collector.go

package main

import (
	"fmt"
	"net"
	"strconv"
	"strings"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/common/log"
	"github.com/soniah/gosnmp"
)

var (
	snmpUnexpectedPduType = prometheus.NewCounter(
		prometheus.CounterOpts{
			Name: "snmp_unexpected_pdu_type_total",
			Help: "Unexpected Go types in a PDU.",
		},
	)
)

func init() {
	prometheus.MustRegister(snmpUnexpectedPduType)
}

func oidToList(oid string) []int {
	result := []int{}
	for _, x := range strings.Split(oid, ".") {
		o, _ := strconv.Atoi(x)
		result = append(result, o)
	}
	return result
}

func ScrapeTarget(target string, config *Module) ([]gosnmp.SnmpPDU, error) {
	// Set the options.
	snmp := gosnmp.GoSNMP{}
	snmp.Retries = 3
	snmp.MaxRepetitions = 25
	snmp.Timeout = time.Second * 60

	snmp.Target = target
	snmp.Port = 161
	if host, port, err := net.SplitHostPort(target); err == nil {
		snmp.Target = host
		p, err := strconv.Atoi(port)
		if err != nil {
			return nil, fmt.Errorf("Error converting port number to int for target %s: %s", target, err)
		}
		snmp.Port = uint16(p)
	}

	// Configure auth.
	config.configureSNMP(&snmp)

	// Do the actual walk.
	err := snmp.Connect()
	if err != nil {
		return nil, fmt.Errorf("Error connecting to target %s: %s", target, err)
	}
	defer snmp.Conn.Close()

	result := []gosnmp.SnmpPDU{}
	for _, subtree := range config.Walk {
		var pdus []gosnmp.SnmpPDU
		if snmp.Version == gosnmp.Version1 {
			pdus, err = snmp.WalkAll(subtree)
		} else {
			pdus, err = snmp.BulkWalkAll(subtree)
		}
		if err != nil {
			return nil, fmt.Errorf("Error walking target %s: %s", snmp.Target, err)
		}
		result = append(result, pdus...)
	}
	return result, nil
}

type MetricNode struct {
	metric *Metric

	children map[int]*MetricNode
}

// Build a tree of metrics from the config, for fast lookup when there's lots of them.
func buildMetricTree(metrics []*Metric) *MetricNode {
	metricTree := &MetricNode{children: map[int]*MetricNode{}}
	for _, metric := range metrics {
		head := metricTree
		for _, o := range oidToList(metric.Oid) {
			_, ok := head.children[o]
			if !ok {
				head.children[o] = &MetricNode{children: map[int]*MetricNode{}}
			}
			head = head.children[o]
		}
		head.metric = metric
	}
	return metricTree
}

type collector struct {
	target string
	module *Module
}

// Describe implements Prometheus.Collector.
func (c collector) Describe(ch chan<- *prometheus.Desc) {
	ch <- prometheus.NewDesc("dummy", "dummy", nil, nil)
}

// Collect implements Prometheus.Collector.
func (c collector) Collect(ch chan<- prometheus.Metric) {
	start := time.Now()
	pdus, err := ScrapeTarget(c.target, c.module)
	if err != nil {
		log.Errorf("Error scraping target %s: %s", c.target, err)
		ch <- prometheus.NewInvalidMetric(prometheus.NewDesc("snmp_error", "Error scraping target", nil, nil), err)
		return
	}
	ch <- prometheus.MustNewConstMetric(
		prometheus.NewDesc("snmp_scrape_walk_duration_seconds", "Time SNMP walk/bulkwalk took.", nil, nil),
		prometheus.GaugeValue,
		float64(time.Since(start).Seconds()))
	ch <- prometheus.MustNewConstMetric(
		prometheus.NewDesc("snmp_scrape_pdus_returned", "PDUs returned from walk.", nil, nil),
		prometheus.GaugeValue,
		float64(len(pdus)))
	oidToPdu := make(map[string]gosnmp.SnmpPDU, len(pdus))
	for _, pdu := range pdus {
		oidToPdu[pdu.Name[1:]] = pdu
	}

	metricTree := buildMetricTree(c.module.Metrics)
	// Look for metrics that match each pdu.
PduLoop:
	for oid, pdu := range oidToPdu {
		head := metricTree
		oidList := oidToList(oid)
		for i, o := range oidList {
			var ok bool
			head, ok = head.children[o]
			if !ok {
				continue PduLoop
			}
			if head.metric != nil {
				// Found a match.
				ch <- pduToSample(oidList[i+1:], &pdu, head.metric, oidToPdu)
				break
			}
		}
	}
	ch <- prometheus.MustNewConstMetric(
		prometheus.NewDesc("snmp_scrape_duration_seconds", "Total SNMP time scrape took (walk and processing).", nil, nil),
		prometheus.GaugeValue,
		float64(time.Since(start).Seconds()))
}

func pduToSample(indexOids []int, pdu *gosnmp.SnmpPDU, metric *Metric, oidToPdu map[string]gosnmp.SnmpPDU) prometheus.Metric {
	// The part of the OID that is the indexes.
	labels := indexesToLabels(indexOids, metric, oidToPdu)

	labelnames := make([]string, 0, len(labels))
	labelvalues := make([]string, 0, len(labels))
	for k, v := range labels {
		labelnames = append(labelnames, k)
		labelvalues = append(labelvalues, v)
	}
	return prometheus.MustNewConstMetric(prometheus.NewDesc(metric.Name, "", labelnames, nil),
		prometheus.UntypedValue,
		float64(gosnmp.ToBigInt(pdu.Value).Int64()),
		labelvalues...,
	)
}

