## Pull Protocol (_PULL_)

The ((_pull_ protocol))(((protocol, _pull_))) is one half of a ((pipeline pattern)).
The other half is the xref:push.adoc[_PUSH_] protocol.

In the pipeline pattern, pushers distribute messages to pullers.
Each message sent by a pusher will be sent to one of its ready peer pullers, chosen in a round-robin fashion.
This property makes this pattern useful in ((load-balancing)) scenarios.

### Socket Operations

The xref:nng_pull_open.adoc[`nng_pull_open`] functions create a puller socket.
This socket may be used to receive messages, but is unable to send them.
Attempts to send messages will result in `NNG_ENOTSUP`.

When receiving messages, the _pull_ protocol accepts messages as they arrive from peers.
If two peers both have a message ready, the order in which messages are handled is undefined.

### Protocol Versions

Only version 0 of this protocol is supported.footnote:[At the time of writing, no other versions of this protocol have been defined.]

### Protocol Options

The _PULL_ protocol has no protocol-specific options.

### Protocol Headers

The _PULL_ protocol has no protocol-specific headers.