[英]How to pass an associative array from a Node.js C++ addon to js code?
[英]Pass Byte Array as std::vector<char> from Node.js to C++ Addon
我有一些限制,插件是用 nan.h 和 v8(不是新的 node-addon-api)构建的。
末端 function 是库的一部分。 它接受表示图像字节的std::vector<char>
。
我尝试从 Node.js 创建一个图像缓冲区:
const img = fs.readFileSync('./myImage.png');
myAddonFunction(Buffer.from(img));
我不确定如何从这里继续。 我尝试使用缓冲区创建一个新向量,如下所示:
std::vector<char> buffer(data);
但似乎我需要给它一个尺寸,我不确定如何获得。 无论如何,即使我使用初始缓冲区大小(来自 Node.js),图像也无法通过 go。
terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc
[1] 16021 abort (core dumped)
但是,当我直接从 C++ 读取图像时,一切正常:
std::ifstream ifs ("./myImage.png", std::ios::binary|std::ios::ate);
std::ifstream::pos_type pos = ifs.tellg();
std::vector<char> buffer(pos);
ifs.seekg(0, std::ios::beg);
ifs.read(&buffer[0], pos);
// further below, I pass "buffer" to the function and it works just fine.
但当然,我需要图像来自 Node.js。 也许缓冲区不是我要找的?
这是一个基于N-API的示例; 我还鼓励您查看基于node-addon-api的类似实现(这是一个易于使用的 C++ 包装器,位于 N-API 之上)
https://github.com/nodejs/node-addon-examples/tree/master/array_buffer_to_native/node-addon-api
#include <assert.h>
#include "addon_api.h"
#include "stdio.h"
napi_value CArrayBuffSum(napi_env env, napi_callback_info info)
{
napi_status status;
const size_t MaxArgExpected = 1;
napi_value args[MaxArgExpected];
size_t argc = sizeof(args) / sizeof(napi_value);
status = napi_get_cb_info(env, info, &argc, args, nullptr, nullptr);
assert(status == napi_ok);
if (argc < 1)
napi_throw_error(env, "EINVAL", "Too few arguments");
napi_value buff = args[0];
napi_valuetype valuetype;
status = napi_typeof(env, buff, &valuetype);
assert(status == napi_ok);
if (valuetype == napi_object)
{
bool isArrayBuff = 0;
status = napi_is_arraybuffer(env, buff, &isArrayBuff);
assert(status == napi_ok);
if (isArrayBuff != true)
napi_throw_error(env, "EINVAL", "Expected an ArrayBuffer");
}
int32_t *buff_data = NULL;
size_t byte_length = 0;
int32_t sum = 0;
napi_get_arraybuffer_info(env, buff, (void **)&buff_data, &byte_length);
assert(status == napi_ok);
printf("\nC: Int32Array size = %d, (ie: bytes=%d)",
(int)(byte_length / sizeof(int32_t)), (int)byte_length);
for (int i = 0; i < byte_length / sizeof(int32_t); ++i)
{
sum += *(buff_data + i);
printf("\nC: Int32ArrayBuff[%d] = %d", i, *(buff_data + i));
}
napi_value rcValue;
napi_create_int32(env, sum, &rcValue);
return (rcValue);
}
JavaScript 代码调用插件
'use strict'
const myaddon = require('bindings')('mync1');
function test1() {
const array = new Int32Array(10);
for (let i = 0; i < 10; ++i)
array[i] = i * 5;
const sum = myaddon.ArrayBuffSum(array.buffer);
console.log();
console.log(`js: Sum of the array = ${sum}`);
}
test1();
代码执行的Output:
C: Int32Array size = 10, (ie: bytes=40)
C: Int32ArrayBuff[0] = 0
C: Int32ArrayBuff[1] = 5
C: Int32ArrayBuff[2] = 10
C: Int32ArrayBuff[3] = 15
C: Int32ArrayBuff[4] = 20
C: Int32ArrayBuff[5] = 25
C: Int32ArrayBuff[6] = 30
C: Int32ArrayBuff[7] = 35
C: Int32ArrayBuff[8] = 40
C: Int32ArrayBuff[9] = 45
js: Sum of the array = 225
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