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https://issues.apache.org/jira/browse/KAFKA-406?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13417367#comment-13417367
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Lorenzo Alberton commented on KAFKA-406:
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I see. It needs to be documented somewhere though, as people writing client
libs might have trouble reverse-engineering the protocol. The fact that only
gzipped messages are double-wrapped (requiring different handling depending on
a flag) can be confusing.
This might be a stupid question, but if a Message can contain a MessageSet with
more than one Message, how is the consumer supposed to iterate through them?
Children of a MessageSet might be Message objects OR MessageSet objects?
> Gzipped payload is a fully wrapped Message (with headers), not just payload
> ---------------------------------------------------------------------------
>
> Key: KAFKA-406
> URL: https://issues.apache.org/jira/browse/KAFKA-406
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 0.7.1
> Environment: N/A
> Reporter: Lorenzo Alberton
>
> When creating a gzipped MessageSet, the collection of Messages is passed to
> CompressionUtils.compress(), where each message is serialised [1] into a
> buffer (not just the payload, the full Message with headers, uncompressed),
> then gripped, and finally wrapped into another Message [2].
> In other words, the consumer has to unwrap the Message flagged as gzipped,
> unzip the payload, and unwrap the unzipped payload again as a non-compressed
> Message.
> Is this double-wrapping the intended behaviour?
> [1] messages.foreach(m => m.serializeTo(messageByteBuffer))
> [2] new Message(outputStream.toByteArray, compressionCodec)
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