Support array-type response body by default

[armsnyder]

🚀 Feature

EDIT: I was able to resolve this by finding the allow_repeated_fields_in_body=true plugin option. However, I suggest changing that option default from false to true.

I would like the openapiv2 and grpc-gateway plugins to support mapping an HTTP response to a repeated field, so that we can have array-type response bodies.

For example, I want my response body to look like:

[{"id":1},{"id":2}]

Instead of:

{"pets":[{"id":1},{"id":2}]}

Example proto:

import "google/api/http.proto";

service PetService {
  rpc GetPets(GetPetsRequest) returns (GetPetsResponse) {
    option (google.api.http) = {
      get: "/pets"
      response_body: "pets"
    };
  }
}

message GetPetsRequest {}

message GetPetsResponse {
  repeated Pet pets = 1;
}

message Pet {
  uint64 id = 1;
}

Plugin output:

Failure: plugin openapiv2: repeated field not allowed in field path: pets in pets
Failure: plugin grpc-gateway: repeated field not allowed in field path: pets in pets

I read the previous discussion in #317; however there are situations where you need an array-type response body, like when you are implementing an existing REST API spec while migrating a codebase to gRPC.

The documentation for the google.api.http is clear that mapping a repeated field to response_body can be supported.

If an API needs to use a JSON array for request or response body, it can map
the request or response body to a repeated field. However, some gRPC
Transcoding implementations may not support this feature.

Thank you 👐

[armsnyder]

I just found the allow_repeated_fields_in_body=true plugin option on both plugins, so this resolves my issue. I suggest changing the default value from false to true, since it is not a breaking change. It adds a capability that otherwise causes the plugin to fail.

[johanbrandhorst]

Hi Adam. This is an interesting point, and I agree that it would be nice to turn this on by default. Would you be willing to contribute a flip of this option from off-by-default to on-by-default?

[armsnyder]

I'll take a look. 😄