Interoperability with libbson

[lucianoiam]

Round-trip encoding/decoding with js-bson works great, but I am having a rough time trying to exchange data with a client written in C using libbson from the MongoDB C driver.

According to the spec the first 4 bytes in a BSON document must be interpreted as an int32 with the total number of bytes comprising the document.

js-bson writes this header by taking the serialized string length:

js-bson/standalone/BSON.js

Line 664 in 77d3b53

return readAsInt32LE( bson.length + 5 ) + bson + '\x00';

The string's length property value is not necessarily equal to the number of bytes comprising the string:

console.log('\80\00'.length)
>> 3

console.log('\00\00'.length)
>> 2

When string length == string byte count libbson correctly deserializes documents, otherwise deserialization fails due to a validation check.

Does this make sense?