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https://issues.apache.org/jira/browse/PROTON-1940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16628992#comment-16628992
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ASF GitHub Bot commented on PROTON-1940:
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Github user alanconway commented on the issue:
https://github.com/apache/qpid-proton/pull/159
Changes prompted by astitcher's comments:
- better explanation of mulitple fields, corrected AMQP spec links
- added block comment for vfill format letters
- factored out pni_normalize_multiple to reduce visual churn in _vfill()
impl
Not changed: still using a new format letter. 2 reasons - consistency and
efficiency/ease of impl:
consistency: the multiple attribute is part of an AMQP composite field
definition. The purpose of _vfill() is to fill in composite fields correctly -
so IMO that is where this belongs. I personally hate the vfill char-based
mini-language; it is hard to read, hard to remember and error-prone. However it
seems like something we should replace entirely or live with for now, rather
than have inconsistent approaches for different fields.
ease of impl: as part of vfill, we can copy exactly as much of the source
data as we need to the target. A normalize function outside of vfill would
either have to modify the source value in-place (side-effects on caller's data
value) or create an intermediate copy (expensive, extra memory management) Both
are inconsistent with existing use of vfill.
> [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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