[squid-dev] Proposal: Helper response: concatenated values with custom delimiter

[Andrey K]

Hello,

I've mentioned this briefly in another thread, but I’d like to start a
dedicated discussion regarding the support for a "concatenated" value
format in helper responses.

In a recent PR discussion (
https://github.com/squid-cache/squid/pull/2395#discussion_r3022844826),
Alex pointed out issues with using concatenated formats for passing tag
values.

I propose adding support for a custom delimiter for concatenated values
within a single KV-pair in the helper output.

The proposed syntax is:
    <key>=<delimiter>"<value1><delimiter><value2>..."

Examples:
    group=,"group1,group2,group3"
    clt_con_tag=;"tag1;tag2;tag3"

Escaping logic:
    If the delimiter appears inside a value within the token, it must be
double-escaped (\\) by the helper.
For example:
    group=,"Staff:accountants\\,lawyers\\,security,Main_Office"
This should produce two separate annotations:
    group=Staff:accountants,lawyers,security
    group=Main_Office

The choice of double escaping is intentional to maintain consistency with
the way strwordtok() processes quoted values in Squid.
This approach ensures that we can preserve the underlying logic for
handling values while correctly splitting the "glued" tokens.

Currently, a comma-separated format is often used de facto, but Squid
stores these as a single Entry, requiring the -m option for annotation
checks.

Proposed Change:
A minor modification to Helper::Reply::parseResponseKeys().

Pros:
- More compact data transfer format.
- Proper data storage on the Squid side (separate values instead of one
blob).
- Flexibility for plugin developers via custom delimiters.
- Eliminates the need for admins to manually manage the -m option for these
cases.

I am interested in implementing this and submitting a PR. Do you think this
solution is needed and fits the project's direction?

Kind regards,
    Ankor.
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