support oneofs in body

examples/proto/examplepb/echo_service.proto

@@ -61,6 +61,10 @@ service EchoService {
 		option (google.api.http) = {
 			post: "/v1/example/echo_body"
 			body: "*"
+			additional_bindings {
+				put: "/v1/example/echo_body/{id}"
+				body: "no"
+			}
 		};
 	}
 	// EchoDelete method receives a simple message and returns it.

examples/proto/examplepb/echo_service.swagger.json

@@ -374,6 +374,39 @@
         ]
       }
     },
+    "/v1/example/echo_body/{id}": {
+      "put": {
+        "summary": "EchoBody method receives a simple message and returns it.",
+        "operationId": "EchoBody2",
+        "responses": {
+          "200": {
+            "description": "",
+            "schema": {
+              "$ref": "#/definitions/examplepbSimpleMessage"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "id",
+            "in": "path",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "name": "body",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/examplepbEmbedded"
+            }
+          }
+        ],
+        "tags": [
+          "EchoService"
+        ]
+      }
+    },
     "/v1/example/echo_delete": {
       "delete": {
         "summary": "EchoDelete method receives a simple message and returns it.",

protoc-gen-grpc-gateway/descriptor/types.go

@@ -240,6 +240,12 @@ func (b Body) AssignableExpr(msgExpr string) string {
 	return b.FieldPath.AssignableExpr(msgExpr)
 }
 
+// AssignableExprPrep returns prepatory statements for an assignable expression to initialize
+// method request object.
+func (b Body) AssignableExprPrep(msgExpr string) string {
+	return b.FieldPath.AssignableExprPrep(msgExpr)
+}
+
 // FieldPath is a path to a field from a request message.
 type FieldPath []FieldPathComponent
 
@@ -261,13 +267,46 @@ func (p FieldPath) IsNestedProto3() bool {
 }
 
 // AssignableExpr is an assignable expression in Go to be used to assign a value to the target field.
-// It starts with "msgExpr", which is the go expression of the method request object.
+// It starts with "msgExpr", which is the go expression of the method request object. Before using
+// such an expression the prep statements must be emitted first, in case the field path includes
+// a oneof. See FieldPath.AssignableExprPrep.
 func (p FieldPath) AssignableExpr(msgExpr string) string {
 	l := len(p)
 	if l == 0 {
 		return msgExpr
 	}
 
+	components := msgExpr
+	for i, c := range p {
+		// Check if it is a oneOf field.
+		if c.Target.OneofIndex != nil {
+			index := c.Target.OneofIndex
+			msg := c.Target.Message
+			oneOfName := gogen.CamelCase(msg.GetOneofDecl()[*index].GetName())
+			oneofFieldName := msg.GetName() + "_" + c.AssignableExpr()
+
+			components = components + "." + oneOfName + ".(*" + oneofFieldName + ")"
+		}
+
+		if i == l-1 {
+			components = components + "." + c.AssignableExpr()
+			continue
+		}
+		components = components + "." + c.ValueExpr()
+	}
+
+	return components
+}
+
+// AssignableExprPrep returns preparation statements for an assignable expression to assign a value
+// to the target field. The go expression of the method request object is "msgExpr". This is only
+// needed for field paths that contain oneofs. Otherwise, an empty string is returned.
+func (p FieldPath) AssignableExprPrep(msgExpr string) string {
+	l := len(p)
+	if l == 0 {
+		return ""
+	}
+
 	var preparations []string
 	components := msgExpr
 	for i, c := range p {
@@ -296,7 +335,6 @@ func (p FieldPath) AssignableExpr(msgExpr string) string {
 		components = components + "." + c.ValueExpr()
 	}
 
-	preparations = append(preparations, components)
 	return strings.Join(preparations, "\n")
 }
 

protoc-gen-grpc-gateway/gengateway/template.go

@@ -207,6 +207,7 @@ var (
 	var protoReq {{.Method.RequestType.GoType .Method.Service.File.GoPkg.Path}}
 	var metadata runtime.ServerMetadata
 {{if .Body}}
+	{{.Body.AssignableExprPrep "protoReq"}}
 	if err := marshaler.NewDecoder(req.Body).Decode(&{{.Body.AssignableExpr "protoReq"}}); err != nil && err != io.EOF  {
 		return nil, metadata, status.Errorf(codes.InvalidArgument, "%v", err)
 	}
@@ -226,6 +227,7 @@ var (
 {{if $param.IsNestedProto3 }}
 	err = runtime.PopulateFieldFromPath(&protoReq, {{$param | printf "%q"}}, val)
 {{else}}
+	{{$param.AssignableExprPrep "protoReq"}}
 	{{$param.AssignableExpr "protoReq"}}, err = {{$param.ConvertFuncExpr}}(val)
 {{end}}
 	if err != nil {