How can we add our own timestamp in Prometheus metric series?

I'm trying to add my own timestamp instead of Prometheus's timestamp.

for ex:

node_value{endpoint="https",instance="xx.xx.xx.xx",job="prometheus,node="node1"}

489846 @1610014796.199

489933 @1610014826.199

Requirement: node_value(above) is a metric with two values and timestamp(Scrape timestamp added by prometheus), Instead of scrape timestamp I want to add my own timestamp which I'm fetching from third-party. Do we have the provision for that?

Note: I'm using golang prometheus client.

This is possible using NewMetricWithTimestamp provided in the prometheus golang client, but for exposing it, you have to do a little code.

At first, you have to write a new promehetus collector that implements Collector interface, then you provide your logic to set the custom timestamp for your metric.

Assume we are going to create a metric my_metric that has custom timestamp, using a collector called myCollector:

package main

import (
    "net/http"
    "time"

    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promhttp"
    "github.com/prometheus/common/log"
)

type myCollector struct {
    metric *prometheus.Desc
}

func (c *myCollector) Describe(ch chan<- *prometheus.Desc) {
    ch <- c.metric
}

func (c *myCollector) Collect(ch chan<- prometheus.Metric) {
    // your logic should be placed here

    t := time.Date(2009, time.November, 10, 23, 0, 0, 12345678, time.UTC)
    s := prometheus.NewMetricWithTimestamp(t, prometheus.MustNewConstMetric(c.metric, prometheus.CounterValue, 123))

    ch <- s
}

func main() {

    collector := &myCollector{
        metric: prometheus.NewDesc(
            "my_metric",
            "This is my metric with custom TS",
            nil,
            nil,
        ),
    }
    prometheus.MustRegister(collector)

    http.Handle("/metrics", promhttp.Handler())
    log.Info("Beginning to serve on port :8080")
    http.ListenAndServe(":2112", nil)
}

Now if you check the localhost:2112/metrics you saw this, with your desired timestamp:

.
.
.
# HELP my_metric This is my metric with custom TS
# TYPE my_metric counter
my_metric 123 1257894000012
.
.
.