Merge pull request #1041 from BitGo/docs/typed-router-cleanup

docs(typed-express-router): Refactor documentation into Diátaxis Reference section

Author: omeradeel26

website/docs/reference/typed-express-router/configuration.md

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+# Configuration Options
+
+You can provide configuration options, primarily hooks for handling errors and
+post-response actions, globally when creating/wrapping a router or on a per-route basis.
+Per-route options override global ones.
+
+## Global Options (`TypedRouterOptions`)
+
+Passed as the optional second argument to [`createRouter`](./create-router) or the
+optional third argument to [`wrapRouter`](./wrap-router).
+
+```typescript
+import express from 'express';
+import * as t from 'io-ts'; // For Errors type
+import { ApiSpec } from '@api-ts/io-ts-http'; // Conceptual
+
+// Simplified representation of hook signatures
+type DecodeErrorHandler<Req = any, Res = any> = (
+  errors: t.Errors,
+  req: express.Request & { decoded?: any }, // May not have decoded fully
+  res: express.Response & { sendEncoded?: any },
+  next: express.NextFunction,
+) => void;
+
+type EncodeErrorHandler<Req = any, Res = any> = (
+  error: unknown, // The error during encoding/validation
+  req: express.Request & { decoded?: any },
+  res: express.Response & { sendEncoded?: any },
+  next: express.NextFunction,
+) => void;
+
+type AfterResponseHandler<Req = any, Res = any> = (
+  status: number,
+  payload: any, // The successfully encoded payload
+  req: express.Request & { decoded?: any },
+  res: express.Response & { sendEncoded?: any },
+) => void;
+
+export type TypedRouterOptions<T extends ApiSpec = any> = {
+  onDecodeError?: DecodeErrorHandler;
+  onEncodeError?: EncodeErrorHandler;
+  afterEncodedResponseSent?: AfterResponseHandler;
+};
+```
+
+- `onDecodeError(errors, req, res, next)`:
+  - **Triggered**: When using a "checked" route method (such as `.get`) and the incoming
+    request fails decoding or validation against the `httpRoute`'s `request` codec.
+  - **Purpose**: Allows custom formatting and sending of error responses (such as 400
+    Bad Request). If not provided, a default basic error handler might be used or the
+    error might propagate.
+  - `errors`: The `t.Errors` array from `io-ts` detailing the validation failures.
+  - **Note**: You typically end the response (`res.status(...).json(...).end()`) within
+    this handler. Calling `next()` might lead to unexpected behavior.
+- `onEncodeError(error, req, res, next)`:
+  - **Triggered**: When `res.sendEncoded(status, payload)` is called, but the provided
+    `payload` fails validation against the `httpRoute`'s `response` codec for the given
+    `status`.
+  - **Purpose**: Handles server-side errors where the application tries to send data
+    inconsistent with the API specification. This usually indicates a bug.
+  - `error`: The validation error encountered.
+  - **Note**: You typically send a 500 Internal Server Error response here and should
+    end the response.
+- `afterEncodedResponseSent(status, payload, req, res)`:
+  - **Triggered**: After `res.sendEncoded(status, payload)` has successfully validated,
+    encoded, and finished sending the response.
+  - **Purpose**: Lets you perform side-effects after a successful response, such as
+    logging, metrics collection, cleanup, etc.
+  - `status`: The status code that was sent.
+  - `payload`: The original (pre-encoding) payload object that was sent.
+  - **Note**: The response stream (`res`) is likely ended at this point. Don't attempt
+    to send further data.
+
+## Per-Route Options (`RouteOptions`)
+
+Pass these as the optional third argument to the route definition methods (such as
+`typedRouter.get(..., ..., routeOptions)`).
+
+```typescript
+// RouteOptions includes the global hooks plus routeAliases
+export type RouteOptions<RouteDef = any> = TypedRouterOptions & {
+  routeAliases?: string[];
+};
+```
+
+- `onDecodeError` / `onEncodeError` / `afterEncodedResponseSent`: Same hooks as the
+  global options, but these versions apply only to the specific route they're defined on
+  and take precedence over any global hooks defined via `createRouter` or `wrapRouter`.
+- `routeAliases` (`string[]`):
+  - An array of additional path strings that should also map to this route handler.
+  - Uses Express path syntax (such as `/path/:param`).
+  - See [`TypedRouter` Object](./typed-router) for more details and caveats regarding
+    path parameters.
+
+## Example (Global and Per-Route):
+
+```typescript
+import { createRouter } from '@api-ts/typed-express-router';
+import { MyApi } from 'my-api-package';
+
+// Global options
+const typedRouter = createRouter(MyApi, {
+  onDecodeError: globalDecodeErrorHandler,
+  afterEncodedResponseSent: globalMetricsHandler,
+});
+
+// Per-route options overriding global and adding alias
+typedRouter.get('some.operation', [myHandler], {
+  routeAliases: ['/legacy/path'],
+  onDecodeError: specificDecodeErrorHandler, // Overrides globalDecodeErrorHandler for this route
+  // afterEncodedResponseSent is inherited from global options
+});
+
+typedRouter.post('another.operation', [otherHandler], {
+  // Inherits onDecodeError from global options
+  // No afterEncodedResponseSent hook will run for this route
+  afterEncodedResponseSent: undefined, // Explicitly disable global hook for this route
+});
+```

