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Add a middleware stack implementation (#42)
* Add a middleware stack implementation * Ensure @aws/types is always compiled during the pretest phase * Restructure middleware stack to reflect new repository format
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‎packages/middleware-stack/.gitignore

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*.js
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*.js.map
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*.d.ts

‎packages/middleware-stack/package.json

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{
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"name": "@aws/middleware-stack",
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"private": true,
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"version": "0.0.1",
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"description": "Provides a means for composing multiple middleware functions into a single handler",
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"scripts": {
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"prepublishOnly": "tsc",
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"pretest": "tsc -p tsconfig.test.json",
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"test": "jest"
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},
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"author": "[email protected]",
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"license": "Apache-2.0",
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"main": "./build/index.js",
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"types": "./build/index.d.ts",
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"dependencies": {
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"@aws/types": "^0.0.1"
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},
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"devDependencies": {
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"@types/jest": "^20.0.2",
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"jest": "^20.0.4",
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"typescript": "^2.3"
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}
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}

‎packages/middleware-stack/src/index.spec.ts

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import {MiddlewareStack} from "./";
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import {HandlerArguments, Middleware} from "@aws/types";
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describe('MiddlewareStack', () => {
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it('should resolve the stack into a composed handler', async () => {
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const stack = new MiddlewareStack<Array<string>, object>();
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stack.prependInit(next => args => next({
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...args,
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input: args.input.concat('first')
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}));
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stack.appendBuild(next => args => next({
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...args,
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input: args.input.concat('fourth')
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}));
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stack.appendInit(next => args => next({
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...args,
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input: args.input.concat('second')
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}));
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stack.prependBuild(next => args => next({
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...args,
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input: args.input.concat('third')
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}));
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stack.appendSign(next => args => next({
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...args,
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input: args.input.concat('sixth')
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}));
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stack.prependSign(next => args => next({
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...args,
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input: args.input.concat('fifth')
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}));
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const inner = jest.fn(({input}: HandlerArguments<Array<string>>) => {
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expect(input).toEqual([
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'first',
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'second',
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'third',
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'fourth',
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'fifth',
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'sixth',
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]);
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return {};
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});
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const composed = stack.resolve(inner);
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await composed({input: []});
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expect(inner.mock.calls.length).toBe(1);
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});
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it('should allow cloning', async () => {
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const stack = new MiddlewareStack<Array<string>, object>();
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stack.appendInit(next => args => next({
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...args,
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input: args.input.concat('second')
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}));
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stack.prependInit(next => args => next({
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...args,
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input: args.input.concat('first')
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}));
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const secondStack = stack.clone();
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let inner = jest.fn(({input}: HandlerArguments<Array<string>>) => {
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expect(input).toEqual([
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'first',
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'second',
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]);
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return Promise.resolve({});
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});
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await secondStack.resolve(inner)({input: []});
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expect(inner.mock.calls.length).toBe(1);
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});
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it('should allow the removal of middleware by object identity', async () => {
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const stack = new MiddlewareStack<Array<string>, object>();
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let middleware: Middleware<Array<string>, object> = next => args => next({
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...args,
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input: args.input.concat('first')
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});
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stack.prependInit(middleware);
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await stack.resolve(({input}: HandlerArguments<Array<string>>) => {
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expect(input).toEqual([
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'first',
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]);
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return Promise.resolve({});
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})({input: []});
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stack.remove(middleware);
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await stack.resolve(({input}: HandlerArguments<Array<string>>) => {
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expect(input).toEqual([]);
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return Promise.resolve({});
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})({input: []});
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});
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it('should allow the removal of middleware by name', async () => {
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const stack = new MiddlewareStack<Array<string>, object>();
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stack.prependInit(next => args => next({
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...args,
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input: args.input.concat('first')
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}), 'first');
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await stack.resolve(({input}: HandlerArguments<Array<string>>) => {
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expect(input).toEqual([
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'first',
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]);
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return Promise.resolve({});
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})({input: []});
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stack.remove('first');
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await stack.resolve(({input}: HandlerArguments<Array<string>>) => {
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expect(input).toEqual([]);
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return Promise.resolve({});
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})({input: []});
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});
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});

