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https://issues.apache.org/jira/browse/PROTON-1940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16631838#comment-16631838
 ] 

ASF subversion and git services commented on PROTON-1940:
---------------------------------------------------------

Commit 5960f15df324daf04387066af55dbb2f79c68f71 in qpid-proton's branch 
refs/heads/master from [~aconway]
[ https://git-wip-us.apache.org/repos/asf?p=qpid-proton.git;h=5960f15 ]

PROTON-1940: [c] normalize encoding of multiple="true" fields

Append src to data after normalizing for "multiple" field encoding.

AMQP composite field definitions can be declared "multiple", see:

- 
http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-types-v1.0-os.html#doc-idp115568
- 
http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-types-v1.0-os.html#section-composite-type-representation

Multiple fields allow redundant encoding of two cases:

1. empty: null or an empty array.
2. single-value: direct encoding of value, or array with one element

For encoding compactness and inter-operability, normalize multiple
field values to always use null for empty, and direct encoding for
single value.


> [c] normalize encoding of multiple="true" fields
> ------------------------------------------------
>
>                 Key: PROTON-1940
>                 URL: https://issues.apache.org/jira/browse/PROTON-1940
>             Project: Qpid Proton
>          Issue Type: Improvement
>          Components: proton-c
>    Affects Versions: proton-c-0.25.0
>            Reporter: Alan Conway
>            Assignee: Alan Conway
>            Priority: Major
>             Fix For: proton-c-0.26.0
>
>
> The AMQP spec defines some frame fields as "multiple".
> [http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-types-v1.0-os.html#section-composite-type-representation]
> "The _multiple_ attribute of a field description controls whether multiple 
> element values are permitted in the representation. A single element of the 
> type specified in the field description is always permitted. Multiple values 
> are represented by the use of an array where the type of the elements in the 
> array is the type defined in the field definition. Note that a null value and 
> a zero-length array (with a correct type for its elements) both describe an 
> absence of a value and MUST be treated as semantically identical. "
> Proton accepts all legal values. This issue is to normalize values written by 
> proton:
>  * empty array becomes null
>  * array of one element becomes a single value
> This is the most efficient encoding, and some clients (.NET) have problems 
> with multiple fields that contain an empty array rather than a null.



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