Subscription Filter Subject Matching

[scottf]

Overview

Ensure filter subject matching when creating subscriptions is consistent. Filter subject matching is required when a subscription is requested against an existing durable.

Glossary

SubscribeSubject - The subject used in the api call for subscription. FilterSubject - The filter subject as set in the existing consumer. null, empty, undefined and '>' are all identical StreamSubject - The subject for the corresponding stream. Is null/empty/undefined when the stream contains more than 1 subject and therefore cannot match.

Clients and Tools

• [ ] Go @piotrpio
• [x] Java @scottf
• [ ] JavaScript @aricart
• [x] .Net @ColinSullivan1 @scottf
• [x] C @kozlovic
• [ ] Python @wallyqs
• [ ] Ruby @wallyqs
• [ ] Rust @Jarema

Implementation Example

isFilterMatch(subscribeSubject string, filterSubject string, streamName string) returns boolean 
{
    // subscribeSubject guaranteed to not be null / empty / undefined
    // filterSubject may be null / empty / undefined or have value

    if (subscribeSubject is exactly equal to filterSubject) {
        return true
    }

    if (filterSubject is null or empty or undefined or equals ">") {
        // lookup stream subject returns null if there is not exactly one subject
        streamSubject = lookupStreamSubject(streamName)
        return (subscribeSubject is exactly equal to streamSubject)
    }

    return false
}

lookupStreamSubject(streamName string) returns string may be null / empty / undefined
{
    1. get StreamInfo for stream name
    2. if stream has more than 1 subject return null / empty / undefined
    3. else return the one subject
}

Unit Tests

1. Create a stream with the Stream Subject(s)
2. Create a push durable with the Filter Subject
3. Try to subscribe with the Subscribe Subject + durable name (not bind)

Stream Subject(s)	Filter Subject	Subscribe Subject	Match	Notes
foo, bar				one subject
	foo	foo	Yes	FS equals SS
	">"	">"	Yes	"
	"*"	"*"	Yes	"
	""	foo	Yes	SS != empty FS, but stream has exactly 1 subject and is a match.
	">"	foo	Yes	SS != FS of '>' but stream has exactly 1 subject and '>' matches.
	"*"	foo	No
foo, bar				multiple subjects no wildcards
	foo	foo	Yes	FS equals SS
	">"	">"	Yes	"
	"*"	"*"	Yes	"
	""	foo	No
	">"	foo	No
	"*"	foo	No
foo.>				multiple subjects via '>'
	foo.A	foo.A	Yes	FS equals SS
	">"	">"	Yes	FS equals SS
	""	foo.A	No
	">"	foo.A	No
	foo_GT	foo.A	No
foo.*				multiple subjects via '*'
	foo.A	foo.A	Yes	FS equals SS
	">"	">"	Yes	FS equals SS
	""	foo.A	No
	">"	foo.A	No
	foo_STAR	foo.A	No

Other Tasks

• [x] Update client features spreadsheet

Client authors please update with your progress. If you open issues in your own repositories as a result of this request, please link them to this one by pasting the issue URL in a comment or main issue description.

[marthaCP]

This will be a non-issue in JS Simplification.