I have some constraints where the addon is built with nan.h and v8 (not the new node-addon-api).
The end function is a part of a library. It accepts std::vector<char>
that represents the bytes of an image.
I tried creating an image buffer from Node.js:
const img = fs.readFileSync('./myImage.png');
myAddonFunction(Buffer.from(img));
I am not really sure how to continue from here. I tried creating a new vector with a buffer, like so:
std::vector<char> buffer(data);
But it seems like I need to give it a size, which I am unsure how to get. Regardless, even when I use the initial buffer size (from Node.js), the image fails to go through.
terminate called after throwing an instance of 'std::bad_alloc'
what(): std::bad_alloc
[1] 16021 abort (core dumped)
However, when I read the image directly from C++, it all works fine:
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.
But of course, I need the image to come from Node.js. Maybe Buffer is not what I am looking for?
Here is an example based on N-API ; I would also encourage you to take a look similar implementation based on node-addon-api (it is an easy to use C++ wrapper on top of N-API)
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);
}
The JavaScript code to call the addon
'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();
The Output of the code execution:
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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