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Reference index

09. XPUB

An extended publisher that also receives subscription events from subscribers, with manual subscription control. XPUB shares zlink_set_pub_option/zlink_get_pub_option and zlink_publish_part with PUB (PUB category) unchanged — this category documents only the one entry point unique to XPUB: receiving the subscription events themselves. The exact signatures are owned by the XPUB specification.

Receives the next subscribe/unsubscribe event from an XPUB socket's subscribers.

const zlink_routing_id_t *subscriber_rid;
int subscribed;
char topic[256];
size_t topic_len;
zlink_xpub_recv_part(xpub, &subscriber_rid, &subscribed, topic, sizeof(topic), &topic_len, ZLINK_RECV_FLAGS_NONE);

Parameters. source_rid_out_ receives a library-owned view of the subscribing peer's routing ID, valid until the next call on this socket. subscribed_out_ is set to 1 for subscribe or 0 for unsubscribe. topic_id_buf_/topic_id_capacity_ is the caller's buffer; topic_id_len_out_ receives the topic's actual length.

Return and errno. Returns zlink_recv_result_t — ZLINK_RECV_OK on success. EFAULT if the socket handle is NULL. EAGAIN with ZLINK_DONTWAIT and no event available. EMSGSIZE if the topic exceeds topic_id_capacity_. EINVAL if the subject isn't XPUB. Detail errnos other than EAGAIN/ETERM surface through the return as ZLINK_RECV_INTERNAL_ERROR, with the specific cause available via zlink_errno().

When to use. This is a recv-mode call specific to XPUB — raw XPUB is the only applicable type. Use ZLINK_PUB_OPT_VERBOSE/ZLINK_PUB_OPT_VERBOSER (PUB category) to control whether duplicate subscribe/unsubscribe events are forwarded, and ZLINK_PUB_OPT_MANUAL if the application wants to approve or reject subscriptions itself via ZLINK_PUB_OPT_APPROVE_SUBSCRIBE/ZLINK_PUB_OPT_REJECT_SUBSCRIBE instead of Core admitting them automatically.

See the XPUB specification for the full rationale. Publish and options use zlink_publish_part/zlink_set_pub_option/zlink_get_pub_option (PUB category) — neither is repeated here.