I'm designing a gRPC service written in Go.
In front of the gRPC service is Envoy which converts incoming HTTP requests to gRPC and converts the gRPC responses to JSON.
The requirement of this application is to have an endpoint that returns the following JSON object:
{
my_id: "AAA"
}
I can model this response pretty simply in Go like this:
// A MyResponse object.
message MyResponse {
// contents is a list of contents.
string my_id = 1;
}
But the requirement that I have is that sometimes my_id might be null. In that case, I want to get the following JSON back:
{
my_id: null
}
it
Is it possible to modify MyResponse such that my_id can be a string or a null in the JSON object that is returned? If so, how? If not, isn't this a pretty big gap in the design of gRPC?
I suggest you to use the StringValue field of the Package google.protobuf:
StringValue Wrapper message for string.
The JSON representation for StringValue is JSON string.
So in your proto files, you should import:
import "google/protobuf/wrappers.proto";
then use as example:
google.protobuf.StringValue name = 2;
For handle the values you can check the wrappers.StringValue
type of the github.com/golang/protobuf/ptypes/wrappers package and the helpers of the google.golang.org/protobuf/types/known/wrapperspb repo.
Related
Given that i have multiple models, each needed to have their own create/get/get list API.
Do i need to add two different types of messages (single and list) for every model?
For example :
If i have a student type -
message Student{
string name = 1;
}
and a rpc:
rpc CreateStudent(Student) returns (google.protobuf.Empty){
..............
}
If i'd like to add a rpc to create a list of students, or get a list of students
rpc CreateStudends(??????) returns (google.protobuf.Empty){
..............
}
rpc GetAllStudents() returns (??????){
..............
}
Do i need to also define
message StudentList{
repeated Student students = 1;
}
Or is there a way to use a list type directly in the message input/output?
Yes, basically - you would want a different message type per element type, or maybe a single root type with a oneof style content. Raw protobuf does not include a concept of generics or templates.
Some libraries do, but: that's outside of the specification.
You can simply add the stream keyword to your RPCs. No need to define a message field as repeated, stream will send or receive multiple independent messages.
message Student {
string name = 1;
}
with RPCs:
rpc CreateStudent(Student) returns (google.protobuf.Empty) {
..............
}
rpc CreateStudents(stream Student) returns (google.protobuf.Empty) {
..............
}
rpc GetAllStudents() returns (stream Student) {
..............
}
It's good practice to send/stream a response object rather than empty. Otherwise, you only have the gRPC response code to indicate a problem and will need to reference the logs to debug.
I have a simple microservice build with go-kit and protocol buffers. And I have a question about where should I transform request into business-ish data.
For instance, I have following protobuf
import "google/protobuf/empty.proto";
service Location {
rpc DeleteLocation(DeleteLocationRequest) returns (google.protobuf.Empty) {};
}
message DeleteLocationRequest {
string locationUID = 1;
}
A request has uid to delete as a string; however, I would like to use my custom struct
type LocationUID struct {
uuid.UUID
}
So, I'm wondering where it's better to transform incoming string into domain object.
Should I do it inside entrypoint? Get data from reqeust, transform it into LocationUID and then call service with business logic to perform a required action.
Or is it better to place inside service? Pass the whole request object from entrypoint into a service and then, inside service, get reqired data, transform it, validate (and return an error if data is invalid)
I am learning golang and want to write generic response from microservices response.
My General Response is like:
type GeneralResponse struct {
Success string
Message string
Data string
Error string
}
In the Data section I want to return any json, say list of Person, Instruments or any type of objects.
But it should be another json.
I tried assigning other json objects but it did not work.
It is fine if I dump json array as string into it but it should unmarshal from receiver end.
How should I go about it?
I am trying over here. https://play.golang.org/p/dc0uKtS76aA
You should use RawMessage in the type definition
type GeneralResponse struct {
Success string
Message string
Data json.RawMessage
Error string
}
and subsequently push a Marshalled json into that attribute.
You can do that by encoding other types in []bytes and setting them to the Data attribute.
Like in https://play.golang.org/p/CyoN5pe_aNV
If you put marshalled JSON into a string, it will be marshalled as a string (because it's a string) and the receiving end will have to unmarshal it twice (because it's been marshalled twice). What you want is probably more along the lines of:
type GeneralResponse struct {
Success string
Message string
Data interface{} // interface{} can be anything
Error string
}
This way you can put any data into Data and it will be marshalled directly into the response.
You can use json.RawMessage for that.
I have implemented the encoding part, you find more here to decode - https://golang.org/pkg/encoding/json/#RawMessage
json.RawMessage comes to rescue in case you wants to capture whole json without knowing its format.
type GeneralResponse struct {
Success string
Message string
Data json.RawMessage
Error string
}
Checkout this code. I have modified your code to dump data into response
Does the rpc syntax in proto3 allow null requests or responses?
e.g. I want the equivalent of the following:
rpc Logout;
rpc Status returns (Status);
rpc Log (LogData);
Or should I just create a null type?
message Null {};
rpc Logout (Null) returns (Null);
rpc Status (Null) returns (Status);
rpc Log (LogData) returns (Null);
Kenton's comment below is sound advice:
... we as developers are really bad at guessing what we might want in the future. So I recommend being safe by always defining custom params and results types for every method, even if they are empty.
Answering my own question:
Looking through the default proto files, I came across Empty that is exactly like the Null type I suggested above :)
excerpt from that file:
// A generic empty message that you can re-use to avoid defining duplicated
// empty messages in your APIs. A typical example is to use it as the request
// or the response type of an API method. For instance:
//
// service Foo {
// rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty);
// }
//
message Empty {
}
You also can use predefined:
import "google/protobuf/empty.proto";
package MyPackage;
service MyService {
rpc Check(google.protobuf.Empty) returns (google.protobuf.Empty) {}
}
you can also use another bool property inside the Reply structure. like this
message Reply {
string result = 1;
bool found = 2;
}
so if you dont find the result or some error happened you can return from the service class this
return new Reply()
{
Found = false
};
I'm trying to use Google protobuf and i 'm having the next descriptions:
message.proto file:
message Request {
required int32 id = 1;
optional string value = 2;
}
service.proto file:
import "message.proto";
service Service {
rpc request (Request) returns (bool);
}
I'm trying to generate c++ sources and getting an error:
$ protoc service.proto --cpp_out=/tmp/proto/build
service.proto:4:40: Expected message type.
Do i have to return user-defined types only? Are primitive (like bool or string) supported? Can i use primitive types as service method argument (instead of Request in my example)?
No, you cannot use a primitive type as either the request or response. You must use a message type.
This is important because a message type can be extended later, in case you decide you want to add a new parameter or return some additional data.
If you want to return a primitive type, wrap it in a message and return it:
message Name {
string name = 1;
}
In case you don't want to return anything, void I mean, you can just create an empty message:
message Void {}
message Name {
string name = 1;
}
..
service MyService{
rpc MyFunc(Name) returns (Void);
}
You can return scalar datatypes like bool, int, etc by making use of wrappers.proto
service.proto file:
import "message.proto";
import "google/protobuf/wrappers.proto";
service Service {
rpc request (Request) returns (.google.protobuf.BoolValue);
}