zmq_msg_gets - get message metadata property

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0MQ 4.3.5                                          03/31/2024                                    ZMQ_MSG_GETS(3)

       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_TYPEZMQ_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.

EINVAL
           The requested property is unknown.

GettingtheZAPauthenticateduseridforamessage:.

           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_msg_gets - get message metadata property

       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.

zmq(7) zmq_setsockopt(3)

constchar*zmq_msg_gets(zmq_msg_t*message,constchar*property);