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
", 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
", 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
", 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,'',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