website/docs/reference/typed-express-router/create-router.md

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+# `createRouter`
+
+Creates a new Express Router instance that's typed according to a provided
+`@api-ts/io-ts-http` API specification.
+
+**Signature:**
+
+```typescript
+import express from 'express';
+import { ApiSpec } from '@api-ts/io-ts-http'; // Conceptual import
+import { TypedRouter } from './typed-router'; // Conceptual import of the return type
+import { TypedRouterOptions } from './configuration'; // Conceptual import
+
+declare function createRouter<T extends ApiSpec>(
+  apiSpec: T,
+  options?: TypedRouterOptions<T>, // Global options/hooks
+): TypedRouter<T>; // Returns the specialized router object
+```
+
+**Parameters:**
+
+- `apiSpec` (`ApiSpec`): An API specification object created using
+  `@api-ts/io-ts-http`'s `apiSpec` function. This defines the routes that you can attach
+  to this router.
+- `options` (Optional `TypedRouterOptions<T>`): An optional object containing global
+  configuration hooks for error handling and post-response actions. See
+  [Configuration Options](./configuration) for details.
+
+**Return Value:**
+
+- `TypedRouter<T>`: A specialized Express Router instance. This object has methods (like
+  `.get`, `.post`) that accept operation names from the `apiSpec` and provide augmented
+  `req` and `res` objects to the handlers. See [`TypedRouter` Object](./typed-router)
+  for details.
+
+**Usage Example:**
+
+```typescript
+import express from 'express';
+import { createRouter } from '@api-ts/typed-express-router';
+import { MyApi } from 'my-api-package'; // Your apiSpec import
+
+const app = express();
+const typedRouter = createRouter(MyApi, {
+  // Optional global configuration
+  onDecodeError: (errs, req, res, next) => {
+    res.status(400).json({ error: 'Invalid request format', details: errs });
+  },
+});
+
+app.use('/api', typedRouter); // Mount the typed router
+```

website/docs/reference/typed-express-router/index.md

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+# Reference: @api-ts/typed-express-router
+
+This section provides detailed technical descriptions of the functions, objects, types,
+and configuration options available in the `@api-ts/typed-express-router` package. Use
+this reference to understand the specific parameters, return values, and behavior of its
+components when integrating `@api-ts/io-ts-http` specifications with Express.
+
+## Components
+
+- [**`createRouter`**](./create-router): Creates a new, typed Express Router instance
+  linked to an API specification.
+- [**`wrapRouter`**](./wrap-router): Wraps an existing Express Router instance, linking
+  it to an API specification.
+- [**`TypedRouter` Object**](./typed-router): Describes the router object returned by
+  `createRouter` and `wrapRouter`, detailing its route definition methods (`.get`,
+  `.post`, `.getUnchecked`, etc.) and middleware usage (`.use`).
+- [**Augmented Request & Response**](./request-response): Explains the properties and
+  methods added to the standard Express `req` (`req.decoded`) and `res`
+  (`res.sendEncoded`) objects within typed route handlers.
+- [**Configuration Options**](./configuration): Details the configurable options for
+  error handling (`onDecodeError`, `onEncodeError`), post-response actions
+  (`afterEncodedResponseSent`), and route aliasing (`routeAliases`).
+- [**`TypedRequestHandler` Type**](./typed-request-handler): Describes the TypeScript
+  helper type for defining route handlers with correctly inferred augmented request and
+  response types.

