Provided by: libnng-dev_1.9.0-1_amd64 bug

NAME

       nng_sub - subscriber protocol

SYNOPSIS

           #include <nng/nng.h>
           #include <nng/protocol/pubsub0/sub.h>

DESCRIPTION

       The sub protocol is one half of a publisher/subscriber pattern. In this pattern, a
       publisher sends data, which is broadcast to all subscribers. The subscribing applications
       only see the data to which they have subscribed.

       The sub protocol is the subscriber side, and the pub protocol is the publisher side.

           Note
           In this implementation, the publisher delivers all messages to all subscribers. The
           subscribers maintain their own subscriptions, and filter them locally. Thus, this
           pattern should not be used in an attempt to reduce bandwidth consumption.

       The topics that subscribers subscribe to is just the first part of the message body.
       Applications should construct their messages accordingly.

   Socket Operations
       The nng_sub0_open() functions create a subscriber socket. This socket may be used to
       receive messages, but is unable to send them. Attempts to send messages will result in
       NNG_ENOTSUP.

   Protocol Versions
       Only version 0 of this protocol is supported. (At the time of writing, no other versions
       of this protocol have been defined.)

   Protocol Options
       The following protocol-specific options are available.

       NNG_OPT_SUB_SUBSCRIBE
           This option registers a topic that the subscriber is interested in. The option is
           write-only, and takes an array of bytes, of arbitrary size. Each incoming message is
           checked against the list of subscribed topics. If the body begins with the entire set
           of bytes in the topic, then the message is accepted. If no topic matches, then the
           message is discarded.

               Note
               This option is a byte array. Thus if you use nng_setopt_string() the NUL
               terminator byte will be included in the topic. If that isn’t desired, consider
               using nng_setopt() and using strlen() of the topic as the topic size.

               Tip
               To receive all messages, an empty topic (zero length) can be used.

       NNG_OPT_SUB_UNSUBSCRIBE
           This option, also write-only, removes a topic from the subscription list. Note that if
           the topic was not previously subscribed to with NNG_OPT_SUB_SUBSCRIBE then an
           NNG_ENOENT error will result.

       NNG_OPT_SUB_PREFNEW
           (bool) This read/write option specifies the behavior of the subscriber when the queue
           is full. When true (the default), the subscriber will make room in the queue by
           removing the oldest message. When false, the subscriber will reject messages if the
           message queue does not have room.

   Protocol Headers
       The sub protocol has no protocol-specific headers.

SEE ALSO

       nng_sub_open(3), nng_pub(7), nng(7)

                                            2024-10-11                                 NNG_SUB(7)