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RE: Testcases for HTTP location grammar [CR130]

From: Rogers, Tony <Tony.Rogers@ca.com>
Date: Fri, 12 Jan 2007 12:50:15 +1100
Message-ID: <BEE2BD647C052D4FA59B42F5E2D946B317B78B@AUSYMS12.ca.com>
To: "John Kaputin \(gmail\)" <jakaputin@gmail.com>, "Philippe Le Hegaret" <plh@w3.org>, <www-ws-desc@w3.org>
I think the parser need to have a stack for braces - I don't believe even a state machine can hold all the information we need - when we match up a pair we need to know what our state was before we opened that pair. My sketch of the processing would go:
if the next character is {
a. if previous character was { and top of stack is { then change top of stack to {{
b. otherwise stack {  (remembering where it was seen)
if the next character is }
a. if top of stack is {{ look for another } immediately following
    i. if next char is }, unstack the {{  - we have a matching pair  {{}}
    ii. if next char is not }, throw error or treat as literal }
b. if top of stack is {, unstack the {  - we have a matching pair {}
c. if stack is empty, throw error or treat as literal }
at the end, the stack should be empty, assuming all { matched }, otherwise unstack the extras and treat as literals (which is why we remembered their locations)
To put it into words, I see } or }} as matching to the nearest unpaired { or {{, but always respecting nesting. I also see longer sequences of { taken as pairs until there's one or none left.
So to my mind {{{{X}}}} parses as {{  {{  X  }}  }}  - even though that's a questionable construct.  Or do we want to add another rule saying that {{ cannot be nested inside {{ ?
How does that sound?
Tony Rogers
CA, Inc
Senior Architect, Development
co-chair UDDI TC at OASIS
co-chair WS-Desc WG at W3C


From: www-ws-desc-request@w3.org on behalf of John Kaputin (gmail)
Sent: Fri 12-Jan-07 8:50
To: Philippe Le Hegaret; www-ws-desc@w3.org
Subject: Testcases for HTTP location grammar [CR130]

Today's working group call concluded that a grammar should define how the http location is parsed and you have the action, so as discussed I'm sending you some of my testcases. My post [1] is now captured as CR130.

In deciding on the grammatical rules, things to consider include the precedence of double curly braces versus single braces and how to match pairs of single braces - e.g. by scanning from left to right, by 'inner most pair' (or whatever the terminology is), etc.

When trying several approaches in Woden I found it's not as simple as 'find a left curly brace, check for a double brace, then scan for a right curly brace'. Also, it appeared from my initial interpretation of the spec that double curly braces should take precedence over single braces, but this produced some unexpected results. A better approach seems to be 'inner most pair' takes precedence, then double curly braces, then other single braces.

Below are some test cases using different approaches. "Valid/invalid" simply indicates whether non-paired single braces end up in the parsed string (literal single braces are okay).

Inner-most pair, then doubles, then unpaired singles. town=Paris:

"{town}"       > {town}           > "Paris"     > valid
"{{town}}"     > {,{town},}       > "{Paris}"   > invalid
"{{{town}}}"   > {{,{town},}}     > "{Paris}"   > valid
"{{{{town}}}}" > {{,{,{town},}},} > "{{Paris}}" > invalid
"{{town}"      > {,{town}         > "{Paris"    > invalid
"{{{town}"     > {{,{town}        > "{Paris"    > valid
"{town}}"      > {town},}         > "Paris}"    > invalid
"{town}}}"     > {town},}}        > "Paris}"    > valid

Double braces first, then pairs of singles left-to-right. town=Paris:

"{town}"       > {town}           > "Paris"     > valid
"{{town}}"     > {{,town,}}       > "{town}"    > valid
"{{{town}}}"   > {{,{,town,}},}   > "{{town}}"  > invalid
"{{{{town}}}}" > {{,{{,town,}},}} > "{{Paris}}" > invalid
"{{town}"      > {{,town,}        > "{town}"    > invalid
"{{{town}"     > {{,{town}        > "{Paris"    > valid
"{town}}"      > {,town,}}        > "{town}"    > invalid
"{town}}}"     > {,town,}},}      > "{town}}"   > invalid

Other test cases:

""                      (is an   empty string location valid?)

It would be good if the spec could include similar examples and/or if the test suite covered the grammar.

John Kaputin

[1] http://lists.w3.org/Archives/Public/www-ws-desc/2007Jan/0045.html
Received on Friday, 12 January 2007 01:50:26 UTC

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