Bubble up to the error_formatter the original exception and the backtrace by dcsg · Pull Request #1652 · ruby-grape/grape

dcsg · 2017-07-04T00:18:43Z

When a custom parser is not able to parse the json input body, it raises an exception that is rescued in the Grape::Middleware::Formatter:111. However, the throw statement does not bubble up the root cause by not setting the backtrace. This makes it harder for the error_formatter to understand what caused the exception and to properly handle it.

I tried to add tests to this but was not that easy, any suggestions?

Before the fix

grape/middleware/formatter.rb:

my_custom_error_formatter.rb:

After the fix

my_custom_error_formatter.rb:

dblock · 2017-07-04T15:44:32Z

            raise e
          rescue StandardError => e
-            throw :error, status: 400, message: e.message
+            throw :error, status: 400, message: e.message, backtrace: e


Is this a standard pattern somehow in Ruby? I mean I would expect backtrace to be an actual backtrace and not the original exception. Is anyone doing it like this elsewhere?

Are there other places we throw :error like this that also need fixing?

Is this a standard pattern somehow in Ruby? I mean I would expect backtrace to be an actual backtrace and not the original exception. Is anyone doing it like this elsewhere?

I am quite new in the Ruby world, so TBH I don't know if this is a standard pattern but I would say no. However the Grape library as a "contract" for the formatter: formatter.call(message, backtrace, options, env).

# lib/grape/middleware/error.rb:90 def error_response(error = {}) status = error[:status] || options[:default_status] message = error[:message] || options[:default_message] headers = { Grape::Http::Headers::CONTENT_TYPE => content_type } headers.merge!(error[:headers]) if error[:headers].is_a?(Hash) backtrace = error[:backtrace] || [] rack_response(format_message(message, backtrace), status, headers) end # lib/grape/middleware/error.rb:103 def format_message(message, backtrace) format = env[Grape::Env::API_FORMAT] || options[:format] formatter = Grape::ErrorFormatter.formatter_for(format, options) throw :error, status: 406, message: "The requested format '#{format}' is not supported." unless formatter formatter.call(message, backtrace, options, env) end

This method is called here:

# lib/grape/middleware/error.rb:29 def call!(env) @env = env begin error_response(catch(:error) do return @app.call(@env) end) rescue StandardError => e # ... end

Are there other places we throw :error like this that also need fixing?

Probably yes, but I didn't investigate any other use cases. This one affected us.

While it works, backtrace is meant to be a backtrace. So I think either adding an original exception into the contract or passing the actual backtrace is the right thing to do.

I can do both, what would be your advice on how to test it?

dblock · 2017-07-05T19:10:21Z

Danger is right, this also needs tests.

dcsg · 2017-07-05T23:58:27Z

@dblock would you care to review the code again? I already did the changes you requested (added both backtrace and original exception) and added a test.

I will update the changelog as soon as I have some feedback regarding the implementation.

dblock · 2017-07-06T16:33:29Z

Thanks for hanging in here @dcsg.

I am not loving this at all :( I think we're going the wrong way. The following passes all kinds of things here which are all properties of e.

throw :error, status: 400, message: e.message, backtrace: e.backtrace, exception: e

I think what we want to write is this:

throw :error, status: 400, original_exception: e

Does this look feasible? It might mean breaking some backwards compat which I am OK with, but maybe we don't have to?

dcsg · 2017-07-06T21:38:06Z

@dblock did the changes, what do you think about them?

dcsg · 2017-07-06T21:45:11Z

        headers.merge!(error[:headers]) if error[:headers].is_a?(Hash)
-        backtrace = error[:backtrace] || []
-        rack_response(format_message(message, backtrace), status, headers)
+        backtrace = error[:backtrace] || error[:original_exception] && error[:original_exception].backtrace || []


@dblock here I could replace this with the following:

backtrace = error[:backtrace] || error[:original_exception]&.backtrace || []

However, rubocop complains because of Ruby 2.1.*. Does Grape still support that Ruby version?

