node_tree_to_json.py

import bpy
import json
import pprint
import re

ng = bpy.data.node_groups[0]
nodes = ng.nodes

# store unsorted, order is important later
layout_dict = {}
not_linked = lambda s: not hasattr(s, 'links') or not s.links

for node in nodes:

    node_dict = {}
    node_items = {}
    for k, v in node.items():
        if isinstance(v, (float, int, str)):
            node_items[k] = v
        else:
            node_items[k] = v[:]

    node_dict['params'] = node_items
        
    # inputs to this node is limited to one per socket.
    node_incoming = {}
    for i in node.inputs:
        if not_linked(i):
            continue

        link = i.links[0]
        n = link.from_node.name
        s = link.from_socket.name
        node_incoming[i.name] = [n, s]
        
    node_dict['incoming'] = node_incoming

    node_outgoing = {}
    for o in node.outputs:
        if not_linked(o):
            continue

        connections = []        
        for link in o.links:
            n = link.to_node.name
            s = link.to_socket.name
            connections.append([n, s])
        node_outgoing[o.name] = connections
    
    node_dict['outgoing'] = node_outgoing
    node_dict['location'] = node.location[:]
    node_dict['bl_idname'] = node.bl_idname

    layout_dict[node.name] = node_dict

m = json.dumps(layout_dict, sort_keys=True, indent=2)

# optional post processing step
post_processing = False
if post_processing:
    flatten = lambda match: r' {}'.format(match.group(1), m)
    m = re.sub(r'\s\s+(\d+)', flatten , m)

with open('node_tree.json', 'w') as node_tree:
    node_tree.writelines(m)