aws/endpoints: Fix SDK resolving endpoint without region (#420)

Fixes the SDK's endpoint resolve incorrectly resolving endpoints for a
service when the region is empty. Also fixes the SDK attempting to
resolve a service when the service value is empty.

Related to: aws/aws-sdk-go#2911

CHANGELOG_PENDING.md

@@ -9,4 +9,6 @@ SDK Enhancements
 
 SDK Bugs
 ---
-
+* `aws/endpoints`: aws/endpoints: Fix SDK resolving endpoint without region ([#420](https://github.com/aws/aws-sdk-go-v2/pull/420))
+  * Fixes the SDK's endpoint resolve incorrectly resolving endpoints for a service when the region is empty. Also fixes the SDK attempting to resolve a service when the service value is empty.
+  * Related to [aws/aws-sdk-go#2909](https://github.com/aws/aws-sdk-go/issues/2909)

aws/endpoints/v3model.go

@@ -74,16 +74,29 @@ func (p partition) canResolveEndpoint(service, region string, strictMatch bool)
 	return p.RegionRegex.MatchString(region)
 }
 
+var allowEmptyRegion = map[string]struct{}{
+	"ec2metadata": {},
+}
+
+func serviceRequiresRegion(service string) bool {
+	_, allowed := allowEmptyRegion[service]
+	return !allowed
+}
+
 func (p partition) EndpointFor(service, region string, opts ResolveOptions) (resolved aws.Endpoint, err error) {
 	s, hasService := p.Services[service]
-	if !hasService && opts.StrictMatching {
+	if len(service) == 0 || (!hasService && opts.StrictMatching) {
 		// Only return error if the resolver will not fallback to creating
 		// endpoint based on service endpoint ID passed in.
 		return resolved, NewUnknownServiceError(p.ID, service, serviceList(p.Services))
 	}
 
+	if len(region) == 0 && !serviceRequiresRegion(service) && len(s.PartitionEndpoint) != 0 {
+		region = s.PartitionEndpoint
+	}
+
 	e, hasEndpoint := s.endpointForRegion(region)
-	if !hasEndpoint && opts.StrictMatching {
+	if len(region) == 0 || (!hasEndpoint && opts.StrictMatching) {
 		return resolved, NewUnknownEndpointError(p.ID, service, region, endpointList(s.Endpoints))
 	}
 

aws/endpoints/v3model_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"reflect"
 	"regexp"
+	"strings"
 	"testing"
 )
 
@@ -522,3 +523,46 @@ func TestResolveEndpoint_AwsGlobal(t *testing.T) {
 		t.Errorf("expect the signing name to be derived")
 	}
 }
+
+func TestEndpointFor_EmptyRegion(t *testing.T) {
+	cases := map[string]struct {
+		Service    string
+		Region     string
+		RealRegion string
+		ExpectErr  string
+	}{
+		// Legacy services that previous accepted empty region
+		"ec2metadata": {Service: "ec2metadata", RealRegion: "aws-global"},
+
+		// Other services
+		"s3":           {Service: "s3", Region: "us-east-1", RealRegion: "us-east-1"},
+		"s3 no region": {Service: "s3", ExpectErr: "could not resolve endpoint"},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			actual, err := NewDefaultResolver().ResolveEndpoint(c.Service, c.Region)
+			if len(c.ExpectErr) != 0 {
+				if e, a := c.ExpectErr, err.Error(); !strings.Contains(a, e) {
+					t.Errorf("expect %q error in %q", e, a)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("expect no error got, %v", err)
+			}
+
+			expect, err := NewDefaultResolver().ResolveEndpoint(c.Service, c.RealRegion)
+			if err != nil {
+				t.Fatalf("failed to get endpoint for default resolver")
+			}
+			if e, a := expect.URL, actual.URL; e != a {
+				t.Errorf("expect %v URL, got %v", e, a)
+			}
+			if e, a := expect.SigningRegion, actual.SigningRegion; e != a {
+				t.Errorf("expect %v signing region, got %v", e, a)
+			}
+
+		})
+	}
+}

example/service/s3/mockPaginator/mockPaginator.go

@@ -5,6 +5,7 @@ package main
 import (
 	"context"
 	"fmt"
+	"log"
 	"os"
 
 	"github.com/aws/aws-sdk-go-v2/aws/external"
@@ -24,12 +25,15 @@ func main() {
 
 	bucket := os.Args[1]
 	svc := s3.New(cfg)
-	keys := getKeys(svc, bucket)
+	keys, err := getKeys(svc, bucket)
+	if err != nil {
+		log.Fatalf("failed to get keys, %v", err)
+	}
 
 	fmt.Printf("keys for bucket %q,\n%v\n", bucket, keys)
 }
 
-func getKeys(svc s3iface.ClientAPI, bucket string) []string {
+func getKeys(svc s3iface.ClientAPI, bucket string) ([]string, error) {
 	req := svc.ListObjectsRequest(&s3.ListObjectsInput{
 		Bucket: &bucket,
 	})
@@ -41,5 +45,9 @@ func getKeys(svc s3iface.ClientAPI, bucket string) []string {
 			keys = append(keys, *obj.Key)
 		}
 	}
-	return keys
+	if err := p.Err(); err != nil {
+		return nil, err
+	}
+
+	return keys, nil
 }

example/service/s3/mockPaginator/mockPaginator_test.go

@@ -72,10 +72,16 @@ func TestListObjectsPagination(t *testing.T) {
 		},
 	}
 
-	svc.Client = s3.New(defaults.Config())
+	cfg := defaults.Config()
+	cfg.Region = "us-west-2"
+
+	svc.Client = s3.New(cfg)
 	svc.objects = objects
 
-	keys := getKeys(svc, "foo")
+	keys, err := getKeys(svc, "foo")
+	if err != nil {
+		t.Fatalf("expect no error, got %v", err)
+	}
 	expected := []string{"1", "2", "3"}
 
 	if e, a := 3, len(keys); e != a {