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import {Internal} from '@feasibleone/blong/types';
import type {FastifyInstance, FastifyReply, FastifyRequest} from 'fastify';
import fp from 'fastify-plugin';
interface IConfig {
/**
* When false (default) the plugin registers nothing and is a no-op.
*/
enabled: boolean;
/**
* Handler (semantic triple) that performs metering for a request.
* It must accept `{bundle, creditCost}` and return
* `{allowed, reason, creditsRemaining, rateLimit, rateCount, rateResetAt}`.
*/
meterHandler: string;
/**
* HTTP status codes for each blocking reason.
*/
statusCodes: {
rate: number;
credits: number;
subscription: number;
};
}
interface IGatewayWithPlugins extends IGateway {
registerPlugin(plugin: unknown, options?: unknown): void;
}
interface IApiRef {
log?: ILog;
gateway?: IGatewayWithPlugins;
local?: ILocal;
}
interface IMeterDecision {
allowed: boolean;
reason: 'ok' | 'rate' | 'credits' | 'subscription';
creditsRemaining?: number;
rateLimit?: number;
rateCount?: number;
rateResetAt?: number;
}
interface IRouteConfig {
bundle?: string;
creditCost?: number;
meter?: boolean;
methodName?: string;
}
export default class ApiGateway extends Internal {
#config: IConfig = {
enabled: false,
meterHandler: 'gateway.meter.check',
statusCodes: {
rate: 429,
credits: 429,
subscription: 403,
},
};
#apiRef: IApiRef;
public constructor(config: IConfig, apiRef: IApiRef) {
super({log: apiRef.log});
this.merge(this.#config, config);
this.#apiRef = apiRef;
}
public async init(): Promise<void> {
if (!this.#config.enabled || !this.#apiRef.gateway) return;
const config = this.#config;
const apiRef = this.#apiRef;
const [subject] = config.meterHandler.split('.');
const reqName = `ports.${subject}.request`;
const plugin = fp(
async (server: FastifyInstance) => {
// Runs AFTER the jwt plugin (auth + authorize). Metering is the
// last gate before the route handler — it does NOT authorize.
server.addHook(
'preHandler',
async (request: FastifyRequest, reply: FastifyReply) => {
const routeConfig = request.routeOptions?.config as
| IRouteConfig
| undefined;
// Opt-in per route: only routes that declare a `bundle`
// are metered. `meter: false` opts a route out.
if (!routeConfig || routeConfig.bundle === undefined) return;
if (routeConfig.meter === false) return;
const handler = apiRef.local?.get(reqName);
if (!handler) {
request.log.error(
{meterHandler: config.meterHandler},
'gateway metering handler unavailable',
);
return reply.code(503).send({error: 'Service Unavailable'});
}
let result: IMeterDecision;
try {
const [res] = (await handler.method(
{
bundle: routeConfig.bundle,
creditCost: routeConfig.creditCost ?? 0,
},
{
method: config.meterHandler,
mtid: 'request',
auth: request.auth?.credentials,
},
)) as [IMeterDecision, unknown];
result = res;
} catch (error) {
// Fail-closed: any metering error (e.g. Redis down)
// blocks the request with 503.
request.log.error({err: error}, 'gateway metering error');
return reply.code(503).send({error: 'Service Unavailable'});
}
if (result && typeof result === 'object') {
if (result.rateLimit !== undefined)
reply.header('X-RateLimit-Limit', String(result.rateLimit));
if (result.rateLimit !== undefined && result.rateCount !== undefined) {
reply.header(
'X-RateLimit-Remaining',
String(Math.max(0, result.rateLimit - result.rateCount)),
);
}
if (result.creditsRemaining !== undefined)
reply.header(
'X-Credits-Remaining',
String(result.creditsRemaining),
);
}
if (!result || result.allowed === false) {
const reason = result?.reason ?? 'subscription';
const status =
(config.statusCodes as Record<string, number>)[reason] ?? 429;
if (result?.rateResetAt)
reply.header(
'Retry-After',
String(
Math.max(
1,
Math.ceil(result.rateResetAt - Date.now() / 1000),
),
),
);
return reply
.code(status)
.send({error: reason, message: `request ${reason} blocked`});
}
},
);
},
{name: 'api-gateway'},
);
apiRef.gateway!.registerPlugin(plugin);
}
}
|