How to pass binary data from C++ to Node.js

Question

I have a binary data in c++ variable buffer as below:

int len = 39767;
uint16_t * buffer = (uint16_t) malloc(len);
FILE * fp = fopen("rahul.jpg", "rb"); // size of file is 39767 byte.
fread(buffer, len, 1, fp);
fclose(fp);
fp = fopen("rahul3.jpg", "wb");
fwrite(buffer, len, 1, fp);  // Here it is written correct.
fclose(fp);

I want to pass this buffer to Node.js and write to a file. I used below line to convert it to Local and then wrapping to an Object:

Local<String> str = Nan::New(buffer).ToLocalChecked();
return scope.Escape(str);

But, in node.js when I am checking length of received data it prints 9 only and value seems corrupted.

console.log(data);
console.log("len = " + data.length );
fs.writeFileSync('rahul2.jpg', data, 'binary');

Here rahul2.jpg is corrupted and is of 9 bytes only. How can we get rahul2.jpg from node.js code same as rahul.jpg in c++? Which Nan::New() we should use to pass binary data unaffected? Please help. Thanks.

I suppose, `ToLocalChecked()` provide a string, and some conversion of data is performed. So consider posibilities of data specification for `New` or use other method insted this — VolAnd, Jun 30 '16 at 17:08
After applying CopyBuffer(), I can see data in node.js as of 10 bytes only. How can I get rahul2.jpg same as rahul.jpg? Thanks. — Bimal Jha, Jun 30 '16 at 19:11

score 0 · Answer 1 · answered Jun 30 '16 at 17:20

0

Try something like this:

   Local<Value> returnValue = Nan::CopyBuffer(buffer, len).ToLocalChecked();

and, by the way, fread returns the number of bytes read from file, so it is better to do as follows:

   int truelen = fread(buffer, len, 1, fp);
   . . .
   fwrite(buffer, truelen, 1, fp);

answered Jun 30 '16 at 17:20

VolAnd

6,367
3
25
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Thanks for quick reply. But, still unable to get full data in node.js. My console.log is printing below data and rahul2.jpg has only 9 bytes. ``` len = 10``` – Bimal Jha Jun 30 '16 at 19:08
No. I am using fs.writeFileSync(). I don't have any fd to close. – Bimal Jha Jun 30 '16 at 19:31
Thanks @VolAnd . CopyBuffer() and NewBuffer() returns Local and updating code has worked. – Bimal Jha Jul 01 '16 at 06:31

score 0 · Answer 2 · answered Jul 01 '16 at 06:34

0

Local<String> str = Nan::NewOneByteString((uint8_t *) buffer, len).ToLocalChecked();

I used above code in C++ which solved the issue. In node.js used the below code to write to file: fs.writeFileSync('rahul2.jpg', data, 'binary');

Thanks.

answered Jul 01 '16 at 06:34

Bimal Jha

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How to pass binary data from C++ to Node.js

2 Answers2