add loadoptions to configure BaseEndpoint

.changelog/024e7efafa274001b8677eb90bd32260.json

@@ -0,0 +1,8 @@
+{
+    "id": "024e7efa-fa27-4001-b867-7eb90bd32260",
+    "type": "feature",
+    "description": "Adds the LoadOptions hook `WithBaseEndpoint` for setting global endpoint override in-code.",
+    "modules": [
+        "config"
+    ]
+}

config/load_options.go

@@ -217,6 +217,10 @@ type LoadOptions struct {
 	S3DisableExpressAuth *bool
 
 	AccountIDEndpointMode aws.AccountIDEndpointMode
+
+	// Service endpoint override. This value is not necessarily final and is
+	// passed to the service's EndpointResolverV2 for further delegation.
+	BaseEndpoint string
 }
 
 func (o LoadOptions) getDefaultsMode(ctx context.Context) (aws.DefaultsMode, bool, error) {
@@ -284,6 +288,19 @@ func (o LoadOptions) getAccountIDEndpointMode(ctx context.Context) (aws.AccountI
 	return o.AccountIDEndpointMode, len(o.AccountIDEndpointMode) > 0, nil
 }
 
+func (o LoadOptions) getBaseEndpoint(context.Context) (string, bool, error) {
+	return o.BaseEndpoint, o.BaseEndpoint != "", nil
+}
+
+// GetServiceBaseEndpoint satisfies (internal/configsources).ServiceBaseEndpointProvider.
+//
+// The sdkID value is unused because LoadOptions only supports setting a GLOBAL
+// endpoint override. In-code, per-service endpoint overrides are performed via
+// functional options in service client space.
+func (o LoadOptions) GetServiceBaseEndpoint(context.Context, string) (string, bool, error) {
+	return o.BaseEndpoint, o.BaseEndpoint != "", nil
+}
+
 // WithRegion is a helper function to construct functional options
 // that sets Region on config's LoadOptions. Setting the region to
 // an empty string, will result in the region value being ignored.
@@ -1139,3 +1156,19 @@ func WithS3DisableExpressAuth(v bool) LoadOptionsFunc {
 		return nil
 	}
 }
+
+// WithBaseEndpoint is a helper function to construct functional options that
+// sets BaseEndpoint on config's LoadOptions. Empty values have no effect, and
+// subsequent calls to this API override previous ones.
+//
+// This is an in-code setting, therefore, any value set using this hook takes
+// precedence over and will override ALL environment and shared config
+// directives that set endpoint URLs. Functional options on service clients
+// have higher specificity, and functional options that modify the value of
+// BaseEndpoint on a client will take precedence over this setting.
+func WithBaseEndpoint(v string) LoadOptionsFunc {
+	return func(o *LoadOptions) error {
+		o.BaseEndpoint = v
+		return nil
+	}
+}

