create-dsc-resource

name	create-dsc-resource
description	Create a complete, accurate DSC resource in this repository following the provided guidelines and design patterns.

Create high‑quality DSC resource

You are a code agent. Your task is to create a complete, accurate DSC resource in this repository.

What is a DSC Resource?

A DSC (Desired State Configuration) resource is an executable that performs configuration tasks for a specific domain. Example domains include Windows features, package manager, services, files, registry, and more. Each resource has a specific schema and set of properties that define its behavior. Management tasks or operations are specific to the resource type, but may include: get, set, test, and export.

Key Principles

• Programming language: Resources in this repository may be implemented in Rust or as scripts (for example, PowerShell). The guidance in this skill primarily applies to Rust-based resources.
• Resource manifest: A JSON file that defines the resource type name, supported operations (including executable and arguments), and JSON schema for input parameters
• Dependency management: All crates must be listed in Cargo.toml specifying to use workspace dependencies. The root level Cargo.toml should be updated to include the new crates or associated to the DSC resource project.
• Project files: A .project.data.json file in the root of the project folder defines properties of the project and non-code files to include during build
• Localization: For Rust-based resources, all user-facing strings must use rust-i18n for internationalization. For script-based resources (such as PowerShell), follow the existing localization and string-handling patterns used by those scripts or any repository-specific localization guidance.
• Copyright headers: Every source file must start with the copyright header:

  // Copyright (c) Microsoft Corporation.
  // Licensed under the MIT License.
  
  

  For PowerShell test files, use # comment syntax instead of //.

File Structure and Content Guidelines

1. Required Setup

• Use cargo new --bin <resource_name> to create a new Rust binary project for the resource under the resources directory
• Create a resource manifest JSON file named <resource_name>.dsc.resource.json in the same directory using ./resources/windows_service/windows_service.dsc.resource.json as an example
• Create a .project.data.json file in the root of the resource project directory
• Create a locales/en-us.toml file for localized strings

2. .project.data.json

This file defines the project metadata used by the build system. Structure:

{
    "Name": "<resource_name>",
    "Kind": "Resource",
    "IsRust": true,
    "SupportedPlatformOS": "Windows",
    "Binaries": [
        "<resource_name>"
    ],
    "CopyFiles": {
        "Windows": [
            "<resource_name>.dsc.resource.json"
        ]
    }
}

• SupportedPlatformOS: Use "Windows" for Windows-only resources. Omit this field for cross-platform resources.
• CopyFiles: Use "Windows" for Windows-only files, "All" for cross-platform files.

3. Cargo.toml

[package]
name = "<resource_name>"
version = "0.1.0"
edition = "2024"

[[bin]]
name = "<resource_name>"
path = "src/main.rs"

[package.metadata.i18n]
available-locales = ["en-us"]
default-locale = "en-us"
load-path = "locales"

[dependencies]
rust-i18n = { workspace = true }
serde = { workspace = true }
serde_json = { workspace = true }

[target.'cfg(windows)'.dependencies]
windows = { workspace = true }

• All dependencies should reference { workspace = true } to use workspace-level version pinning.
• Use [target.'cfg(windows)'.dependencies] for Windows-only crates like windows.
• The [package.metadata.i18n] section configures the rust-i18n crate.

4. Resource Manifest (<resource_name>.dsc.resource.json)

Key fields:

{
    "$schema": "https://aka.ms/dsc/schemas/v3/bundled/resource/manifest.json",
    "type": "Microsoft.<Namespace>/<Resource>",
    "description": "Short description of the resource",
    "tags": ["Windows"],
    "version": "0.1.0",
    "get": {
        "executable": "<resource_name>",
        "args": ["get", { "jsonInputArg": "--input", "mandatory": true }]
    },
    "set": {
        "executable": "<resource_name>",
        "args": ["set", { "jsonInputArg": "--input", "mandatory": true }],
        "implementsPretest": false,
        "return": "state",
        "requireSecurityContext": "elevated"
    },
    "export": {
        "executable": "<resource_name>",
        "args": ["export", { "jsonInputArg": "--input", "mandatory": false }]
    },
    "exitCodes": {
        "0": "Success",
        "1": "Invalid arguments",
        "2": "Invalid input",
        "3": "Resource-specific error description"
    },
    "schema": {
        "embedded": { ... }
    }
}

• implementsPretest: Set to false if set does not internally perform a test first. DSC will call test before set automatically.
• return: Use "state" if the set operation returns the final state of the resource.
• requireSecurityContext: Use "elevated" for operations that require administrator privileges.
• schema.embedded: Define the JSON schema inline with "additionalProperties": false. Schema property names use camelCase. Use "readOnly": true for properties that are output-only (e.g., _exist).