Grape supports whatever is in https://github.com/ruby-grape/grape/blob/master/.travis.yml, so 2.2+, so we can tame Rubocop accordingly. Since we don't use &. anywhere else maybe just expanding it is better.

This is fine.

dblock

I have some minor comments left and I am OK merging this because it does what it does. However I'd like us to go further and get rid of passing backtrace through, maybe in a future PR?

Basically I want

throw :error, status: 400, message: e.message, backtrace: e.backtrace, exception: e

to become

throw :error, status: 400, original_exception: e

dblock · 2017-07-07T15:06:14Z

+        def call(message, backtrace, options = {}, env = nil, original_exception = nil)
          result = wrap_message(present(message, env))

          if (options[:rescue_options] || {})[:backtrace] && backtrace && !backtrace.empty?


The if (options[:rescue_options] || {}) is dup, so unwrap it.

rescue_options = options[:rescue_options] if (rescue_options) if ... end

dblock · 2017-07-07T15:07:05Z

      end

-      def error!(message, status = options[:default_status], headers = {}, backtrace = [])
+      def error!(message, status = options[:default_status], headers = {}, backtrace = [], original_exception = '')


Here original_exception should be defaulted to nil.

dblock · 2017-07-07T15:07:24Z

        headers.merge!(error[:headers]) if error[:headers].is_a?(Hash)
-        backtrace = error[:backtrace] || []
-        rack_response(format_message(message, backtrace), status, headers)
+        backtrace = error[:backtrace] || error[:original_exception] && error[:original_exception].backtrace || []


This is fine.

dblock · 2017-07-07T15:08:35Z

        end
      rescue Grape::Exceptions::InvalidFormatter => e
-        throw :error, status: 500, message: e.message
+        throw :error, status: 500, message: e.message, backtrace: e.backtrace, exception: e


Sholdn't this be original_exception: e?

dblock · 2017-07-07T15:09:37Z

 #### Fixes

-* Your contribution here.
+* [#1652](https://github.com/ruby-grape/grape/pull/1652): Bubble up to the error_formatter the root exception - [@dcsg](https://github.com/dcsg).


root -> original

dcsg · 2017-07-07T15:36:20Z

I have some minor comments left and I am OK merging this because it does what it does. However I'd like us to go further and get rid of passing backtrace through, maybe in a future PR?

Doing this change it will break backwards compatibility. Do you want to do it now?

dcsg · 2017-07-07T15:43:10Z

@dblock did the changes.

dblock · 2017-07-07T17:36:29Z

            raise e
          rescue StandardError => e
-            throw :error, status: 400, message: e.message
+            throw :error, status: 400, message: e.message, backtrace: e.backtrace, exception: e


This is still exception: ..., which tells me there's no tests for it cause this doesn't work.

Yeah, I didn't find a way to test these use cases. Do you have any suggestion?

Use a trivial custom parser that raises an exception, it will throw on parser.call and hit this code.

dblock · 2017-07-07T17:36:55Z

 #### Fixes

-* Your contribution here.
+* [#1652](https://github.com/ruby-grape/grape/pull/1652): Bubble up to the error_formatter the original exception - [@dcsg](https://github.com/dcsg).


Oh and this is a feature, not a fix, right? Should be above.

IMO is both a new feature (the original_exception) and a fix (the backtrace).

dcsg · 2017-07-11T00:00:19Z

add to run rubocop --auto-gen-config because of this:

spec/grape/middleware/formatter_spec.rb:330:19: C: Avoid using {...} for multi-line blocks.
    let(:options) {
                  ^
spec/grape/middleware/formatter_spec.rb:339:29: C: Avoid using {...} for multi-line blocks.
      error = catch(:error) {
                            ^

dcsg · 2017-07-11T00:01:21Z

@dblock added the missing test!

dcsg · 2017-07-11T00:27:09Z

quite odd the tests that are failing. Any ideas? I didn't change at all anything related to those tests that are failing in the past 2 commits

dblock · 2017-07-11T17:18:07Z

Found the problem with the build, #1655. I'll rebase/merge this one next.

dblock · 2017-07-11T18:00:40Z

You can rebase on master, otherwise I'll get to this soon.

