Adding Emit Defaults Option (#281)

## Problem Statement

When using gRPC UI, I came across a scenario where I did not want
default values emitted to the Response tab. While gRPCurl has an option
to enable/disable emit-defaults, gRPC UI does not since the call it
makes to gRPCurl hard-codes emit-defaults to true. Thus, there was an
inconsistency between these two closely related tools.

## Example Proto File

```Proto
service Greeter {
   rpc SayHello (HelloRequest) returns (HelloReply);
}

message HelloRequest {
   string name = 1;
}

message TwoNums {
   int32 abc = 1;
   int32 xyz = 2;
}

message HelloReply {
   oneof HelloReplies {
      TwoNums nums = 1;
      int32 num = 2;
   }
   string answer = 3;
}
```

## Sample Server Implementation - Written in Go


[server.txt](https://github.com/fullstorydev/grpcui/files/13245072/server.txt)

## gRPC UI Output

```JSON
{
  "nums": {
    "abc": 3,
    "xyz": 3
  },
  "answer": ""
}
```

## gRPCurl Output with `-emit-defaults=false`

```JSON
{
  "nums": {
    "abc": 3,
    "xyz": 3
  }
}
```

## Fix

- Added `emit-defaults` flag to the `cmd/grpcui.go` file.
- Set a global variable in `handlers.go` to accept value of
`emit-defaults` flag.
- The default value of this flag is `true`, to preserve existing
behavior

```bash
grpcui -h
...
-emit-defaults
        Emit default values for JSON-encoded responses. (default true)
...
```

## gRPC UI Output After Fix with `-emit-defaults=false`

```JSON
{
  "nums": {
    "abc": 3,
    "xyz": 3
  }
}
```

---------

Co-authored-by: = <[email protected]>

Author: James-Bartman

cmd/grpcui/grpcui.go

@@ -116,6 +116,8 @@ var (
 	maxMsgSz = flags.Int("max-msg-sz", 0, prettify(`
 		The maximum encoded size of a message that grpcui will accept. If not
 		specified, defaults to 4mb.`))
+	emitDefaults = flags.Bool("emit-defaults", true, prettify(`
+		Emit default values for JSON-encoded responses.`))
 	debug   optionalBoolFlag
 	verbose = flags.Bool("v", false, prettify(`
 		Enable verbose output.`))
@@ -625,6 +627,7 @@ func main() {
 	if examplesOpt != nil {
 		handlerOpts = append(handlerOpts, examplesOpt)
 	}
+	handlerOpts = append(handlerOpts, standalone.EmitDefaults(*emitDefaults))
 	handlerOpts = append(handlerOpts, configureJSandCSS(extraJS, standalone.AddJSFile)...)
 	handlerOpts = append(handlerOpts, configureJSandCSS(extraCSS, standalone.AddCSSFile)...)
 	handlerOpts = append(handlerOpts, configureAssets(otherAssets)...)

handlers.go

@@ -58,6 +58,8 @@ type InvokeOptions struct {
 	// includes conflicting metadata, the values in the HTTP request headers
 	// will override, and the values in the request will not be sent.
 	PreserveHeaders []string
+	// Whether or not default values should be emitted in the JSON response
+	EmitDefaults bool
 	// If verbosity is greater than zero, the handler may log events, such as
 	// cases where the request included metadata that conflicts with the
 	// ExtraMetadata and PreserveHeaders fields above. It is an int, instead
@@ -457,8 +459,9 @@ func invokeRPC(ctx context.Context, methodName string, ch grpc.ClientConnInterfa
 	}
 
 	result := rpcResult{
-		descSource: descSource,
-		Requests:   &reqStats,
+		descSource:   descSource,
+		emitDefaults: options.EmitDefaults,
+		Requests:     &reqStats,
 	}
 	if err := grpcurl.InvokeRPC(ctx, descSource, ch, methodName, invokeHdrs, &result, requestFunc); err != nil {
 		return nil, err
@@ -539,12 +542,13 @@ type rpcError struct {
 }
 
 type rpcResult struct {
-	descSource grpcurl.DescriptorSource
-	Headers    []rpcMetadata        `json:"headers"`
-	Error      *rpcError            `json:"error"`
-	Responses  []rpcResponseElement `json:"responses"`
-	Requests   *rpcRequestStats     `json:"requests"`
-	Trailers   []rpcMetadata        `json:"trailers"`
+	descSource   grpcurl.DescriptorSource
+	emitDefaults bool
+	Headers      []rpcMetadata        `json:"headers"`
+	Error        *rpcError            `json:"error"`
+	Responses    []rpcResponseElement `json:"responses"`
+	Requests     *rpcRequestStats     `json:"requests"`
+	Trailers     []rpcMetadata        `json:"trailers"`
 }
 
