Golang Parsing of ProtoBuf - go

Question

I'm new to Golang and I am trying to write an home automation framework in Golang, using the Micro framework and Protobuf framework.
I am currently having a hard time trying to implement a simple registry type service.
An example of the problem I am having is that I have the following, I want to be able to get a list of devices, provided a client does a GET request to http://localhost:8080/view/devices
I have the following protobuf definition:
syntax = "proto3";
service DRegistry {
rpc View(ViewRequest) returns (DeviceRegistry) {}
}
message DeviceRegistry {
repeated Device devices = 1;
}
message ViewRequest {
string Alias = 1;
}
message Device {
string Alias = 1;
string HWAddress = 2;
string WakeUpMethod = 3;
repeated string BoundServices = 4;
}
Then in my service defination I have the following:
package main
import (
"log"
micro "github.com/micro/go-micro"
proto "github.com/srizzling/gotham/proto/device"
"golang.org/x/net/context"
)
// DRegistry stands for Device Registry and is how devices register to Gotham.
type DRegistry struct{}
var devices map[string]proto.Device
func (g *DRegistry) View(ctx context.Context, req *proto.ViewRequest, rsp *proto.DeviceRegistry) error {
filter := req.Alias
devices, err := filterDevices(filter)
rsp.Devices = devices
}
func filterDevices(filter string) (*[]proto.Device, error) {
// Currently only supports listing a single service for now
// TODO: expand filter to be more consise
filteredDevices := make([]proto.Device, 0, len(devices))
for _, e := range devices {
for _, f := range e.BoundServices {
if f == filter {
filteredDevices = append(filteredDevices, e)
}
}
}
return &filteredDevices, nil
}
func main() {
service := micro.NewService(
micro.Name("DRegistry"),
)
proto.RegisterDRegistryHandler(service.Server(), new(DRegistry))
if err := service.Run(); err != nil {
log.Fatal(err)
}
}
The problem I am having is that my IDE (Visual Studio Code) is complianing that I cannot use devices (type *[]device.Device) as type []*device.Device in assignment which is confusing.
TLDR: How do I assign a collection of proto.Devices to the proto.DeviceRegistry?

Answer 1

func filterDevices(filter string) ([]*proto.Device, error) {
// Currently only supports listing a single service for now
// TODO: expand filter to be more consise
filteredDevices := make([]*proto.Device, 0, len(devices))
for _, e := range devices {
for _, f := range e.BoundServices {
if f == filter {
filteredDevices = append(filteredDevices, &e)
}
}
}
return filteredDevices, nil
}
There is a difference between a slice of pointers ([]*) and a pointer to a slice (*[]). You are returning a pointer to slice, whereas what you want is a slice of pointers. We can solve this by:
Updating your filterDevices signature to return a slice of pointers
Updating your make call to make a slice of pointers
Taking the address of e in your call to append (we want a slice of pointers to devices)
Not returning the address of the slice