…rser is not able to parse a json input body.

Add backtrace in missing `throw :error` Add tests

dcsg · 2017-07-11T19:54:18Z

@dblock rebase done

dblock · 2017-07-12T15:15:27Z

Merged, thank you.

dblock · 2017-07-12T15:15:53Z

Want to try to make the backward (in)compatible change to reduce the number of things we pass into the raise on top of this?

dcsg · 2017-07-12T15:39:44Z

@dblock yes, I can do it

dcsg · 2017-07-12T15:40:34Z

BTW when do you expect to release a new tag with this fix?

dcsg · 2017-07-13T22:38:29Z

@dblock I guess it will be kind of hard or almost impossible to do the refactor you want.

# lib/grape/dsl/inside_route.rb:103

      # End the request and display an error to the
      # end user with the specified message.
      #
      # @param message [String] The message to display.
      # @param status [Integer] the HTTP Status Code. Defaults to default_error_status, 500 if not set.
      def error!(message, status = nil, headers = nil)
        self.status(status || namespace_inheritable(:default_error_status))
        throw :error, message: message, status: self.status, headers: headers
      end

What do you think?

dblock · 2017-07-14T12:57:52Z

We'll do a release soon.

Give the refactor a shot and lets see if we can come up with something!

Updates README according to ruby-grape#1652 Prevents `ArgumentError: wrong number of arguments (given 5, expected 4)` from happening when following the README.

dblock reviewed Jul 4, 2017

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dcsg force-pushed the bubble-up-exception branch from 9db6988 to b6f30b1 Compare July 5, 2017 23:55

dcsg changed the title ~~Bubble up to the error_formatter the root exception~~ Bubble up to the error_formatter the root exception and the backtrace Jul 6, 2017

ruby-grape deleted a comment from dcsg Jul 6, 2017

dcsg commented Jul 6, 2017

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dblock requested changes Jul 7, 2017

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dcsg changed the title ~~Bubble up to the error_formatter the root exception and the backtrace~~ Bubble up to the error_formatter the original exception and the backtrace Jul 7, 2017

dblock reviewed Jul 7, 2017

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dcsg force-pushed the bubble-up-exception branch 5 times, most recently from e850d37 to 261de9e Compare July 7, 2017 20:49

dcsg force-pushed the bubble-up-exception branch from 6b08b4f to 4521544 Compare July 11, 2017 00:17

dcsg force-pushed the bubble-up-exception branch from ef0c192 to 264aee1 Compare July 11, 2017 00:49

dcsg added 3 commits July 11, 2017 20:53

Bubbles up to the error_formatter the root exception when a custom pa…

05bff0b

…rser is not able to parse a json input body.

update the changelog

25b1dcd

Add exception to the formatter.call contract

93670da

Add backtrace in missing `throw :error` Add tests

dcsg added 5 commits July 11, 2017 20:53

Refactor exception to original_exception.

2c90e6f

Code review changes

35fcf6f

add missing test

d9f5e51

rubocop fixes

0476231

trying to fix random test failures

469b05d

dcsg force-pushed the bubble-up-exception branch from 264aee1 to 469b05d Compare July 11, 2017 19:54

dblock approved these changes Jul 12, 2017

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dblock merged commit 3c0be5e into ruby-grape:master Jul 12, 2017

dcsg deleted the bubble-up-exception branch July 12, 2017 15:39

vrinek added a commit to vrinek/grape that referenced this pull request Sep 27, 2017

Update README

0c096e3

Updates README according to ruby-grape#1652 Prevents `ArgumentError: wrong number of arguments (given 5, expected 4)` from happening when following the README.

milap-neupane mentioned this pull request Oct 11, 2017

Include original_exception in Readme for custom error formatter #1692

Merged

Timunas mentioned this pull request Sep 10, 2019

Error formatter new argument change not documented #1905

Open

ericproulx mentioned this pull request May 14, 2026

Pass Grape::Exceptions::ErrorResponse to error_formatter#call #2712

Merged

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