Example which shows C allocated memory we set on a buffer and we know how it is getting freed.

node_buffer_free.cc

#include <v8.h>
#include <node.h>
#include <node_buffer.h>

using namespace v8;

typedef unsigned char byte;

Handle<Value> ReturnBufferWithCAllocatedMemory(const Arguments &args) {
    HandleScope scope;
    
    byte* bytes = (byte*) malloc(1000);

    byte[3] = 0x04;
    byte[9] = 0x76;
    
    // would call error because buffer looses memory
    // free(bytes);
    
    return scope.Close(node::Buffer::New((char*) bytes, 1000)->handle_);
};

void init(Handle<Object> exports) {
    exports->Set(String::New("returnBuffer"), 
            FunctionTemplate::New(ReturnBufferWithCAllocatedMemory)->GetFunction());

};

NODE_MODULE(c_allocated_buffer, init)