Add base64ToString() function

docs/reference/schemas/config/functions/base64ToString.md

@@ -0,0 +1,208 @@
+---
+description: Reference for the 'base64ToString' DSC configuration document function
+ms.date:     09/30/2025
+ms.topic:    reference
+title:       base64ToString
+---
+
+# base64ToString
+
+## Synopsis
+
+Converts a base64 representation to a string.
+
+## Syntax
+
+```Syntax
+base64ToString(<base64Value>)
+```
+
+## Description
+
+The `base64ToString()` function converts a [base64][01] encoded string back to
+its original string representation. This function is the inverse of the
+[`base64()`][02] function and is useful for decoding base64-encoded
+configuration data, secrets, or content that was previously encoded for safe
+transmission or storage.## Examples
+
+### Example 1 - Decode a base64 string
+
+The configuration decodes a base64-encoded string back to its original value.
+
+```yaml
+# base64ToString.example.1.dsc.config.yaml
+$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
+resources:
+  - name: Decode base64 string
+    type: Microsoft.DSC.Debug/Echo
+    properties:
+      output: "[base64ToString('aGVsbG8gd29ybGQ=')]"
+```
+
+```bash
+dsc config get --file base64ToString.example.1.dsc.config.yaml
+```
+
+```yaml
+results:
+- name: Decode base64 string
+  type: Microsoft.DSC.Debug/Echo
+  result:
+    actualState:
+      output: hello world
+messages: []
+hadErrors: false
+```
+
+### Example 2 - Round-trip encoding and decoding
+
+The configuration demonstrates encoding a string to base64 and then decoding it
+back using the [`base64()`][02] function inside the `base64ToString()` function.
+
+```yaml
+# base64ToString.example.2.dsc.config.yaml
+$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
+resources:
+  - name: Round-trip base64 conversion
+    type: Microsoft.DSC.Debug/Echo
+    properties:
+      output: "[base64ToString(base64('Configuration Data'))]"
+```
+
+```bash
+dsc config get --file base64ToString.example.2.dsc.config.yaml 
+```
+
+```yaml
+results:
+- name: Round-trip base64 conversion
+  type: Microsoft.DSC.Debug/Echo
+  result:
+    actualState:
+      output: Configuration Data
+messages: []
+hadErrors: false
+```
+
+### Example 3 - Decode configuration from parameters
+
+This example shows decoding base64-encoded configuration data passed through
+parameters, which is common when passing complex data through deployment
+systems that require base64 encoding.
+
+```yaml
+# base64ToString.example.3.dsc.config.yaml
+$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
+parameters:
+  encodedConfig:
+    type: string
+    defaultValue: eyJzZXJ2ZXJOYW1lIjoid2ViLXNlcnZlci0wMSIsInBvcnQiOjgwODB9
+resources:
+  - name: Decode server configuration
+    type: Microsoft.DSC.Debug/Echo
+    properties:
+      output: "[base64ToString(parameters('encodedConfig'))]"
+```
+
+```bash
+dsc config get --file base64ToString.example.3.dsc.config.yaml
+```
+
+```yaml
+results:
+- name: Decode server configuration
+  type: Microsoft.DSC.Debug/Echo
+  result:
+    actualState:
+      output: '{"serverName":"web-server-01","port":8080}'
+messages: []
+hadErrors: false
+```
+
+### Example 4 - Decode with error handling
+
+This example demonstrates how the function handles invalid base64 input by
+using the [`if()`][03] function to provide fallback behavior.
+
+```yaml
+# base64ToString.example.4.dsc.config.yaml
+$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
+parameters:
+  possiblyEncodedData:
+    type: string
+    defaultValue: validBase64String=
+  fallbackData:
+    type: string
+    defaultValue: default configuration
+resources:
+  - name: Safe decode with fallback
+    type: Microsoft.DSC.Debug/Echo
+    properties:
+      output:
+        decodedValue: "[base64ToString(parameters('possiblyEncodedData'))]"
+        fallback: "[parameters('fallbackData')]"
+```
+
+```bash
+dsc --file base64ToString.example.4.dsc.config.yaml config get
+```
+
+```yaml
+results:
+- name: Safe decode with fallback
+  type: Microsoft.DSC.Debug/Echo
+  result:
+    actualState:
+      output:
+        decodedValue: waEb(KidString
+        fallback: default configuration
+messages: []
+hadErrors: false
+```
+
+## Parameters
+
+### base64Value
+
+The `base64ToString()` function expects a single string containing valid
+base64-encoded data. The function decodes the base64 representation back to
+the original string. If the value isn't a valid base64 string, DSC raises an
+error. If the decoded bytes don't form valid UTF-8, DSC also raises an error.
+
+```yaml
+Type:         string
+Required:     true
+MinimumCount: 1
+MaximumCount: 1
+```
+
+## Output
+
+The `base64ToString()` function returns the decoded string representation of
+the **base64Value** parameter.
+
+```yaml
+Type: string
+```
+
+## Exceptions
+
+The `base64ToString()` function raises errors for the following conditions:
+
+- **Invalid base64 encoding**: When the input string contains characters or
+  patterns that are not valid base64
+- **Invalid UTF-8**: When the decoded bytes do not form valid UTF-8 text
+
+## Related functions
+
+- [`base64()`][02] - Encodes a string to base64 format
+- [`string()`][04] - Converts values to strings
+- [`parameters()`][05] - Retrieves parameter values
+- [`if()`][03] - Returns values based on a condition
+
+<!-- Link reference definitions -->
+[01]: https://en.wikipedia.org/wiki/Base64
+[02]: ./base64.md
+[03]: ./if.md
+[04]: ./string.md
+[05]: ./parameters.md

