizeof(buff);

     unsigned char *input_string = (unsigned char*)malloc(input_len+1);
     unsigned char *key_string   = (unsigned char*)malloc(key_len+1);

18     memcpy(input_string, ebinary_input.data, input_len);
19     memcpy(key_string, ebinary_input.data, key_len);
     //printf("input_string=%s,input_len=%d,key_string=%s,key_len=%d\n", input_string,input_len,key_string,key_len);

     SM4_KEY iKey;
     sm4_SetKey(&iKey, key_string, 1);

     memset(buff,0x00,sizeof(buff));
     enin_sm4(input_string,input_len,buff,&output_len, &iKey, 1);
     memset(buff+output_len,'\0',sizeof(buff)-output_len);

     free(input_string);
     free(key_string);
     return enif_make_string_len(env, (const char *)buff, output_len,ERL_NIF_LATIN1);
 }

二、nif返回string的两种方式

1、enif_make_string

ERL_NIF_TERM enif_make_string(ErlNifEnv* env, const char* string, ErlNifCharEncoding encoding)

返回一个以空字符结尾的string

2、enif_make_string_len

ERL_NIF_TERM enif_make_string_len(ErlNifEnv* env, const char* string, size_t len, ErlNifCharEncoding encoding)

返回一个长度为len的字符串string，空字符当做普通字符处理