Add GoSNMP logger (#1157)

Add a debug logging to calls to GoSNMP.
* Requires `--log.level=debug`.
* Enable with `--snmp.debug-packets` or `snmp_debug_packets=true` URL
  param.

Signed-off-by: SuperQ <superq@gmail.com>

Author: SuperQ

collector/collector.go

@@ -300,10 +300,22 @@ type Collector struct {
 	metrics     Metrics
 	concurrency int
 	snmpContext string
+	debugSNMP   bool
 }
 
-func New(ctx context.Context, target, authName, snmpContext string, auth *config.Auth, modules []*NamedModule, logger log.Logger, metrics Metrics, conc int) *Collector {
-	return &Collector{ctx: ctx, target: target, authName: authName, auth: auth, modules: modules, logger: logger, metrics: metrics, concurrency: conc, snmpContext: snmpContext}
+func New(ctx context.Context, target, authName, snmpContext string, auth *config.Auth, modules []*NamedModule, logger log.Logger, metrics Metrics, conc int, debugSNMP bool) *Collector {
+	return &Collector{
+		ctx:         ctx,
+		target:      target,
+		authName:    authName,
+		auth:        auth,
+		modules:     modules,
+		snmpContext: snmpContext,
+		logger:      log.With(logger, "source_address", *srcAddress),
+		metrics:     metrics,
+		concurrency: conc,
+		debugSNMP:   debugSNMP,
+	}
 }
 
 // Describe implements Prometheus.Collector.
@@ -420,7 +432,7 @@ func (c Collector) Collect(ch chan<- prometheus.Metric) {
 		go func(i int) {
 			defer wg.Done()
 			logger := log.With(c.logger, "worker", i)
-			client, err := scraper.NewGoSNMP(logger, c.target, *srcAddress)
+			client, err := scraper.NewGoSNMP(logger, c.target, *srcAddress, c.debugSNMP)
 			if err != nil {
 				level.Info(logger).Log("msg", err)
 				cancel()

main.go

@@ -49,6 +49,7 @@ var (
 	configFile    = kingpin.Flag("config.file", "Path to configuration file.").Default("snmp.yml").Strings()
 	dryRun        = kingpin.Flag("dry-run", "Only verify configuration is valid and exit.").Default("false").Bool()
 	concurrency   = kingpin.Flag("snmp.module-concurrency", "The number of modules to fetch concurrently per scrape").Default("1").Int()
+	debugSNMP     = kingpin.Flag("snmp.debug-packets", "Include a full debug trace of SNMP packet traffics.").Default("false").Bool()
 	expandEnvVars = kingpin.Flag("config.expand-environment-variables", "Expand environment variables to source secrets").Default("false").Bool()
 	metricsPath   = kingpin.Flag(
 		"web.telemetry-path",
@@ -86,6 +87,14 @@ const (
 func handler(w http.ResponseWriter, r *http.Request, logger log.Logger, exporterMetrics collector.Metrics) {
 	query := r.URL.Query()
 
+	debug := *debugSNMP
+	if query.Get("snmp_debug_packets") == "true" {
+		debug = true
+		// TODO: This doesn't work the way I want.
+		// logger = level.NewFilter(logger, level.AllowDebug())
+		level.Debug(logger).Log("msg", "Debug query param enabled")
+	}
+
 	target := query.Get("target")
 	if len(query["target"]) != 1 || target == "" {
 		http.Error(w, "'target' parameter must be specified once", http.StatusBadRequest)
@@ -149,7 +158,7 @@ func handler(w http.ResponseWriter, r *http.Request, logger log.Logger, exporter
 	sc.RUnlock()
 	logger = log.With(logger, "auth", authName, "target", target)
 	registry := prometheus.NewRegistry()
-	c := collector.New(r.Context(), target, authName, snmpContext, auth, nmodules, logger, exporterMetrics, *concurrency)
+	c := collector.New(r.Context(), target, authName, snmpContext, auth, nmodules, logger, exporterMetrics, *concurrency, debug)
 	registry.MustRegister(c)
 	// Delegate http serving to Prometheus client library, which will call collector.Collect.
 	h := promhttp.HandlerFor(registry, promhttp.HandlerOpts{})
@@ -200,7 +209,7 @@ func main() {
 		*concurrency = 1
 	}
 
-	level.Info(logger).Log("msg", "Starting snmp_exporter", "version", version.Info(), "concurrency", concurrency)
+	level.Info(logger).Log("msg", "Starting snmp_exporter", "version", version.Info(), "concurrency", concurrency, "debug_snmp", debugSNMP)
 	level.Info(logger).Log("build_context", version.BuildContext())
 
 	prometheus.MustRegister(versioncollector.NewCollector("snmp_exporter"))

scraper/gosnmp.go

@@ -16,6 +16,7 @@ package scraper
 import (
 	"context"
 	"fmt"
+	stdlog "log"
 	"net"
 	"strconv"
 	"strings"
@@ -31,7 +32,7 @@ type GoSNMPWrapper struct {
 	logger log.Logger
 }
 
-func NewGoSNMP(logger log.Logger, target, srcAddress string) (*GoSNMPWrapper, error) {
+func NewGoSNMP(logger log.Logger, target, srcAddress string, debug bool) (*GoSNMPWrapper, error) {
 	transport := "udp"
 	if s := strings.SplitN(target, "://", 2); len(s) == 2 {
 		transport = s[0]
@@ -52,6 +53,9 @@ func NewGoSNMP(logger log.Logger, target, srcAddress string) (*GoSNMPWrapper, er
 		Port:      port,
 		LocalAddr: srcAddress,
 	}
+	if debug {
+		g.Logger = gosnmp.NewLogger(stdlog.New(log.NewStdlibAdapter(level.Debug(logger)), "", 0))
+	}
 	return &GoSNMPWrapper{c: g, logger: logger}, nil
 }