outlet/core: accept flows where interface names are missing

This matches the pre-2.0.0 behavior. This may not be a bug, but the idea
is that one interface is enough to be valid. Some implementations seem
to use bogus indexes.

See https://github.com/akvorado/akvorado/discussions/1998#discussioncomment-14992940

console/data/docs/99-changelog.md

@@ -17,6 +17,7 @@ identified with a specific icon:
   false by default)
 - 🩹 *outlet*: provide additional gracetime for a worker to send to ClickHouse
 - 🩹 *outlet*: enhance scaling up and down workers to avoid hysteresis
+- 🩹 *outlet*: accept flows where interface names or descriptions are missing
 - 🩹 *docker*: update Traefik to 3.6.1 (for compatibility with Docker Engine 29)
 - 🌱 *common*: enable block and mutex profiling
 - 🌱 *config*: rename `verify` to `skip-verify` in TLS configurations for

outlet/core/enricher.go

@@ -38,10 +38,7 @@ func (w *worker) enrichFlow(exporterIP netip.Addr, exporterStr string) bool {
 
 	if flow.InIf != 0 {
 		answer := c.d.Metadata.Lookup(t, exporterIP, uint(flow.InIf))
-		if !answer.Found {
-			c.metrics.flowsErrors.WithLabelValues(exporterStr, "metadata cache miss").Inc()
-			skip = true
-		} else {
+		if answer.Found {
 			flowExporterName = answer.Exporter.Name
 			expClassification.Region = answer.Exporter.Region
 			expClassification.Role = answer.Exporter.Role
@@ -61,14 +58,7 @@ func (w *worker) enrichFlow(exporterIP netip.Addr, exporterStr string) bool {
 
 	if flow.OutIf != 0 {
 		answer := c.d.Metadata.Lookup(t, exporterIP, uint(flow.OutIf))
-		if !answer.Found {
-			// Only register a cache miss if we don't have one.
-			// TODO: maybe we could do one SNMP query for both interfaces.
-			if !skip {
-				c.metrics.flowsErrors.WithLabelValues(exporterStr, "metadata cache miss").Inc()
-				skip = true
-			}
-		} else {
+		if answer.Found {
 			flowExporterName = answer.Exporter.Name
 			expClassification.Region = answer.Exporter.Region
 			expClassification.Role = answer.Exporter.Role
@@ -90,6 +80,9 @@ func (w *worker) enrichFlow(exporterIP netip.Addr, exporterStr string) bool {
 	if flow.OutIf == 0 && flow.InIf == 0 {
 		c.metrics.flowsErrors.WithLabelValues(exporterStr, "input and output interfaces missing").Inc()
 		skip = true
+	} else if flowExporterName == "" {
+		c.metrics.flowsErrors.WithLabelValues(exporterStr, "metadata cache miss").Inc()
+		skip = true
 	}
 
 	if samplingRate, ok := c.config.OverrideSamplingRate.Lookup(exporterIP); ok && samplingRate > 0 {

outlet/core/enricher_test.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"encoding/gob"
 	"fmt"
+	"maps"
 	"net/netip"
 	"sync"
 	"testing"
@@ -35,6 +36,7 @@ func TestEnrich(t *testing.T) {
 		Configuration   gin.H
 		InputFlow       func() *schema.FlowMessage
 		OutputFlow      *schema.FlowMessage
+		ExpectedMetrics map[string]string
 	}{
 		{
 			Name:          "no rule",
@@ -583,6 +585,38 @@ ClassifyProviderRegex(Interface.Description, "^Transit: ([^ ]+)", "$1")`,
 				},
 			},
 		},
+		{
+			Name:          "flow with missing interfaces",
+			Configuration: gin.H{},
+			InputFlow: func() *schema.FlowMessage {
+				return &schema.FlowMessage{
+					SamplingRate:    1000,
+					ExporterAddress: netip.MustParseAddr("::ffff:192.0.2.142"),
+					InIf:            0,
+					OutIf:           0,
+				}
+			},
+			OutputFlow: nil,
+			ExpectedMetrics: map[string]string{
+				`flows_errors_total{error="input and output interfaces missing",exporter="192.0.2.142"}`: "1",
+			},
+		},
+		{
+			Name:          "flow with metadata cache miss",
+			Configuration: gin.H{},
+			InputFlow: func() *schema.FlowMessage {
+				return &schema.FlowMessage{
+					SamplingRate:    1000,
+					ExporterAddress: netip.MustParseAddr("::ffff:192.0.2.142"),
+					InIf:            999,
+					OutIf:           0,
+				}
+			},
+			OutputFlow: nil,
+			ExpectedMetrics: map[string]string{
+				`flows_errors_total{error="metadata cache miss",exporter="192.0.2.142"}`: "1",
+			},
+		},
 	}
 	for _, tc := range cases {
 		t.Run(tc.Name, func(t *testing.T) {
@@ -684,6 +718,7 @@ ClassifyProviderRegex(Interface.Description, "^Transit: ([^ ]+)", "$1")`,
 			if tc.OutputFlow != nil {
 				expectedMetrics[`forwarded_flows_total{exporter="192.0.2.142"}`] = "1"
 			}
+			maps.Copy(expectedMetrics, tc.ExpectedMetrics)
 			if diff := helpers.Diff(gotMetrics, expectedMetrics); diff != "" {
 				t.Fatalf("Metrics (-got, +want):\n%s", diff)
 			}