5. Essential Design Patterns

main.rs file

• Initialize rust-i18n with rust_i18n::i18n!("locales", fallback = "en-us");
• Define named exit code constants at the module level:

  const EXIT_SUCCESS: i32 = 0;
  const EXIT_INVALID_ARGS: i32 = 1;
  const EXIT_INVALID_INPUT: i32 = 2;
  const EXIT_RESOURCE_ERROR: i32 = 3;
  

• Implement common helper functions:
  • write_error(message) — writes {"error": "<message>"} to stderr
  • require_input(input_json) — deserializes the JSON input or exits with an error
  • print_json(value) — serializes and prints to stdout, or exits with an error
  • parse_input_arg(args) — parses --input <json> from command-line arguments
• Use t!("key") macro from rust-i18n for all user-facing strings (error messages, etc.)
• For platform-specific resources, use conditional compilation:

  #[cfg(not(windows))]
  fn main() {
      write_error(&t!("main.windowsOnly"));
      exit(EXIT_RESOURCE_ERROR);
  }
  
  #[cfg(windows)]
  fn main() {
      // ... actual implementation
  }
  

• Parse operations as the first positional argument (e.g., get, set, export), with --input <json> as the input argument

types.rs file

• Define Rust structs that represent the input parameters for each operation, matching the JSON schema defined in the resource manifest
• Implement serialization and deserialization for these types using Serde
• Use Serde attributes to map between Rust snake_case and JSON camelCase:

  #[derive(Debug, Default, Serialize, Deserialize, Clone)]
  #[serde(rename_all = "camelCase")]
  pub struct MyResource {
      #[serde(skip_serializing_if = "Option::is_none")]
      pub some_field: Option<String>,
  
      #[serde(rename = "_exist", skip_serializing_if = "Option::is_none")]
      pub exist: Option<bool>,
  }
  

• Use Option<T> for all fields so that partial input is accepted (only specified fields are acted upon)
• Define enums for properties with constrained values, each with Serialize, Deserialize, PartialEq, Clone derives
• Implement std::fmt::Display for enums that need string representation
• Define a custom error type with std::error::Error and std::fmt::Display implementations, plus a From<String> conversion

Localization (locales/en-us.toml)

All user-facing strings must be defined in a TOML locale file and referenced via the t!() macro. Structure:

_version = 1

[main]
missingOperation = "Missing operation. Usage: <resource_name> get --input <json> | set --input <json>"
unknownOperation = "Unknown operation: '%{operation}'. Expected: get, set, or export"
missingInput = "Missing --input argument"
invalidJson = "Invalid JSON input: %{error}"

[get]
someError = "Failed to do something: %{error}"

[set]
someError = "Failed to do something: %{error}"

• Group messages by operation (main, get, set, export)
• Use %{variable} syntax for interpolated values
• Reference in Rust code as t!("section.key", variable = value)

Calling native APIs

• Create a separate module (e.g., service.rs) for interacting with native OS APIs that contains unsafe code and FFI bindings
• Gate the module with #[cfg(windows)] if it uses Windows-specific APIs
• Use RAII wrappers for OS handles that call cleanup functions on Drop (e.g., CloseServiceHandle, CloseHandle)
• Use helper functions for UTF-16 string conversion (to_wide, pwstr_to_string)
• The code should be designed to be architecture agnostic, working on both x64 and ARM64 systems

Error handling

• Use Rust's Result type for error handling in operation handlers
• Writing of errors should only be done in the main.rs file, with error messages that are clear and actionable for users of the resource
• Errors are written as a JSONLine to stderr using the format: {"error": "Error message here"}
• Warnings are written as a JSONLine to stderr using the format: {"warn": "Warning message here"}
• A non-zero exit code should be returned for any operation that encounters an error, while warnings should not affect the exit code
• Use different exit codes for different types of errors. Define named constants (e.g., EXIT_INVALID_ARGS, EXIT_INVALID_INPUT) and document each in the resource manifest exitCodes section.

