Remove DAGNode.create?

[achingbrain]

Sort of related to #131 but if DAGNode.create can now calculate the serialized size of a node synchronously, why not do that in the DAGNode constructor if the serialized size is not passed and remove the .create function?

[vmx]

I had a look. the problem is that we would need to call serialize() which does a call to DAGNode.isDAGNode(). So you'd have a circular reference that would make things fail.

[achingbrain]

It only does a call to DAGNode.isDAGNode() to find out if the data argument passed to util.serialize is a DAGNode, which it should not be if we are in the constructor of DAGNode outside of programmer error so that could be factored out and you'd have an internal _serialize function that did the same thing as util.serialize just without that check which util.serialize would call.

...

Anyway I've found this is only a concern when creating trees of DAGNodes and DAGLinks prior to serialization so we don't even know the serialized size at that point.

We only assert on serialized size in the DAGNode constructor if it's non-zero in order to do this sort of thing:

const node = new DAGNode(buf, links, 0) // dunno

How about defaulting it (and the links?) in the constructor?

class DAGNode {
  constructor (data, links = [], serializedSize = 0) {
    if (serializedSize !== 0) {
      assert(serializedSize, 'A DAGNode requires it\'s serialized size')
    }
...

This way you can use new DAGNode(...) and new DAGLink(...) symmetrically, ditch the DAGNode.create method and you don't need the weird 0 argument at the end of the DAGNode constructor.

If fact you could probably remove the assert from the constructor entirely as it seems pretty low value at this point.