Fix Stop Index Check in strSubstring Function for Accurate Substring Extraction! ( Update functions.go )

[lichenliang666]

Issue Description:
The current strSubstring function has a potential issue with the stop index check. The condition if stop >= len(str) may result in undesired behavior, especially when attempting to include the last character in the substring. Since the slicing operation v = str[start : stop+1] is left-closed and right-open, the character at the stop index is excluded.

Proposed Solution:
To address this, it is suggested to modify the condition to if stop > len(str) || stop < 0 for a more accurate check on invalid stop indices. Additionally, the error message should be updated to reflect this change:

if stop > len(str) || stop < 0 {
    return nil, fmt.Errorf("invalid stop index for string in strSubstring: %d", stop)
}
v = str[start : stop+1]

This modification ensures correct substring extraction, even when attempting to include the character at the stop index.

Required checklist

• Sample config files updated (both /etc folder and NewDemoConfig methods) (influxdb and plutonium)
• openapi swagger.yml updated (if modified API) - link openapi PR
• Signed CLA (if not already signed)

Description

1-3 sentences describing the PR (or link to well written issue)

Context

Why was this added? What value does it add? What are risks/best practices?

Affected areas (if applicable):

List of user-visible changes. As a user, what would I need to see in docs?
Examples:
CLI commands, subcommands, and flags
API changes
Configuration (sample config blocks)

Severity (optional)

i.e., ("recommend to upgrade immediately", "upgrade at your leasure", etc.)

Note for reviewers:

Check the semantic commit type:

• Feat: a feature with user-visible changes
• Fix: a bug fix that we might tell a user “upgrade to get this fix for your issue”
• Chore: version bumps, internal doc (e.g. README) changes, code comment updates, code formatting fixes… must not be user facing (except dependency version changes)
• Build: build script changes, CI config changes, build tool updates
• Refactor: non-user-visible refactoring
• Check the PR title: we should be able to put this as a one-liner in the release notes