Rate Limiting works incorrectly if `PeriodTimespan` value is greater than `Period`

[sergio-str]

Expected Behavior

Rate Limiting works as documented for such parameter values:

• Period: 1 second
• PeriodTimespan: 30 seconds
• Limit: 100

Scenario:
Request flow, 10-20 requests per sec, should be allowed.

Status: not equal to 429

Actual Behavior / Motivation for New Feature

With the same parameter values from Expected Behavior Ocelot returns status 429 aka "Rate limit exceeded".
It seems this issue caused by code in the if (entry.HasValue) block:

Ocelot/src/Ocelot/RateLimit/RateLimitCore.cs

Lines 31 to 39 in 0b247af

	// entry has not expired
	if (entry.Value.Timestamp + TimeSpan.FromSeconds(rule.PeriodTimespan) >= DateTime.UtcNow)
	{
	// increment request count
	var totalRequests = entry.Value.TotalRequests + 1;
	// deep copy
	counter = new RateLimitCounter(entry.Value.Timestamp, totalRequests);
	}

Ocelot increments request counter if request has been received in interval: [FirstRequestTime : FirstRequestTime + PeriodTimeSpan]
According to the documentation counter should be incremented if request is in interval: [FirstRequestTime : FirstRequestTime + Period].

Steps to Reproduce the Problem

1. Set Rate Limiting configuration parameters:

• Period: 1 second
• PeriodTimespan: 30 seconds
• Limit: 100

3. Generate a consequent request flow (10-20 requests per second) for more than 12 seconds
4. Ensure Ocelot returns status 429

Specifications

• Ocelot Version: Latest, 19.0.2
• Feature: Rate Limiting

[raman-m]

Hi Sergii!

Do not you mind if we collaborate on the issue description first?

[raman-m]

Check the issue Title please!
Is this title correct?

[raman-m]

Sergii,
I've changed Expected Behavior description.
Could you confirm it's correct please?
I need to know we are on the same page.

[sergio-str]

I think yes. But give me a little time, please, to dive into the context. Also I apologize for inacurate title.

[raman-m]

So, bug description has been changed and updated.
Could you review it plz?