Eliminate protocol Jason.Encoder not implemented for... error

[vbaranov]

Motivation

The errors of the next types periodically appear:
1.

2020-09-10T09:28:06.463 [error] GenServer #PID<0.2423.0> terminating
** (Protocol.UndefinedError) protocol Jason.Encoder not implemented for %Explorer.ExchangeRates.Token{available_supply: #Decimal<279261188.720888>, btc_value: #Decimal<0.000002396024029452239812522812910>, id: "poa-network", last_updated: ~U[2020-09-10 09:24:20.408Z], market_cap_usd: #Decimal<6824341>, name: "POA Network", symbol: "POA", total_supply: #Decimal<279261188.720888>, usd_value: #Decimal<0.02459655>, volume_24h_usd: #Decimal<551215>} of type Explorer.ExchangeRates.Token (a struct), Jason.Encoder protocol must always be explicitly implemented.

If you own the struct, you can derive the implementation specifying which fields should be encoded to JSON:

    @derive {Jason.Encoder, only: [....]}
    defstruct ...

It is also possible to encode all fields, although this should be used carefully to avoid accidentally leaking private information when new fields are added:

    @derive Jason.Encoder
    defstruct ...

Finally, if you don't own the struct you want to encode to JSON, you may use Protocol.derive/3 placed outside of any module:

