for debugging, use a walk file to return fake results (#712)

cmd/ktranslate/main.go

@@ -696,6 +696,8 @@ func applyFlags(cfg *ktranslate.Config) error {
 					return
 				}
 				cfg.SNMPInput.ValidateMIBs = v
+			case "snmp_walk_file":
+				cfg.SNMPInput.RunFromWalkFile = val
 			// pkg/inputs/vpc/gcp
 			case "gcp.project":
 				cfg.GCPVPCInput.Enable = true

config.go

@@ -190,6 +190,7 @@ type SNMPInputConfig struct {
 	DiscoveryIntervalMinutes int
 	DiscoveryOnStart         bool
 	ValidateMIBs             bool
+	RunFromWalkFile          string
 	PollNowTarget            string
 }
 
@@ -491,6 +492,7 @@ func DefaultConfig() *Config {
 			DiscoveryIntervalMinutes: 0,
 			DiscoveryOnStart:         false,
 			ValidateMIBs:             false,
+			RunFromWalkFile:          "",
 		},
 		GCPVPCInput: &GCPVPCInputConfig{
 			Enable:     false,

pkg/inputs/snmp/snmp.go

@@ -30,17 +30,18 @@ var (
 	mibdb       *mibs.MibDB // Global singleton instance here.
 	ServiceName = ""
 
-	dumpMibTable   bool
-	flowOnly       bool
-	jsonToYaml     string
-	snmpWalk       string
-	snmpWalkOid    string
-	snmpWalkFormat string
-	snmpOutFile    string
-	snmpPollNow    string
-	snmpDiscoDur   int
-	snmpDiscoSt    bool
-	validateMib    bool
+	dumpMibTable    bool
+	flowOnly        bool
+	jsonToYaml      string
+	snmpWalk        string
+	snmpWalkOid     string
+	snmpWalkFormat  string
+	snmpOutFile     string
+	snmpPollNow     string
+	snmpDiscoDur    int
+	snmpDiscoSt     bool
+	validateMib     bool
+	runFromWalkFile string
 )
 
 func init() {
@@ -55,6 +56,7 @@ func init() {
 	flag.IntVar(&snmpDiscoDur, "snmp_discovery_min", 0, "If set, run snmp discovery on this interval (in minutes).")
 	flag.BoolVar(&snmpDiscoSt, "snmp_discovery_on_start", false, "If set, run snmp discovery on application start.")
 	flag.BoolVar(&validateMib, "snmp_validate", false, "If true, validate mib profiles and exit.")
+	flag.StringVar(&runFromWalkFile, "snmp_walk_file", "", "If set, use the walk file instead of polling.")
 }
 
 func StartSNMPPolls(ctx context.Context, jchfChan chan []*kt.JCHF, metrics *kt.SnmpMetricSet, registry go_metrics.Registry, apic *api.KentikApi, log logger.ContextL, cfg *ktranslate.SNMPInputConfig, resolv *resolv.Resolver, confMgr config.ConfigManager, logchan chan string) error {
@@ -73,6 +75,13 @@ func StartSNMPPolls(ctx context.Context, jchfChan chan []*kt.JCHF, metrics *kt.S
 		return snmp_util.DoWalk(v, cfg.WalkOID, cfg.WalkFormat, conf, connectTimeout, retries, log)
 	}
 
+	if v := cfg.RunFromWalkFile; v != "" { // If this flag is set, tell the util function to return responses based only on the walk.
+		err := snmp_util.LoadFromWalk(ctx, cfg.RunFromWalkFile, log)
+		if err != nil {
+			return err
+		}
+	}
+
 	// Load a mibdb if we have one.
 	if conf.Global != nil {
 		mdb, err := mibs.NewMibDB(conf.Global.MibDB, conf.Global.MibProfileDir, cfg.ValidateMIBs, log)

pkg/inputs/snmp/util/util.go

@@ -58,6 +58,8 @@ var (
 	TRUNCATE     = true
 	NO_TRUNCATE  = false
 	MAX_SNMP_LEN = 128
+
+	walkCacheMap map[string]gosnmp.SnmpPDU
 )
 
 func ReadOctetString(variable gosnmp.SnmpPDU, truncate bool) (string, bool) {
@@ -152,6 +154,11 @@ func WalkOID(ctx context.Context, device *kt.SnmpDeviceConfig, oid string, serve
 		tries = []pollTry{pollTry{walk: walker.WalkAll, sleep: time.Duration(0)}}
 	} else if device.NoUseBulkWalkAll { // If the device says to not use bulkwalkall, trim this out now.
 		tries = tries[1:]
+	} else if len(walkCacheMap) != 0 { // If we are using canned responses.
+		tries = []pollTry{
+			pollTry{walk: useCachedMap, sleep: time.Duration(0)},
+			pollTry{walk: server.BulkWalkAll, sleep: time.Duration(0)},
+			pollTry{walk: server.WalkAll, sleep: time.Duration(0)}}
 	}
 
 	var err error

pkg/inputs/snmp/util/walk.go

@@ -0,0 +1,73 @@
+package util
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/kentik/ktranslate/pkg/eggs/logger"
+
+	"github.com/gosnmp/gosnmp"
+)
+
+// Load a snmpwalk response from the given file and use it for debugging.
+func LoadFromWalk(ctx context.Context, file string, log logger.ContextL) error {
+	data, err := os.ReadFile(file)
+	if err != nil {
+		return err
+	}
+
+	res := map[string]gosnmp.SnmpPDU{}
+	for _, line := range strings.Split(string(data), "\n") {
+		pts := strings.SplitN(line, " = ", 2)
+		if len(pts) != 2 {
+			continue
+		}
+		oid := strings.TrimSpace(pts[0])
+		if oid[0:1] == "." { // Strip off leading dot.
+			oid = oid[1:]
+		}
+		pp := strings.SplitN(pts[1], ": ", 2)
+		if len(pp) != 2 {
+			continue
+		}
+		val := pp[1]
+
+		switch strings.ToLower(pp[0]) {
+		case "string":
+			res[oid] = gosnmp.SnmpPDU{Value: []byte(val), Type: gosnmp.OctetString, Name: oid}
+		case "integer":
+			res[oid] = gosnmp.SnmpPDU{Value: val, Type: gosnmp.Integer, Name: oid}
+		case "counter64":
+			res[oid] = gosnmp.SnmpPDU{Value: val, Type: gosnmp.Counter64, Name: oid}
+		case "counter32":
+			res[oid] = gosnmp.SnmpPDU{Value: val, Type: gosnmp.Counter32, Name: oid}
+		default:
+			log.Errorf("Skipping unknown walk type: %s", pp[0])
+		}
+	}
+
+	walkCacheMap = res
+	log.Infof("Loaded up %d entries to the walk cache map", len(res))
+
+	return nil
+}
+
+func useCachedMap(oid string) ([]gosnmp.SnmpPDU, error) {
+	res := []gosnmp.SnmpPDU{}
+
+	if oid[0:1] == "." { // Strip off leading dot.
+		oid = oid[1:]
+	}
+	for k, v := range walkCacheMap {
+		if strings.HasPrefix(k, oid) {
+			res = append(res, v)
+		}
+	}
+
+	if len(res) == 0 {
+		return nil, fmt.Errorf("Nothing to see")
+	}
+	return res, nil
+}