method_to_url config

Instead of making up symbolic names for the different types of URLs we
need, have the configuration be a base `url` for a fallback and then
entries under `method_to_url` which maps a JSONRPC method name to a the
URL to use.  This allows the devops running the JSONRPC nodes to say
which nodes support which methods specifically, which is easier than
knowing which symbolic name uses which methods.  It also means we don't
need separate variant specific symbolic names since the variants will
be able to use their own method names in this new format for the config.

apps/ethereum_jsonrpc/config/geth.exs

@@ -1,6 +1,5 @@
 use Mix.Config
 
 config :ethereum_jsonrpc,
-  trace_url: "https://mainnet.infura.io/mew",
   url: "https://mainnet.infura.io/mew",
   variant: EthereumJSONRPC.Geth

apps/ethereum_jsonrpc/config/parity.exs

@@ -1,6 +1,9 @@
 use Mix.Config
 
 config :ethereum_jsonrpc,
-  trace_url: "https://sokol-trace.poa.network",
   url: "https://sokol.poa.network",
+  method_to_url: [
+    eth_getBalance: "https://sokol-trace.poa.network",
+    trace_replayTransaction: "https://sokol-trace.poa.network"
+  ],
   variant: EthereumJSONRPC.Parity

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc.ex

@@ -89,6 +89,27 @@ defmodule EthereumJSONRPC do
     Application.fetch_env!(:ethereum_jsonrpc, key)
   end
 
+  @doc """
+  Fetches the configured url for the specific `method` or the fallback `url`
+
+  Configuration for a specific `method` can be set in `method_to_url` `config`
+
+      config :ethereum_jsonrpc,
+        method_to_url: [
+          eth_getBalance: "method_to_url"
+        ]
+
+  The fallback 'url' MUST we set if not all methods have a url set.
+
+      config :ethereum_jsonrpc,
+        url:
+  """
+  def method_to_url(method) when is_atom(method) do
+    :ethereum_jsonrpc
+    |> Application.get_env(:method_to_url, [])
+    |> Keyword.get_lazy(method, fn -> config(:url) end)
+  end
+
   @doc """
   Fetches balance for each address `hash` at the `block_number`
   """
@@ -108,7 +129,7 @@ defmodule EthereumJSONRPC do
     with {:ok, responses} <-
            id_to_params
            |> get_balance_requests()
-           |> json_rpc(config(:trace_url)) do
+           |> json_rpc(method_to_url(:eth_getBalance)) do
       get_balance_responses_to_addresses_params(responses, id_to_params)
     end
   end
@@ -121,7 +142,7 @@ defmodule EthereumJSONRPC do
   def fetch_blocks_by_hash(block_hashes) do
     block_hashes
     |> get_block_by_hash_requests()
-    |> json_rpc(config(:url))
+    |> json_rpc(method_to_url(:eth_getBlockByHash))
     |> handle_get_blocks()
     |> case do
       {:ok, _next, results} -> {:ok, results}
@@ -135,7 +156,7 @@ defmodule EthereumJSONRPC do
   def fetch_blocks_by_range(_first.._last = range) do
     range
     |> get_block_by_number_requests()
-    |> json_rpc(config(:url))
+    |> json_rpc(method_to_url(:eth_getBlockByNumber))
     |> handle_get_blocks()
   end
 
@@ -158,7 +179,7 @@ defmodule EthereumJSONRPC do
   def fetch_block_number_by_tag(tag) when tag in ~w(earliest latest pending) do
     tag
     |> get_block_by_tag_request()
-    |> json_rpc(config(:url))
+    |> json_rpc(method_to_url(:eth_getBlockByNumber))
     |> handle_get_block_by_tag()
   end
 

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/parity.ex

@@ -3,7 +3,7 @@ defmodule EthereumJSONRPC.Parity do
   Ethereum JSONRPC methods that are only supported by [Parity](https://wiki.parity.io/).
   """
 
-  import EthereumJSONRPC, only: [config: 1, id_to_params: 1, json_rpc: 2, request: 1]
+  import EthereumJSONRPC, only: [id_to_params: 1, method_to_url: 1, json_rpc: 2, request: 1]
 
   alias EthereumJSONRPC.Parity.Traces
   alias EthereumJSONRPC.{Transaction, Transactions}
@@ -19,7 +19,7 @@ defmodule EthereumJSONRPC.Parity do
     with {:ok, responses} <-
            id_to_params
            |> trace_replay_transaction_requests()
-           |> json_rpc(config(:trace_url)) do
+           |> json_rpc(method_to_url(:trace_replayTransaction)) do
       trace_replay_transaction_responses_to_internal_transactions_params(responses, id_to_params)
     end
   end
@@ -35,7 +35,7 @@ defmodule EthereumJSONRPC.Parity do
     with {:ok, transactions} <-
            %{id: 1, method: "parity_pendingTransactions", params: []}
            |> request()
-           |> json_rpc(config(:url)) do
+           |> json_rpc(method_to_url(:parity_pendingTransactions)) do
       transactions_params =
         transactions
         |> Transactions.to_elixir()

coveralls.json

@@ -1,7 +1,7 @@
 {
   "coverage_options": {
     "treat_no_relevant_lines_as_covered": true,
-    "minimum_coverage": 94.4
+    "minimum_coverage": 94.5
   },
   "terminal_options": {
     "file_column_width": 120