make handler cache configurable

.changeset/tall-cameras-reply.md

@@ -1,5 +1,4 @@
 ---
-"@smithy/middleware-stack": minor
 "@smithy/smithy-client": minor
 ---
 

packages/middleware-stack/src/MiddlewareStack.ts

@@ -32,14 +32,7 @@ const getMiddlewareNameWithAliases = (name: string | undefined, aliases: Array<s
   return `${name || "anonymous"}${aliases && aliases.length > 0 ? ` (a.k.a. ${aliases.join(",")})` : ""}`;
 };
 
-export const constructStack = <Input extends object, Output extends object>(
-  stackOptions: {
-    /**
-     * Optional change listener, called with stack instance when middleware added/removed.
-     */
-    onChange?: (middlewareStack: MiddlewareStack<any, any>) => void;
-  } = {}
-): MiddlewareStack<Input, Output> => {
+export const constructStack = <Input extends object, Output extends object>(): MiddlewareStack<Input, Output> => {
   let absoluteEntries: AbsoluteMiddlewareEntry<Input, Output>[] = [];
   let relativeEntries: RelativeMiddlewareEntry<Input, Output>[] = [];
   let identifyOnResolve = false;
@@ -229,7 +222,6 @@ export const constructStack = <Input extends object, Output extends object>(
         }
       }
       absoluteEntries.push(entry);
-      stackOptions.onChange?.(stack);
     },
 
     addRelativeTo: (middleware: MiddlewareType<Input, Output>, options: HandlerOptions & RelativeLocation) => {
@@ -266,7 +258,6 @@ export const constructStack = <Input extends object, Output extends object>(
         }
       }
       relativeEntries.push(entry);
-      stackOptions.onChange?.(stack);
     },
 
     clone: () => cloneTo(constructStack<Input, Output>()),
@@ -276,14 +267,8 @@ export const constructStack = <Input extends object, Output extends object>(
     },
 
     remove: (toRemove: MiddlewareType<Input, Output> | string): boolean => {
-      let isRemoved: boolean;
-      if (typeof toRemove === "string") {
-        isRemoved = removeByName(toRemove);
-      } else {
-        isRemoved = removeByReference(toRemove);
-      }
-      stackOptions.onChange?.(stack);
-      return isRemoved;
+      if (typeof toRemove === "string") return removeByName(toRemove);
+      else return removeByReference(toRemove);
     },
 
     removeByTag: (toRemove: string): boolean => {
@@ -302,7 +287,6 @@ export const constructStack = <Input extends object, Output extends object>(
       };
       absoluteEntries = absoluteEntries.filter(filterCb);
       relativeEntries = relativeEntries.filter(filterCb);
-      stackOptions?.onChange?.(stack);
       return isRemoved;
     },
 

packages/smithy-client/src/client.spec.ts

@@ -9,7 +9,7 @@ describe("SmithyClient", () => {
   const getCommandWithOutput = (output: string) => ({
     resolveMiddleware: mockResolveMiddleware,
   });
-  const client = new Client({} as any);
+  const client = new Client({ cacheMiddleware: true } as any);
 
   beforeEach(() => {
     jest.clearAllMocks();
@@ -67,11 +67,5 @@ describe("SmithyClient", () => {
       await expect(client.send(getCommandWithOutput("foo") as any, {})).resolves.toEqual("foo");
       expect(privateAccess()).toBeUndefined();
     });
-
-    it("should clear the handler cache when the middleareStack is modified", async () => {
-      await expect(client.send(getCommandWithOutput("foo") as any)).resolves.toEqual("foo");
-      client.middlewareStack.add((n) => (a) => n(a));
-      expect(privateAccess()).toBeUndefined();
-    });
   });
 });

packages/smithy-client/src/client.ts

@@ -25,6 +25,22 @@ export interface SmithyConfiguration<HandlerOptions> {
    * @internal
    */
   readonly apiVersion: string;
+  /**
+   * @public
+   *
+   * Default false.
+   *
+   * When true, the client will only resolve the middleware stack once per
+   * Command class. This means modifying the middlewareStack of the
+   * command or client after requests have been made will not be
+   * recognized.
+   *
+   * Calling client.destroy() also clears this cache.
+   *
+   * Enable this only if needing the additional time saved (0-1ms per request)
+   * and not needing middleware modifications between requests.
+   */
+  cacheMiddleware?: boolean;
 }
 
 /**
@@ -33,6 +49,7 @@ export interface SmithyConfiguration<HandlerOptions> {
 export type SmithyResolvedConfiguration<HandlerOptions> = {
   requestHandler: RequestHandler<any, any, HandlerOptions>;
   readonly apiVersion: string;
+  cacheMiddleware?: boolean;
 };
 
 /**
@@ -45,20 +62,13 @@ export class Client<
   ResolvedClientConfiguration extends SmithyResolvedConfiguration<HandlerOptions>,
 > implements IClient<ClientInput, ClientOutput, ResolvedClientConfiguration>
 {
-  public middlewareStack: MiddlewareStack<ClientInput, ClientOutput> = constructStack<ClientInput, ClientOutput>({
-    onChange: () => {
-      delete this.handlers;
-    },
-  });
+  public middlewareStack: MiddlewareStack<ClientInput, ClientOutput> = constructStack<ClientInput, ClientOutput>();
   /**
    * May be used to cache the resolved handler function for a Command class.
    */
   private handlers?: WeakMap<Function, Handler<any, any>> | undefined;
-  private configRef?: ResolvedClientConfiguration | undefined;
 
-  constructor(public readonly config: ResolvedClientConfiguration) {
-    this.configRef = this.config;
-  }
+  constructor(public readonly config: ResolvedClientConfiguration) {}
 
   send<InputType extends ClientInput, OutputType extends ClientOutput>(
     command: Command<ClientInput, InputType, ClientOutput, OutputType, SmithyResolvedConfiguration<HandlerOptions>>,
@@ -81,7 +91,7 @@ export class Client<
     const options = typeof optionsOrCb !== "function" ? optionsOrCb : undefined;
     const callback = typeof optionsOrCb === "function" ? (optionsOrCb as (err: any, data?: OutputType) => void) : cb;
 
-    const useHandlerCache = options === undefined && this.config === this.configRef;
+    const useHandlerCache = options === undefined && this.config.cacheMiddleware === true;
 
     let handler: Handler<any, any>;
 
@@ -100,7 +110,6 @@ export class Client<
     } else {
       delete this.handlers;
       handler = command.resolveMiddleware(this.middlewareStack as any, this.config, options);
-      this.configRef = this.config;
     }
 
     if (callback) {