Cowboy handlers proably exit, not being logged or reported anywhere

Phoenix Forum Questions / Help
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Sort of. Not fully.

So I have installed monitor on the cowboy processes that handle requests so I learn about their exit reasons. I caught this thing:

%Plug.Parsers.RequestTooLargeError{..}

Which doesn’t appear anywhere else in my logs or caught exceptions. It looks like some requests coming in are exceeding default 8MB of payload sizez, which triggers this error.

Now this is not really a kill reason I at all but this exception. I can replicate this reliabily against my app with:

curl --data "@/path/to/large/file" http://localhost:8080/webhooks/outbound/test

if my file size exceeds 8MB it crashes with no log line saying that response was sent.

Now, with log level set to :debug I see the actual error:

iex(a@127.0.0.1)8> 11:56:03.286 http_method=POST http_path=/webhooks/outbound/asdfasdf request_id=Fnh0I9UHbqEMJXkAAEjC remote_ip=127.0.0.1 [info] POST /webhooks/outbound/asdfasdf
11:56:03.288 http_method=POST http_path=/webhooks/outbound/asdfasdf request_id=Fnh0I9UHbqEMJXkAAEjC remote_ip=127.0.0.1 [info] Elixir.Infra.ExceptionCatcher.catch_exits/1 starts monitoring a pid: #PID<0.4378.0>
11:56:03.548 http_method=POST http_path=/webhooks/outbound/asdfasdf request_id=Fnh0I9UHbqEMJXkAAEjC remote_ip=127.0.0.1 [debug] ** (Plug.Parsers.RequestTooLargeError) the request is too large. If you are willing to process larger requests, please give a :length to Plug.Parsers
    (plug 1.11.1) lib/plug/parsers.ex:348: Plug.Parsers.reduce/8
    (webhooks 0.1.0) lib/webhooks/endpoint.ex:1: Webhooks.Endpoint.plug_builder_call/2
    (webhooks 0.1.0) lib/webhooks/endpoint.ex:4: anonymous fn/3 in Webhooks.Endpoint."call (overridable 3)"/2
    (appsignal 2.1.3) lib/appsignal/instrumentation.ex:9: Appsignal.Instrumentation.instrument/1
    (webhooks 0.1.0) lib/plug/debugger.ex:136: Webhooks.Endpoint."call (overridable 4)"/2
    (webhooks 0.1.0) lib/webhooks/endpoint.ex:1: Webhooks.Endpoint."call (overridable 5)"/2
    (webhooks 0.1.0) lib/plug/error_handler.ex:65: Webhooks.Endpoint.call/2
    (phoenix 1.5.8) lib/phoenix/endpoint/cowboy2_handler.ex:65: Phoenix.Endpoint.Cowboy2Handler.init/4
    ...
    (stdlib 3.13.2) proc_lib.erl:226: :proc_lib.init_p_do_apply/3

11:56:03.549 [error] Elixir.Infra.ExceptionCatcher.catch_exits/1 detected a process that crashed: #PID<0.4378.0>

Note the last line is added by me and I cut off some project-specific lines from stacktrace.

I don’t quite understand why this exception is not handled similar way to others, other than it’s happening early in the Endpoint life cycle, during parsing the request body.

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