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RootContext.ts
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RootContext.ts
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/*
* Copyright 2021 The Backstage Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import { DateTime, Duration } from 'luxon';
import { AbortSignal } from 'node-abort-controller';
import {
abortManually,
abortOnTimeout,
ContextAbortState,
} from './features/abort';
import {
ContextValues,
findInContextValues,
unshiftContextValues,
} from './features/values';
import { Context, ContextDecorator } from './types';
// The context value key used for holding abort related state
const abortKey = Symbol('Context.abort');
/**
* A context that is meant to be passed as a ctx variable down the call chain,
* to pass along scoped information and abort signals.
*
* @public
*/
export class RootContext implements Context {
/**
* Creates a root context.
*
* @remarks
*
* This should normally only be called near the root of an application. The
* created context is meant to be passed down into deeper levels, which may
* or may not make derived contexts out of it.
*/
static create() {
return new RootContext(undefined).withValue<ContextAbortState>(
abortKey,
abortManually(),
);
}
/**
* {@inheritdoc Context.abortSignal}
*/
public get abortSignal(): AbortSignal {
return this.value<ContextAbortState>(abortKey)!.signal;
}
/**
* {@inheritdoc Context.abortPromise}
*/
public get abortPromise(): Promise<void> {
return this.value<ContextAbortState>(abortKey)!.promise;
}
/**
* {@inheritdoc Context.deadline}
*/
public get deadline(): DateTime | undefined {
return this.value<ContextAbortState>(abortKey)!.deadline;
}
private constructor(private readonly values: ContextValues) {}
/**
* {@inheritdoc Context.withAbort}
*/
withAbort(): { ctx: Context; abort: () => void } {
const state = abortManually(this.value<ContextAbortState>(abortKey));
return {
ctx: this.withValue(abortKey, state),
abort: state.abort,
};
}
/**
* {@inheritdoc Context.withTimeout}
*/
withTimeout(timeout: Duration): Context {
return this.withValue<ContextAbortState>(abortKey, previous =>
abortOnTimeout(timeout, previous),
);
}
/**
* {@inheritdoc Context.with}
*/
with(...items: ContextDecorator[]): Context {
return items.reduce<Context>((prev, curr) => curr(prev), this);
}
/**
* {@inheritdoc Context.withValue}
*/
withValue<T = unknown>(
key: string | symbol,
value: T | ((previous: T | undefined) => T),
): Context {
return new RootContext(unshiftContextValues(this.values, key, value));
}
/**
* {@inheritdoc Context.value}
*/
value<T = unknown>(key: string | symbol): T | undefined {
return findInContextValues<T>(this.values, key);
}
}