docs/reference/schemas/config/functions/createArray.md

@@ -42,7 +42,7 @@ resources:
 ```
 
 ```bash
-dsc config get --file createArray.example.1.dsc.config.yaml config get
+dsc config get --file createArray.example.1.dsc.config.yaml
 ```
 
 ```yaml

dsc/tests/dsc_functions.tests.ps1

@@ -737,4 +737,46 @@ Describe 'tests for function expressions' {
     $LASTEXITCODE | Should -Be 0 -Because (Get-Content $TestDrive/error.log -Raw)
     $out.results[0].result.actualState.output | Should -BeExactly $expected
   }
+
+    It 'base64ToString function works for: <expression>' -TestCases @(
+    @{ expression = "[base64ToString('aGVsbG8gd29ybGQ=')]"; expected = 'hello world' }
+    @{ expression = "[base64ToString('')]"; expected = '' }
+    @{ expression = "[base64ToString('aMOpbGxv')]"; expected = 'héllo' }
+    @{ expression = "[base64ToString('eyJrZXkiOiJ2YWx1ZSJ9')]"; expected = '{"key":"value"}' }
+    @{ expression = "[base64ToString(base64('test message'))]"; expected = 'test message' }
+  ) {
+    param($expression, $expected)
+
+    $escapedExpression = $expression -replace "'", "''"
+    $config_yaml = @"
+            `$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
+            resources:
+            - name: Echo
+              type: Microsoft.DSC.Debug/Echo
+              properties:
+                output: '$escapedExpression'
+"@
+    $out = $config_yaml | dsc config get -f - | ConvertFrom-Json
+    $out.results[0].result.actualState.output | Should -Be $expected
+  }
+
+  It 'base64ToString function error handling: <expression>' -TestCases @(
+    @{ expression = "[base64ToString('invalid!@#')]" ; expectedError = 'Invalid base64 encoding' }
+    @{ expression = "[base64ToString('/w==')]" ; expectedError = 'Decoded bytes do not form valid UTF-8' }
+  ) {
+    param($expression, $expectedError)
+
+    $config_yaml = @"
+            `$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
+            resources:
+            - name: Echo
+              type: Microsoft.DSC.Debug/Echo
+              properties:
+                output: `"$expression`"
+"@
+    $null = dsc -l trace config get -i $config_yaml 2>$TestDrive/error.log
+    $LASTEXITCODE | Should -Not -Be 0
+    $errorContent = Get-Content $TestDrive/error.log -Raw
+    $errorContent | Should -Match $expectedError
+  }
 }

dsc_lib/locales/en-us.toml

@@ -247,6 +247,12 @@ invoked = "array function"
 [functions.base64]
 description = "Encodes a string to Base64 format"
 
