Source: https://datafa.st/docs/firebase-proxy
Markdown source: https://datafa.st/docs/firebase-proxy.md
Description: How to proxy DataFast analytics through Firebase Hosting using Cloud Functions to bypass adblockers and improve tracking accuracy.

# Proxy DataFast with Firebase Hosting

Learn how to proxy DataFast analytics through Firebase Hosting using Cloud Functions to bypass adblockers and improve accuracy.

> Note: Firebase Hosting does not support reverse proxy and rewrite rules for external destinations natively. This guide uses Firebase Cloud Functions as a workaround.

## 1. Set up Firebase Functions (if not already done)

If you haven't yet, add support of Firebase Functions to your Firebase project:

```bash
firebase init functions
```

Follow the instructions according to your setup. At the end, you should have a `/functions` folder in your project.

## 2. Install Dependencies

Make sure you're in the `functions/` folder and install required dependencies:

```bash
cd functions/
npm i -s express express-http-proxy
```

## 3. Create ReverseProxy Firebase Function

Create or update your `functions/index.js` file with the following code:

```javascript
const { onRequest } = require("firebase-functions/v2/https");
const express = require("express");
const proxy = require("express-http-proxy");

const app = express();

app.set("trust proxy", true);

// Proxy the DataFast script
app.use(
  "/js/script.js", proxy("https://datafa.st", {
    proxyReqPathResolver: () => "/js/script.js",
  }),
);

// Proxy the events endpoint
app.use(
  "/api/events", proxy("https://datafa.st", {
    proxyReqPathResolver: () => "/api/events",
    proxyReqOptDecorator: (proxyReqOpts, srcReq) => {
      // Forward client IP for accurate location analytics
      const clientIp = srcReq.headers['x-real-ip'] || 
                        srcReq.headers['x-forwarded-for']?.split(',')[0]?.trim() || 
                        srcReq.ip;
      proxyReqOpts.headers['x-datafast-real-ip'] = clientIp;
      return proxyReqOpts;
    }
  }),
);

exports.reverseProxy = onRequest(app);
```

> **Note:** If you already have an `/api/events` API endpoint, add `data-api-url` to the DataFast script tag to send events to your own API endpoint. For example, `data-api-url="/datafast-events"` will send events to `/datafast-events` instead of `/api/events`. Read more [here](/docs/script-configuration#api-url-data-api-url-optional)

> **Important:** If you notice all visitors showing from the same location in your analytics, make sure you're sending the `x-datafast-real-ip` header with the actual visitor IP address (not your proxy server IP) when forwarding events to DataFast's `/api/events` endpoint.

## 4. Configure Firebase Hosting Rewrites

Update your `firebase.json` to point to the `reverseProxy` function:

```json
{
  "hosting": {
    "public": "public",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ],
    "rewrites": [
      {
        "source": "/js/script.js",
        "function": "reverseProxy"
      },
      {
        "source": "/api/events",
        "function": "reverseProxy"
      }
    ]
  },
  "functions": [
    {
      "source": "functions",
      "codebase": "default",
      "ignore": ["node_modules", ".git", "firebase-debug.log", "firebase-debug.*.log", "*.local"]
    }
  ]
}
```

## 5. Update Your Script Tag

Replace your existing DataFast script with the proxied version:

```html
<script
  defer
  data-website-id="dfid_******"
  data-domain="your_domain.com"
  src="/js/script.js"
></script>
```

## 6. Deploy Firebase Hosting and Functions

Deploy both hosting and functions:

```bash
firebase deploy --only hosting,functions
```

## Verification

To verify the proxy is working:
1. Visit your website
2. Open the network tab in your browser's developer tools  
3. Check that analytics requests are going through your domain instead of datafa.st

## Troubleshooting

#### *All visitors showing from the same location*

If your analytics show all visitors from a single location (usually your server's location), your proxy isn't forwarding visitor IPs.

**To fix:**
1. Make sure your proxy sends the `x-datafast-real-ip` header with the actual visitor IP address (not your proxy server IP) when forwarding events to DataFast's `/api/events` endpoint