seyfert/vendor/gateway/shard/resume.ts

import { GatewayOpcodes } from "../../types/shared.ts";
import { Shard, ShardSocketCloseCodes, ShardState } from "./types.ts";

export async function resume(shard: Shard): Promise<void> {
    //   gateway.debug("GW RESUMING", { shardId });
    // It has been requested to resume the Shards session.
    // It's possible that the shard is still connected with Discord's gateway therefore we need to forcefully close it.
    if (shard.isOpen()) {
        shard.close(
            ShardSocketCloseCodes.ResumeClosingOldConnection,
            "Reconnecting the shard, closing old connection.",
        );
    }

    // Shard has never identified, so we cannot resume.
    if (!shard.sessionId) {
        // gateway.debug(
        //   "GW DEBUG",
        //   `[Error] Trying to resume a shard (id: ${shardId}) that was not first identified.`,
        // );

        return await shard.identify();

        // throw new Error(`[SHARD] Trying to resume a shard (id: ${shard.id}) which was never identified`);
    }

    shard.state = ShardState.Resuming;

    // Before we can resume, we need to create a new connection with Discord's gateway.
    await shard.connect();

    shard.send({
        op: GatewayOpcodes.Resume,
        d: {
            token: `Bot ${shard.gatewayConfig.token}`,
            session_id: shard.sessionId,
            seq: shard.previousSequenceNumber ?? 0,
        },
    }, true);

    return new Promise((resolve) => {
        shard.resolves.set("RESUMED", () => resolve());
        // If it is attempted to resume with an invalid session id,
        // Discord sends an invalid session payload
        // Not erroring here since it is easy that this happens, also it would be not catchable
        shard.resolves.set("INVALID_SESSION", () => {
            shard.resolves.delete("RESUMED");
            resolve();
        });
    });
}