JSON parse error in RPC call

Game Design
#1

Hi,

I have this error in Firefox when trying to call an RPC function frome the JS client:
SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

The client code:
const response = await client.rpc(session, "create_match_rpc", {})

The RPC function:

type response struct {
	MatchID string   `json:"matchID"`
}

func createMatchRPC(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, payload string) (string, error) {
	params := make(map[string]interface{})
	if err := json.Unmarshal([]byte(payload), &params); err != nil {
			return "", err
	}

	matchID, err := nk.MatchCreate(ctx, "MatchHandler", params)

	if err != nil {
			return "", err
	}

	r := response{matchID}
	rr, err := json.Marshal(r)
	logger.Printf("rr:")
	logger.Printf(string(rr))
	return string(rr), nil
}

In Chrome everything works fine, the response’s payload looks like this: {"matchID":"caf156d8-55c6-47fe-89c2-acbeb9c7c77d.nakama1"}

But in Firefox, when looking at firebug’s network tab, I can see that the response’s payload looks like this: H4sIAAAAAAAA/6pWKkiszMlPTFGyUqqOUcpNLEnO8HSJUbKKUUpLTDFPtDQ20DU0NzXVNTE2NtBNMjY10jUwsjC0SDYysTQwM9bLS8xOzE00jFGqVaoFBAAA//8kAbCZTAAAAA==

I’m using Nakama JS client version 2.0.1

#2

I believe you need to wrap the result in nk.json_encode().

Here is what our client code looks like in lua (stripped of entry fees and other details).

You might want to re-check the go example module in the docs as well.


local function create_match(context, payload)
    local modulename = "match_handler"
    local setupstate = {initialstate = nk.json_decode(payload)}

    local matchid = nk.match_create(modulename, setupstate)

    return nk.json_encode({["match_id"] = matchid, ["setupstate"] = setupstate})
end
nk.register_rpc(create_match, "create_match_rpc")
#3

Also make sure you grab the latest build of the Nakama JavaScript client directly from the dist folder here https://github.com/heroiclabs/nakama-js/tree/master/dist - it’s newer than the tagged 2.0.1 release and contains a lot of fixes and updates.

We’ll tag a new official version of the client very soon, with even more improvements included.

#4

Hi, thanks for your answers

@GroovyAntoidDev The Go example in the doc is the following:

func CreateMatchRPC(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, payload string) (string, error) {
    params := make(map[string]interface{})
    if err := json.Unmarshal([]byte(payload), params); err != nil {
        return "", err
    }

    modulename := "pingpong" // Name with which match handler was registered in InitModule, see example above.
    if matchId, err := nk.MatchCreate(ctx, modulename, params); err != nil {
        return "", err
    } else {
        return matchId, nil
    }
}

(source: https://heroiclabs.com/docs/gameplay-multiplayer-server-multiplayer/#manually )

As you can see, it returns the matchId, not a JSON formatted string.

In my code I use jsonResponse, err := json.Marshal(response) which is I believe the equivalent of local jsonResponse = nk.json_encode(response).

@zyro I’m already using the latest Nakama JS client, I redownloaded nakama-js.umd.js yesterday from this folder.

From what I’ve tested, it happens here: https://github.com/heroiclabs/nakama-js/blob/master/src/api.gen.ts#L572
But only in Firefox, because here the response body is not a JSON.

#5

Circling back to this we haven’t had any luck reproducing this issue. It would really help if you can set up a single-page test case that uses the Nakama JavaScript client and we can just open the page to see the issue.

#6

Hi, the following code should raise the JSON parse error (in Firefox only, it works fine in Chrome):

(note the rpc function “create_match_rpc” should exist in the server)

const Nakama = require("@heroiclabs/nakama-js");

async function start() {
  const client = new Nakama.Client(
    "defaultkey",
    "gameserverurl.com",
    7350,
    true
  );

  const session = await client.authenticateCustom({
    id: "123",
    create: true,
    username: "username"
  });
  console.info("Successfully authenticated:", session);

  const response = await client.rpc(session, "create_match_rpc", {});
  console.log("rpc response", response);
}

start().catch(err => {
  console.error(err);
  alert(err);
});

(I’m using Nakama 2.7 with Docker and Go)

#7

It would be great if you can package this as a repo on GitHub with the Go plugin code as well as an index.html file (packaged together with a copy of the exact Nakama JS client you use) we can just open in browser. I think that would help to avoid any unintended differences that might be introduced as we try to reproduce on our own environment.

#8

I understand, I’ll try to do this when I got the time.

Also I found that this happen only with client.rpc(...), it works fine with socket.send({ rpc: { ... } }).

#9

For someone still having this issue. In the example used by @doguh

func CreateMatchRPC(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, payload string) (string, error) {
    params := make(map[string]interface{})
    if err := json.Unmarshal([]byte(payload), params); err != nil {
        return "", err
    }

    modulename := "pingpong" // Name with which match handler was registered in InitModule, see example above.
    if matchId, err := nk.MatchCreate(ctx, modulename, params); err != nil {
        return "", err
    } else {
        return matchId, nil
    }
}

the RPC function only returns a string matchID. But many client libraries expect a valid JSON. For example the javascript library parses the payload with JSON.parse(response.payload). To fix this the RPC functions have to return a valid JSON. So a quick fix would be:

return "{\"matchId\": \""+matchId+"\"}", nil