Rego Built-in Function: time.format

time.format is Rego's built-in function that takes a time in nanoseconds since the Unix epoch and formats it as a string. This is useful for displaying timestamps in a human-readable format and presenting times in a given timezone.

The function accepts arguments in three formats, making it slightly more complicated to use. These are either:

A single value representing the nanoseconds since the Unix epoch

time.format(1720021249361794300)
time.format(1712345679361794300)

A two-element array consisting of:

The number of nanoseconds since the Unix epoch
A timezone (TZ identifier)

# Using a named timezone identifier
time.format([1720021249361794300, "Europe/Paris"])
# Using a timezone code
time.format([1720021249361794300, "PDT"])

A three-element array consisting of:

The number of nanoseconds since the Unix epoch
A timezone (TZ identifier)
Golang time layout string or formatting constant, see time package documentation.

# Using time format constant
time.format([1720021249361794300, "Europe/Paris", "RFC822Z"])
# Using a custom time layout string
time.format([1720021249361794300, "Europe/Paris", "2006_01_02_15_04_05"])

Examples

Show the local time in a response

time.format can be used to provide information to the user in a human-readable format in error messages. Error codes and local times can be useful when debugging or troubleshooting and so in many cases returning them from policy decisions can be helpful.

In this example we see a user is not an admin and is denied access, the policy response is a message that includes the current time and an error code to help them debug.

policy.rego
package play

import rego.v1

request_time := time.parse_ns(
	"RFC822Z",
	input.request_utc_time,
)

local_time := time.format([
	request_time,
	input.tz,
	"15:04:05",
])

default allow := false

allow if count(reasons) == 0

reasons contains message if {
	input.role != "admin"
	message := sprintf("E123 %s", [local_time])
}

input.json
{
  "user": "yamada-hanako@example.com",
  "tz": "Asia/Tokyo",
  "role": "developer",
  "request_utc_time": "03 Jul 24 14:04 +0000"
}

data.json

{}

Open in OPA Playground

Rule	Output Value	Notes
allow	`false`	The user is not an admin
reasons	`["E123 23:04:00"]`	This contains the error code and the local time

Examples​

Show the local time in a response

Examples