Segment decoding

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1

Imported from previous forum

2

Hi,

How do I know if after a PMAP I will have to decode a TemplateID or not? I wanted to code a generic function “DecodeSegment(…)” like

Decoder::DecodeSegment(params)
{
LoadPresenceMAP(); /// PMAP stuff
u32 TID = DecodeTemplateID(); /// But will I have a template ID here ???

Template * pTemplate = Templates::GetTemplate(TID);

pTemplate->Decode(); /// DecodeSegment might be recursively called here, because of sequence elements and groups encoded as segment in stream
}

But it seems this cannot be done because I need to know where I am in a Template.

In other words, how to know while decoding a segment, if this segment is described by a template, or if this segment is the stream of a sequence element / group.

This is maybe completly wrong, but I was more expecting something like this :

stream ::= message* | block*
block ::= BlockSize message+
message ::= segment
segment ::= PresenceMap TemplateIdentifier (field | segment_no_tid)*
segment_no_tid ::= PresenceMap (field | segment_no_tid)*
field ::= integer | string | delta | ScaledNumber | ByteVector
integer ::= UnsignedInteger | SignedInteger
string ::= ASCIIString | UnicodeString
delta ::= IntegerDelta | ScaledNumberDelta | ASCIIStringDelta | ByteVectorDelta

Thanks in advance,

Regards.

3

How do I know if after a PMAP I will have to decode a TemplateID or not?

The only time that a template id appears in a segment is at the start of a new message, or when a dynamic template reference is encountered. When decoding groups or sequences, segments do not contain a template id.

From Section 10 - Transfer Encoding:

“A segment has a header consisting of a Presence Map followed by an optional Template Identifier. The segment has a template identifier either if it is a message segment, or if the segment appears as the result of a dynamic template reference instruction.”

Your expectations would be correct if not for the dynamic template reference instruction.

Jake

4

Thank you for that fast answer.

This is clear now.

Olivier

How do I know if after a PMAP I will have to decode a
TemplateID or not?

The only time that a template id appears in a segment is at the start of
a new message, or when a dynamic template reference is encountered. When
decoding groups or sequences, segments do not contain a template id.

From Section 10 - Transfer Encoding:

“A segment has a header consisting of a Presence Map followed by an
optional Template Identifier. The segment has a template identifier
either if it is a message segment, or if the segment appears as the
result of a dynamic template reference instruction.”

Your expectations would be correct if not for the dynamic template
reference instruction.

Jake