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Subject: [OASIS Issue Tracker] (MQTT-236) Consolidate Acks, enable negative acknowledgements.
[ https://issues.oasis-open.org/browse/MQTT-236?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=62323#comment-62323 ]
Ken Borgendale commented on MQTT-236:
-------------------------------------
Comments on the above proposals:
I do not see the point of returning a protocol error (malformed packet) as a PUBLISH or SUBSCRIBE error. This should really cause a DISCONNECT. The same is true if the receiver finds a system fault. Valid MQTT which this provider does not support (the Unicode SHOULD clause, character set restrictions, or topic space restrictions) are valid things to return reason codes.
I actually do like the 0x01 and 0x02 return codes shown for PUBLISH. Worded correctly the receiver of the publish could always return a 0x00 return code. In any case the full QoS flow should happen in these cases.
In the case of other codes, we need to separate these so that the receiver (which could be either the client or the server) can tell what action to take. My list of errors for PUBLISH would look like:
- Not authorized (probably needs an admin fix)
- Topic name not valid
- Packet ID in use (this might indicate a session state issue)
- QoS not supported
- Retain not supported
- Message too big (probably needs an admin fix)
- Message rate too high (wait and retry might work)
- Sender quota exceeded (might be temporary)
- Receiver capacity reached (wait and retry might work)
For SUBSCRIBE
- Not authorized
- Topic filter not valid
- Packet ID in use
- Shared subs not supported
- Overlapping subscription not allowed (if this is one of the solutions for shared subs)
- Client quota exceeded
- Server capacity reached
For UNSUBSCRIBE
- Not authorized (I hope this is not common)
- Topic filter not valid
- Packet ID in use
It always seems a problem to report quota or capacity problems when doing an UNSUBSCIBE (or in general when trying to remove resource), and indeed returning not authorized is somewhat problematic. These are some of the actions we tell people to take when they have reached a quota or capacity problem.
> Consolidate Acks, enable negative acknowledgements.
> ---------------------------------------------------
>
> Key: MQTT-236
> URL: https://issues.oasis-open.org/browse/MQTT-236
> Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
> Issue Type: New Feature
> Components: futures
> Affects Versions: 3.1.1
> Reporter: Andrew Banks
> Priority: Critical
>
> Consolidate Acks, enable negative acknowledgements.
> ---------------------------------------------------
> Connack, SubAck, UnsubAck, PubAck, PubRec, PubRel, PubComp, PingResp
> are all flavours of an Ack. Currently there are no negative Acks.
> I suggest consolidating all of the acks into a single packet type eg the current Connack
> and using bits 3-0 of the fixed header to indicate the ack'd packet type.
> Connect Ack : 0010 0001 RL, SP, RC
> Publish Ack : 0010 0011 RL, ID, RC (Ack Qos=0,1)
> Publish Ack : 0010 0100 RL, ID, RC (Ack Qos=2)
> Publish Ack : 0010 0101 RL, ID (Rel Qos=2)
> Publish Ack : 0010 0110 RL, ID, RC (Comp Qos=2)
> Subscribe Ack : 0010 1000 RL, ID, RC(,RC)(,RC)... (Per topic)
> UnSubscribe Ack : 0010 1010 RL, ID, RC(,RC)(,RC)... (Per topic)
> Ping Ack : 0010 1011 RL
> RL=RamainingLength, SP=SessionPresent, RC=ResponseCode ID=PacketIdentifier
> This would free up the remaining SubAck, UnsubAck, PubAck, PubRec, PubRel, PubComp,
> PingResp packet types for other uses.
> Connect Ack response codes
> --------------------------
> 0 0x00 Connection Accepted.
> 1-127 Reserved for future use.
> 128 0x80 Connection Refused, Malformed Packet, eg user name indicated but not present. Followed by network disconnection.
> 129 0x81 Connection Refused, reason unspecified. Followed by network disconnection.
> 130 0x82 Connection Refused, the Client is not authorized to connect. Followed by network disconnection.
> 131 0x83 Connection Refused, implementation specific, eg. server capacity reached.
> Followed by network disconnection.
> 132 0x84 Connection Refused, unacceptable protocol version. The Server does not support
> the level of the MQTT protocol requested by the Client.
> Followed by network disconnection.
> 133 0x85 Connection Refused, identifier rejected. The Client identifier is correct UTF-8
> but not allowed by the Server. Followed by network disconnection.
