A cute little bug

I have been working on https://rentobase.com - a rental property management SaaS.

One of the features is the ability to record a rental income collection.

There are two important date atrributes things that you have to record:

the date when the rental payment goes into effect
the date when the rental payment becomes due.

How do you do this simplistically?

Validate that the start date is not in the past.
Validate that the end date is not in the past as well.
Check that the end date and start date are not the same.

What was I doing?

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startDate, _ := time.Parse("2006-01-02", req.StartDate)
endDate, _ := time.Parse("2006-01-02", req.EndDate)

if startDate.Before(time.Now()) || endDate.Before(time.Now()) {
	c.JSON(http.StatusBadRequest, gin.H{"message": "Dates cannot be in the past"})
	return
}   

if startDate.After(endDate) {
	c.JSON(http.StatusBadRequest, gin.H{"message": "Start date cannot be after end date"})
	return
}

Here’s where it gets interesting. If you validate using the above code, you will get a false negative because startDate.Before(time.Now()) will return false if startDate is today.

I spent quite a chunk of my afternoon wondering why this was the case.

The fix is quite simple. Truncate the current time to midnight using time.Now().Truncate(24 * time.Hour) to compare dates at the day level rather than exact timestamps.

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startDate, _ := time.Parse("2006-01-02", req.StartDate)
	endDate, _ := time.Parse("2006-01-02", req.EndDate)

	currentDate := time.Now().Truncate(24 * time.Hour)
	if startDate.Before(currentDate) {
		//throw error
		return
	}

There you have it!