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Subject: [OASIS Issue Tracker] Commented: (MQTT-2) UTF-8 for will messages
[ http://tools.oasis-open.org/issues/browse/MQTT-2?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=33862#action_33862 ]
Rahul Gupta commented on MQTT-2:
--------------------------------
Changes done in WD05 -
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line 601 -> The payload contains one or more encoded fields
line 775 -> The payload of the CONNECT control packet contains one or more encoded fields, based on the flags in the variable header.
line 780 -> The Client Identifier is always present and is the first field in the payload. The Client identifier is a UTF-8 encoded string,
line 797 -> If Will Flag=1, this is the next field in payload. Will Topic is a UTF-8 encoded string. The
line 808 -> If the Will Flag=1, this is the next field in payload. Will Message is a UTF-8 encoded string. The Will Message defines the payload content of the message that is published to the Will Topic if the client is unexpectedly disconnected. This field, if present, must consist of a 2-byte length (MSB followed by LSB) followed by the payload for the Will Message expressed as a sequence of zero or more bytes. The length gives the number of bytes in the payload that follows and does not include the 2 bytes taken up by the length itself.
line 815 -> When the Will Message is published to the Will Topic its payload consists only of the payload portion of this field, not the first two length bytes
line 818 -> If the User Name Flag=1, this is the next field in payload. User Name is a UTF-8 encoded string.
line 825 -> If the Password flag is set (1), then next field is the password corresponding to the user name which is connecting, and can be used by the server for authentication of the client. Password is a UTF-8 encoded string.
> UTF-8 for will messages
> -----------------------
>
> Key: MQTT-2
> URL: http://tools.oasis-open.org/issues/browse/MQTT-2
> Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
> Issue Type: Improvement
> Components: core
> Affects Versions: 3.1.1
> Reporter: Dominik Obermaier
> Assignee: Rahul Gupta
>
> The current 3.1 specification states that the will message is encoded in UTF-8 in the CONNECT message but will be published in ASCII encoding by a MQTT broker. This is a major inconsistency in the specification since this is the only case where ASCII encoding is used.
> Here's the relevant citation from the specification:
> "Although the Will Message is UTF-8 encoded in the CONNECT message, when it is published to the Will Topic only the bytes of the message are sent, not the first two length bytes. The message must therefore only consist of 7-bit ASCII characters."
> A payload for a PUBLISH can of course be any raw bytes, in case of the will message we should think of removing the inconsistency from the spec. I see two possibilities:
> 1. The will message in the CONNECT message is *not* UTF-8 encoded but ASCII encoded.
> 2. The will message in the will PUBLISH is UTF-8. This would collide with the current spec because empty payloads are possible regarding to the 3.1 spec (in case of UTF-8 IIRC two length bytes have to be sent even with an empty message).
> I would vote for option two because this would remove this inconsistency in the spec and the will message is encoded in the CONNECT message in UTF-8 anyway. I don't think the overhead of the two length bytes in case of an empty message are a serious problem. We could discuss if it would be reasonable that in case of an empty payload (= empty UTF-8 String) the length bytes should be removed automatically by broker implementations to reduce the overhead in PUBLISH messages.
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