Testing Instructions

• Create a tests folder in the resource project directory
• For each operation supported by the resource (get, set, test, export as applicable), create a separate test file (e.g., <resource_name>_get.tests.ps1, <resource_name>_set.tests.ps1, etc.)
• The resource should be tested using dsc resource command instead of calling the executable directly
• Pipe JSON input via stdin using the -f - flag: $json | dsc resource get -r $resourceType -f -
• Redirect stderr to a file for debugging: 2>$testdrive/error.log
• Use -Because with $LASTEXITCODE assertions to include stderr output for diagnostics:

  $out = $json | dsc resource get -r $resourceType -f - 2>$testdrive/error.log
  $LASTEXITCODE | Should -Be 0 -Because (Get-Content -Raw $testdrive/error.log)
  

• Parse the output and access the actual state via $output.actualState:

  $output = $out | ConvertFrom-Json
  $result = $output.actualState
  

• For platform-specific resources, use -Skip on the top-level Describe block:

  Describe 'Resource tests' -Skip:(!$IsWindows) { ... }
  

• For tests requiring elevated privileges, add an admin check to the skip condition
• Use -ForEach or -TestCases for data-driven tests (e.g., validating enum property values)
• Follow the PowerShell Pester v5 testing instructions for structuring the tests and making assertions

Code Style Guidelines

• Use Rust pedantic clippy linting rules for all code in the resource project

Build and Deployment

• The resource should be built using build.ps1 -project <resource_name> from the root of the repository, which will handle building the Rust code and ensure it is found in PATH for testing

What-If support

Follow this pattern exactly when adding what-if (a.k.a. dsc config set --what-if) support to any resource so the implementation path, manifest changes, tests, and naming stay consistent across the repository.

What-if must:

1. Project the final state the resource would produce, without mutating the system.
2. Echo back the relevant input fields (keyPath, valueName, valueData, etc.) so the engine can diff before/after.
3. Attach human-readable "would do …" messages under _metadata.whatIf (an array of strings).
4. Exit 0 on success — what-if is not an error path.

1. Resource manifest changes

In the resource's *.dsc.resource.json, add whatIfArg to the set (and delete, if it supports what-if) args array, and declare whatIfReturns: "state" on set:

"set": {
    "executable": "<resource_name>",
    "args": [
        "config", "set",
        { "jsonInputArg": "--input", "mandatory": true },
        { "whatIfArg": "--what-if" }
    ],
    "whatIfReturns": "state"
},
"delete": {
    "executable": "<resource_name>",
    "args": [
        "config", "delete",
        { "jsonInputArg": "--input", "mandatory": true },
        { "whatIfArg": "--what-if" }
    ]
}

• whatIfArg is the literal CLI flag DSC will append when the user runs dsc config set --what-if. Always use "--what-if" (long form) for consistency across resources.
• whatIfReturns: "state" tells DSC the executable prints the projected post-state JSON on stdout (same shape as get/set returns).
• The --list (bulk) variant of a resource uses the same two manifest additions; do not invent new flag names.

2. CLI args (args.rs) changes

Add a -w / --what-if boolean to every ConfigSubCommand variant that can support what-if:

#[derive(Debug, PartialEq, Eq, Subcommand)]
pub enum ConfigSubCommand {
    #[clap(name = "set", about = t!("args.configSetAbout").to_string())]
    Set {
        #[clap(short, long, required = true, help = t!("args.configArgsInputHelp").to_string())]
        input: String,
        #[clap(short = 'w', long, help = t!("args.configArgsWhatIfHelp").to_string())]
        what_if: bool,
    },
    #[clap(name = "delete", about = t!("args.configDeleteAbout").to_string())]
    Delete {
        #[clap(short, long, required = true, help = t!("args.configArgsInputHelp").to_string())]
        input: String,
        #[clap(short = 'w', long, help = t!("args.configArgsWhatIfHelp").to_string())]
        what_if: bool,
    },
}

Naming is fixed: clap field is what_if, short flag is -w, long flag is --what-if, help key is args.configArgsWhatIfHelp.