website/docs/reference/typed-express-router/request-response.md

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+# Augmented Request & Response
+
+When you use route handlers registered via a [`TypedRouter`](./typed-router) object
+(using methods like `.get`, `.post`, `.getUnchecked`, etc.), the standard Express
+`request` and `response` objects are augmented with additional properties and methods
+related to the API specification.
+
+## Augmented Request (`req`)
+
+The Express `request` object (`req`) passed to typed route handlers includes an
+additional property:
+
+### `req.decoded`
+
+- **Type (Checked Routes):** `DecodedRequest`
+  - In handlers attached using the "checked" methods (such as `typedRouter.get(...)`),
+    `req.decoded` holds the successfully decoded and validated request data. Its
+    TypeScript type is inferred directly from the `request` codec defined in the
+    corresponding `httpRoute` of the `ApiSpec`. This object contains the flattened
+    combination of path parameters, query parameters, headers, and body properties as
+    defined by the `httpRequest` codec used in the spec.
+- **Type (Unchecked Routes & Middleware):** `Either<t.Errors, DecodedRequest>`
+  - In handlers attached using the "unchecked" methods (such as
+    `typedRouter.getUnchecked(...)`) or in middleware added via `typedRouter.use(...)`,
+    `req.decoded` holds the raw result of the decoding attempt from `io-ts`. This is an
+    `Either` type from the `fp-ts` library.
+  - Use `E.isRight(req.decoded)` to check if decoding was successful. If true,
+    `req.decoded.right` contains the `DecodedRequest`.
+  - Use `E.isLeft(req.decoded)` to check if decoding failed. If true, `req.decoded.left`
+    contains the `t.Errors` object detailing the validation failures.
+
+## Augmented Response (`res`)
+
+The Express `response` object (`res`) passed to typed route handlers includes an
+additional method:
+
+### `res.sendEncoded(status, payload)`
+
+Use this method instead of `res.json()` or `res.send()` when sending responses that
+should conform to the API specification.
+
+**Parameters:**
+
+- `status` (`number`): The HTTP status code for the response. This status code **must**
+  be a key defined in the `response` object of the `httpRoute` associated with the
+  current route in the `ApiSpec`.
+- `payload` (`any`): The data to be sent as the response body.
+
+**Behavior:**
+
+1.  **Type Checking:** Validates that the provided `payload` conforms to the `io-ts`
+    codec associated with the given `status` in the `httpRoute`'s `response` definition.
+2.  **Encoding:** Encodes the `payload` using the same `io-ts` codec. This handles
+    necessary transformations (such as converting a `Date` object to an ISO string if
+    using `DateFromISOString`, or a `bigint` to a string if using `BigIntFromString`).
+3.  **Sending Response:** Sets the response status code to `status`, sets the
+    `Content-Type` header to `application/json`, and sends the JSON-stringified encoded
+    payload as the response body.
+4.  **Error Handling:** If the `payload` fails validation against the codec for the
+    specified `status`, calls the `onEncodeError` hook (route-specific or global).
+5.  **Post-Response Hook:** After the response has been successfully sent, calls the
+    `afterEncodedResponseSent` hook (route-specific or global).
+
+**Example:**
+
+```typescript
+import { TypedRequestHandler } from '@api-ts/typed-express-router';
+import { MyApi } from 'my-api-package';
+
+// Assuming 'api.v1.getUser' route expects a { user: UserType } payload for status 200
+const getUserHandler: TypedRequestHandler<MyApi['api.v1.getUser']['get']> = (
+  req,
+  res,
+) => {
+  const userId = req.decoded.userId; // Access decoded request data
+  const user = findUserById(userId);
+
+  if (!user) {
+    // Assuming 404 is defined in the spec with an error object payload
+    res.sendEncoded(404, { error: 'User not found' });
+    return;
+  }
+
+  // Send status 200 with the UserType payload
+  // 'sendEncoded' ensures 'user' matches the spec for status 200
+  res.sendEncoded(200, { user: user });
+};
+```

