nng(7) Manual Page

cc ['flags'] 'files' -lnng ['libraries']

The nng library provides a common messaging framework intended to solve common communication problems in distributed applications. It offers a number of protocols, and also a number of transports.

The protocols implement the semantics associated with particular communications scenarios, such as RPC style services, service discovery, publish/subscribe, and so forth.

The transports provide support for underlying transport methods, such as TCP, IPC, websockets, and so forth.

The nng library is designed to permit easy creation of new transports and, to a lesser extent, new protocols.

The nng library is wire compatible with the SP protocols described in the nanomsg project; projects using libnanomsg can inter-operate with nng as well as other conforming implementations. (One such implementation is mangos.) Applications using nng which wish to communicate with older libraries must ensure that they only use protocols or transports offered by the earlier library.

The nng library also offers a compatible API, permitting legacy code to be recompiled or relinked against nng. When doing this, support for certain enhancements or features will likely be absent, requiring the application developer to use the new-style API.

The nng library is implemented in pure C; if you need bindings for other languages please check the website.

nng presents a socket view of networking. The sockets are constructed using protocol-specific functions, as a given socket implements precisely one nng protocol.

Each socket can be used to send and receive messages (if the protocol) supports it, and implements the appropriate protocol semantics. For example, nng_sub(7) sockets automatically filter incoming messages to discard those for topics that have not been subscribed.

nng sockets are message oriented, so that messages are either delivered wholly, or not at all. Partial delivery is not possible. Furthermore, nng does not provide any other delivery or ordering guarantees; messages may be dropped or reordered. (Some protocols, such as nng_req(7) may offer stronger guarantees by performing their own retry and validation schemes.)

Each socket can have zero, one, or many "endpoints", which are either listeners or dialers. (A given socket may freely choose whether it uses listeners, dialers, or both.) These "endpoints" provide access to underlying transports, such as TCP, etc.

Each endpoint is associated with a URL, which is a service address. For dialers, this will be the service address that will be contacted, whereas for listeners this is where the listener will bind and watch for new connections.

Endpoints do not themselves transport data. They are instead responsible for the creation of pipes, which can be thought of as message-oriented, connected, streams. Pipes frequently correspond to a single underlying byte stream — for example both IPC and TCP transports implement their pipes using a 1:1 relationship with a connected socket.

Endpoints create pipes as needed. Listeners will create them when a new client connection request arrives, and dialers will generally create one, then wait for it to disconnect before reconnecting.

Most applications should not have to worry about endpoints or pipes at all; the socket abstraction should provide all the functionality needed other than in a few specific circumstances.

The library API is documented at libnng(3).

libnng(3), nng_compat(3)