 func (*rpcResult) OnResolveMethod(*desc.MethodDescriptor) {}
@@ -556,12 +560,12 @@ func (r *rpcResult) OnReceiveHeaders(md metadata.MD) {
 }
 
 func (r *rpcResult) OnReceiveResponse(m proto.Message) {
-	r.Responses = append(r.Responses, responseToJSON(r.descSource, m))
+	r.Responses = append(r.Responses, responseToJSON(r.descSource, m, r.emitDefaults))
 }
 
 func (r *rpcResult) OnReceiveTrailers(stat *status.Status, md metadata.MD) {
 	r.Trailers = responseMetadata(md)
-	r.Error = toRpcError(r.descSource, stat)
+	r.Error = toRpcError(r.descSource, stat, r.emitDefaults)
 }
 
 func responseMetadata(md metadata.MD) []rpcMetadata {
@@ -583,15 +587,15 @@ func responseMetadata(md metadata.MD) []rpcMetadata {
 	return ret
 }
 
-func toRpcError(descSource grpcurl.DescriptorSource, stat *status.Status) *rpcError {
+func toRpcError(descSource grpcurl.DescriptorSource, stat *status.Status, emitDefaults bool) *rpcError {
 	if stat.Code() == codes.OK {
 		return nil
 	}
 
 	details := stat.Proto().Details
 	msgs := make([]rpcResponseElement, len(details))
 	for i, d := range details {
-		msgs[i] = responseToJSON(descSource, d)
+		msgs[i] = responseToJSON(descSource, d, emitDefaults)
 	}
 	return &rpcError{
 		Code:    uint32(stat.Code()),
@@ -601,9 +605,9 @@ func toRpcError(descSource grpcurl.DescriptorSource, stat *status.Status) *rpcEr
 	}
 }
 
-func responseToJSON(descSource grpcurl.DescriptorSource, msg proto.Message) rpcResponseElement {
+func responseToJSON(descSource grpcurl.DescriptorSource, msg proto.Message, emitDefaults bool) rpcResponseElement {
 	anyResolver := grpcurl.AnyResolverFromDescriptorSourceWithFallback(descSource)
-	jsm := jsonpb.Marshaler{EmitDefaults: true, OrigName: true, Indent: "  ", AnyResolver: anyResolver}
+	jsm := jsonpb.Marshaler{EmitDefaults: emitDefaults, OrigName: true, Indent: "  ", AnyResolver: anyResolver}
 	var b bytes.Buffer
 	if err := jsm.Marshal(&b, msg); err == nil {
 		return rpcResponseElement{Data: json.RawMessage(b.Bytes())}

standalone/opts.go

@@ -188,6 +188,13 @@ func PreserveHeaders(headerNames []string) HandlerOption {
 	})
 }
 
+// EmitDefaults tells gRPCurl whether or not default values should be emitted
+func EmitDefaults(emit bool) HandlerOption {
+	return optFunc(func(opts *handlerOptions) {
+		opts.emitDefaults = emit
+	})
+}
+
 // WithInvokeVerbosity indicates the level of log output from the gRPC UI server
 // handler that performs RPC invocations.
 func WithInvokeVerbosity(verbosity int) HandlerOption {
@@ -229,6 +236,7 @@ type handlerOptions struct {
 	defaultMetadata     []string
 	extraMetadata       []string
 	preserveHeaders     []string
+	emitDefaults        bool
 	invokeVerbosity     int
 	debug               *bool
 }

standalone/standalone.go

@@ -93,6 +93,7 @@ func Handler(ch grpcdynamic.Channel, target string, methods []*desc.MethodDescri
 	invokeOpts := grpcui.InvokeOptions{
 		ExtraMetadata:   uiOpts.extraMetadata,
 		PreserveHeaders: uiOpts.preserveHeaders,
+		EmitDefaults:    uiOpts.emitDefaults,
 		Verbosity:       uiOpts.invokeVerbosity,
 	}
 	rpcInvokeHandler := http.StripPrefix("/invoke", grpcui.RPCInvokeHandlerWithOptions(ch, methods, invokeOpts))