// Right pad oid with zeros, and split at the given point.
// Some routers exclude trailing 0s in responses.
func splitOid(oid []int, count int) ([]int, []int) {
	head := make([]int, count)
	tail := []int{}
	for i, v := range oid {
		if i < count {
			head[i] = v
		} else {
			tail = append(tail, v)
		}
	}
	return head, tail
}

// This mirrors decodeValue in gosnmp's helper.go.
func pduValueAsString(pdu *gosnmp.SnmpPDU) string {
	switch pdu.Value.(type) {
	case int:
		return strconv.Itoa(pdu.Value.(int))
	case uint:
		return strconv.FormatUint(uint64(pdu.Value.(uint)), 10)
	case int64:
		return strconv.FormatInt(pdu.Value.(int64), 10)
	case string:
		if pdu.Type == gosnmp.ObjectIdentifier {
			// Trim leading period.
			return pdu.Value.(string)[1:]
		}
		return pdu.Value.(string)
	case []byte:
		// OctetString
		return string(pdu.Value.([]byte))
	case nil:
		return ""
	default:
		// This shouldn't happen.
		log.Infof("Got PDU with unexpected type: Name: %s Value: '%s', Go Type: %T SNMP Type: %s", pdu.Name, pdu.Value, pdu.Value, pdu.Type)
		snmpUnexpectedPduType.Inc()
		return fmt.Sprintf("%s", pdu.Value)
	}
}

func indexesToLabels(indexOids []int, metric *Metric, oidToPdu map[string]gosnmp.SnmpPDU) map[string]string {
	labels := map[string]string{}
	labelOids := map[string][]int{}

	// Covert indexes to useful strings.
	for _, index := range metric.Indexes {
		var subOid, content, addressType, octets, address []int
		switch index.Type {
		case "Integer32":
			// Extract the oid for this index, and keep the remainder for the next index.
			subOid, indexOids = splitOid(indexOids, 1)
			// Save its oid in case we need it for lookups.
			labelOids[index.Labelname] = subOid
			// The labelname is the text form of the index oids.
			labels[index.Labelname] = fmt.Sprintf("%d", subOid[0])
		case "PhysAddress48":
			subOid, indexOids = splitOid(indexOids, 6)
			labelOids[index.Labelname] = subOid
			parts := make([]string, 6)
			for i, o := range subOid {
				parts[i] = fmt.Sprintf("%02X", o)
			}
			labels[index.Labelname] = strings.Join(parts, ":")
		case "OctetString":
			subOid, indexOids = splitOid(indexOids, 1)
			length := subOid[0]
			content, indexOids = splitOid(indexOids, length)
			labelOids[index.Labelname] = append(subOid, content...)
			parts := make([]byte, length)
			for i, o := range content {
				parts[i] = byte(o)
			}
			labels[index.Labelname] = string(parts)
		case "InetAddress":
			addressType, indexOids = splitOid(indexOids, 1)
			octets, indexOids = splitOid(indexOids, 1)
			address, indexOids = splitOid(indexOids, octets[0])
			labelOids[index.Labelname] = append(addressType, octets...)
			labelOids[index.Labelname] = append(labelOids[index.Labelname], address...)
			if addressType[0] == 1 { // IPv4.
				parts := make([]string, 4)
				for i, o := range address {
					parts[i] = strconv.Itoa(o)
				}
				labels[index.Labelname] = strings.Join(parts, ".")
			} else if addressType[0] == 2 { // IPv6.
				parts := make([]string, 8)
				for i := 0; i < 8; i++ {
					parts[i] = fmt.Sprintf("%02X%02X", address[i*2], address[i*2+1])
				}
				labels[index.Labelname] = strings.Join(parts, ":")
			}
		case "IpAddress":
			subOid, indexOids = splitOid(indexOids, 4)
			labelOids[index.Labelname] = subOid
			parts := make([]string, 4)
			for i, o := range subOid {
				parts[i] = strconv.Itoa(o)
			}
			labels[index.Labelname] = strings.Join(parts, ".")
		case "InetAddressType":
			subOid, indexOids = splitOid(indexOids, 1)
			labelOids[index.Labelname] = subOid
			switch subOid[0] {
			case 0:
				labels[index.Labelname] = "unknown"
			case 1:
				labels[index.Labelname] = "ipv4"
			case 2:
				labels[index.Labelname] = "ipv6"
			case 3:
				labels[index.Labelname] = "ipv4z"
			case 4:
				labels[index.Labelname] = "ipv6z"
			case 16:
				labels[index.Labelname] = "dns"
			default:
				labels[index.Labelname] = strconv.Itoa(subOid[0])
			}
		}
	}

	// Perform lookups.
	for _, lookup := range metric.Lookups {
		oid := lookup.Oid
		for _, label := range lookup.Labels {
			for _, o := range labelOids[label] {
				oid = fmt.Sprintf("%s.%d", oid, o)
			}
		}
		if pdu, ok := oidToPdu[oid]; ok {
			labels[lookup.Labelname] = pduValueAsString(&pdu)
		}
	}

	return labels
}