> 134 0x86 Connection Refused, Server unavailable. The Network Connection has been made but the
> MQTT service is unavailable. Followed by network disconnection.
> 135 0x87 Connection Refused, bad user name or password. The data in the user name or
> password is malformed. Followed by network disconnection.
> 136-255 Reserved for future use.
> Publish Ack response codes, Ack Qos=0,1
> ---------------------------------------
> A packet identifier of zero indicates an ack for a Qos=0 message,
> rc=0,1 is not allowed for Qos=0 messages, instead no Ack should be sent.
> 0 0x00 Message Accepted, Publication of Qos=1 message proceeds, not allowed for Qos=0.
> 1 0x01 Message Accepted, No matching subscribers. Not allowed for Qos=0.
> 2-127 Reserved for future use.
> 128 0x80 Message Refused, Malformed Packet, eg invalid topic name. Followed by network disconnection.
> 129 0x81 Message Refused, reason unspecified.
> 130 0x82 Message Refused, publication not authorized.
> 131 0x83 Message Refused, implementation specific, eg. client quota reached.
> 132-255 Reserved for future use.
> Publish Ack response codes, Ack Qos=2
> -------------------------------------
> 0 0x00 Message Accepted, Publication of Qos=2 message proceeds.
> 1 0x01 Message Accepted, No matching subscribers. Should be used in preference to 0x00
> If the server cannot determine whether there are any subscribers, eg because it is
> in a cluster, then use response code 0x00.
> No PubRel,PubComp expected.
> 2-127 Reserved for future use.
> 128 0x80 Message Refused, Malformed Packet, eg packet identifier=0. Followed by network disconnection.
> 129 0x81 Message Refused, reason unspecified. No PubRel,PubComp expected.
> 130 0x82 Message Refused, publication not authorized. No PubRel,PubComp expected.
> 131 0x83 Message Refused, implementation specific, eg. client quota reached. No PubRel,PubComp expected.
> 132-255 Reserved for future use.
> Publish Ack response codes, Rel Qos=2
> -------------------------------------
> There are no Publish Ack Rel Qos=2 response codes, should we add a 0x00 byte as a placeholder?
> Publish Ack response codes, Comp Qos=2
> --------------------------------------
> 0 0x00 Message Released, Publication of Qos=2 message completed.
> 1 0x01 Message Released, No matching subscribers. Should be used in preference to 0x00
> If the server cannot determine whether there are any subscribers, eg because it is
> in a cluster, then use response code 0x00.
> 2 0x02 Message Released, No message existed eg. expired.
> 3-127 Reserved for future use.
> 128 0x80 Message Release Refused, Malformed Packet, eg packet identifier=0. Followed by network disconnection.
> 129 0x81 Message Release Refused, reason unspecified.
> 130 0x82 Message Release Completed without publication, publication not authorized.
> 131 0x83 Message Release Refused, implementation specific, eg. client quota reached.
> 132-255 Reserved for future use.
> Subscribe Ack response codes
> ----------------------------
> 0 0x00 Subscribe Success - Maximum QoS 0.
> 1 0x01 Subscribe Success - Maximum QoS 1.
> 2 0x02 Subscribe Success - Maximum QoS 2.
> 3-127 Reserved for future use.
> 128 0x80 Subscribe Refused, Malformed Packet, eg packet identifier=0. Followed by network disconnection.
> 129 0x81 Subscribe Refused, reason unspecified.
> 130 0x82 Subscribe Refused, not authorized.
> 131 0x83 Subscribe Refused, implementation specific, eg. client quota reached.
> 132-255 Reserved for future use.
> UnSubscribe Ack response codes
> ------------------------------
> 0 0x00 UnSubscribe Success.
> 1 0x01 UnSubscribe Success, No subscription existed.
> 2-127 Reserved for future use.
> 128 0x80 UnSubscribe Refused, Malformed Packet, eg. packet identifier=0. Followed by network disconnection.
> 129 0x81 UnSubscribe Refused, reason unspecified.
> 130 0x82 UnSubscribe Refused, not authorized.
> 131 0x83 UnSubscribe Refused, implementation specific, eg. client quota reached.
> 122-255 Reserved for future use.
> Ping Resp response codes
> -------------------------
> There are no Ping Resp response codes, should we add a 0x00 byte as a placeholder?
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