[Changelog] flespi MQTT broker

adsa

Use cases, implementation features, changelog for flespi MQTT broker.

shal

We are migrating from 32-bit to 64-bit IDs of various broker elements. Broker was just upgraded with new binaries capable or working with both types of entities and in a hour we will upgrade the database schema. We do not expect any problems to the broker, may be short service interruptions in a second or two.

adsa

Latest broker API changes:
'recursive' parameter added to GET mqtt/messages method. Parameter is optional and has value 'true' by default. If you want to fetch your own messages, i.e. skip subaccount's messages, just set parameter value to 'false'.

Method parameters, behavior and returning result are compatible with previous implementation.

adsa

We introduced a new rule for processing overflowed sessions.
Broker keeps unacknowledged messages in the internal buffer wich has limit up to 1Gb per each MQTT session.
If session buffer is overflowed, the connection will be disconnected and undelivered messages will be deleted.

shal

In flespi we are using timestamp user property automatically set by the broker as the time of message appearance.
We had some messages, like telematics messages telemetry, with expiry interval set that were outdated twice earlier then expected (twice shorter messages life). This was because broker, before delivering retained message marked expiry interval in seconds from current time, but at the same time it checked for message actuality starting from this timestamp time.

Now we fixed this behavior - broker will not decrement expiry interval based on current time, but will always count it from message timestamp. This not conforms to standard MQTT protocol and can be counted as flespi broker specifics.

adsa

Rejected messages counter was added to the session log record upon disconnection.
Message can be rejected by one of these reasons:

Permissions denied for publisher token.
Message has reserved prefix flespi/
Access denied to specified subaccount passed through cid property.

shal

One of our users has reported a security issue in flespi broker that allowed to use will message for publishing into topics protected by ACL (all topics except flespi/ were affected). We have installed a fix that prohibits session connections with invalid for given token at this moment of time will message topic.

adsa

A bunch of internal updates have been deployed. Please contact us if you notice an incorrect broker behavior.

adsa

Some hardware MQTT implementations have limitations for username/password field length of authorization packet. The typical limitation is 32 bytes per field.
Thus regular authorization via 64-byte token is not possible.

So we have implemented an alternative way to authorize such MQTT connections.
To do it, use token id as username and at least 32 first bytes of the token key as a password. The token MUST be of ACL type.

Example:
username=123
password=at-least-32-first-bytes-of-token-key

shal

It is now possible to specify for ACL tokens MQTT topics using flespi comma-separated topic selectors.

Imagine, you have this topics:

path/1/field1
path/1/field2
path/1/field3

If you want to limit publish/subscribe access to to field1 and field2 only, leaving field3 protected you need to specify this in ACL section of ACL token.

Before today update you need to specify each topic separately, e.g. define two mqtt sections in the token:
path/1/field1 and path/1/field2.

After today update you may use flespi special topic selector for providing correct topics and have everything in just one rule:
path/1/field1,field2

Same applies if you have multiple identifiers in path, e.g. 1,2,3,4,5,6. You may describe full ACL with just one rule: path/1,2,3,4,5,6/field1,field2 Previously you need to define 12 MQTT ACL rules for this construction or use topic wildcards.

This is applicable for both publish and subscribe sections of mqtt ACL rule.

adsa

Dear flespi users!

The latest broker update, which proposed an alternative way to authorize the MQTT connection, also closed the security vulnerability. It was possible to log in with any string as a username and a valid token as a password.

Please refer Authorization section on the broker description page: https://flespi.com/mqtt-broker and review your connection settings and correct it if necessary.

adsa

Two more properties were added to the MQTT session state.

Pending messages queue size in bytes:
flespi/state/mqtt/sessions/+/bytes_out_queue

In-flight, i.e. not ACK'ed QoS(1,2) messages count:
flespi/state/mqtt/sessions/+/puback_queue

The growth of these properties usually indicates insufficient bandwidth of the client network or the bottleneck of ACK processing.