How to debug phoenix framework's log error? - erlang

Question

I am installing this pheonix web app: https://github.com/poanetwork/blockscout
after installed all the dependencies, I run this command ( following the document) :
$ mix phx.server
and got error:
$ iex -S mix phx.server
Erlang/OTP 25 [erts-13.1.2] [source] [64-bit] [smp:2:2] [ds:2:2:10] [async-threads:1] [jit:ns]
2022-12-13T04:25:43.083 [notice] Application ethereum_jsonrpc exited: EthereumJSONRPC.Application.start(:normal, []) returned an error: shutdown: failed to start child: :worker
** (EXIT) an exception was raised:
** (MatchError) no match of right hand side value: {:error, :badarg}
(poolboy 1.5.2) /opt/app/blockscout/deps/poolboy/src/poolboy.erl:283: :poolboy.new_worker/1
(poolboy 1.5.2) /opt/app/blockscout/deps/poolboy/src/poolboy.erl:304: :poolboy.prepopulate/3
(poolboy 1.5.2) /opt/app/blockscout/deps/poolboy/src/poolboy.erl:153: :poolboy.init/3
(stdlib 4.1.1) gen_server.erl:851: :gen_server.init_it/2
(stdlib 4.1.1) gen_server.erl:814: :gen_server.init_it/6
(stdlib 4.1.1) proc_lib.erl:240: :proc_lib.init_p_do_apply/3
2022-12-13T04:25:43.106 [notice] Application poolboy exited: :stopped
2022-12-13T04:25:43.106 [notice] Application decorator exited: :stopped
2022-12-13T04:25:43.106 [notice] Application decimal exited: :stopped
2022-12-13T04:25:43.106 [notice] Application websocket_client exited: :stopped
2022-12-13T04:25:43.106 [notice] Application ex_abi exited: :stopped
2022-12-13T04:25:43.106 [notice] Application ex_keccak exited: :stopped
2022-12-13T04:25:43.106 [notice] Application rustler exited: :stopped
2022-12-13T04:25:43.107 [notice] Application timex exited: :stopped
2022-12-13T04:25:43.107 [notice] Application gettext exited: :stopped
2022-12-13T04:25:43.108 [notice] Application combine exited: :stopped
2022-12-13T04:25:43.110 [notice] Application tzdata exited: :stopped
2022-12-13T04:25:43.110 [notice] Application spandex_datadog exited: :stopped
2022-12-13T04:25:43.111 [notice] Application msgpax exited: :stopped
2022-12-13T04:25:43.111 [notice] Application spandex exited: :stopped
2022-12-13T04:25:43.111 [notice] Application plug exited: :stopped
2022-12-13T04:25:43.111 [notice] Application telemetry exited: :stopped
2022-12-13T04:25:43.112 [notice] Application plug_crypto exited: :stopped
2022-12-13T04:25:43.112 [notice] Application mime exited: :stopped
2022-12-13T04:25:43.112 [notice] Application eex exited: :stopped
2022-12-13T04:25:43.112 [notice] Application optimal exited: :stopped
2022-12-13T04:25:43.112 [notice] Application logger_file_backend exited: :stopped
2022-12-13T04:25:43.112 [notice] Application jason exited: :stopped
2022-12-13T04:25:43.112 [notice] Application httpoison exited: :stopped
2022-12-13T04:25:43.113 [notice] Application hackney exited: :stopped
2022-12-13T04:25:43.113 [notice] Application metrics exited: :stopped
2022-12-13T04:25:43.113 [notice] Application ssl_verify_fun exited: :stopped
2022-12-13T04:25:43.113 [notice] Application parse_trans exited: :stopped
2022-12-13T04:25:43.113 [notice] Application syntax_tools exited: :stopped
2022-12-13T04:25:43.113 [notice] Application mimerl exited: :stopped
2022-12-13T04:25:43.113 [notice] Application idna exited: :stopped
2022-12-13T04:25:43.113 [notice] Application unicode_util_compat exited: :stopped
2022-12-13T04:25:43.113 [notice] Application cowboy exited: :stopped
2022-12-13T04:25:43.114 [notice] Application ranch exited: :stopped
2022-12-13T04:25:43.114 [notice] Application cowlib exited: :stopped
2022-12-13T04:25:43.114 [notice] Application certifi exited: :stopped
** (Mix) Could not start application ethereum_jsonrpc: EthereumJSONRPC.Application.start(:normal, []) returned an error: shutdown: failed to start child: :worker
** (EXIT) an exception was raised:
** (MatchError) no match of right hand side value: {:error, :badarg}
(poolboy 1.5.2) /opt/app/blockscout/deps/poolboy/src/poolboy.erl:283: :poolboy.new_worker/1
(poolboy 1.5.2) /opt/app/blockscout/deps/poolboy/src/poolboy.erl:304: :poolboy.prepopulate/3
(poolboy 1.5.2) /opt/app/blockscout/deps/poolboy/src/poolboy.erl:153: :poolboy.init/3
(stdlib 4.1.1) gen_server.erl:851: :gen_server.init_it/2
(stdlib 4.1.1) gen_server.erl:814: :gen_server.init_it/6
(stdlib 4.1.1) proc_lib.erl:240: :proc_lib.init_p_do_apply/3
I found there is no stack trace for the source code, all the stack trace that can be seen is the dependencies'.
so my question is: how to know which line of the source code of this eror occured at?
thanks.

Answer 1

The error happened before your application even attempted to start.
ErlangVM attempts to start all the applications yours depends on upfront, and the error
Application ethereum_jsonrpc exited:
EthereumJSONRPC.Application.start(:normal, []) returned an error:
shutdown: failed to start child: :worker
** (EXIT) an exception was raised:
** (MatchError) no match of right hand side value: {:error, :badarg}
basically means that ethereum_jsonrpc application failed to start preventing ErlangVM from trying to start the main application. To narrow down the issue, one might try to start the failing ethereum_jsonrpc explicitly, e. g. from iex session with Application.ensure_all_started(:ethereum_jsonrpc) or with more explicit EthereumJSONRPC.Application.start(:normal, []).

Answer 2

Ok, I got it resolved.
finally I don't know which line of code failed.
Solution
1.print many debug logs into the source code and guess in which step it failed.
+ IO.puts "== config: #{ inspect config}"
+ IO.puts "== rolling_window_opts: #{ inspect rolling_window_opts}"
and also, in pheonix framework, you can guess the source code file from its CalssName, e.g.
EthereumJSONRPC.Application maps to apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/application.ex
2.change the logger level.
3.edit the config/config.exs file to enable DB log:
database: database_api,
hostname: hostname_api,
// add this line of code
show_sensitive_data_on_connection_error: true