3. main.rs dispatch

In each Set / Delete arm, destructure what_if, call helper.enable_what_if() when true, and print the returned projected state on stdout. Never mutate state when what_if is true.

args::ConfigSubCommand::Set { input, what_if } => {
    trace!("Set input: {input}, what_if: {what_if}");
    let mut helper = match Helper::new_from_json(&input) {
        Ok(h) => h,
        Err(err) => { error!("{err}"); exit(EXIT_INVALID_INPUT); }
    };
    if what_if { helper.enable_what_if(); }

    match helper.set() {
        Ok(Some(state)) => {
            // Set returns Some(state) when what_if is true (projected state)
            // OR when whatIfReturns == "state" and the resource emits final state.
            let json = serde_json::to_string(&state).unwrap();
            println!("{json}");
        }
        Ok(None) => {}
        Err(err) => { error!("{err}"); exit(EXIT_RESOURCE_ERROR); }
    }
    exit(EXIT_SUCCESS);
}

For the --list bulk variant, accumulate projected states in a Vec, then print the whole list once at the end.

4. Library / helper changes

In the resource's dsc-lib-* crate:

• Add a what_if: bool field on the helper struct, defaulting to false in every constructor.

• Expose pub fn enable_what_if(&mut self) { self.what_if = true; }.

• Change set() (and remove()) to return Result<Option<T>, Error> where Some(T) is the projected state when what_if is true.

• Inside set / remove, build a Vec<String> what_if_metadata, push localized "Would …" strings at each side-effecting branch, and short-circuit before the real OS call when self.what_if:

  if self.what_if {
      what_if_metadata.push(t!("<resource>_helper.whatIfCreate<Thing>", name = name).to_string());
  } else {
      // perform the real OS mutation
  }
  

• Return the projected state with the metadata attached:

  return Ok(Some(<ResourceState> {
      // identity + projected fields the engine needs to diff
      metadata: if what_if_metadata.is_empty() {
          None
      } else {
          Some(Metadata { what_if: Some(what_if_metadata) })
      },
      ..Default::default()
  }));
  

• Add a handle_error_or_what_if(error) helper that, in what-if mode, turns an error into a projected state whose _metadata.whatIf contains the error message, instead of failing the run:

  fn handle_error_or_what_if(&self, error: Error) -> Result<Option<T>, Error> {
      if self.what_if {
          return Ok(Some(T {
              // identity fields from self.config
              metadata: Some(Metadata { what_if: Some(vec![error.to_string()]) }),
              ..Default::default()
          }));
      }
      Err(error)
  }
  

• Handle the _exist: false delete case inside set() by routing through remove() (with what_if honored), so users get a single what-if message describing the deletion.

5. Types (config.rs / types.rs) changes

Add a _metadata field of type Option<Metadata> to every public state struct, and define Metadata exactly once per crate:

#[derive(Debug, Default, Clone, PartialEq, Serialize, Deserialize, JsonSchema)]
#[serde(rename = "<ResourceName>", deny_unknown_fields)]
pub struct <ResourceName> {
    // ... resource properties ...

    #[serde(rename = "_metadata", skip_serializing_if = "Option::is_none")]
    pub metadata: Option<Metadata>,

    #[serde(rename = "_exist", skip_serializing_if = "Option::is_none")]
    pub exist: Option<bool>,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, JsonSchema)]
#[serde(deny_unknown_fields)]
pub struct Metadata {
    #[serde(rename = "whatIf", skip_serializing_if = "Option::is_none")]
    pub what_if: Option<Vec<String>>,
}

Naming is fixed: JSON field is _metadata, nested array is whatIf, Rust field is what_if: Option<Vec<String>>.

6. Localization strings

Add localized what-if messages to locales/en-us.toml under the helper's section, all starting with the verb "Would":

[<resource>_helper]
whatIfCreate<Thing>  = "Would create %{name}"
whatIfUpdate<Thing>  = "Would update %{name} to '%{value}'"
whatIfDelete<Thing>  = "Would delete %{name} '%{value}'"

Examples:

whatIfCreate<Thing>  = "<Thing> '%{name}' not found, would create it"
whatIfDelete<Thing>  = "Would delete <thing> '%{name}'"

Also add args.configArgsWhatIfHelp = "Run the operation in what-if mode" (or equivalent) for the clap flag.

