common/helpers: make subnetmap work with struct as values

The way it was converted from a mapstruct made it not possible to have
struct as values. Fix that by checking if keys look like IP or not.

common/helpers/subnetmap.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net"
 	"reflect"
+	"regexp"
 	"strings"
 
 	"github.com/kentik/patricia"
@@ -77,6 +78,8 @@ func MustNewSubnetMap[V any](from map[string]V) *SubnetMap[V] {
 	return trie
 }
 
+var subnetLookAlikeRegex = regexp.MustCompile("^([a-fA-F:.0-9]+)(/([0-9]+))?$")
+
 // SubnetMapUnmarshallerHook decodes SubnetMap and notably check that
 // valid networks are provided as key. It also accepts a single value
 // instead of a map for backward compatibility.
@@ -87,7 +90,23 @@ func SubnetMapUnmarshallerHook[V any]() mapstructure.DecodeHookFunc {
 		}
 		output := map[string]interface{}{}
 		var zero V
+		var plausibleSubnetMap bool
 		if from.Kind() == reflect.Map {
+			// When we have a map, we check if all keys look like a subnet.
+			plausibleSubnetMap = true
+			for _, key := range from.MapKeys() {
+				key = ElemOrIdentity(key)
+				if key.Kind() != reflect.String {
+					plausibleSubnetMap = false
+					break
+				}
+				if !subnetLookAlikeRegex.MatchString(key.String()) {
+					plausibleSubnetMap = false
+					break
+				}
+			}
+		}
+		if plausibleSubnetMap {
 			// First case, we have a map
 			iter := from.MapRange()
 			for i := 0; iter.Next(); i++ {
@@ -130,11 +149,9 @@ func SubnetMapUnmarshallerHook[V any]() mapstructure.DecodeHookFunc {
 				}
 				output[key] = v.Interface()
 			}
-		} else if from.Type() == reflect.TypeOf(zero) || from.Type().ConvertibleTo(reflect.TypeOf(zero)) {
-			// Second case, we have a single value
-			output["::/0"] = from.Interface()
 		} else {
-			return from.Interface(), nil
+			// Second case, we have a single value and we let mapstructure handles it
+			output["::/0"] = from.Interface()
 		}
 
 		// We have to decode output map, then turn it into a SubnetMap[V]
@@ -164,5 +181,5 @@ func (sm SubnetMap[V]) MarshalYAML() (interface{}, error) {
 
 func (sm SubnetMap[V]) String() string {
 	out := sm.ToMap()
-	return fmt.Sprintf("%v", out)
+	return fmt.Sprintf("%+v", out)
 }

common/helpers/subnetmap_test.go

@@ -97,6 +97,10 @@ func TestSubnetMapUnmarshalHook(t *testing.T) {
 			Description: "Invalid IP",
 			Input:       gin.H{"200.33.300.1": "customer"},
 			Error:       true,
+		}, {
+			Description: "Random key",
+			Input:       gin.H{"kfgdjgkfj": "customer"},
+			Error:       true,
 		}, {
 			Description: "Single value",
 			Input:       "customer",
@@ -158,3 +162,72 @@ func TestSubnetMapUnmarshalHook(t *testing.T) {
 		})
 	}
 }
+
+func TestSubnetMapUnmarshalHookWithMapValue(t *testing.T) {
+	type SomeStruct struct {
+		Blip string
+		Blop string
+	}
+	cases := []struct {
+		Description string
+		Input       gin.H
+		Expected    gin.H
+	}{
+		{
+			Description: "single value",
+			Input: gin.H{
+				"blip": "some",
+				"blop": "thing",
+			},
+			Expected: gin.H{
+				"::/0": gin.H{
+					"Blip": "some",
+					"Blop": "thing",
+				},
+			},
+		}, {
+			Description: "proper map",
+			Input: gin.H{
+				"::/0": gin.H{
+					"blip": "some",
+					"blop": "thing",
+				},
+				"203.0.113.14": gin.H{
+					"blip": "other",
+					"blop": "stuff",
+				},
+			},
+			Expected: gin.H{
+				"::/0": gin.H{
+					"Blip": "some",
+					"Blop": "thing",
+				},
+				"203.0.113.14/32": gin.H{
+					"Blip": "other",
+					"Blop": "stuff",
+				},
+			},
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.Description, func(t *testing.T) {
+			var tree helpers.SubnetMap[SomeStruct]
+			decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
+				Result:      &tree,
+				ErrorUnused: true,
+				Metadata:    nil,
+				DecodeHook:  helpers.SubnetMapUnmarshallerHook[SomeStruct](),
+			})
+			if err != nil {
+				t.Fatalf("NewDecoder() error:\n%+v", err)
+			}
+			err = decoder.Decode(tc.Input)
+			if err != nil {
+				t.Fatalf("Decode() error:\n%+v", err)
+			}
+			if diff := helpers.Diff(tree.ToMap(), tc.Expected); diff != "" {
+				t.Fatalf("Decode() (-got, +want):\n%s", diff)
+			}
+		})
+	}
+}