example.ts

import * as bodyParser from 'body-parser';
import * as express from 'express';
import {
    BadRequest,
    JsValue,
    jsValueWriteable,
    Ok,
    Result,
} from 'express-result-types/target/result';
import * as session from 'express-session';
import * as http from 'http';
import * as t from 'io-ts';

import { NumberFromString } from './helpers/example';
import { formatValidationErrors } from './helpers/other';
import { wrap } from './index';

const app = express();
app.use(session({ secret: 'foo' }));
// Don't parse body using middleware. Body parsing is instead handled in the request handler.
app.use(bodyParser.text({ type: 'application/json' }));

const Body = t.interface({
    name: t.string,
});

const Query = t.interface({
    age: NumberFromString,
});

const requestHandler = wrap(req => {
    const jsonBody = req.body.asJson();

    const maybeQuery = Query.decode({
        age: req.query.get('age').toNullable(),
    }).mapLeft(formatValidationErrors('query'));

    const maybeBody = jsonBody.chain(jsValue =>
        jsValue.validate(Body).mapLeft(formatValidationErrors('body')),
    );

    return maybeQuery
        .chain(query => maybeBody.map(body => ({ query, body })))
        .map(({ query, body }) =>
            Ok.apply(
                new JsValue({
                    // We defined the shape of the request body and the request query parameter
                    // 'age' for validation purposes, but it also gives us static types! For
                    // example, here the type checker knows the types:
                    // - `body.name` is type `string`
                    // - `age` is type `number`
                    name: body.name,
                    age: query.age,
                }),
                jsValueWriteable,
            ),
        )
        .getOrElseL(error => BadRequest.apply(new JsValue(error), jsValueWriteable));
});

const sessionRequestHandler = wrap(req => {
    const maybeUserId = req.session.get('userId');

    return maybeUserId.foldL(
        () => Ok.apply(new JsValue({}), jsValueWriteable).withSession(new Map([['userId', 'foo']])),
        userId => Ok.apply(new JsValue({ userId }), jsValueWriteable),
    );
});

app.post('/', requestHandler);
app.get('/session', sessionRequestHandler);

const onListen = (server: http.Server) => {
    const { port } = server.address();

    console.log(`Server running on port ${port}`);
};

const httpServer = http.createServer(app);
httpServer.listen(8080, () => {
    onListen(httpServer);
});

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": "bob" }' "localhost:8080/" | jq '.'
// "Validation errors for query: Expecting NumberFromString at age but instead got: null."

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": "bob" }' "localhost:8080/?age=foo" | jq '.'
// "Validation errors for query: Expecting NumberFromString at age but instead got: \"foo\"."

// ❯ curl --request POST --silent --header 'Content-Type: invalid' \
//     --data '{ "name": "bob" }' "localhost:8080/?age=5" | jq '.'
// "Expecting request header 'Content-Type' to equal 'application/json', but instead got 'invalid'."

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data 'invalid' "localhost:8080/?age=5" | jq '.'
// "JSON parsing error: Unexpected token i in JSON at position 0"

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": 1 }' "localhost:8080/?age=5" | jq '.'
// "Validation errors for body: Expecting string at name but instead got: 1."

// ❯ curl --request POST --silent --header 'Content-Type: application/json' \
//     --data '{ "name": "bob" }' "localhost:8080/?age=5" | jq '.'
// {
//   "name": "bob",
//   "age": 5
// }