    Protocol.derive(Jason.Encoder, NameOfTheStruct, only: [...])
    Protocol.derive(Jason.Encoder, NameOfTheStruct)
. This protocol is implemented for the following type(s): BlockScoutWeb.API.RPC.EthRPCView, Explorer.Chain.BridgedToken, Explorer.Chain.Token, Explorer.Chain.Transaction, Explorer.Chain.Hash, Explorer.Chain.DecompiledSmartContract, Explorer.Chain.Address, Explorer.Chain.Data, Cldr.LanguageTag, Ecto.Schema.Metadata, Ecto.Association.NotLoaded, Any, Atom, BitString, Date, DateTime, Decimal, Float, Integer, Jason.Fragment, List, Map, NaiveDateTime, Time
    (jason 1.2.1) lib/jason.ex:199: Jason.encode_to_iodata!/2
    (phoenix 1.5.4) lib/phoenix/socket/serializers/v2_json_serializer.ex:28: Phoenix.Socket.V2.JSONSerializer.encode!/1
    (phoenix 1.5.4) lib/phoenix/channel/server.ex:241: Phoenix.Channel.Server.push/5
    (block_scout_web 0.0.1) lib/block_scout_web/channels/exchange_rate_channel.ex:14: BlockScoutWeb.ExchangeRateChannel.handle_out/3
    (phoenix 1.5.4) lib/phoenix/channel/server.ex:328: Phoenix.Channel.Server.handle_info/2
    (stdlib 3.9) gen_server.erl:637: :gen_server.try_dispatch/4
    (stdlib 3.9) gen_server.erl:711: :gen_server.handle_msg/6
    (stdlib 3.9) proc_lib.erl:259: :proc_lib.wake_up/3
Last message: %Phoenix.Socket.Broadcast{event: "new_rate", payload: %{exchange_rate: %Explorer.ExchangeRates.Token{available_supply: #Decimal<279261188.720888>, btc_value: #Decimal<0.000002396024029452239812522812910>, id: "poa-network", last_updated: ~U[2020-09-10 09:24:20.408Z], market_cap_usd: #Decimal<6824341>, name: "POA Network", symbol: "POA", total_supply: #Decimal<279261188.720888>, usd_value: #Decimal<0.02459655>, volume_24h_usd: #Decimal<551215>}, market_history_data: [%{closing_price: #Decimal<0.02459655>, date: ~D[2020-09-10]}, %{closing_price: #Decimal<0.0215>, date: ~D[2020-09-09]}, %{closing_price: #Decimal<0.02262>, date: ~D[2020-09-08]}, %{closing_price: #Decimal<0.0238>, date: ~D[2020-09-07]}, %{closing_price: #Decimal<0.02135>, date: ~D[2020-09-06]}, %{closing_price: #Decimal<0.02648>, date: ~D[2020-09-05]}, %{closing_price: #Decimal<0.02573>, date: ~D[2020-09-04]}, %{closing_price: #Decimal<0.03358>, date: ~D[2020-09-03]}, %{closing_price: #Decimal<0.03788>, date: ~D[2020-09-02]}, %{closing_price: #Decimal<0.04218>, date: ~D[2020-09-01]}, %{closing_price: #Decimal<0.04296>, date: ~D[2020-08-31]}, %{closing_price: #Decimal<0.04308>, date: ~D[2020-08-30]}, %{closing_price: #Decimal<0.04633>, date: ~D[2020-08-29]}, %{closing_price: #Decimal<0.04383>, date: ~D[2020-08-28]}, %{closing_price: #Decimal<0.05018>, date: ~D[2020-08-27]}, %{closing_price: #Decimal<0.03881>, date: ~D[2020-08-26]}, %{closing_price: #Decimal<0.04733>, date: ~D[2020-08-25]}, %{closing_price: #Decimal<0.04384>, date: ~D[2020-08-24]}, %{closing_price: #Decimal<0.05309>, date: ~D[2020-08-23]}, %{closing_price: #Decimal<0.04946>, date: ~D[2020-08-22]}, %{closing_price: #Decimal<0.06786>, date: ~D[2020-08-21]}, %{closing_price: #Decimal<0.06792>, date: ~D[2020-08-20]}, %{closing_price: #Decimal<0.05675>, date: ~D[2020-08-19]}, %{closing_price: #Decimal<0.06902>, date: ~D[2020-08-18]}, %{closing_price: #Decimal<0.03638>, date: ~D[2020-08-17]}, %{closing_price: #Decimal<0.03464>, date: ~D[2020-08-16]}, %{closing_price: #Decimal<0.0366>, date: ~D[2020-08-15]}, %{closing_price: #Decimal<0.02767>, date: ~D[2020-08-14]}, %{closing_price: #Decimal<0.02493>, date: ~D[2020-08-13]}, %{closing_price: #Decimal<0.02109>, date: ~D[2020-08-12]}]}, topic: "exchange_rate:new_rate"}
State: %Phoenix.Socket{assigns: %{locale: "en"}, channel: BlockScoutWeb.ExchangeRateChannel, channel_pid: #PID<0.2423.0>, endpoint: BlockScoutWeb.Endpoint, handler: BlockScoutWeb.UserSocket, id: nil, join_ref: "6", joined: true, private: %{log_handle_in: :debug, log_join: :info}, pubsub_server: BlockScoutWeb.PubSub, ref: nil, serializer: Phoenix.Socket.V2.JSONSerializer, topic: "exchange_rate:new_rate", transport: :websocket, transport_pid: #PID<0.2417.0>}

2020-09-10T09:30:07.239 [error] GenServer BlockScoutWeb.RealtimeEventHandler terminating
** (Protocol.UndefinedError) protocol Jason.Encoder not implemented for %{__struct__: Explorer.Chain.Transaction.History.TransactionStats, date: ~D[2020-09-10], id: 4436, number_of_transactions: 6505} of type Explorer.Chain.Transaction.History.TransactionStats (a struct), Jason.Encoder protocol must always be explicitly implemented.

If you own the struct, you can derive the implementation specifying which fields should be encoded to JSON:

    @derive {Jason.Encoder, only: [....]}
    defstruct ...

It is also possible to encode all fields, although this should be used carefully to avoid accidentally leaking private information when new fields are added:

    @derive Jason.Encoder
    defstruct ...

