Add Advanced Validation for AWS::Serverless::Api GET Query Params: A Step-by-Step Guide

Welcome to the world of serverless APIs! With AWS::Serverless::Api, you can build scalable and efficient APIs with ease. However, as your API grows, so does the importance of validating user input. In this article, we’ll dive into the world of advanced validation for AWS::Serverless::Api GET query params. Buckle up, folks!

Why Validate GET Query Params?

Validation is crucial in ensuring the integrity and security of your API. Without proper validation, your API becomes vulnerable to attacks and errors. Here are a few reasons why you should validate GET query params:

• Security**: Malicious users can inject harmful data, leading to security breaches and API crashes.
• Data Integrity**: Invalid data can lead to incorrect results, affecting your API’s performance and credibility.
• UX**: Validating user input ensures a smooth user experience, reducing errors and frustration.

Getting Started with AWS::Serverless::Api Validation

Before we dive into advanced validation, let’s cover the basics. AWS::Serverless::Api provides a built-in validation mechanism using the `requestValidator` property. You can define a schema for your API using AWS API Gateway’s Request Validator.

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "MyApi": {
      "Type": "AWS::Serverless::Api",
      "Properties": {
        "StageName": "dev",
        "EndpointConfiguration": "EDGE",
        "RequestValidator": {
          "ValidateRequestBody": true,
          "ValidateRequestParameters": true
        }
      }
    }
  }
}

The above code snippet enables request body and parameter validation for our API. However, this built-in validation is limited and doesn’t provide advanced features like custom validation logic or conditional validation. That’s where we come in!

Advanced Validation using AWS Lambda and AWS SDK

To add advanced validation, we’ll use an AWS Lambda function and the AWS SDK. We’ll create a separate Lambda function for validation, which will handle the validation logic for our GET query params.

Step 1: Create a Lambda Function for Validation

Create a new Lambda function using your preferred programming language (e.g., Node.js, Python, or Java). Name it something like `validationLambda`. This function will receive the GET query params as an event object.

// Node.js example
exports.handler = async (event) => {
  // TO DO: Implement validation logic here
  return {
    statusCode: 200,
    body: JSON.stringify({ message: 'Validation successful!' }),
  };
};

Step 2: Configure the API Gateway to use the Validation Lambda

Update your `serverless.yml` file to integrate the validation Lambda function with your API Gateway:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "MyApi": {
      "Type": "AWS::Serverless::Api",
      "Properties": {
        "StageName": "dev",
        "EndpointConfiguration": "EDGE",
        "RequestValidator": {
          "ValidateRequestBody": true,
          "ValidateRequestParameters": true
        },
        "ApiGatewayRestApi": {
          "Events": {
            "GET /": {
              "Integration": {
                "IntegrationHttpMethod": "POST",
                "IntegrationUri": {
                  "Fn::Sub": "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${ValidationLambdaFunction}/invocations"
                },
                "RequestTemplates": {
                  "application/json": "{ \"params\": $input.params() }"
                },
                "Responses": [
                  {
                    "StatusCode": 200,
                    "SelectionPattern": "2.."
                  }
                ]
              }
            }
          }
        }
      }
    }
  }
}

Step 3: Implement Custom Validation Logic

Now it’s time to implement the custom validation logic in your Lambda function. Let’s assume we want to validate a `searchQuery` param, which should be a string with a minimum length of 3 characters.

// Node.js example
exports.handler = async (event) => {
  const { params } = event;
  const searchQuery = params.searchQuery;

  if (!searchQuery || typeof searchQuery !== 'string' || searchQuery.length < 3) {
    return {
      statusCode: 400,
      body: JSON.stringify({ message: 'Invalid search query' }),
    };
  }

  // Validation successful! Return a 200 status code
  return {
    statusCode: 200,
    body: JSON.stringify({ message: 'Validation successful!' }),
  };
};

Conditional Validation using Environment Variables

Sometimes, you might need to validate different query params based on specific conditions. You can use environment variables to achieve conditional validation.

Step 1: Define Environment Variables

In your `serverless.yml` file, define environment variables for your Lambda function:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "MyApi": {
      "Type": "AWS::Serverless::Api",
      "Properties": {
        "StageName": "dev",
        "EndpointConfiguration": "EDGE",
        "Environment": {
          "NODE_ENV": "dev",
          "VALIDATE_QUERY_PARAM": "searchQuery"
        }
      }
    }
  }
}

Step 2: Implement Conditional Validation in your Lambda Function

Update your Lambda function to use the environment variable to determine which query param to validate:

// Node.js example
exports.handler = async (event) => {
  const { params } = event;
  const validateQueryParam = process.env.VALIDATE_QUERY_PARAM;

  if (validateQueryParam === 'searchQuery') {
    const searchQuery = params.searchQuery;
    if (!searchQuery || typeof searchQuery !== 'string' || searchQuery.length < 3) {
      return {
        statusCode: 400,
        body: JSON.stringify({ message: 'Invalid search query' }),
      };
    }
  } else if (validateQueryParam === 'filterParam') {
    const filterParam = params.filterParam;
    if (!filterParam || typeof filterParam !== 'string' || filterParam.length < 2) {
      return {
        statusCode: 400,
        body: JSON.stringify({ message: 'Invalid filter param' }),
      };
    }
  }

  // Validation successful! Return a 200 status code
  return {
    statusCode: 200,
    body: JSON.stringify({ message: 'Validation successful!' }),
  };
};

Conclusion

And that's it! You've successfully implemented advanced validation for AWS::Serverless::Api GET query params using AWS Lambda and environment variables. By following these steps, you can ensure your API is secure, efficient, and provides a better user experience.

Best Practices

• Use a separate Lambda function for validation to keep your API logic organized.
• Use environment variables to make your validation logic more flexible and conditional.
• Test your validation logic thoroughly to ensure it's working as expected.

Happy coding, and remember to validate those query params!

Keyword	Learn More
AWS::Serverless::Api	AWS SAM API Documentation
AWS Lambda	AWS Lambda Documentation
Request Validator	API Gateway Request Validation Documentation

10. Additional Resources
    • Using API Gateway and Lambda Functions to Validate API Requests
    • Validation in Serverless APIs: AWS API Gateway and Lambda

Frequently Asked Question

Are you struggling to add advanced validation for AWS::Serverless::Api GET query params? You're not alone! Here are some frequently asked questions to help you navigate the process: