Duration validation incorrectly rejects valid values with zero fractional digits #1847

Description

The validation regex for duration values does not correctly match the documented allowed range.

According to the validation error message, the duration must be between 0s and 999.999s, for example:

• 1s
• 0.100s
• 12.345s

The current validation regex is:

^[0-9]{1,3}s|[0-9]{1,3}\.(?:[0-9]{2}[1-9]|[0-9][1-9][0-9]|[1-9][0-9]{2})s$

This regex unnecessarily restricts the fractional part by requiring at least one non-zero digit.

For example, 1.000s is within the documented range but does not match the current regex.

A regex supporting durations between 0s and 999.999s with up to three decimal places could be:

^[0-9]{1,3}(?:\.[0-9]{1,3})?s$

Steps to reproduce

Use a duration value with a fractional part containing only zeros, for example:

# Example configuration containing a duration field
some_duration = "1.000s"

1. Configure a duration value such as 1.000s.
2. Run:

terraform plan

3. Observe the validation error.

Actual behavior

A duration such as:

1.000s

is rejected by the STACKIT Terraform provider.

The current regex:

^[0-9]{1,3}s|[0-9]{1,3}\.(?:[0-9]{2}[1-9]|[0-9][1-9][0-9]|[1-9][0-9]{2})s$

requires at least one of the three fractional digits to be non-zero.

As a result, values such as the following are rejected:

0.000s
1.000s
12.000s
999.000s

although they are within the documented range.

Additionally, the two alternatives in the regex are not grouped. Therefore, the ^ anchor applies only to the first alternative and the $ anchor only to the second alternative.

Expected behavior

The provider should accept all correctly formatted duration values between 0s and 999.999s.

For example:

0s
1s
999s
0.100s
1.000s
12.345s
999.999s

If one to three fractional digits are supported, the validation regex could be:

^[0-9]{1,3}(?:\.[0-9]{1,3})?s$

If exactly three fractional digits are required whenever a fractional part is specified, the regex could instead be:

^[0-9]{1,3}(?:\.[0-9]{3})?s$

Environment

• OS: Windows / WSL Ubuntu
• Terraform version (see terraform --version): OpenTofu v1.12.6
• Version of the STACKIT Terraform provider: 0.110.0

Additional information

The validation rule and the validation error message appear to be inconsistent.

The error message states:

The duration must be between 0s and 999.999s (e.g.: 1s or 0.100s or 12.345s)

Based on this description, values such as 1.000s should be valid because they are correctly formatted and fall within the specified range.