Build a Gacha Machine

Messaging

• Message Definition: Same as DeCharge (XephyDechargeMessage), but typically only processes Request to Working and Status back to Available.

• Mention Tag (Machine Pubkey): Identifies the GaCha machine (e.g., PublicKey::parse("gacha_machine_pubkey")).

• Session Tag: Scopes events (e.g., "xephy-gacha-controller").

• Publishing and Subscription

  Copy

  let filter = Filter::new()
      .kind(EVENT_KIND)
      .since(Timestamp::now())
      .custom_tag(SESSION_TAG, ["gacha_session"])
      .custom_tag(MENTION_TAG, [gacha_machine_pubkey.to_hex()]);
  let sub_id = relay_client.subscribe(Timestamp::now(), [gacha_machine_pubkey]).await?;

  • Sender: User requesting a dispense.

  • Receiver: Gacha node controller.

• Message Handling: Processes a single transaction and reverts state.

Building Controller

• Node: Unlike DeCharge, Gacha’s simpler transaction (one payment, one action) doesn’t require a separate server. The node handles both state and payment in a single step using pay, making it lightweight.

Solana Interaction

Uses pay for a one-time transaction:

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// Before: Received Request event to start machine
if let Err(e) = xephy_balance_payment_sdk::pay(
    &self.solana_rpc_url,
    &self.solana_keypair_path,
    parsed_payload.namespace_id,
    &parsed_payload.user,
    PAY_AMOUNT,
    &parsed_payload.recover_info,
)
.await
{
    tracing::error!("Failed to pay, error: {:?} skip event: {:?}", e, event);
    return Ok(());
};

self.client
    .send_event(mention, &XephyGachaMessage::Status {
        status: *to_status,
        reason: *reason,
        initial_request: event.id,
        payload: serde_json::to_string(&XephyGachaMessageStatusPayload {
            namespace_id: parsed_payload.namespace_id,
            user: parsed_payload.user.clone(),
            nonce: parsed_payload.nonce,
            recover_info: parsed_payload.recover_info.clone(),
        })?,
    })
    .await?;