@pagopa/handler-kit
v1.1.0
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A minimal toolkit to make `handlers` in TypeScript & `fp-ts`
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@pagopa/handler-kit
A minimal toolkit to make handlers
in TypeScript & fp-ts
What is an Handler?
An Handler
is a specialization of fp-ts' ReaderTaskEither
that takes a value as input
and ensures uniform error handling and validation.
It is particularly useful for creating HTTP-agnostic "controllers" that can be adapted to any framework.
This package contains useful functions for creating handlers, manipulating them, abstracting HTTP controllers, and uniformly handling errors
How to use it
import * as H from "@pagopa/handler-kit";
import * as L from "@pagopa/logger";
import * as E from "fp-ts/Either";
import * as RTE from "fp-ts/ReaderTaskEither";
import * as TE from "fp-ts/TaskEither";
import { pipe, flow } from "fp-ts/function";
import { lookup } from "fp-ts/Record";
import * as t from "io-ts";
const GetMoviesBody = t.type({
genre: t.keyof({
action: null,
comedy: null,
drama: null,
horror: null,
"sci-fi": null,
}),
});
type GetMoviesBody = t.TypeOf<typeof GetMoviesBody>;
const movies = {
action: ["die hard"],
horror: ["shining", "the exorcist"],
};
const getMoviesByGenre =
(genre: GetMoviesBody["genre"]) =>
(r: { movies: Record<string, string[]> }) =>
pipe(
r.movies,
lookup(genre),
TE.fromOption(
() => new H.HttpNotFoundError("there are no movies for this genre")
)
);
// Reads genre from HTTP body,
// then performs an effecful search
// and returns an HTTP response.
const GetMovies = H.of((req: H.HttpRequest) =>
pipe(
req.body,
// perform a refinement with io-ts, and returns a ValidationError
// that represents a 422 HTTP response
H.parse(GetMoviesBody),
E.map(({ genre }) => genre),
RTE.fromEither,
RTE.chainW(getMoviesByGenre),
RTE.map((movies) => ({ items: movies })),
// wrap in a 200 HTTP response, with content-type JSON
RTE.map(H.successJson),
// converts Error instances to problem json (RFC 7807) objects
RTE.orElseW(flow(H.toProblemJson, H.problemJson, RTE.of))
)
);
// Run the handler
// too boilerplate? :P don't panic, see the handler-kit adapters
const httpRequest = {
method: "POST",
body: {
genre: "sci-fi",
},
url: "https://my-req.url/",
query: {},
headers: {},
path: {},
};
GetMovies({
input: httpRequest,
inputDecoder: H.HttpRequest,
logger: {
log: (r) => () => console.log(r),
format: L.format.simple,
},
movies,
})();
See the unit tests for other examples