‎packages/middleware-stack/src/index.ts

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import {Handler, Middleware} from '@aws/types';
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interface Step<
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InputType extends object,
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OutputType extends object,
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StreamType
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> {
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middleware: Middleware<InputType, OutputType, StreamType>;
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name?: string;
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}
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/**
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* Builds a single handler function from zero or more middleware functions and a
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* handler. The single handler is meant to send command objects to AWS services
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* and return promises that will resolve with the operation result or be
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* rejected with an error.
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*
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* When a composed handler is invoked, the arguments will pass through all
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* middleware in a defined order, and the return from the innermost handler will
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* pass through all middleware in the reverse of that order. Handlers are
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* ordered using a "step" that describes the step at which the SDK is when
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* sending a command. The available steps are:
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*
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* - init: The command is being initialized, allowing you to do things like add
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* default options.
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* - build: The command is being serialized into an HTTP request.
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* - sign: The request is being signed and prepared to be sent over the wire.
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*
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* You can add middleware to the top of the stack (i.e., make middleware the
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* first to receive incoming arguments and the last to receive a response) by
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* using the "prependInit" method or to the bottom of the stack (i.e., the first
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* to receive the response and the last to receive incoming arguments) by using
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* the "appendSign" method. Each step has comparable "prepend" and "append"
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* methods.
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*
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* Middleware can be registered with a name to allow you to easily add a
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* middleware before or after another middleware by name. This also allows you
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* to remove a middleware by name (in addition to removing by instance).
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*/
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export class MiddlewareStack<
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InputType extends object,
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OutputType extends object,
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StreamType = Uint8Array
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> {
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private initSteps: Array<Step<InputType, OutputType, StreamType>> = [];
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private buildSteps: Array<Step<InputType, OutputType, StreamType>> = [];
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private signSteps: Array<Step<InputType, OutputType, StreamType>> = [];
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/**
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* Add middleware to be executed after other members of the build phase.
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*/
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appendBuild(
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middleware: Middleware<InputType, OutputType, StreamType>,
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name?: string
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): void {
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this.buildSteps.unshift({middleware, name});
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}
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/**
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* Add middleware to be executed after other members of the init phase.
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*/
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appendInit(
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middleware: Middleware<InputType, OutputType, StreamType>,
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name?: string
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): void {
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this.initSteps.unshift({middleware, name});
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}
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/**
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* Add middleware to be executed after other members of the sign phase.
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*/
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appendSign(
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middleware: Middleware<InputType, OutputType, StreamType>,
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name?: string
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): void {
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this.signSteps.unshift({middleware, name});
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}
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/**
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* Copy the stack into a new instance.
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*/
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clone(): MiddlewareStack<InputType, OutputType, StreamType> {
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const stack = new MiddlewareStack<InputType, OutputType, StreamType>();
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stack.initSteps = this.initSteps.slice(0);
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stack.buildSteps = this.buildSteps.slice(0);
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stack.signSteps = this.signSteps.slice(0);
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return stack;
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}
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/**
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* Add middleware to be executed before other members of the build phase.
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*/
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prependBuild(
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middleware: Middleware<InputType, OutputType, StreamType>,
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name?: string
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): void {
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this.buildSteps.push({middleware, name});
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}
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/**
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* Add middleware to be executed before other members of the init phase.
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*/
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prependInit(
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middleware: Middleware<InputType, OutputType, StreamType>,
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name?: string
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): void {
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this.initSteps.push({middleware, name});
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}
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/**
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* Add middleware to be executed before other members of the sign phase.
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*/
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prependSign(
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middleware: Middleware<InputType, OutputType, StreamType>,
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name?: string
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): void {
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this.signSteps.push({middleware, name});
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}
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/**
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* Remove middleware with the provided name or identity.
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*/
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remove(nameOrType: string|Middleware<InputType, OutputType, StreamType>): void {
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if (typeof nameOrType === 'string') {
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this.filterSteps(named => nameOrType !== named.name);
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} else {
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this.filterSteps(named => nameOrType !== named.middleware);
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}
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}
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/**
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* Reduce the stack into a composite handler function.
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*/
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resolve(
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handler: Handler<InputType, OutputType, StreamType>
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): Handler<InputType, OutputType, StreamType> {
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for (let steps of [this.signSteps, this.buildSteps, this.initSteps]) {
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for (let step of steps) {
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handler = step.middleware(handler);
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}
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}
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return handler;
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}
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private filterSteps(
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predicate: (
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named: Step<InputType, OutputType, StreamType>
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) => boolean
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): void {
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this.initSteps = this.initSteps.filter(predicate);
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this.buildSteps = this.buildSteps.filter(predicate);
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this.signSteps = this.signSteps.filter(predicate);
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}
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}

‎packages/middleware-stack/tsconfig.json

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{
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"compilerOptions": {
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"target": "es5",
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"module": "commonjs",
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"declaration": true,
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"strict": true,
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"sourceMap": true,
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"lib": [
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"es5",
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"es2015.promise",
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"es2015.collection"
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],
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"rootDir": "./src",
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"outDir": "./build"
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}
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}

‎packages/middleware-stack/tsconfig.test.json

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{
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"extends": "./tsconfig.json",
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"compilerOptions": {
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"sourceMap": false,
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"inlineSourceMap": true,
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"inlineSources": true,
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"rootDir": "./src",
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"outDir": "./build"
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}
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}

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