Fix user agent to add business metrics at the end instead of prepend them

.changelog/c482c2c837a74c7e9082800b55a8bbf7.json

@@ -0,0 +1,8 @@
+{
+    "id": "c482c2c8-37a7-4c7e-9082-800b55a8bbf7",
+    "type": "bugfix",
+    "description": "Fix user agent to add business metrics at the end instead of prepend them",
+    "modules": [
+        "."
+    ]
+}

aws/middleware/user_agent.go

@@ -34,6 +34,9 @@ const (
 	FeatureMetadata2
 )
 
+// Hardcoded value to specify which version of the user agent we're using
+const uaMetadata = "ua/2.1"
+
 func (k SDKAgentKeyType) string() string {
 	switch k {
 	case APIMetadata:
@@ -107,6 +110,7 @@ type RequestUserAgent struct {
 func NewRequestUserAgent() *RequestUserAgent {
 	userAgent, sdkAgent := smithyhttp.NewUserAgentBuilder(), smithyhttp.NewUserAgentBuilder()
 	addProductName(userAgent)
+	addUserAgentMetadata(userAgent)
 	addProductName(sdkAgent)
 
 	r := &RequestUserAgent{
@@ -134,6 +138,10 @@ func addProductName(builder *smithyhttp.UserAgentBuilder) {
 	builder.AddKeyValue(aws.SDKName, aws.SDKVersion)
 }
 
+func addUserAgentMetadata(builder *smithyhttp.UserAgentBuilder) {
+	builder.AddKey(uaMetadata)
+}
+
 // AddUserAgentKey retrieves a requestUserAgent from the provided stack, or initializes one.
 func AddUserAgentKey(key string) func(*middleware.Stack) error {
 	return func(stack *middleware.Stack) error {
@@ -258,10 +266,10 @@ func (u *RequestUserAgent) HandleBuild(ctx context.Context, in middleware.BuildI
 
 func (u *RequestUserAgent) addHTTPUserAgent(request *smithyhttp.Request) {
 	const userAgent = "User-Agent"
-	updateHTTPHeader(request, userAgent, u.userAgent.Build())
 	if len(u.features) > 0 {
 		updateHTTPHeader(request, userAgent, buildFeatureMetrics(u.features))
 	}
+	updateHTTPHeader(request, userAgent, u.userAgent.Build())
 }
 
 func (u *RequestUserAgent) addHTTPSDKAgent(request *smithyhttp.Request) {

aws/middleware/user_agent_test.go

@@ -16,6 +16,7 @@ import (
 )
 
 var expectedAgent = aws.SDKName + "/" + aws.SDKVersion +
+	" ua/2.1" +
 	" os/" + getNormalizedOSName() +
 	" lang/go#" + strings.Map(rules, languageVersion) + // normalize as the user-agent builder will
 	" md/GOOS#" + runtime.GOOS +
@@ -251,15 +252,15 @@ func TestAddUserAgentFeature(t *testing.T) {
 			Features: []UserAgentFeature{
 				UserAgentFeatureWaiter,
 			},
-			Expect: "m/B " + expectedAgent,
+			Expect: expectedAgent + " " + "m/B",
 		},
 		"two": {
 			Features: []UserAgentFeature{
 				UserAgentFeatureRetryModeAdaptive, // ensure stable order, and idempotent
 				UserAgentFeatureRetryModeAdaptive,
 				UserAgentFeatureWaiter,
 			},
-			Expect: "m/B,F " + expectedAgent,
+			Expect: expectedAgent + " " + "m/B,F",
 		},
 	}
 
@@ -403,7 +404,7 @@ func TestAddSDKAgentKeyValue(t *testing.T) {
 				t.Fatalf("expect User-Agent to be present")
 			}
 			if ua[0] != c.Expect {
-				t.Errorf("User-Agent: %q != %q", c.Expect, ua[0])
+				t.Errorf("User-Agent: expected %q != actual %q", c.Expect, ua[0])
 			}
 		})
 	}