Allow snmp_context to be passed as optional parameter to override the snmp.ContextName

Makefile.common

@@ -55,7 +55,7 @@ ifneq ($(shell which gotestsum),)
 endif
 endif
 
-PROMU_VERSION ?= 0.13.0
+PROMU_VERSION ?= 0.14.0
 PROMU_URL     := https://github.com/prometheus/promu/releases/download/v$(PROMU_VERSION)/promu-$(PROMU_VERSION).$(GO_BUILD_PLATFORM).tar.gz
 
 SKIP_GOLANGCI_LINT :=

collector/collector.go

@@ -115,7 +115,7 @@ type ScrapeResults struct {
 	retries uint64
 }
 
-func ScrapeTarget(ctx context.Context, target string, config *config.Module, logger log.Logger) (ScrapeResults, error) {
+func ScrapeTarget(ctx context.Context, target string, snmp_context string, config *config.Module, logger log.Logger) (ScrapeResults, error) {
 	results := ScrapeResults{}
 	// Set the options.
 	snmp := gosnmp.GoSNMP{}
@@ -158,7 +158,7 @@ func ScrapeTarget(ctx context.Context, target string, config *config.Module, log
 	}
 
 	// Configure auth.
-	config.WalkParams.ConfigureSNMP(&snmp)
+	config.WalkParams.ConfigureSNMP(&snmp, snmp_context)
 
 	// Do the actual walk.
 	err := snmp.Connect()
@@ -259,14 +259,15 @@ func buildMetricTree(metrics []*config.Metric) *MetricNode {
 }
 
 type collector struct {
-	ctx    context.Context
-	target string
-	module *config.Module
-	logger log.Logger
+	ctx          context.Context
+	target       string
+	snmp_context string
+	module       *config.Module
+	logger       log.Logger
 }
 
-func New(ctx context.Context, target string, module *config.Module, logger log.Logger) *collector {
-	return &collector{ctx: ctx, target: target, module: module, logger: logger}
+func New(ctx context.Context, target string, snmp_context string, module *config.Module, logger log.Logger) *collector {
+	return &collector{ctx: ctx, target: target, snmp_context: snmp_context, module: module, logger: logger}
 }
 
 // Describe implements Prometheus.Collector.
@@ -277,7 +278,7 @@ func (c collector) Describe(ch chan<- *prometheus.Desc) {
 // Collect implements Prometheus.Collector.
 func (c collector) Collect(ch chan<- prometheus.Metric) {
 	start := time.Now()
-	results, err := ScrapeTarget(c.ctx, c.target, c.module, c.logger)
+	results, err := ScrapeTarget(c.ctx, c.target, c.snmp_context, c.module, c.logger)
 	if err != nil {
 		level.Info(c.logger).Log("msg", "Error scraping target", "err", err)
 		ch <- prometheus.NewInvalidMetric(prometheus.NewDesc("snmp_error", "Error scraping target", nil, nil), err)

config/config.go

@@ -125,7 +125,7 @@ func (c *Module) UnmarshalYAML(unmarshal func(interface{}) error) error {
 }
 
 // ConfigureSNMP sets the various version and auth settings.
-func (c WalkParams) ConfigureSNMP(g *gosnmp.GoSNMP) {
+func (c WalkParams) ConfigureSNMP(g *gosnmp.GoSNMP, snmp_context string) {
 	switch c.Version {
 	case 1:
 		g.Version = gosnmp.Version1
@@ -135,8 +135,11 @@ func (c WalkParams) ConfigureSNMP(g *gosnmp.GoSNMP) {
 		g.Version = gosnmp.Version3
 	}
 	g.Community = string(c.Auth.Community)
-	g.ContextName = c.Auth.ContextName
-
+	if snmp_context == "" {
+		g.ContextName = c.Auth.ContextName
+	} else {
+		g.ContextName = snmp_context
+	}
 	// v3 security settings.
 	g.SecurityModel = gosnmp.UserSecurityModel
 	usm := &gosnmp.UsmSecurityParameters{

main.go

@@ -84,6 +84,14 @@ func handler(w http.ResponseWriter, r *http.Request, logger log.Logger) {
 	if moduleName == "" {
 		moduleName = "if_mib"
 	}
+
+	snmp_context := query.Get("snmp_context")
+	if len(query["snmp_context"]) > 1 {
+		http.Error(w, "'snmp_context' parameter must only be specified once", 400)
+		snmpRequestErrors.Inc()
+		return
+	}
+
 	sc.RLock()
 	module, ok := (*(sc.C))[moduleName]
 	sc.RUnlock()
@@ -98,7 +106,7 @@ func handler(w http.ResponseWriter, r *http.Request, logger log.Logger) {
 
 	start := time.Now()
 	registry := prometheus.NewRegistry()
-	c := collector.New(r.Context(), target, module, logger)
+	c := collector.New(r.Context(), target, snmp_context, module, logger)
 	registry.MustRegister(c)
 	// Delegate http serving to Prometheus client library, which will call collector.Collect.
 	h := promhttp.HandlerFor(registry, promhttp.HandlerOpts{})