Add 'endpoints.PartitionForRegion'.

endpoints/partition.go

@@ -4,6 +4,7 @@
 package endpoints
 
 import (
+	"maps"
 	"regexp"
 )
 
@@ -36,13 +37,39 @@ func (p Partition) RegionRegex() *regexp.Regexp {
 	return p.regionRegex
 }
 
+// Regions returns a map of Regions for the partition, indexed by their ID.
+func (p Partition) Regions() map[string]Region {
+	partitionAndRegion, ok := partitionsAndRegions[p.id]
+	if !ok {
+		return nil
+	}
+
+	return maps.Clone(partitionAndRegion.regions)
+}
+
 // DefaultPartitions returns a list of the partitions.
 func DefaultPartitions() []Partition {
-	partitions := make([]Partition, len(partitionsAndRegions))
+	ps := make([]Partition, len(partitionsAndRegions))
 
 	for _, v := range partitionsAndRegions {
-		partitions = append(partitions, v.partition)
+		ps = append(ps, v.partition)
+	}
+
+	return ps
+}
+
+// PartitionForRegion returns the first partition which includes the specific Region.
+func PartitionForRegion(ps []Partition, regionID string) (Partition, bool) {
+	for _, p := range ps {
+		partitionAndRegion, ok := partitionsAndRegions[p.id]
+		if !ok {
+			continue
+		}
+
+		if _, ok := partitionAndRegion.regions[regionID]; ok || partitionAndRegion.partition.regionRegex.MatchString(regionID) {
+			return p, true
+		}
 	}
 
-	return partitions
+	return Partition{}, false
 }

endpoints/partition_test.go

@@ -17,3 +17,41 @@ func TestDefaultPartitions(t *testing.T) {
 		t.Fatalf("expected partitions, got none")
 	}
 }
+
+func TestPartitionForRegion(t *testing.T) {
+	t.Parallel()
+
+	testcases := map[string]struct {
+		expectedFound bool
+		expectedID    string
+	}{
+		"us-east-1": {
+			expectedFound: true,
+			expectedID:    "aws",
+		},
+		"us-gov-west-1": {
+			expectedFound: true,
+			expectedID:    "aws-us-gov",
+		},
+		"not-found": {
+			expectedFound: false,
+		},
+		"us-east-17": {
+			expectedFound: true,
+			expectedID:    "aws",
+		},
+	}
+
+	ps := endpoints.DefaultPartitions()
+	for region, testcase := range testcases {
+		gotID, gotFound := endpoints.PartitionForRegion(ps, region)
+
+		if gotFound != testcase.expectedFound {
+			t.Errorf("expected PartitionFound %t for Region %q, got %t", testcase.expectedFound, region, gotFound)
+		}
+		if gotID.ID() != testcase.expectedID {
+			t.Errorf("expected PartitionID %q for Region %q, got %q", testcase.expectedID, region, gotID.ID())
+		}
+	}
+
+}