JSON serialisation of numbers (specifically u64)

[jacogr]

Currently we serialise u64 (e.g. BlockNumber) into a plain number in the JSON over RPC, e.g. for a header we would return -

  "result": {
    "digest": {
      "logs": [
        {
          "Seal": [
            256804359,
            "0x2c0e0ee8a5d1a073da3f8db002b8eaebcd7b1a7eb25662e09f9ef0ac58d96bf17896256cd5f0bc672f96aab49fe5163ca5cb4c1a0f047dc39e89cd4a9eb2ea05"
          ]
        }
      ]
    },
    "extrinsicsRoot": "0x1da0d30001d07991baef3c5c65234c2e88bec659dc0d7138a7e7267e2bacbeb7",
    "number": 2918,
    "parentHash": "0xb58e4d84c2e0db1cdc8c8830aa719015f8c855f29a0dff2b158a160f29f73ba0",
    "stateRoot": "0x22f6f5b6992ab87ea5f52b2732ed9e22a88643ed3a97251986857633687fbc54"
  },
  "id": 1
}

(This is a good example since BlockNumber = u64 and Seal = (u64, Signature))

This is problematic for some middleware, e.g. in JavaScript where the maximum integer number is 2^53 - 1, anything over this and the JSON will not be parsed. We have not run into this yet, since we are reasonably far from limits, however there is a possibility of problems down the line. I would suggest that anything over u32 be encoded as the hex value.

[gavofyork]

@tomusdrw any chance you could look into this?

[tomusdrw]

@gavofyork yeah, I'm actually working on it just now.