'\" t
.\"     Title: zmq_msg_gets
.\"    Author: [see the "AUTHORS" section]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 09/06/2020
.\"    Manual: 0MQ Manual
.\"    Source: 0MQ 4.3.1
.\"  Language: English
.\"
.TH "ZMQ_MSG_GETS" "3" "09/06/2020" "0MQ 4\&.3\&.1" "0MQ Manual"
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.SH "NAME"
zmq_msg_gets \- get message metadata property
.SH "SYNOPSIS"
.sp
\fBconst char *zmq_msg_gets (zmq_msg_t \fR\fB\fI*message\fR\fR\fB, const char *\fR\fB\fIproperty\fR\fR\fB);\fR
.SH "DESCRIPTION"
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The \fIzmq_msg_gets()\fR function shall return the string value for the metadata property specified by the \fIproperty\fR argument for the message pointed to by the \fImessage\fR argument\&. Both the \fIproperty\fR argument and the \fIvalue\fR shall be NULL\-terminated UTF8\-encoded strings\&.
.sp
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 \fBzmq_setsockopt\fR(3) option ZMQ_METADATA\&. Application metadata properties must be prefixed with \fIX\-\fR\&.
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In addition to application metadata, the following ZMTP properties can be retrieved with the \fIzmq_msg_gets()\fR function:
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.if n \{\
.RS 4
.\}
.nf
Socket\-Type
Routing\-Id
.fi
.if n \{\
.RE
.\}
.sp
Note: \fIIdentity\fR is a deprecated alias for \fIRouting\-Id\fR\&.
.sp
Additionally, when available for the underlying transport, the \fBPeer\-Address\fR property will return the IP address of the remote endpoint as returned by getnameinfo(2)\&.
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The names of these properties are also defined in \fIzmq\&.h\fR as \fIZMQ_MSG_PROPERTY_SOCKET_TYPE\fR \fIZMQ_MSG_PROPERTY_ROUTING_ID\fR, and \fIZMQ_MSG_PROPERTY_PEER_ADDRESS\fR\&. Currently, these definitions are only available as a DRAFT API\&.
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Other properties may be defined based on the underlying security mechanism, see ZAP authenticated connection sample below\&.
.SH "RETURN VALUE"
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The \fIzmq_msg_gets()\fR function shall return the string value for the property if successful\&. Otherwise it shall return NULL and set \fIerrno\fR 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\&.
.SH "ERRORS"
.PP
\fBEINVAL\fR
.RS 4
The requested
\fIproperty\fR
is unknown\&.
.RE
.SH "EXAMPLE"
.PP
\fBGetting the ZAP authenticated user id for a message:\fR. 
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.if n \{\
.RS 4
.\}
.nf
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);
.fi
.if n \{\
.RE
.\}
.sp
.SH "SEE ALSO"
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\fBzmq\fR(7) \fBzmq_setsockopt\fR(3)
.SH "AUTHORS"
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This page was written by the 0MQ community\&. To make a change please read the 0MQ Contribution Policy at \m[blue]\fBhttp://www\&.zeromq\&.org/docs:contributing\fR\m[]\&.