Finally, if you don't own the struct you want to encode to JSON, you may use Protocol.derive/3 placed outside of any module:

    Protocol.derive(Jason.Encoder, NameOfTheStruct, only: [...])
    Protocol.derive(Jason.Encoder, NameOfTheStruct)
. This protocol is implemented for the following type(s): BlockScoutWeb.API.RPC.EthRPCView, Explorer.Chain.BridgedToken, Explorer.Chain.Token, Explorer.Chain.Transaction, Explorer.Chain.Hash, Explorer.Chain.DecompiledSmartContract, Explorer.Chain.Address, Explorer.Chain.Data, Cldr.LanguageTag, Ecto.Schema.Metadata, Ecto.Association.NotLoaded, Any, Atom, BitString, Date, DateTime, Decimal, Float, Integer, Jason.Fragment, List, Map, NaiveDateTime, Time
    (jason 1.2.1) lib/jason.ex:199: Jason.encode_to_iodata!/2
    (phoenix 1.5.4) lib/phoenix/socket/serializers/v2_json_serializer.ex:9: Phoenix.Socket.V2.JSONSerializer.fastlane!/1
    (phoenix 1.5.4) lib/phoenix/channel/server.ex:102: anonymous fn/5 in Phoenix.Channel.Server.dispatch/3
    (elixir 1.10.3) lib/enum.ex:2111: Enum."-reduce/3-lists^foldl/2-0-"/3
    (phoenix 1.5.4) lib/phoenix/channel/server.ex:87: Phoenix.Channel.Server.dispatch/3
    (elixir 1.10.3) lib/registry.ex:468: Registry.dispatch/4
    (phoenix_pubsub 2.0.0) lib/phoenix/pubsub.ex:286: Phoenix.PubSub.dispatch/5
    (block_scout_web 0.0.1) lib/block_scout_web/realtime_event_handler.ex:35: BlockScoutWeb.RealtimeEventHandler.handle_info/2
Last message: {:chain_event, :transaction_stats}
State: []

2020-09-10T12:24:35.253 [error] GenServer BlockScoutWeb.RealtimeEventHandler terminating
** (Protocol.UndefinedError) protocol Jason.Encoder not implemented for #Explorer.Chain.Wei<0> of type Explorer.Chain.Wei (a struct), Jason.Encoder protocol must always be explicitly implemented.

If you own the struct, you can derive the implementation specifying which fields should be encoded to JSON:

    @derive {Jason.Encoder, only: [....]}
    defstruct ...

It is also possible to encode all fields, although this should be used carefully to avoid accidentally leaking private information when new fields are added:

    @derive Jason.Encoder
    defstruct ...

Finally, if you don't own the struct you want to encode to JSON, you may use Protocol.derive/3 placed outside of any module:

