fix serializer throw at writing host prefix (smithy-lang#206)

Author: AllanZhengYP

smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/integration/HttpProtocolGeneratorUtils.java

@@ -380,7 +380,7 @@ static void writeHostPrefix(GenerationContext context, OperationShape operation)
         TypeScriptWriter writer = context.getWriter();
         SymbolProvider symbolProvider = context.getSymbolProvider();
         EndpointTrait trait = operation.getTrait(EndpointTrait.class).get();
-        writer.write("let resolvedHostname = (context.endpoint as any).hostname;");
+        writer.write("let { hostname: resolvedHostname } = await context.endpoint();");
         // Check if disableHostPrefixInjection has been set to true at runtime
         writer.openBlock("if (context.disableHostPrefix !== true) {", "}", () -> {
             writer.addImport("isValidHostname", "__isValidHostname",

smithy-typescript-codegen/src/test/java/software/amazon/smithy/typescript/codegen/integration/HttpProtocolGeneratorUtilsTest.java

@@ -64,7 +64,7 @@ public void writesCorrectHostPrefix() {
 
         OperationShape operation = (OperationShape) model.expectShape(ShapeId.from("smithy.example#GetFoo"));
         HttpProtocolGeneratorUtils.writeHostPrefix(mockContext, operation);
-        assertThat(writer.toString(), containsString("let resolvedHostname = (context.endpoint as any).hostname;"));
+        assertThat(writer.toString(), containsString("let { hostname: resolvedHostname } = await context.endpoint();"));
         assertThat(writer.toString(), containsString("if (context.disableHostPrefix !== true) {"));
         assertThat(writer.toString(), containsString("resolvedHostname = \"{foo}.data.\" + resolvedHostname;"));
         assertThat(writer.toString(), containsString("resolvedHostname = resolvedHostname.replace(\"{foo}\", input.foo)"));