protoc-gen-swagger: return error when encoding swagger file

[elliots]

Json marshalling errors were being ignored, and it was generating a blank string swagger file.

This PR causes the error to be returned.

I ran into this (and it very well could be the only way this could happen) when using the json schema example option, which must be valid json.

For example:

message Request {
    option (grpc.gateway.protoc_gen_swagger.options.openapiv2_schema) = {
        example: { value: 'this is not json'}
    };

    bytes content = 90;
}

would silently fail.

Now, it fails like this:

failed to encode swagger for attachment/web/attachment.proto: json: error calling MarshalJSON for type json.RawMessage: invalid character 'h' in literal true (expecting 'r')

which isn't great, but is better.

I'm using this from inside https://github.com/utrack/clay/ but I think it would apply the same using it directly.

[codecov-io]

Codecov Report

Merging #878 into master will decrease coverage by 0.1%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #878      +/-   ##
==========================================
- Coverage   52.99%   52.88%   -0.11%     
==========================================
  Files          39       39              
  Lines        3910     3918       +8     
==========================================
  Hits         2072     2072              
- Misses       1642     1650       +8     
  Partials      196      196

Impacted Files	Coverage Δ
protoc-gen-swagger/genswagger/generator.go	13.82% <0%> (-1.29%)	⬇️

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[johanbrandhorst]

Great work! Do you think you could add some tests here that trigger this behaviour as well?

Thanks!

[johanbrandhorst]

Ah this is fine as it is, don't want it to be forgotten.

[johanbrandhorst]

Thanks for your contribution!