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Reference index

06. PAIR

A 1:1 bidirectional raw socket type. PAIR has no type-specific options and no dedicated receive function — it shares zlink_recv_part (Raw receive category) and blocking or completion-backed zlink_send_part (Socket lifecycle category) with other socket types. Its one type-specific entry is the send side. The exact signatures are owned by the PAIR specification.

Sends one message part on a PAIR (also DEALER — see the DEALER category) socket.

zlink_msg_t part;
zlink_msg_init_size(&part, payload_len);
memcpy(zlink_msg_data(&part), payload, payload_len);
zlink_submit_result_t result = zlink_send_part(
    s, &part, ZLINK_SEND_FLAGS_NONE, ZLINK_PART_FINAL, NULL, NULL);

Parameters. part_ is the message to send — its content is consumed on both success and failure (copy it first if it must be sent again; re-initialize it before reuse). flags_ is ZLINK_SEND_FLAGS_NONE or ZLINK_DONTWAIT. part_flag_ is ZLINK_PART_FINAL for a single-part message, or ZLINK_PART_MORE to start a multipart sequence continued by further calls to this same function on the same thread through a final ZLINK_PART_FINAL call.

Return and errno. Returns zlink_submit_result_t — ZLINK_SUBMIT_OK on success (see the Errors, results, and version category for the full result mapping). ZLINK_SUBMIT_BACKPRESSURED for a non-blocking call that can't proceed immediately.

When to use. Core stages successful intermediate parts of a multipart sequence as one record until the final part succeeds; if any part in the open sequence fails, Core atomically discards every staged part along with the failed one, and no part of that record becomes visible to the peer. Because the failed call still consumes its part_, retry the entire record from its first part using copies you retained before the original calls — don't call a different send helper or switch flags partway through one sequence.

See the PAIR specification for the full rationale. Receive uses zlink_recv_part (Raw receive category); completion-backed send uses DONTWAIT zlink_send_part plus zlink_completion_recv (Socket lifecycle category) — neither is repeated here.