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/*
This file is part of GNU Taler
(C) 2018-2019 GNUnet e.V.
GNU Taler is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation; either version 3, or (at your option) any later version.
GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
GNU Taler; see the file COPYING. If not, see <http://www.gnu.org/licenses/>
*/
/**
* Type-safe codecs for converting from/to JSON.
*/
/**
* Error thrown when decoding fails.
*/
export class DecodingError extends Error {
constructor(message: string) {
super(message);
Object.setPrototypeOf(this, DecodingError.prototype);
this.name = "DecodingError";
}
}
/**
* Context information to show nicer error messages when decoding fails.
*/
interface Context {
readonly path?: string[];
}
function renderContext(c?: Context): string {
const p = c?.path;
if (p) {
return p.join(".");
} else {
return "(unknown)";
}
}
function joinContext(c: Context | undefined, part: string): Context {
const path = c?.path ?? [];
return {
path: path.concat([part]),
};
}
/**
* A codec converts untyped JSON to a typed object.
*/
export interface Codec<V> {
/**
* Decode untyped JSON to an object of type [[V]].
*/
readonly decode: (x: any, c?: Context) => V;
}
type SingletonRecord<K extends keyof any, V> = { [Y in K]: V };
interface Prop {
name: string;
codec: Codec<any>;
}
class ObjectCodecBuilder<T, TC> {
private propList: Prop[] = [];
/**
* Define a property for the object.
*/
property<K extends keyof T & string, V>(
x: K,
codec: Codec<V>,
): ObjectCodecBuilder<T, TC & SingletonRecord<K, V>> {
this.propList.push({ name: x, codec: codec });
return this as any;
}
/**
* Return the built codec.
*
* @param objectDisplayName name of the object that this codec operates on,
* used in error messages.
*/
build(objectDisplayName: string): Codec<TC> {
const propList = this.propList;
return {
decode(x: any, c?: Context): TC {
if (!c) {
c = {
path: [`(${objectDisplayName})`],
};
}
const obj: any = {};
for (const prop of propList) {
const propRawVal = x[prop.name];
const propVal = prop.codec.decode(
propRawVal,
joinContext(c, prop.name),
);
obj[prop.name] = propVal;
}
return obj as TC;
},
};
}
}
/**
* Return a codec for a value that must be a string.
*/
export const stringCodec: Codec<string> = {
decode(x: any, c?: Context): string {
if (typeof x === "string") {
return x;
}
throw new DecodingError(`expected string at ${renderContext(c)}`);
},
};
/**
* Return a codec for a value that must be a number.
*/
export const numberCodec: Codec<number> = {
decode(x: any, c?: Context): number {
if (typeof x === "number") {
return x;
}
throw new DecodingError(`expected number at ${renderContext(c)}`);
},
};
/**
* Return a codec for a list, containing values described by the inner codec.
*/
export function listCodec<T>(innerCodec: Codec<T>): Codec<T[]> {
return {
decode(x: any, c?: Context): T[] {
const arr: T[] = [];
if (!Array.isArray(x)) {
throw new DecodingError(`expected array at ${renderContext(c)}`);
}
for (const i in x) {
arr.push(innerCodec.decode(x[i], joinContext(c, `[${i}]`)));
}
return arr;
},
};
}
/**
* Return a codec for a mapping from a string to values described by the inner codec.
*/
export function mapCodec<T>(innerCodec: Codec<T>): Codec<{ [x: string]: T }> {
return {
decode(x: any, c?: Context): { [x: string]: T } {
const map: { [x: string]: T } = {};
if (typeof x !== "object") {
throw new DecodingError(`expected object at ${renderContext(c)}`);
}
for (const i in x) {
map[i] = innerCodec.decode(x[i], joinContext(c, `[${i}]`));
}
return map;
},
};
}
/**
* Return a builder for a codec that decodes an object with properties.
*/
export function objectCodec<T>(): ObjectCodecBuilder<T, {}> {
return new ObjectCodecBuilder<T, {}>();
}
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