This documentation is for the TIP (development tree) of NNG and may represent unreleased changes or functionality that is experimental, and is subject to change before release. The latest released version is v1.3.2. See the documentation for v1.3.2 for the most up-to-date information.



nng_ws - WebSocket transport


#include <nng/transport/websocket/ws.h>

int nng_ws_register(void);
int nng_wss_register(void);


(transport, ws and wss) The ws transport provides communication support between peers across a TCP/IP network using WebSockets. Both IPv4 and IPv6 are supported when the underlying platform also supports it.

The protocol details are documented in WebSocket Mapping for Scalability Protocols.


Depending upon how the library was built, it may be necessary to register the transport by calling nng_ws_register().

If TLS support is enabled in the library, secure WebSockets (over TLS v1.2) can be used as well, but the secure transport may have to be registered using the nng_wss_register() function.

URI Format

(URI, ws://) This transport uses URIs using the scheme ws://, followed by an IP address or hostname, optionally followed by a colon and an TCP port number, optionally followed by a path. (If no port number is specified then port 80 is assumed. If no path is specified then a path of / is assumed.) For example, the URI ws://localhost/app/pubsub would use port 80 on localhost, with the path /app/pubsub.

Secure WebSockets (URI, wss://) (if enabled) use the scheme wss://, and the default TCP port number of 443. Otherwise the format is the same as for regular WebSockets.

A URI may be restricted to IPv6 using the scheme ws6:// or wss6://, and may be restricted to IPv4 using the scheme ws4:// or wss4://.

Specifying ws6:// or wss6:// may not prevent IPv4 hosts from being used with IPv4-in-IPv6 addresses, particularly when using a wildcard hostname with listeners. The details of this varies across operating systems.
The ws4:// , ws6://, wss4:// and wss6:// schemes are specific to NNG, and might not be understood by other implementations.
We recommend using either numeric IP addresses, or names that are specific to either IPv4 or IPv6 to prevent confusion and surprises.

When specifying IPv6 addresses, the address must be enclosed in square brackets ([]) to avoid confusion with the final colon separating the port.

For example, the same path and port on the IPv6 loopback address (::1) would be specified as ws://[::1]/app/pubsub.

The value specified as the host, if any, will also be used in the Host: HTTP header during HTTP negotiation.

To listen to all ports on the system, the host name may be elided from the URL on the listener. This will wind up listening to all interfaces on the system, with possible caveats for IPv4 and IPv6 depending on what the underlying system supports. (On most modern systems it will map to the special IPv6 address ::, and both IPv4 and IPv6 connections will be permitted, with IPv4 addresses mapped to IPv6 addresses.)

Socket Address

When using an nng_sockaddr structure, the actual structure is either of type nng_sockaddr_in (for IPv4) or nng_sockaddr_in6 (for IPv6).

Server Instances

This transport makes use of shared HTTP server instances, permitting multiple sockets or listeners to be configured with the same hostname and port. When creating a new listener, it is registered with an existing HTTP server instance if one can be found. Note that the matching algorithm is somewhat simple, using only a string based hostname or IP address and port to match. Therefore it is recommended to use only IP addresses or the empty string as the hostname in listener URLs.

Likewise, when sharing a server instance, it may not be possible to alter TLS configuration if the server is already running, as there is only a single TLS configuration context for the entire server instance.

All sharing of server instances is only typically possible within the same process.

The server may also be used by other things (for example to serve static content), in the same process.

Transport Options

The following transport options are available. Note that setting these must be done before the transport is started.

The TLS specific options (beginning with NNG_OPT_TLS_) are only available for wss:// endpoints.

(string) Concatenation of multiple lines terminated by CRLF sequences, that can be used to add further headers to the HTTP request sent when connecting. This option can be set on dialers, and retrieved from pipes.


(string) Concatenation of multiple lines terminated by CRLF sequences, that can be used to add further headers to the HTTP response sent when connecting. This option can be set on listeners, and retrieved from pipes.


(bool) Enable receiving of TEXT frames at the WebSocket layer. This option should only be used with the low level nng_stream API. When set, the stream will accept in-bound TEXT frames as well as BINARY frames.

The SP protocols (such as REQ) require BINARY frames as they pass binary protocol data. Hence this option should not be used with such protocols.
RFC 6455 requires that TEXT frames be discarded and the connection closed if the frame does not contain valid UTF-8 data. NNG does not perform any such validation. Applications that need to be strictly conformant should check for this themselves.

(bool) Enable sending of TEXT frames at the WebSocket layer. This option should only be used with the low level nng_stream API. When set, the stream will send TEXT frames instead of BINARY frames.

NNG does not check the frame data, and will attempt to send whatever the client requests. Peers that are compliant with RFC 6455 will discard TEXT frames (and break the connection) if they do not contain valid UTF-8.

(nng_tls_config *) The underlying TLS configuration object for wss:// endpoints. A hold is placed on the underlying configuration object before returning it. The caller should release the object with nng_tls_config_free() when it no longer needs the TLS configuration.

Use this option when advanced TLS configuration is required.

(string) Write-only option naming a file containing certificates to use for peer validation. See nng_tls_config_ca_file() for more information.


(string) Write-only option naming a file containing the local certificate and associated private key. The private key used must be unencrypted. See nng_tls_config_own_cert() for more information.


(int) Write-only option used to configure the authentication mode used. See nng_tls_config_auth_mode() for more details.


(bool) Whether the remote peer has been properly verified using TLS authentication. May return incorrect results if peer authentication is disabled.