This PR introduces native support for MQTT clients. It requires use
of accounts with JetStream enabled. Since as of now clustering is
not available, MQTT will be limited to single instance.
Only QoS 0 and 1 are supported at the moment. MQTT clients can
exchange messages with NATS clients and vice-versa.
Since JetStream is required, accounts with JetStream enabled must
exist in order for an MQTT client to connect to the NATS Server.
The administrator can limit the users that can use MQTT with the
allowed_connection_types option in the user section. For instance:
```
accounts {
mqtt {
users [
{user: all, password: pwd, allowed_connection_types: ["STANDARD", "WEBSOCKET", "MQTT"]}
{user: mqtt_only, password: pwd, allowed_connection_types: "MQTT"}
]
jetstream: enabled
}
}
```
The "mqtt_only" can only be used for MQTT connections, which the user
"all" accepts standard, websocket and MQTT clients.
Here is what a configuration to enable MQTT looks like:
```
mqtt {
# Specify a host and port to listen for websocket connections
#
# listen: "host:port"
# It can also be configured with individual parameters,
# namely host and port.
#
# host: "hostname"
port: 1883
# TLS configuration section
#
# tls {
# cert_file: "/path/to/cert.pem"
# key_file: "/path/to/key.pem"
# ca_file: "/path/to/ca.pem"
#
# # Time allowed for the TLS handshake to complete
# timeout: 2.0
#
# # Takes the user name from the certificate
# #
# # verify_an_map: true
#}
# Authentication override. Here are possible options.
#
# authorization {
# # Simple username/password
# #
# user: "some_user_name"
# password: "some_password"
#
# # Token. The server will check the MQTT's password in the connect
# # protocol against this token.
# #
# # token: "some_token"
#
# # Time allowed for the client to send the MQTT connect protocol
# # after the TCP connection is established.
# #
# timeout: 2.0
#}
# If an MQTT client connects and does not provide a username/password and
# this option is set, the server will use this client (and therefore account).
#
# no_auth_user: "some_user_name"
# This is the time after which the server will redeliver a QoS 1 message
# sent to a subscription that has not acknowledged (PUBACK) the message.
# The default is 30 seconds.
#
# ack_wait: "1m"
# This limits the number of QoS1 messages sent to a session without receiving
# acknowledgement (PUBACK) from that session. MQTT specification defines
# a packet identifier as an unsigned int 16, which means that the maximum
# value is 65535. The default value is 1024.
#
# max_ack_pending: 100
}
```
Signed-off-by: Ivan Kozlovic <ivan@synadia.com>
NATS is a simple, secure and performant communications system for digital systems, services and devices. NATS is part of the Cloud Native Computing Foundation (CNCF). NATS has over 40 client language implementations, and its server can run on-premise, in the cloud, at the edge, and even on a Raspberry Pi. NATS can secure and simplify design and operation of modern distributed systems.
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