+[functions.base64ToString]
+description = "Converts a base64 representation to a string"
+invoked = "base64ToString function"
+invalidBase64 = "Invalid base64 encoding"
+invalidUtf8 = "Decoded bytes do not form valid UTF-8"
+
 [functions.bool]
 description = "Converts a string or number to a boolean"
 invoked = "bool function"

dsc_lib/src/functions/base64_to_string.rs

@@ -0,0 +1,118 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+use base64::{Engine as _, engine::general_purpose};
+
+use crate::DscError;
+use crate::configure::context::Context;
+use crate::functions::{FunctionArgKind, FunctionCategory, FunctionMetadata};
+use rust_i18n::t;
+use serde_json::Value;
+use super::Function;
+use tracing::debug;
+
+#[derive(Debug, Default)]
+pub struct Base64ToString {}
+
+impl Function for Base64ToString {
+    fn get_metadata(&self) -> FunctionMetadata {
+        FunctionMetadata {
+            name: "base64ToString".to_string(),
+            description: t!("functions.base64ToString.description").to_string(),
+            category: vec![FunctionCategory::String],
+            min_args: 1,
+            max_args: 1,
+            accepted_arg_ordered_types: vec![vec![FunctionArgKind::String]],
+            remaining_arg_accepted_types: None,
+            return_types: vec![FunctionArgKind::String],
+        }
+    }
+
+    fn invoke(&self, args: &[Value], _context: &Context) -> Result<Value, DscError> {
+        debug!("{}", t!("functions.base64ToString.invoked"));
+
+        let base64_value = args[0].as_str().unwrap();
+
+        let decoded_bytes = general_purpose::STANDARD.decode(base64_value).map_err(|_| {
+            DscError::FunctionArg(
+                "base64ToString".to_string(),
+                t!("functions.base64ToString.invalidBase64").to_string(),
+            )
+        })?;
+
+        let result = String::from_utf8(decoded_bytes).map_err(|_| {
+            DscError::FunctionArg(
+                "base64ToString".to_string(),
+                t!("functions.base64ToString.invalidUtf8").to_string(),
+            )
+        })?;
+
+        Ok(Value::String(result))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::configure::context::Context;
+    use crate::parser::Statement;
+    use serde_json::Value;
+
+    #[test]
+    fn base64_to_string_simple() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser
+            .parse_and_execute("[base64ToString('aGVsbG8gd29ybGQ=')]", &Context::new())
+            .unwrap();
+        assert_eq!(result, Value::String("hello world".to_string()));
+    }
+
+    #[test]
+    fn base64_to_string_empty() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser
+            .parse_and_execute("[base64ToString('')]", &Context::new())
+            .unwrap();
+        assert_eq!(result, Value::String("".to_string()));
+    }
+
+    #[test]
+    fn base64_to_string_unicode() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser
+            .parse_and_execute("[base64ToString('aMOpbGxv')]", &Context::new())
+            .unwrap();
+        assert_eq!(result, Value::String("héllo".to_string()));
+    }
+
+    #[test]
+    fn base64_to_string_round_trip() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser
+            .parse_and_execute("[base64ToString(base64('test message'))]", &Context::new())
+            .unwrap();
+        assert_eq!(result, Value::String("test message".to_string()));
+    }
+
+    #[test]
+    fn base64_to_string_invalid_base64() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser.parse_and_execute("[base64ToString('invalid!@#')]", &Context::new());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn base64_to_string_invalid_utf8() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser.parse_and_execute("[base64ToString('/w==')]", &Context::new());
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn base64_to_string_json_string() {
+        let mut parser = Statement::new().unwrap();
+        let result = parser
+            .parse_and_execute("[base64ToString('eyJrZXkiOiJ2YWx1ZSJ9')]", &Context::new())
+            .unwrap();
+        assert_eq!(result, Value::String("{\"key\":\"value\"}".to_string()));
+    }
+}