website/docs/reference/typed-express-router/typed-request-handler.md

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+# `TypedRequestHandler` Type
+
+A TypeScript helper type provided by `@api-ts/typed-express-router` to help you define
+Express route handlers with correctly inferred types for the augmented `request` and
+`response` objects.
+
+**Purpose:**
+
+When defining handlers for "checked" routes (such as using `typedRouter.get(...)`), this
+type automatically infers:
+
+- The type of `req.decoded` based on the `request` codec of the specific `httpRoute`
+  linked via the `operationName`.
+- The type signature of `res.sendEncoded`, ensuring the `payload` type is checked
+  against the appropriate `response` codec for the given `status` code from the
+  `httpRoute`.
+
+**Definition (Conceptual):**
+
+```typescript
+import express from 'express';
+import { HttpRoute } from '@api-ts/io-ts-http'; // Conceptual import
+import * as t from 'io-ts'; // For TypeOf and OutputOf
+
+// RouteDefinition represents the specific httpRoute object from the ApiSpec
+// e.g., MyApi['my.operation']['get']
+type RouteDefinition = HttpRoute<any, any>;
+
+// Extracts the decoded request type from the route's request codec
+type DecodedRequest<R extends RouteDefinition> = t.TypeOf<R['request']>;
+
+// Represents the augmented response object
+type TypedResponse<R extends RouteDefinition> = express.Response & {
+  sendEncoded<Status extends keyof R['response'] & number>( // Status must be a key in response obj
+    status: Status,
+    // Payload type must match the codec for the given status
+    payload: t.TypeOf<R['response'][Status]>,
+  ): TypedResponse<R>; // Allows chaining like standard Express res
+};
+
+export type TypedRequestHandler<RouteDef extends RouteDefinition = any> = (
+  req: express.Request & { decoded: DecodedRequest<RouteDef> },
+  res: TypedResponse<RouteDef>,
+  next: express.NextFunction,
+) => void | Promise<void>; // Allow async handlers
+```
+
+(Note: The actual implementation may involve more complex generic constraints)
+
+**Usage:** Import the type and use it when defining your handler functions. Provide the
+specific `httpRoute` definition type from your imported `ApiSpec` as the generic
+argument.
+
+```typescript
+import express from 'express';
+import { TypedRequestHandler } from '@api-ts/typed-express-router';
+import { MyApi } from 'my-api-package'; // Your generated ApiSpec object
+
+// Define the type for the specific route handler
+type HelloWorldRouteHandler = TypedRequestHandler<MyApi['hello.world']['get']>;
+//                                             ^------------------------------^
+//         Generic argument points to the specific httpRoute definition in the spec
+
+const handler: HelloWorldRouteHandler = (req, res, next) => {
+  // req.decoded is strongly typed based on MyApi['hello.world']['get'].request
+  const name = req.decoded.name || 'World';
+
+  // Payload for status 200 is type-checked against MyApi['hello.world']['get'].response[200]
+  res.sendEncoded(200, { message: `Hello, ${name}!` });
+
+  // If status 400 was defined in the spec with a different payload type:
+  // const errorPayload = { error: 'Missing name' };
+  // res.sendEncoded(400, errorPayload); // This would also be type-checked
+};
+
+// Use the handler
+// typedRouter.get('hello.world', [handler]);
+```
+
+Using `TypedRequestHandler` significantly improves your developer experience by
+providing type safety and autocompletion for the decoded request properties and the
+`sendEncoded` payload within route handlers.