Simplify Service Client Configuration Resolving (#478)

Author: skmcgrail

aws/config.go

@@ -79,15 +79,9 @@ type Config struct {
 	// for testing that do not support the modeled host prefix pattern.
 	DisableEndpointHostPrefix bool
 
-	// ConfigResolver defines how additional configuration can be loaded by clients.
-	AdditionalConfig ConfigResolver
-}
-
-// ConfigResolver is an interface that encapsulates the behavior of loading
-// additional configuration.
-type ConfigResolver interface {
-	// ResolveConfig calls the provide function passing a slice of configuration sources
-	ResolveConfig(func(configs []interface{}) error) error
+	// ConfigSources are the sources that were used to construct the Config.
+	// Allows for additional configuration can be loaded by clients.
+	ConfigSources []interface{}
 }
 
 // NewConfig returns a new Config pointer that can be chained with builder

aws/external/config.go

@@ -97,6 +97,12 @@ func (cs Configs) ResolveAWSConfig(resolvers []AWSConfigResolver) (aws.Config, e
 		}
 	}
 
+	var sources []interface{}
+	for _, s := range cs {
+		sources = append(sources, s)
+	}
+	cfg.ConfigSources = sources
+
 	return cfg, nil
 }
 

aws/external/config_test.go

@@ -76,13 +76,15 @@ func TestConfigs_AppendFromLoaders(t *testing.T) {
 }
 
 func TestConfigs_ResolveAWSConfig(t *testing.T) {
-	cfg, err := Configs{
+	configSources := Configs{
 		WithRegion("mock-region"),
 		WithCredentialsValue(aws.Credentials{
 			AccessKeyID: "AKID", SecretAccessKey: "SECRET",
 			Source: "provider",
 		}),
-	}.ResolveAWSConfig([]AWSConfigResolver{
+	}
+
+	cfg, err := configSources.ResolveAWSConfig([]AWSConfigResolver{
 		ResolveRegion,
 		ResolveCredentialsValue,
 	})
@@ -101,4 +103,13 @@ func TestConfigs_ResolveAWSConfig(t *testing.T) {
 	if e, a := "provider", creds.Source; e != a {
 		t.Errorf("expect %v provider, got %v", e, a)
 	}
+
+	var expectedSources []interface{}
+	for _, s := range cfg.ConfigSources {
+		expectedSources = append(expectedSources, s)
+	}
+
+	if e, a := expectedSources, cfg.ConfigSources; !reflect.DeepEqual(e, a) {
+		t.Errorf("expected %v, got %v", e, a)
+	}
 }

private/model/api/api.go

@@ -699,10 +699,8 @@ func New(config aws.Config) *{{ .StructName }} {
     }
 
 	{{ if .HasExternalClientConfigFields }}
-		if config.AdditionalConfig != nil {
-			if err := config.AdditionalConfig.ResolveConfig(resolveClientConfig(svc)); err != nil {
-				panic(fmt.Errorf("failed to resolve service configuration: %v", err))
-			}
+		if err := resolveClientConfig(svc, config.ConfigSources); err != nil {
+			panic(fmt.Errorf("failed to resolve service configuration: %v", err))
 		}
 	{{- end }}
 
@@ -1130,18 +1128,20 @@ func (a *API) hasNonIOShapes() bool {
 var tplClientConfig = template.Must(template.New("tplClientConfig").Funcs(map[string]interface{}{
 	"ExternalConfigFields": externalConfigFields,
 }).Parse(`
-func resolveClientConfig(svc *{{ .StructName }}) func(configs []interface{}) error {
-	return func(configs []interface{}) error {
-		{{- $fields := ExternalConfigFields . -}}
-		{{- range $idx, $field := $fields }}
-			if value, ok, err := {{ $.InternalConfigResolverPackageName }}.{{ $field.ExternalConfigResolverName }}(configs); err != nil {
-				return err
-			} else if ok {
-				svc.{{ $field.Name }} = value
-			}
-		{{ end }}
+func resolveClientConfig(svc *{{ .StructName }}, configs []interface{}) error {
+	if len(configs) == 0 {
 		return nil
 	}
+
+	{{ $fields := ExternalConfigFields . -}}
+	{{- range $idx, $field := $fields }}
+		if value, ok, err := {{ $.InternalConfigResolverPackageName }}.{{ $field.ExternalConfigResolverName }}(configs); err != nil {
+			return err
+		} else if ok {
+			svc.{{ $field.Name }} = value
+		}
+	{{ end }}
+	return nil
 }
 `))
 
@@ -1188,7 +1188,7 @@ func TestExternalConfigResolver(t *testing.T) {
 	t.Run("{{ $field.Name }}", func(t *testing.T) {
 		t.Run("value not found", func(t *testing.T) {
 			svc := &{{ $.StructName }}{}
-			err := resolveClientConfig(svc)([]interface{}{
+			err := resolveClientConfig(svc, []interface{}{
 				mock{{ $field.Name }}(func() (value {{ $field.Type }}, ok bool, err error) {
 					return value, ok, err
 				}),
@@ -1202,7 +1202,7 @@ func TestExternalConfigResolver(t *testing.T) {
 		})
 		t.Run("resolve error", func(t *testing.T) {
 			svc := &{{ $.StructName }}{}
-			err := resolveClientConfig(svc)([]interface{}{
+			err := resolveClientConfig(svc, []interface{}{
 				mock{{ $field.Name }}(func() (value {{ $field.Type }}, ok bool, err error) {
 					err = fmt.Errorf("resolve error")
 					return value, ok, err
@@ -1218,7 +1218,7 @@ func TestExternalConfigResolver(t *testing.T) {
 		t.Run("value found", func(t *testing.T) {
 			{{- $mockValue := MockConfigFieldValue $field -}}
 			svc := &{{ $.StructName }}{}
-			err := resolveClientConfig(svc)([]interface{}{
+			err := resolveClientConfig(svc, []interface{}{
 				mock{{ $field.Name }}(func() (value {{ $field.Type }}, ok bool, err error) {
 					value = {{ $mockValue }}
 					return value, true, err