/fiddler-mock-api-response

Efficient Fiddler script for mocking API responses. Tailored for developers to simulate APIs during testing, ensuring easy integration and usage.

Fiddler Mock API Response

This script for Fiddler allows you to mock API responses based on specific request criteria. It is particularly useful for testing and development purposes when you need to simulate API responses without actually hitting the live endpoints.

How to Use

  1. Install Fiddler: If you haven't already, install Fiddler, a free web debugging tool.

  2. Configure Fiddler:

    • In Fiddler, and go to Tools > Options > HTTPS.
    • Ensure the Capture HTTPS CONNECTs and Decrypt HTTPS traffic options are checked.

  3. Configure the Script:

    • In Fiddler, go to Rules > Customize Rules... to open the Fiddler Script Editor.
    • In Fiddler Script Editor, go to Go > to OnBeforeResponse.
    • Inside the OnBeforeResponse function, add the CheckAndMockResponse lines and ConvertPathToFilePath functions (see below).
    • Ensure the file paths in the ConvertPathToFilePath function reflect the structure and location of your mock JSON files.

  4. Create Mock JSON Files:

    • Create JSON files corresponding to the API responses you want to mock.
    • Save these files in the directory specified in the ConvertPathToFilePath function.
    • Note: The script replaces forward slashes (/) with backslashes (\) and question marks (?) with underscores (_) in the file paths.

  5. Run Fiddler:

    • Open https://web.develop.danskespil.dk/ in your browser to ensure Fiddler is capturing traffic.
    • Fiddler should open a "Certificate Error" modal. You need to click "Yes" to trust the Fiddler root certificate, and ignore the errors.
    • With Fiddler running, it will intercept requests and, where matching criteria are met, respond with the contents of the specified mock files.

  6. Test Your Application:

    • Run your application or make requests to the API endpoints you're mocking. Fiddler will serve the mock responses you've set up.
    • If a mock file is not found, Fiddler will log a message to the console with the required file path.

Script Functions

Add the following functions to your Fiddler script:

static function OnBeforeResponse(oSession: Session) {
    CheckAndMockResponse(oSession, "web.", "/dlo/scapi/danskespil/numbergames/groupplay/groups?includePlayers");
    CheckAndMockResponse(oSession, "web.", "/dli/scapi/danskespil/playeraccountmanagement/playergames/1/365/1/aktive/forhandler");
}

// Checks if the session matches the specified criteria and mocks the response if it does.
static function CheckAndMockResponse(oSession: Session, hostnamePrefix: String, pathAndQueryPrefix: String) {
    if (oSession.hostname.StartsWith(hostnamePrefix) && oSession.PathAndQuery.StartsWith(pathAndQueryPrefix) && oSession.oResponse.headers.ExistsAndContains("Content-Type", "application/json")) {
        var filePath = ConvertPathToFilePath(pathAndQueryPrefix);
        if (System.IO.File.Exists(filePath)) {
            oSession.responseCode = 200;
            var fileContents = System.IO.File.ReadAllText(filePath);
            oSession.utilSetResponseBody(fileContents);
        } else {
            FiddlerObject.log("\n\n    FILE NOT FOUND: " + filePath + "\n");
        }
    }
}

// Converts a given API path to a local file path by replacing slashes with backslashes, 
// replacing invalid filename characters, and appending '.json'.
static function ConvertPathToFilePath(path: String) : String {
    var basePath = "C:\\Projects\\fiddler-mock-api-response";
    var sanitizedPath = path.replace("/", "\\").replace("?", "_");
    var filePath = basePath + sanitizedPath + ".json";
    return filePath;
}