@alexshelkov/lambda v1.7.3
Type-safe middleware for AWS Lambda
Leveraging the power of Typescript to build middleware-like request handlers for lambda functions with type-based dependency checking.
An example
A service which parse request body as JSON, get a
and b
from it,
check if both are valid numbers, then adds them and return result.
import { Err, ok, fail } from '@alexshelkov/result';
import { MiddlewareCreator, Handler, JsonBodyService, creator, addService, jsonBodyService } from '@alexshelkov/lambda';
type NumberService = { a: number; b: number };
type NumberErrNaN = Err<'NaA'>;
type NumberDependencies = JsonBodyService;
const numbers: MiddlewareCreator<{}, NumberService, NumberErrNaN, NumberDependencies> = () => {
return async (request) => {
const body = request.service.jsonBody;
if (!(Number.isFinite(body.a) && Number.isFinite(body.b))) {
return fail<NumberErrNaN>('NaA');
}
const service = body as NumberService;
return addService(request, service);
};
};
type Options = { acceptFloat: boolean };
type AdderService = { add: (a: number, b: number) => number };
type AdderErrNoFloats = Err<'Float'>;
const adder: MiddlewareCreator<Options, AdderService, AdderErrNoFloats> = (options, { throws }) => {
return async (request) => {
const service: AdderService = {
add: (a: number, b: number) => {
if (!options.acceptFloat && !(Number.isInteger(a) && Number.isInteger(b))) {
throws<AdderErrNoFloats>('Float');
}
return a + b;
},
};
return addService(request, service);
};
};
const handler: Handler<AdderService & NumberService, number, never> = async ({
service: { a, b, add },
}) => {
return ok(add(a, b));
};
const lambda = creator(jsonBodyService).srv(numbers).srv(adder).ok(handler);
API
Services
MiddlewareCreator
Type used for creating new services.
Params:
Options
Service
Errors
ServiceDeps
Event
import { Err } from '@alexshelkov/result';
import { MiddlewareCreator, addService } from '@alexshelkov/lambda';
type Options = { };
type Service = { add: (a: number, b: number) => number };
type Errors = never;
const service: MiddlewareCreator<Options, Service, Errors> = () => {
return async (request) => {
return addService(request, {
add: (a: number, b: number) => {
return a + b;
},
});
};
};
creator
Starts the creation of the lambda chain.
Params:
creator
:MiddlewareCreator
import { creator, empty } from '@alexshelkov/lambda';
const res = creator(empty); // now you can use other methods, for example: .srv
srv
Adds a new service.
Params:
creator
:MiddlewareCreator
import { MiddlewareCreator, creator, empty, addService } from '@alexshelkov/lambda';
const service: MiddlewareCreator<{}, {}, never> = () => {
return async (request) => {
return addService(request, {});
}
};
const res = creator(empty).srv(service);
opt
Set the options.
Params:
options
Handlers
ok
Adds a handler which will be run if all middleware creators executed successfully.
Params:
handler
:Handler
import { ok } from '@alexshelkov/result';
import { creator, empty } from '@alexshelkov/lambda';
const res = creator(empty).ok(async () => {
return ok('success'); // can be used in onOk
});
fail
Adds a handler which runs on middleware failure.
Params:
handler
:HandlerError
import { ok } from '@alexshelkov/result';
import { creator, empty } from '@alexshelkov/lambda';
const res = creator(empty).fail(async () => {
// this handler will not runs because
// empty middleware not fails
return ok('success'); // can be used in onFail
});
fatal
Adds an unknown exception handler.
Params:
handler
:HandlerException
import { ok } from '@alexshelkov/result';
import { creator, empty } from '@alexshelkov/lambda';
const res = creator(empty).fatal(async () => {
// this handler will not runs because
// empty middleware won't throw fatal errors
return ok('success'); // can be used in onFatal
});
Transforms
onOk
Sets the result transformation of ok handler.
Params:
transform
:Transform
import { ok } from '@alexshelkov/result';
import { creator, empty } from '@alexshelkov/lambda';
const res = creator(empty).ok(async () => {
return ok('success');
}).onOk(async (result) => {
return result; // result equals to 'success'
});
onFail
Sets the result transformation of fail handler.
Params:
transform
:TransformError
import { ok } from '@alexshelkov/result';
import { creator, empty } from '@alexshelkov/lambda';
const res = creator(empty).fail(async () => {
return ok('fail');
}).onFail(async (result) => {
return result; // result equals to 'fail'
});
onFatal
Sets the result transformation of fatal handler.
Params:
transform
:TransformError
import { ok } from '@alexshelkov/result';
import { creator, empty } from '@alexshelkov/lambda';
const res = creator(empty).fatal(async () => {
return ok('fatal');
}).onFatal(async (result) => {
return result; // result equals to 'fatal'
});
on
Same as calling onOk
, onFail
and onFatal
.
req
Returns AWS Lambda handler.
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