feat: Support global endpoint in go natively

PiperOrigin-RevId: 738046161

Author: yinghsienwu

client.go

@@ -137,7 +137,11 @@ func NewClient(ctx context.Context, cc *ClientConfig) (*Client, error) {
 	}
 
 	if cc.HTTPOptions.BaseURL == "" && cc.Backend == BackendVertexAI {
-		cc.HTTPOptions.BaseURL = fmt.Sprintf("https://%s-aiplatform.googleapis.com/", cc.Location)
+		if cc.Location == "global" {
+			cc.HTTPOptions.BaseURL = "https://aiplatform.googleapis.com/"
+		} else {
+			cc.HTTPOptions.BaseURL = fmt.Sprintf("https://%s-aiplatform.googleapis.com/", cc.Location)
+		}
 	} else if cc.HTTPOptions.BaseURL == "" {
 		cc.HTTPOptions.BaseURL = "https://generativelanguage.googleapis.com/"
 	}

client_test.go

@@ -404,6 +404,18 @@ func TestClientConfigHTTPOptions(t *testing.T) {
 			expectedBaseURL:    "https://us-central1-aiplatform.googleapis.com/",
 			expectedAPIVersion: "v1beta1",
 		},
+		{
+			name: "Vertex AI Backend with global location",
+			clientConfig: ClientConfig{
+				Backend:     BackendVertexAI,
+				Project:     "test-project",
+				Location:    "global",
+				HTTPOptions: HTTPOptions{},
+				Credentials: &google.Credentials{},
+			},
+			expectedBaseURL:    "https://aiplatform.googleapis.com/",
+			expectedAPIVersion: "v1beta1",
+		},
 		{
 			name: "Google AI Backend with HTTP Client Timeout and no HTTPOptions",
 			clientConfig: ClientConfig{