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composeTransferHandler.ts
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composeTransferHandler.ts
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// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
import {
Middleware,
MiddlewareHandler,
TransferHandler,
Request as RequestBase,
Response as ResponseBase,
} from '../types';
/**
* Compose a transfer handler with a core transfer handler and a list of middleware.
* @param coreHandler Core transfer handler
* @param middleware List of middleware
* @returns A transfer handler whose option type is the union of the core
* transfer handler's option type and the middleware's option type.
* @internal
*/
export const composeTransferHandler =
<
MiddlewareOptionsArr extends any[] = [],
Request extends RequestBase = RequestBase,
Response extends ResponseBase = ResponseBase,
CoreHandler extends TransferHandler<
Request,
Response,
any
> = TransferHandler<Request, Response, {}>
>(
coreHandler: CoreHandler,
middleware: OptionToMiddleware<Request, Response, MiddlewareOptionsArr>
) =>
(
request: Request,
options: MergeNoConflictKeys<
[...MiddlewareOptionsArr, InferOptionTypeFromTransferHandler<CoreHandler>]
>
) => {
const context = {};
let composedHandler: MiddlewareHandler<Request, Response> = (
request: Request
) => coreHandler(request, options);
for (let i = middleware.length - 1; i >= 0; i--) {
const m = middleware[i];
const resolvedMiddleware = m(options);
composedHandler = resolvedMiddleware(composedHandler, context);
}
return composedHandler(request);
};
/**
* Type to convert a middleware option type to a middleware type with the given
* option type.
*/
type OptionToMiddleware<
Request extends RequestBase,
Response extends ResponseBase,
Options extends any[]
> = Options extends []
? []
: Options extends [infer LastOption]
? [Middleware<Request, Response, LastOption>]
: Options extends [infer FirstOption, ...infer RestOptions]
? [
Middleware<Request, Response, FirstOption>,
...OptionToMiddleware<Request, Response, RestOptions>
]
: never;
/**
* Type to intersect multiple types if they have no conflict keys.
*/
type MergeNoConflictKeys<Options extends any[]> = Options extends [
infer OnlyOption
]
? OnlyOption
: Options extends [infer FirstOption, infer SecondOption]
? FirstOption & SecondOption
: Options extends [infer FirstOption, ...infer RestOptions]
? FirstOption & MergeNoConflictKeys<RestOptions>
: never;
/**
* Type to infer the option type of a transfer handler type.
*/
type InferOptionTypeFromTransferHandler<
T extends TransferHandler<any, any, any>
> = Parameters<T>[1];