Add message field to the error message emitted by grpc-gateway

[ffredsh]

This is to make it more consistent with the Status proto message in order to make the error more consistent between grpc and json.

We currently use grpc-gateway for local developement and ESP in production and having to deal with the message in two different fields is a bit annoying. This makes the behaviour of grpc-gateway a bit more consistent with ESP.

[codecov-io]

Codecov Report

Merging #718 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #718      +/-   ##
=========================================
+ Coverage   56.28%   56.3%   +0.01%     
=========================================
  Files          30      30              
  Lines        3061    3062       +1     
=========================================
+ Hits         1723    1724       +1     
  Misses       1167    1167              
  Partials      171     171

Impacted Files	Coverage Δ
runtime/errors.go	45.83% <100%> (+0.76%)	⬆️

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[achew22]

Could you add a link to https://github.com/grpc/grpc/blob/master/src/proto/grpc/status/status.proto?

[ffredsh]

done!

[ti]

this is really ugly. how to fix "error" and "message" repeat problem ?
before this code:

{
    "error": "something error",
    "code": 3
}

after:

{
    "error": "something error",
    "message": "something error",
    "code": 3
}

should web restore the code?

[ti]

you can just use to fix it before:

type Error struct {
	Message string   `json:"error,omitempty"`

@ffredsh

[johanbrandhorst]

I agree, but unfortunately we have to keep the old "error" field for backwards compatibility purposes. We'll want to remove it come 2.0.

[ti]

@johanbrandhorst web should not remove the "error" field in http response json, the "error" field is defined for compatible for some rfc documents,
For exp:
https://tools.ietf.org/html/rfc6749#page-45

more:
the "error" means some "enmu text" for the front apps, but he "message" just means some error details, if you want add it, you should add the "message" to the 2.0

@ffredsh

[johanbrandhorst]

I apologize, but you have confused me a bit. Your PR suggested that we should remove the message in 1.x, which is unacceptable as we have releases with it in. Are you now saying we definitely must keep the error field in 2.0 and remove the message again because error is declared as a response field by RFC6749 (Oath Framework)?

[ti]

This change if really affect our current restful document for open apis 😢

[ti]

@ffredsh