calc_head_size.cc

#include "parser.h"

Handle<Value> CalcHeadSize(const Arguments &args) {
    HandleScope scope;
    
    Local<Object> object = args[0]->ToObject();

    if (node::Buffer::HasInstance(object)) {
        if (node::Buffer::Length(object) < 2) {
            ThrowException(Exception::TypeError(
                        String::New("Buffer must have at least two bytes.")));

            return scope.Close(Undefined());
        }
        
        return scope.Close(Number::New(calcHeadSizeFromBuffer(object)));
    }

    if (object->IsObject() && !object->IsArray()) {
        if (!object->Has(String::New("length"))) {
            ThrowException(Exception::TypeError(
                        String::New("State must have property length.")));

            return scope.Close(Undefined());
        }

        return scope.Close(Number::New(calcHeadSizeFromBuffer(object)));
    }

    ThrowException(Exception::TypeError(
                String::New("Argument must be a either object or buffer.")));

    return scope.Close(Undefined());
}

bool isMasking(Local<Object> masking) {
    if (masking->IsUndefined())
        return false;

    if (!node::Buffer::HasInstance(masking))
        return false;

    if (node::Buffer::Length(masking) != 4)
        return false;

    return true;
}

int calcHeadSizeFromObject(Local<Object> state) {
    int size = 2;

    bool mask = state->Get(String::New("mask"))
        ->BooleanValue();

    int length = state->Get(String::New("length"))
        ->NumberValue();

    Local<Object> masking = state->Get(String::New("masking"))
        ->ToObject();

    if (length > 125 && length < 0x10000) {
        size += 2;
    } else if (length > 0xffff) {
        size += 8;
    }

    if (mask || isMasking(masking)) {
        size += 4;
    }

    return size;
}

int calcHeadSizeFromBuffer(Local<Object> chunk) {
    int length = 2;

    byte* head = (byte*) node::Buffer::Data(chunk);

    if (head[1] & 0x80)
        length += 4;

    switch (head[1] & 0x7f) {
        case 126:
            length += 2;
            break;
        case 127:
            length += 8;
            break;
    }

    return length;
}