first commit

index.js

@@ -0,0 +1,176 @@
+const express = require("express");
+const app = express();
+const port = 3000;
+var logger = require("morgan");
+
+// logs for development
+app.use(logger("dev"));
+
+// parse application/json
+app.use(express.json());
+app.use(express.urlencoded({ extended: false }));
+
+let configuration = {
+  routes: [],
+  clients: [],
+};
+/**
+ * SCHEMA
+ * configuration = {
+ *      routes: [{
+ *          sourcePath: string,
+ *          destinationUrl: number,
+ *      }],
+ *      clients: [{
+ *          clientId: string,
+ *          limit: number,
+ *          seconds: number,
+ *      }]
+ * }
+ */
+let rateLimitData = {};
+/**
+ * SCHEMA
+ * rateLimitData = [
+ *    clientId[string]: {
+ *      requestCount: number,
+ *      startingTime: Date,
+ *    }
+ * ]
+ */
+
+app.post("/configure", (request, response) => {
+  const { routes, clients } = request.body;
+
+  for (var i = 0; i < routes.length; i++) {
+    const route = routes[i];
+    if (
+      "sourcePath" in route &&
+      "destinationUrl" in route &&
+      typeof route.sourcePath === "string" &&
+      typeof route.destinationUrl === "string"
+    ) {
+      if (route.sourcePath.startsWith("/configure")) {
+        // Invalid sourcePath.
+        return response.sendStatus(400);
+      }
+    } else {
+      // Invalid route object.
+      return response.sendStatus(400);
+    }
+  }
+
+  for (var j = 0; j < clients.length; j++) {
+    const client = clients[j];
+    if ("clientId" in client && typeof client.clientId === "string") {
+      let defaultValue = 1;
+
+      if (client.limit === undefined) {
+        client.limit = defaultValue;
+      } else if (typeof client.limit !== "number") {
+        // Invalid client object.
+        return response.sendStatus(400);
+      }
+      if (client.seconds === undefined) {
+        client.seconds = defaultValue;
+      } else if (typeof client.seconds !== "number") {
+        // Invalid client object.
+        return response.sendStatus(400);
+      }
+    } else {
+      // Invalid client object.
+      return response.sendStatus(400);
+    }
+  }
+
+  configuration = {
+    routes,
+    clients,
+  };
+
+  console.log("configuration", configuration);
+  // Configuration Implemented Successfully.
+  return response.sendStatus(200);
+});
+
+function rateLimitChecker(client) {
+  // This function checks if the request made with a particular clientId should be throttled or not.
+
+  if (client.limit === 0) {
+    return {
+      isValid: false,
+    };
+  }
+
+  const rateLimitObject = rateLimitData[client.clientId];
+  if (rateLimitObject === undefined) {
+    rateLimitData[client.clientId] = {
+      requestCount: 1,
+      startingTime: new Date(),
+    };
+  } else {
+    const timeNow = new Date();
+    var diff = timeNow.getTime() - rateLimitObject.startingTime.getTime();
+    var diff_seconds = Math.abs(diff / 1000);
+
+    if (diff_seconds > client.seconds) {
+      rateLimitData[client.clientId] = {
+        requestCount: 1,
+        startingTime: new Date(),
+      };
+    } else if (rateLimitObject.requestCount >= client.limit) {
+      return {
+        isValid: false,
+      };
+    } else {
+      rateLimitObject.requestCount += 1;
+    }
+  }
+
+  return {
+    isValid: true,
+  };
+}
+
+app.get("/:name", function (request, response) {
+  // since each request is required to have "client-id" header, we will check it first.
+  const client_id = request.headers["client-id"];
+  if (!client_id) {
+    // ClientId not found.
+    return response.sendStatus(400);
+  }
+
+  if (configuration.clients.length > 0) {
+    // since configuration.clients.length is greater than 0, it means rate-limits need to be applied.
+
+    const client = configuration.clients.find((c) => {
+      return c.clientId === client_id;
+    });
+
+    if (client === undefined) {
+      // Invalid clientId.
+      return response.sendStatus(403);
+    }
+
+    const rateLimitCheckerResponse = rateLimitChecker(client);
+    if (rateLimitCheckerResponse.isValid === false) {
+      // Limit exceeded.
+      return response.sendStatus(429);
+    }
+  }
+
+  const route = configuration.routes.find((r) => {
+    return r.sourcePath === request.path;
+  });
+
+  if (route) {
+    return response.redirect(302, route.destinationUrl);
+  } else {
+    // Invalid path.
+    return response.sendStatus(404);
+  }
+});
+
+app.listen(port, () => {
+  console.log(`Listening on port ${port}`);
+});