SLIDE 1
VWRAP Type System Experience & Issues
March 2010 Mark Lentczner / “Zero Linden”
Tuesday, March 23, 2010
Experience Report
Tuesday, March 23, 2010
VWRAP Type System Experience & Issues March 2010 Mark - - PowerPoint PPT Presentation
VWRAP Type System Experience & Issues March 2010 Mark - - PowerPoint PPT Presentation
VWRAP Type System Experience & Issues March 2010 Mark Lentczner / Zero Linden Tuesday, March 23, 2010 Experience Report Tuesday, March 23, 2010 Tuesday, March 23, 2010 Time Line 2005 I n i t i a l D B i e n s a i g
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Time Line
2005 2006 2007 2008 2009 2010
I n i t i a l D e s i g n & I m p l . B i n a r y & N
- t
a t i
- n
S e r . 2 n d D e s i g n & I m p l . X M L S e r i a l i z a t i
- n
U s e i n m e s s a g e s y s t e m B a s i s f
- r
O G P d r a f t s F i r s t I D ( I E T F 7 5 )
Tuesday, March 23, 2010
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Implementations
C++: Linden Lab C#: OpenMetaverse Haskell: Linden Lab Java: Linden Lab, University of St. Andrews JavaScript: Linden Lab Perl: Linden Lab PHP: Linden Lab, SignpostMarv Python: Linden Lab Ruby: Linden Lab
Tuesday, March 23, 2010
SLIDE 5
Usage
Code: 9% of modules in LL main codebase use LLSD (~8k modules, ~3M lines of code)
Tuesday, March 23, 2010
SLIDE 6
Usage
Counts: 253k log messages / minute daily peak (notation) 9.7M objects created / day (XML)
Tuesday, March 23, 2010
SLIDE 7
Usage
Data Volume: 6.4 TiB / day for 2M teleports average of 3.3MiB each (binary) big LLSD! 55.7 TiB / day for 749k simulation checkpoints gzip’d to 42% of original (XML)
Tuesday, March 23, 2010
SLIDE 8
Pain Points
Content Negotiation Unicode Strings vs. XML Mixing LLSD and non-LLSD Documentation Validation Big data sets
Tuesday, March 23, 2010
SLIDE 9
Issues
Tuesday, March 23, 2010
SLIDE 10
Types: Date Range
The range of dates is currently bounded: “Data of type Date may have the value of any time in the from January 1, 1970 though at least January 1, 2038, to at least second accuracy.” Is this a worry?
Tuesday, March 23, 2010
SLIDE 11
Encoding: JSON Subtlety
1) RFC 4627 vs. ECMA-262 2) RFC 4627’s JSON-text vs. ECMA-262’s JSONvalue 3) String literals are escaped UTF-16, not Unicode! U+1D11E (𝄟) is encoded in JSON as: "\ud834\udd1e"
Tuesday, March 23, 2010
SLIDE 12
Encoding: XML Base64
1) The encoding attribute is defaulted to base64, it is not #REQUIRED 2) Which alphabet? RFC 4648 § 4. Base 64 Encoding 3) Linebreaking, Padding and Non-Alphabet RFC 4648 § 3. Implementation Discrepancies
Tuesday, March 23, 2010
SLIDE 13
LLIDL: REST vs. HTTP
1) Clear community dislike of binding to HTTP 2) Agreement on focus on REST semantics 3) Which REST like operations do we support? Operational
POST
<- -> Readable
GET
<< Read/Write
GET/PUT
<> Read/Write/Deletable GET/PUT/DELETE <x>
Tuesday, March 23, 2010
SLIDE 14
LLIDL: Events
An event, as cast into REST, would be like a request with no response. This does seem to map onto the communication needs
- f VWRAP.
Do we add this? Perhaps: Event
POST?
>>
Tuesday, March 23, 2010
SLIDE 15
LLIDL: Semantics of Matching
LLIDL describes shapes LLSD describes defaulting and conversion What constitutes conformance of an LLSD value to an LLIDL description? One approach:
match(actual) -- matches structurally and all conversions are valid (non-defaulted) valid(actual) -- matches structurally though defaulted or additional data is acceptable has_additional(actual) -- has additional data has_defaulted(actual) -- has defaulted data incompatible(actual) -- the value is incompatible
Tuesday, March 23, 2010
SLIDE 16
LLIDL: Stand Alone Values
There a need to be able to reference (and check conformance) for individual values. The named type facility serves this purpose for now.
Tuesday, March 23, 2010
SLIDE 17
LLIDL: Path Arguments
Astute readers will have noticed the addition of query argument specifications to LLIDL (the ?? syntax). While not strictly part of the current VWRAP usage, internally the need for specifying the query arguments to a resource was pressing. The need for path arguments is similar, though at present, LLIDL doesn’t consider the URL to access a resource.
Tuesday, March 23, 2010
SLIDE 18
VWRAP Foundation Issues
March 2010 Mark Lentczner / “Zero Linden”
Tuesday, March 23, 2010
SLIDE 19
Additions:
Minor nit: “Capability Host” Minor nit: Resource Base URI Medium issue: Required Serialization Formats
Tuesday, March 23, 2010
SLIDE 20
Issues
Tuesday, March 23, 2010
SLIDE 21
Seed Capability Format
In draft: %% seed
- > { capabilities: [ string, ... ] }
<- { capabilities: { $: uri } } But should it be? %% seed
- > { capabilities: [ string, ... ] }
<- { capabilities: [ &cap, ...] &cap = { name: string, loc: uri }
Tuesday, March 23, 2010
SLIDE 22
Event Queues
1) Are events to be handled differently than other resource types? 2) How should server invoked resources be implemented? 3) Is the current long-poll queue mechanism good enough for now?
Tuesday, March 23, 2010
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Capability Host
The “capability host” is responsible for both granting and proxying Should split out into two: “granting host” “proxying host”
Tuesday, March 23, 2010
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Resource Name Base URI
Currently: http://xmlns.secondlife.com/capability/name Propose something like: urn:vwrap:res:
Tuesday, March 23, 2010
SLIDE 25
Serialization
Currently “XML and JSON ... MUST be supported” Is there a point to forcing everyone to do both? We could put the burden on: just providers? just consumers? How does that work in our more symmetric world?
Tuesday, March 23, 2010