    Protocol.derive(Jason.Encoder, NameOfTheStruct, only: [...])
    Protocol.derive(Jason.Encoder, NameOfTheStruct)
. This protocol is implemented for the following type(s): BlockScoutWeb.API.RPC.EthRPCView, Explorer.ExchangeRates.Token, Explorer.Chain.Transaction, Explorer.Chain.Transaction.History.TransactionStats, Explorer.Chain.BridgedToken, Explorer.Chain.Hash, Explorer.Chain.Data, Explorer.Chain.DecompiledSmartContract, Explorer.Chain.Address, Explorer.Chain.Token, Cldr.LanguageTag, Ecto.Association.NotLoaded, Ecto.Schema.Metadata, Jason.Fragment, List, Map, DateTime, Any, Decimal, Date, Float, Time, NaiveDateTime, Atom, Integer, BitString
    (jason 1.2.1) lib/jason.ex:199: Jason.encode_to_iodata!/2
    (phoenix 1.5.4) lib/phoenix/socket/serializers/v2_json_serializer.ex:9: Phoenix.Socket.V2.JSONSerializer.fastlane!/1
    (phoenix 1.5.4) lib/phoenix/channel/server.ex:102: anonymous fn/5 in Phoenix.Channel.Server.dispatch/3
    (elixir 1.10.3) lib/enum.ex:2111: Enum."-reduce/3-lists^foldl/2-0-"/3
    (phoenix 1.5.4) lib/phoenix/channel/server.ex:87: Phoenix.Channel.Server.dispatch/3
    (elixir 1.10.3) lib/registry.ex:493: Registry.dispatch_serial/4
    (elixir 1.10.3) lib/registry.ex:476: Registry.dispatch/4
    (phoenix_pubsub 2.0.0) lib/phoenix/pubsub.ex:286: Phoenix.PubSub.dispatch/5
Last message: {:chain_event, :transactions, :realtime, [%Explorer.Chain.Transaction{earliest_processing_start: ~U[2020-09-10 12:24:34.244928Z], inserted_at: ~U[2020-09-10 12:24:34.245665Z], cumulative_gas_used: nil, hash: %Explorer.Chain.Hash{byte_count: 32, bytes: <<11, 31, 192, 152, 111, 20, 91, 248, 185, 220, 193, 31, 136, 52, 148, 141, 231, 106, 87, 175, 67, 37, 131, 250, 80, 16, 237, 88, 211, 91, 226, 15>>}, r: #Decimal<109707930281350757237995081842377944010502090433086538622625154544755721418955>, __meta__: #Ecto.Schema.Metadata<:loaded, "transactions">, status: nil, created_contract_code_indexed_at: nil, block_hash: nil, gas_used: nil, uncles: #Ecto.Association.NotLoaded<association :uncles is not loaded>, internal_transactions: #Ecto.Association.NotLoaded<association :internal_transactions is not loaded>, index: nil, to_address: #Ecto.Association.NotLoaded<association :to_address is not loaded>, gas: #Decimal<200000>, to_address_hash: %Explorer.Chain.Hash{byte_count: 20, bytes: <<60, 212, 180, 217, 125, 202, 212, 238, 119, 43, 196, 240, 251, 14, 118, 5, 252, 134, 168, 91>>}, v: #Decimal<236>, created_contract_address: #Ecto.Association.NotLoaded<association :created_contract_address is not loaded>, gas_price: #Explorer.Chain.Wei<1000000000>, s: #Decimal<50373490975905187701609483132229362331749212624285429008801877903283509287232>, error: nil, token_transfers: #Ecto.Association.NotLoaded<association :token_transfers is not loaded>, created_contract_address_hash: nil, nonce: 724, from_address_hash: %Explorer.Chain.Hash{byte_count: 20, bytes: <<3, 228, 1, 58, 144, 47, 200, 180, 204, 131, 234, 65, 206, 61, 149, 13, 61, 216, ...>>}, revert_reason: nil, logs: #Ecto.Association.NotLoaded<association :logs is not loaded>, forks: #Ecto.Association.NotLoaded<association :forks is not loaded>, input: %Explorer.Chain.Data{bytes: <<169, 5, 156, 187, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...>>}, block_number: nil, updated_at: ~U[2020-09-10 12:24:34.245665Z], block: #Ecto.Association.NotLoaded<association :block is not loaded>, value: #Explorer.Chain.Wei<0>, from_address: #Ecto.Association.NotLoaded<association :from_address is not loaded>, old_block_hash: nil}]}
State: []v

Changelog

Explicitly enable Jason encoding for mentioned schemas in the errors:

1. Explorer.Chain.Transaction.History.TransactionStats
2. Explorer.ExchangeRates.Token
3. Explorer.Chain.Wei

Upgrading

If you have any Incompatible Changes in the above Changelog, outline how users of prior versions can upgrade once this PR lands or when reviewers are testing locally. A common upgrading step is "Database reset and re-index required".

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build dbe6856272d60afd146518174e6bae7fc5074ba9-PR-3290

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+20.7%) to 75.876%

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Totals
Change from base Build 7a67da2968faecf3024f06d55aac0171c839f5a3:	20.7%
Covered Lines:	1928
Relevant Lines:	2541

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💛 - Coveralls