Fix batch JSON-RPC request support

[unnawut]

Issue/Task Number: -

Overview

This PR fixes the error when Potterhat receives a JSON-RPC batch request.

This bug was found while integrating Potterhat with omisego/ewallet's eth-blockchain branch.

Changes

• Updated PotterhatRPC.Router

Implementation Details

When Phoenix receives a JSON array as body params, it wraps those params in a %{"_json" => _} map before passing it to the router. So an extra condition is added to support this quirk.

Usage

Try send a batch request to Potterhat. E.g.

curl -X POST http://localhost:8545 \
-H "Content-Type: application/json" \
--data '[
  {
    "id" => 1001,
    "jsonrpc" => "2.0",
    "method" => "eth_getBalance",
    "params" => ["0x0000000000000000000000000000000000000001", "latest"]
  },
  {
    "id" => 1002,
    "jsonrpc" => "2.0",
    "method" => "eth_getBalance",
    "params" => ["0x0000000000000000000000000000000000000002", "latest"]
  }
]'

A successful response should be returned instead of an internal server error.

Impact

No changes to API or DB.