How Can I Efficiently Parse Prometheus Exposition Format Data Using Go\'s `expfmt` Package?

Parsing Prometheus Data: Leveraging expfmt Package for Effortless Parsing

The Prometheus exposition format (EBNF syntax) presents a challenge when parsing the metrices obtained through HTTP GET. This article will guide you through the process of parsing Prometheus data using the expfmt package, developed by the Prometheus authors themselves.

Leveraging expfmt

The expfmt package provides a reliable and efficient way to decode and encode Prometheus's Exposition Format. Its usage simplifies the parsing process significantly:

package main

import (
    expfmt "github.com/prometheus/common/expfmt"
    dto "github.com/prometheus/client_model/go"
    "fmt"
    "os"
)

func main() {
    // Parse the Prometheus data from a file
    mf, err := parseMF("path/to/file.txt")
    if err != nil {
        fmt.Println(err)
        return
    }

    // Iterate over the metric families
    for k, v := range mf {
        fmt.Printf("KEY: %s\n", k)
        fmt.Printf("VAL: %+v\n", v)
    }
}

func parseMF(path string) (map[string]*dto.MetricFamily, error) {
    reader, err := os.Open(path)
    if err != nil {
        return nil, err
    }
    defer reader.Close()

    // Use the expfmt parser to parse the data
    var parser expfmt.TextParser
    mf, err := parser.TextToMetricFamilies(reader)
    if err != nil {
        return nil, err
    }
    return mf, nil
}

Example Usage

# HELP net_conntrack_dialer_conn_attempted_total
# TYPE net_conntrack_dialer_conn_attempted_total untyped
net_conntrack_dialer_conn_attempted_total{dialer_name="federate",instance="localhost:9090",job="prometheus"} 1 1608520832877

Sample Output

KEY:  net_conntrack_dialer_conn_attempted_total
VAL:  name: "net_conntrack_dialer_conn_attempted_total" type: UNTYPED metric:<label: value:> label:<name: value:> label:<name: value:> untyped:<value:> timestamp_ms: 1608520832877 ></value:></name:></name:></label:>

Addressing Formatting Issues

It's important to ensure that the Prometheus data is formatted correctly. If you encounter a protocol error, verify that each line ends with a line-feed character (n), as required by the text protocol.

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