RPC

Remote procedure calls are opaque byte payloads routed by target and delivered through the on_rpc callback during tick. An RPC always names a specific object (netid); for the object-less sibling see Custom events.

lattice_rpc

LATTICE_API lattice_result lattice_rpc(lattice_runner* r, lattice_netid id, uint16_t rpc_id,
                                       lattice_rpc_target target, const uint8_t* payload,
                                       uint32_t len, int reliable);

Send an RPC. Role: both (a client implicitly targets the server).

Param	Meaning
id	The object the RPC is about (its netid).
rpc_id	Your typed RPC tag, delivered verbatim to on_rpc.
target	A lattice_rpc_target fan-out policy.
payload / len	Arbitrary serialized bytes (e.g. from a lattice_bw_* writer); may be NULL when len == 0. Delivered byte-exact; copied by the core.
reliable	Non-zero ⇒ reliable, ordered delivery; zero ⇒ best-effort.

Returns: LATTICE_OK on accept, or an error (e.g. LATTICE_ERR_NOT_CONNECTED for a client with no session, LATTICE_ERR_UNKNOWN_OBJECT).

lattice_rpc_target

typedef enum {
    LATTICE_RPC_SERVER = 0,   /* client -> authority                          */
    LATTICE_RPC_OWNER,        /* authority -> the object's owner               */
    LATTICE_RPC_ALL,          /* authority -> every peer                       */
    LATTICE_RPC_ALL_BUT_OWNER /* authority -> every peer except the owner      */
} lattice_rpc_target;

Example

/* Client -> server: */
const uint8_t ping[4] = {'p','i','n','g'};
lattice_rpc(r, nid, /*rpc_id*/7, LATTICE_RPC_SERVER, ping, 4, /*reliable*/1);

/* Server -> everyone: */
const uint8_t pong[4] = {'p','o','n','g'};
lattice_rpc(r, nid, /*rpc_id*/9, LATTICE_RPC_ALL, pong, 4, /*reliable*/1);

Receiving side — the callback fires inside tick; do no blocking work:

static void on_rpc(void* user, lattice_netid id, uint16_t rpc_id,
                   const uint8_t* payload, uint32_t len) {
    /* dispatch on rpc_id; payload/len is owned by the core for the call only */
}

RPC vs. event

Use an RPC when the message is about a specific object you have a netid for. Use a custom event for object-less / session-scoped messages (chat, match state, a global ping) — it shares the same fan-out policy but doesn't require a netid.