7. What-if Pester tests

Create one dedicated test file per resource variant. Names are fixed:

• <resource>.config.whatif.tests.ps1 — single-instance what-if
• <resource>list_whatif.tests.ps1 — --list bulk what-if (only if the resource has a list variant)

Structure:

# Copyright (c) Microsoft Corporation.
# Licensed under the MIT License.

Describe '<resource> config whatif tests' {
    BeforeAll {
        # Ensure a clean starting state
    }

    AfterEach {
        # Roll back anything a test may have created
    }

    It 'Can whatif a new <thing>' -Skip:(!$IsWindows) {
        $json = @'
        { "<key>": "<value>" }
'@
        # 1. Capture pre-state
        $get_before = <resource> config get --input $json 2>$null

        # 2. Run what-if
        $result = <resource> config set -w --input $json 2>$null | ConvertFrom-Json

        # 3. Assert success + projected state + whatIf metadata
        $LASTEXITCODE       | Should -Be 0
        $result.<key>       | Should -Be '<value>'
        $result._metadata.whatIf[0] | Should -Match '.*<expected fragment>.*'

        # 4. Assert NO mutation happened
        $get_after = <resource> config get --input $json 2>$null
        $get_before | Should -EQ $get_after
    }

    It 'Can whatif delete an existing <thing> using _exist is false' -Skip:(!$IsWindows) {
        # ... arrange real state via plain `config set` ...
        $whatif_delete = @'
        { "<key>": "<value>", "_exist": false }
'@
        $result = <resource> config set -w --input $whatif_delete 2>$null | ConvertFrom-Json
        $LASTEXITCODE | Should -Be 0
        $result._metadata.whatIf | Should -Match "Would delete .*"
    }

    It 'Can whatif delete an existing <thing>' -Skip:(!$IsWindows) {
        # Same as above, but via the `delete` subcommand:
        $result = <resource> config delete -w --input $whatif_delete 2>$null | ConvertFrom-Json
        $LASTEXITCODE | Should -Be 0
        $result._metadata.whatIf | Should -Match "Would delete .*"
        # For delete what-if, payload should only include identity fields (and _metadata)
        ($result.psobject.properties | Where-Object { $_.Name -ne '_metadata' } | Measure-Object).Count |
            Should -Be 1
    }
}

Rules for what-if tests:

• Always call the executable directly (<resource> config set -w --input ...), not via dsc resource, so the test pins the CLI contract used by the manifest.
• Use -w (not --what-if) in tests to lock in the short flag.
• Redirect stderr with 2>$null to keep test output clean; for failing-test debugging, prefer 2>$testdrive/error.log + -Because.
• Pipe through ConvertFrom-Json and assert on _metadata.whatIf entries with Should -Match.
• Always include at least one assertion that the system state did not change (compare config get before/after).
• Always include both set -w (with and without _exist: false) and delete -w coverage if the manifest exposes delete what-if.
• Top-level Describe block uses -Skip:(!$IsWindows) for Windows-only resources (or the appropriate platform guard).

8. Naming convention summary (do not deviate)

Concern	Name
CLI short flag	-w
CLI long flag	--what-if
Clap field	what_if: bool
Helper field	what_if: bool
Helper enable method	enable_what_if()
Manifest arg entry	{ "whatIfArg": "--what-if" }
Manifest declaration	"whatIfReturns": "state" (on set)
State field	_metadata (metadata: Option<Metadata> in Rust)
Metadata field	whatIf (what_if: Option<Vec<String>> in Rust)
Locale section	[<resource>_helper]
Locale key prefix	whatIfCreate*, whatIfUpdate*, whatIfDelete*
Locale message style	starts with "Would "
Error-to-whatif helper	handle_error_or_what_if(error)
Test file (single)	<resource>.config.whatif.tests.ps1
Test file (list)	<resource>list_whatif.tests.ps1
Describe block title	'<resource> config whatif tests'

9. Implementation checklist

When asked to add what-if to a new resource, perform these steps in order:

1. Update the resource manifest: add whatIfArg to set (and delete) args, add whatIfReturns: "state" to set.
2. Add what_if: bool to the relevant clap ConfigSubCommand variants in args.rs.
3. Destructure what_if in main.rs, call helper.enable_what_if(), print projected state JSON.
4. Add what_if field, enable_what_if() method, and handle_error_or_what_if() helper to the resource library struct.
5. Change set() / remove() to short-circuit OS mutations when what_if, accumulate Vec<String> of "Would …" messages, return Some(state) with _metadata.whatIf attached.
6. Add _metadata: Option<Metadata> to public state structs and define Metadata { what_if: Option<Vec<String>> } with the JSON renames shown above.
7. Add whatIf* localized strings under [<resource>_helper] and args.configArgsWhatIfHelp in locales/en-us.toml.
8. Create <resource>.config.whatif.tests.ps1 (and the list variant if applicable) following the test template; cover create, update, delete-via-_exist, and delete -w.
9. Build with ./build.ps1 -project <resource_name> and run the new Pester file.