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[Help] [ProtoBuf] [: Not sure if I am using 'repeated' right.

Posted by

u/ValourValkyria

3 years ago

[Help] [ProtoBuf] [: Not sure if I am using 'repeated' right.

Not a lot of documentation talks about what 'repeated' does in messages.

Scenario: I got multiple replies to the client program from servers. Repeating the whole thing would look hideous and inefficient.

The whole thing is like a struct, in Go I can do such thing: (I got a json example as well but I read the sidebar and I removed it.)

...
type Server struct {
  ServerNo uint32
  IP string
  Port uint32
  Status string
  UserOnline uint32
}
var Server1 = Server{1, "127.0.0.1",12345,"UP",8}
var Server2 = Server{2, "127.0.0.2",12346,"DOWN",0}
...

And I can repeat this thing for all the servers I got.

What I got in my .proto file is this:

...
message ServerDetails {
  message Server {
    uint32 ServerNo = 1; //server no
    string Status = 2; //server up or down?
    uint32 UserOnline = 3; //how many users online?
    string ServerIP  = 4; //server ip?
    uint32 ServerPort = 5; //server port?
  }
  repeated Server server = 1; //how many servers?
}
...

How do you write the return in function then? a for loop?

I am writing Golang, by the way. But any language/solutions are welcomed.

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missblit

2 points·3 years ago·edited 3 years ago

The generated code API is documented here: https://developers.google.com/protocol-buffers/docs/reference/overview

In particular for Go: https://developers.google.com/protocol-buffers/docs/reference/go-generated#repeated

A repeated field can occur "zero or more times". This can be thought of as like an arbitrarily sized array.

In C++ you can write a pretty standard for loop to iterate over an embedded message field:

ServerDetails details = ...;
int size = details.server_size();
for(int i = 0; i < size; i++) {
    auto Server* server =  details.server(i);
}

Generating the list on the server side is similar (still C++):

ServerDetails details = ...;
for(Server &s : my_list_of_servers) {
    Server *ptr = details.add_server();
    *ptr = s;
}

I'm still a noob at protocol buffers, so hopefully that's all correct! There's fancier stuff you can do such as reserving X number of elements before adding them, check out the documentation.