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Bun shield reference

Arcjet Shield protects your application against common attacks, including the OWASP Top 10.

Configuration

Shield is configured by specifying which mode you want it to run in.

The configuration definition is:

type ShieldOptions = {
  mode?: "LIVE" | "DRY_RUN";
};

The arcjet client is configured with one or more shield rules which take one or many ShieldOptions.

This sets up a simple server with Arcjet configured in the handler:

import arcjet, { shield } from "@arcjet/bun";
import { env } from "bun";


const aj = arcjet({
  key: env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com
  rules: [
    // Shield protects your app from common attacks like SQL injection
    shield({ mode: "LIVE" }),
  ],
});


export default {
  port: 3000,
  fetch: aj.handler(async (req) => {
    const decision = await aj.protect(req);
    console.log("Arcjet decision", decision);


    if (decision.isDenied()) {
      return new Response("Forbidden", { status: 403 });
    }


    return new Response("Hello world");
  }),
};

Decision

The quick start example will deny requests that are determined to be suspicious, immediately returning a response to the client.

Arcjet also provides a single protect function that is used to execute your protection rules. This requires a request argument which is the request context as passed to the request handler.

This function returns a Promise that resolves to an ArcjetDecision object. This contains the following properties:

  • id (string) - The unique ID for the request. This can be used to look up the request in the Arcjet dashboard. It is prefixed with req_ for decisions involving the Arcjet cloud API. For decisions taken locally, the prefix is lreq_.
  • conclusion (ArcjetConclusion) - The final conclusion based on evaluating each of the configured rules. If you wish to accept Arcjet’s recommended action based on the configured rules then you can use this property.
  • reason (ArcjetReason) - An object containing more detailed information about the conclusion.
  • results (ArcjetRuleResult[]) - An array of ArcjetRuleResult objects containing the results of each rule that was executed.
  • ip (ArcjetIpDetails) - An object containing Arcjet’s analysis of the client IP address. See IP analysis in the SDK reference for more information.

See the SDK reference for more details about the rule results.

You check if a deny conclusion has been returned by a shield rule by using decision.isDenied() and decision.reason.isShield() respectively.

You can iterate through the results and check whether a shield rule was applied:

for (const result of decision.results) {
  console.log("Rule Result", result);
}

This example will log the full result as well as the shield rule:

import arcjet, { fixedWindow, shield } from "@arcjet/bun";
import { env } from "bun";


const aj = arcjet({
  key: env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com
  rules: [
    fixedWindow({
      mode: "LIVE",
      window: "1h",
      max: 60,
    }),
    shield({
      mode: "LIVE",
    }),
  ],
});


export default {
  port: 3000,
  fetch: aj.handler(async (req) => {
    const decision = await aj.protect(req);


    for (const result of decision.results) {
      console.log("Rule Result", result);


      if (result.reason.isRateLimit()) {
        console.log("Rate limit rule", result);
      }


      if (result.reason.isShield()) {
        console.log("Shield rule", result);
      }
    }


    if (decision.isDenied()) {
      return new Response("Forbidden", { status: 403 });
    }


    return new Response("Hello world");
  }),
};

Error handling

Arcjet is designed to fail open so that a service issue or misconfiguration does not block all requests. The SDK will also time out and fail open after 1000ms when NODE_ENV or ARCJET_ENV is development and 500ms otherwise. However, in most cases, the response time will be less than 20-30ms.

If there is an error condition, Arcjet will return an ERROR type and you can check the reason property for more information, like accessing decision.reason.message.

import arcjet, { shield } from "@arcjet/bun";
import { env } from "bun";


const aj = arcjet({
  key: env.ARCJET_KEY!, // Get your site key from https://app.arcjet.com
  rules: [
    shield({
      mode: "LIVE",
    }),
  ],
});


export default {
  port: 3000,
  fetch: aj.handler(async (req) => {
    const decision = await aj.protect(req);


    if (decision.isErrored()) {
      // Fail open by logging the error and continuing
      console.warn("Arcjet error", decision.reason.message);
      // You could also fail closed here for very sensitive routes
      //return new Response("Service unavailable", { status: 503 });
    }


    if (decision.isDenied()) {
      return new Response("You are suspicious!", { status: 403 });
    }


    return new Response("Hello world");
  }),
};

Testing

Arcjet runs the same in any environment, including locally and in CI. You can use the mode set to DRY_RUN to log the results of rule execution without blocking any requests.

We have an example test framework you can use to automatically test your rules. Arcjet can also be triggered based using a sample of your traffic.

See the Testing section of the docs for details.

Discussion