zmq_msg_gets - Man Page

const char *zmq_msg_gets (zmq_msg_t *message, const char *property);

The zmq_msg_gets() function shall return the string value for the metadata property specified by the property argument for the message pointed to by the message argument. Both the property argument and the value shall be NULL-terminated UTF8-encoded strings.

Metadata is defined on a per-connection basis during the ZeroMQ connection handshake as specified in <rfc.zeromq.org/spec:37>. Applications can set metadata properties using zmq_setsockopt(3) option ZMQ_METADATA. Application metadata properties must be prefixed with X-.

In addition to application metadata, the following ZMTP properties can be retrieved with the zmq_msg_gets() function:

Socket-Type
Routing-Id

Note: Identity is a deprecated alias for Routing-Id.

Additionally, when available for the underlying transport, the Peer-Address property will return the IP address of the remote endpoint as returned by getnameinfo(2).

The names of these properties are also defined in zmq.h as ZMQ_MSG_PROPERTY_SOCKET_TYPE ZMQ_MSG_PROPERTY_ROUTING_ID, and ZMQ_MSG_PROPERTY_PEER_ADDRESS. Currently, these definitions are only available as a DRAFT API.

Other properties may be defined based on the underlying security mechanism, see ZAP authenticated connection sample below.

The zmq_msg_gets() function shall return the string value for the property if successful. Otherwise it shall return NULL and set errno to one of the values defined below. The caller shall not modify or free the returned value, which shall be owned by the message. The encoding of the property and value shall be UTF8.

EINVAL

The requested property is unknown.

Getting the ZAP authenticated user id for a message:.

zmq_msg_t msg;
zmq_msg_init (&msg);
rc = zmq_msg_recv (&msg, dealer, 0);
assert (rc != -1);
const char *user_id = zmq_msg_gets (&msg, ZMQ_MSG_PROPERTY_USER_ID);
zmq_msg_close (&msg);

zmq(7) zmq_setsockopt(3)

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zmq(7).