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userId, ok := ctx.Value(runtime.RUNTIME_CTX_USER_ID).(string)
if !ok {
  // User ID not found in the context.
}

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// NOTE: All Go runtime registrations must be made in the module's InitModule function.
//       Function arguments have been omitted in the example.

// If you are sending requests to the server via the real-time connection, ensure that you use this variant of the function.
initializer.RegisterBeforeRt()
initializer.RegisterAfterRt()

// Otherwise use the relevant before / after hook, e.g.
initializer.RegisterBeforeAddFriends()
initializer.RegisterAfterAddFriends()
// (...)

// If you'd like to run server code when the matchmaker has matched players together, register your function using the following.
initializer.RegisterMatchmakerMatched()

// If you'd like to run server code when the leaderboard/tournament resets register your function using the following.
initializer.RegisterLeaderboardReset()
initializer.RegisterTournamentReset()

// Similarly, you can run server code when the tournament ends.
initializer.RegisterTournamentEnd()

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func BeforeAddFriends(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, in *api.AddFriendsRequest) (*api.AddFriendsRequest, error) {
    userID, ok := ctx.Value(runtime.RUNTIME_CTX_USER_ID).(string)
    if !ok {
            return nil, errors.New("Missing user ID.")
    }

    account, err := nk.UsersGetId(ctx, []string{userID})
    if err != nil {
            return nil, err
    }

    var metadata map[string]interface{}
    if err := json.Unmarshal([]byte(account.GetUser().GetMetadata()), &metadata); err != nil {
            return nil, errors.New("Corrupted user metadata.")
    }

    // Let's assume we've stored a user's level in their metadata.
    if level, ok := metadata["level"].(int); !ok || level < 10 {
            return nil, errors.New("Must reach level 10 before you can add friends.")
    }

    return in, nil
}

// Register as a before hook for the appropriate feature, this call should be in InitModule.
if err := initializer.RegisterBeforeAddFriends(BeforeAddFriends); err != nil {
    logger.Error("Unable to register: %v", err)
    return err
}

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func AfterAddFriends(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, in *api.AddFriendsRequest) error {
    userID, ok := ctx.Value(runtime.RUNTIME_CTX_USER_ID).(string)
    if !ok {
        return errors.New("Missing user ID.")
    }

    value, err := json.Marshal(map[string]interface{}{"user_ids": in.GetIds()})
    if err != nil {
        return err
    }

    if _, err := nk.StorageWrite(ctx, []*runtime.StorageWrite{
        &runtime.StorageWrite{
            Collection: "rewards",
            Key:        "reward",
            UserID:     userID,
            Value:      string(value),
        },
    }); err != nil {
        return err
    }

    return nil
}

// Register as an after hook for the appropriate feature, this call should be in InitModule.
if err := initializer.RegisterAfterAddFriends(AfterAddFriends); err != nil {
  logger.Error("Unable to register: %v", err)
  return err
}

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func CustomRpcFunc(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, payload string) (string, error) {
		logger.Info("Payload: %s", payload)

		// "payload" is bytes sent by the client we'll JSON decode it.
		var value interface{}
		if err := json.Unmarshal([]byte(payload), &value); err != nil {
				return "", err
		}

		response, err := json.Marshal(value)
		if err != nil {
				return "", err
		}

    return string(response), nil
}

// Register as an RPC function, this call should be in InitModule.
if err := initializer.RegisterRpc("custom_rpc_func_id", CustomRpcFunc); err != nil {
  logger.Error("Unable to register: %v", err)
  return err
}

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

		logger.Info("Message: %v", message)

		response, err := json.Marshal(map[string]interface{}{"message": message})
		if err != nil {
				return "", err
		}

		return string(response), nil
}

// Register as an RPC function, this call should be in InitModule.
if err := initializer.RegisterRpc("http_handler_path", HttpHandler); err != nil {
  logger.Error("Unable to register: %v", err)
  return err
}

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import (
    "context"
    "database/sql"
    "encoding/json"
    "github.com/heroiclabs/nakama-common/runtime"
)

// All Go modules must have a InitModule function with this exact signature.
func InitModule(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, initializer runtime.Initializer) error {
    // Register the RPC function.
    if err := initializer.RegisterRpc("my_unique_id", SomeExample); err != nil {
        logger.Error("Unable to register: %v", err)
        return err
    }
    return nil
}

func SomeExample(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, payload string) (string, error) {
    meta := make(map[string]interface{})
    // Note below, json.Unmarshal can only take a pointer as second argument
    if err := json.Unmarshal([]byte(payload), &meta); err != nil {
        // Handle error
        return "", err
    }

    id := "SomeId"
    authoritative := false
    sort := "desc"
    operator := "best"
    reset := "0 0 * * 1"

    if err := nk.LeaderboardCreate(ctx, id, authoritative, sort, operator, reset, meta); err != nil {
        // Handle error
        return "", err
    }

    return "Success", nil
}

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import (
		"context"
		"database/sql"
		"encoding/json"
		"errors"
		"io/ioutil"
		"net/http"

		"github.com/heroiclabs/nakama-common/runtime"
)

const apiBaseUrl = "https://pokeapi.co/api/v2"

// All Go modules must have a InitModule function with this exact signature.
func InitModule(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, initializer runtime.Initializer) error {
		// Register the RPC function.
		if err := initializer.RegisterRpc("get_pokemon", GetPokemon); err != nil {
				logger.Error("Unable to register: %v", err)
				return err
		}

		return nil
	}

func LookupPokemon(logger runtime.Logger, name string) (map[string]interface{}, error) {
		resp, err := http.Get(apiBaseUrl + "/pokemon/" + name)

		if err != nil {
				logger.Error("Failed request %v", err.Error())
				return nil, err
		}

		defer resp.Body.Close()
		body, err := ioutil.ReadAll(resp.Body)

		if err != nil {
				logger.Error("Failed to read body %v", err.Error())
				return nil, err
		}

		if resp.StatusCode >= 400 {
				logger.Error("Failed request %v %v", resp.StatusCode, body)
				return nil, errors.New(string(body))
		}

		var result map[string]interface{}
		err = json.Unmarshal(body, &result)

		return result, err
}

func GetPokemon(ctx context.Context, logger runtime.Logger, db *sql.DB, nk runtime.NakamaModule, payload string) (string, error) {
		// We'll assume payload was sent as JSON and decode it.
		var input map[string]string
		err := json.Unmarshal([]byte(payload), &input)

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

		result, err := LookupPokemon(logger, input["PokemonName"])

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

		response, err := json.Marshal(result)

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

		return string(response), nil
}