Update README.md

middleware/README.md

@@ -117,6 +117,115 @@ Package expose following functions to process raw HTTP payloads:
 Also it is totally legit to use standard `Buffer` functions like `indexOf` for processing the HTTP payload. Just do not forget that if you modify the body, update the `Content-Length` header with a new value. And if you modify any of the headers, line endings should be `\r\n`. Rest is up to your imagination.
 
 
+## Masking PII Data
+
+This middleware provides functionality to mask Personally Identifiable Information (PII) data in HTTP requests based on specified headers and JSON paths. It allows you to define a configuration object that specifies which headers and JSON fields should be masked and the type of data they represent.
+
+```javascript
+const gor = require("goreplay_middleware");
+const faker = require("faker");
+
+// Initialize the middleware
+gor.init();
+
+// Configuration for masking PII data
+const maskConfig = {
+  headers: [
+    { name: "Authorization", type: "token" },
+    { name: "X-API-Key", type: "token" },
+    { name: "X-User-Email", type: "email" },
+    { name: "X-User-Name", type: "name" },
+  ],
+  jsonPaths: [
+    { path: "$.user.email", type: "email" },
+    { path: "$.user.name", type: "name" },
+    { path: "$.user.phone", type: "phone" },
+    { path: "$.user.address", type: "address" },
+  ],
+};
+
+// Function to mask a value based on its type
+function maskValue(type) {
+  switch (type) {
+    case "email":
+      return faker.internet.email();
+    case "name":
+      return faker.name.findName();
+    case "phone":
+      return faker.phone.phoneNumber();
+    case "address":
+      return faker.address.streetAddress();
+    case "token":
+      return faker.random.alphaNumeric(32);
+    default:
+      return "***";
+  }
+}
+
+// Middleware function to mask PII data
+gor.on("message", (data) => {
+  // Mask headers
+  maskConfig.headers.forEach((header) => {
+    const value = gor.httpHeader(data.http, header.name);
+    if (value) {
+      data.http = gor.setHttpHeader(data.http, header.name, maskValue(header.type));
+    }
+  });
+
+  // Mask JSON fields
+  const body = gor.httpBody(data.http);
+  if (body) {
+    try {
+      const jsonBody = JSON.parse(body.toString());
+      maskConfig.jsonPaths.forEach((field) => {
+        const value = eval(`jsonBody${field.path.slice(1)}`);
+        if (value) {
+          eval(`jsonBody${field.path.slice(1)} = maskValue(field.type)`);
+        }
+      });
+      data.http = gor.setHttpBody(data.http, Buffer.from(JSON.stringify(jsonBody)));
+    } catch (error) {
+      console.error("Error parsing JSON body:", error);
+    }
+  }
+
+  return data;
+});
+```
+
+### Configuration
+
+The `maskConfig` object is used to configure the masking behavior. It consists of two properties:
+
+- `headers`: An array of objects representing the headers to be masked. Each object should have the following properties:
+  - `name`: The name of the header.
+  - `type`: The type of data the header represents (e.g., "email", "name", "token").
+
+- `jsonPaths`: An array of objects representing the JSON paths to be masked. Each object should have the following properties:
+  - `path`: The JSON path to the field to be masked (e.g., "$.user.email").
+  - `type`: The type of data the field represents (e.g., "email", "name", "phone", "address").
+
+### Masking Function
+
+The `maskValue` function is responsible for generating masked values based on the data type. It uses the Faker library to generate realistic-looking masked data for different types such as email, name, phone, address, and token. You can extend this function to support additional data types or customize the masking behavior.
+
+### Middleware Function
+
+The middleware function is triggered for each HTTP message (request or response) processed by GoReplay. It performs the following steps:
+
+1. Iterate over the specified headers in the `maskConfig` and mask their values using the `maskValue` function based on the associated data type.
+
+2. Parse the JSON body of the request (if present) and iterate over the specified JSON paths in the `maskConfig`. If a value exists at a given path, replace it with a masked value generated by the `maskValue` function based on the associated data type.
+
+3. Update the request body with the masked JSON data.
+
+4. Return the modified HTTP message.
+
+Note: The middleware uses the `eval` function to dynamically access and modify the JSON object based on the provided paths. Exercise caution when using `eval` and ensure that the paths are properly validated to prevent potential security risks.
+
+To use this middleware, make sure to install the required dependencies (`goreplay_middleware` and `faker`), configure the `maskConfig` object according to your needs, and run the middleware with GoReplay.
+
+
 ## Support
 
 Feel free to ask questions here and by sending email to [support@goreplay.org](mailto:support@goreplay.org). Commercial support is available and welcomed 🙈.