zmq_msg_gets(3)

zmq_msg_gets(3)

ØMQ Manual - ØMQ/4.2.0

Name

zmq_msg_gets - get message metadata property

Synopsis

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

Description

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>.

The following ZMTP properties can be retrieved with the zmq_msg_gets() function:

Socket-Type
Identity
Resource

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).

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

Return value

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.

Errors

EINVAL
The requested property is unknown.

Example

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, "User-Id"); zmq_msg_close (&msg);

See also

zmq(7)

Authors

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