feat: Put request rate limit at application server (#3857)

* feat: Put request rate limit at application server

This PR contains implementation for a blanket rate limiter at
application server level. Currently the allowed throughput is set high
only to be changed later as per the actual data gathered.

* Simplify implementation

1. Remove shutdown handler to purge rate limiter keys
2. Have separate keys for default and custom(route-based) rate limiters
3. Do not kill default rate limiter because it is not needed anymore due
   to (2) above

* Set 60s as default for rate limiting window

* Fix env types

server/middlewares/rateLimiter.ts

@@ -0,0 +1,60 @@
+import { Context, Next } from "koa";
+import { defaults } from "lodash";
+import RateLimiter from "@server/RateLimiter";
+import env from "@server/env";
+import { RateLimitExceededError } from "@server/errors";
+import Redis from "@server/redis";
+import { RateLimiterConfig } from "@server/types";
+
+export function rateLimiter() {
+  return async function rateLimiterMiddleware(ctx: Context, next: Next) {
+    if (!env.RATE_LIMITER_ENABLED) {
+      return next();
+    }
+
+    const key = RateLimiter.hasRateLimiter(ctx.path)
+      ? `${ctx.path}:${ctx.ip}`
+      : `${ctx.ip}`;
+    const limiter = RateLimiter.getRateLimiter(ctx.path);
+
+    try {
+      await limiter.consume(key);
+    } catch (rateLimiterRes) {
+      ctx.set("Retry-After", `${rateLimiterRes.msBeforeNext / 1000}`);
+      ctx.set("RateLimit-Limit", `${limiter.points}`);
+      ctx.set("RateLimit-Remaining", `${rateLimiterRes.remainingPoints}`);
+      ctx.set(
+        "RateLimit-Reset",
+        `${new Date(Date.now() + rateLimiterRes.msBeforeNext)}`
+      );
+
+      throw RateLimitExceededError();
+    }
+
+    return next();
+  };
+}
+
+export function registerRateLimiter(config: RateLimiterConfig) {
+  return async function registerRateLimiterMiddleware(
+    ctx: Context,
+    next: Next
+  ) {
+    if (!env.RATE_LIMITER_ENABLED) {
+      return next();
+    }
+
+    if (!RateLimiter.hasRateLimiter(ctx.path)) {
+      RateLimiter.setRateLimiter(
+        ctx.path,
+        defaults(config, {
+          duration: env.RATE_LIMITER_DURATION_WINDOW,
+          keyPrefix: RateLimiter.RATE_LIMITER_REDIS_KEY_PREFIX,
+          storeClient: Redis.defaultClient,
+        })
+      );
+    }
+
+    return next();
+  };
+}