How to perform URL encoding/decoding in Terraform

In this tutorial, we’ll explore how to perform URL encoding and decoding within Terraform, a popular infrastructure as code (IaC) tool used for automating the deployment of infrastructure across multiple service providers. Terraform uses the HashiCorp Configuration Language (HCL), which is designed for ease of use and readability. Understanding how to encode and decode URLs is crucial when working with web-based resources and APIs within your Terraform configurations.

Introduction to URL Encoding/Decoding

URL encoding, also known as percent encoding, converts characters into a format that can be transmitted over the Internet. URL decoding is the reverse process. It’s essential when URLs contain characters that may not be interpreted correctly by the server or could potentially cause security issues.

Basics of URL Encoding/Decoding in Terraform

To begin, Terraform does not include built-in functions specifically named for URL encoding or decoding. However, you can utilize the replace function alongside Go’s string formatting capabilities, which are available in Terraform, to perform these tasks.

Example 1: Basic URL Encoding

variable "input_url" {
  description = "The URL to be encoded"
  type        = string
  default     = "https://example.com/query?name=John Doe&age=30"
}

output "encoded_url" {
  value = replace(var.input_url, " ", "%20")
}

This basic example demonstrates how to replace spaces with %20, a common requirement in URL encoding. While this method works for spaces, encoding URLs often requires replacing additional characters.

Advanced URL Encoding

For more comprehensive encoding, consider every character that needs encoding and systematically replace them using multiple replace functions or by integrating external tools or scripts that handle URL encoding.

Example 2: Comprehensive URL Encoding using External Tool

One method to achieve comprehensive URL encoding is by invoking an external tool or script from within a Terraform local-exec provisioner.

resource "null_resource" "urlencode" {
  triggers = {
    input_url = var.input_url
  }

  provisioner "local-exec" {
    command = "echo -n '${var.input_url}' | python -c 'import sys, urllib.parse; print(urllib.parse.quote_plus(sys.stdin.read()))'"
  }
}

This example uses Python’s urllib.parse.quote_plus function to perform URL encoding. The output of this command can be captured and utilized within your Terraform configuration, although capturing output from local-exec can be complex and may involve directing the output to a file and then reading it back into Terraform.

URL Decoding

Decoding involves converting percent-encoded characters back to their original representation. Similar to encoding, Terraform doesn’t provide a direct function for decoding. You can use an external tool or script for this purpose as well.

Example 3: URL Decoding Using External Tool

resource "null_resource" "urldecode" {
  triggers = {
    encoded_url = "https%3A%2F%2Fexample.com%2Fquery%3Fname%3DJohn%20Doe%26age%3D30"
  }

  provisioner "local-exec" {
    command = "echo -n '${self.triggers.encoded_url}' | python -c 'import sys, urllib.parse; print(urllib.parse.unquote_plus(sys.stdin.read()))'"
  }
}

Here, the urllib.parse.unquote_plus Python function is used for URL decoding. As with encoding, handling the output requires directing it to a file or using other methods to capture and utilize it within Terraform.

Handling Special Characters

When URLs contain characters beyond spaces, such as ?, =, or &, encoding becomes more challenging. Each of these characters has a specific encoded representation (e.g., %3F for ?, %3D for =, and %26 for &). Automating the encoding process for multiple characters can significantly streamline your Terraform configurations when dealing with APIs and web-based resources.

Conclusion

While Terraform does not provide direct functions for URL encoding and decoding, you can leverage external tools and scripts, along with strategic use of the replace function, to manage this process. Understanding how to encode and decode URLs in Terraform is invaluable for safely and accurately working with web-based APIs and resources.