service/internal/integrationtest/s3/endpoint_url_test.go

@@ -0,0 +1,187 @@
+package main
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/config"
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+)
+
+// From the SEP:
+// Service-specific endpoint configuration MUST be resolved with an endpoint URL provider chain with the following precedence:
+//   - The value provided through code to an AWS SDK or tool via a command line
+//     parameter or a client or configuration constructor; for example the
+//     --endpoint-url command line parameter or the endpoint_url parameter
+//     provided to the Python SDK client.
+//   - The value provided by a service-specific environment variable.
+//   - The value provided by the global endpoint environment variable
+//     (AWS_ENDPOINT_URL).
+//   - The value provided by a service-specific parameter from a services
+//     definition section referenced in a profile in the shared configuration
+//     file.
+//   - The value provided by the global parameter from a profile in the shared
+//     configuration file.
+//   - The value resolved through the methods provided by the SDK or tool when
+//     no explicit endpoint URL is provided.
+
+func TestEndpointURL(t *testing.T) {
+	for name, tt := range map[string]struct {
+		Env          map[string]string
+		SharedConfig string
+		LoadOpts     []func(*config.LoadOptions) error
+		ClientOpts   []func(*s3.Options)
+		Expect       string
+	}{
+		"no values": {
+			SharedConfig: `
+[default]
+`,
+			Expect: "",
+		},
+
+		"precedence 0: in-code, set via s3.Options": {
+			Env: map[string]string{
+				"AWS_ENDPOINT_URL":    "https://global-env.com",
+				"AWS_ENDPOINT_URL_S3": "https://service-env.com",
+			},
+			SharedConfig: `
+[default]
+endpoint_url = https://global-cfg.com
+services = service_cfg
+
+[services service_cfg]
+s3 =
+  endpoint_url = https://service-cfg.com
+`,
+			LoadOpts: []func(*config.LoadOptions) error{
+				config.WithBaseEndpoint("https://loadopts.com"),
+			},
+			ClientOpts: []func(*s3.Options){
+				func(o *s3.Options) {
+					o.BaseEndpoint = aws.String("https://clientopts.com")
+				},
+			},
+			Expect: "https://clientopts.com",
+		},
+
+		"precedence 0: in-code, set via config.LoadOptions": {
+			Env: map[string]string{
+				"AWS_ENDPOINT_URL":    "https://global-env.com",
+				"AWS_ENDPOINT_URL_S3": "https://service-env.com",
+			},
+			SharedConfig: `
+			[default]
+			endpoint_url = https://global-cfg.com
+			services = service_cfg
+
+			[services service_cfg]
+			s3 =
+			  endpoint_url = https://service-cfg.com
+			`,
+			LoadOpts: []func(*config.LoadOptions) error{
+				config.WithBaseEndpoint("https://loadopts.com"),
+			},
+			Expect: "https://loadopts.com",
+		},
+
+		"precedence 1: service env": {
+			Env: map[string]string{
+				"AWS_ENDPOINT_URL":    "https://global-env.com",
+				"AWS_ENDPOINT_URL_S3": "https://service-env.com",
+			},
+			SharedConfig: `
+[default]
+endpoint_url = https://global-cfg.com
+services = service_cfg
+
+[services service_cfg]
+s3 =
+  endpoint_url = https://service-cfg.com
+`,
+			Expect: "https://service-env.com",
+		},
+
+		"precedence 2: global env": {
+			Env: map[string]string{
+				"AWS_ENDPOINT_URL": "https://global-env.com",
+			},
+			SharedConfig: `
+[default]
+endpoint_url = https://global-cfg.com
+services = service_cfg
+
+[services service_cfg]
+s3 =
+  endpoint_url = https://service-cfg.com
+`,
+			Expect: "https://global-env.com",
+		},
+
+		"precedence 3: service cfg": {
+			SharedConfig: `
+[default]
+endpoint_url = https://global-cfg.com
+services = service_cfg
+
+[services service_cfg]
+s3 =
+  endpoint_url = https://service-cfg.com
+`,
+			Expect: "https://service-cfg.com",
+		},
+
+		"precedence 4: global cfg": {
+			SharedConfig: `
+[default]
+endpoint_url = https://global-cfg.com
+`,
+			Expect: "https://global-cfg.com",
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			reset, err := mockEnvironment(tt.Env, tt.SharedConfig)
+			if err != nil {
+				t.Fatalf("mock environment: %v", err)
+			}
+			defer reset()
+
+			loadopts := append(tt.LoadOpts,
+				config.WithSharedConfigFiles([]string{"test_shared_config"}))
+			cfg, err := config.LoadDefaultConfig(context.Background(), loadopts...)
+			if err != nil {
+				t.Fatalf("load config: %v", err)
+			}
+
+			svc := s3.NewFromConfig(cfg, tt.ClientOpts...)
+			actual := aws.ToString(svc.Options().BaseEndpoint)
+			if tt.Expect != actual {
+				t.Errorf("expect endpoint: %q != %q", tt.Expect, actual)
+			}
+		})
+	}
+}
+
+func mockEnvironment(env map[string]string, sharedCfg string) (func(), error) {
+	for k, v := range env {
+		os.Setenv(k, v)
+	}
+	f, err := os.Create("test_shared_config")
+	if err != nil {
+		return nil, err
+	}
+	if _, err := f.Write([]byte(sharedCfg)); err != nil {
+		return nil, err
+	}
+
+	return func() {
+		for k := range env {
+			os.Unsetenv(k)
+		}
+		if err := os.Remove("test_shared_config"); err != nil {
+			panic(err)
+		}
+	}, nil
+}