---
schema_version: "1"
id: 65d1d0d6e7ab8c6b8f0aa911dfdc6f06616f9449be9da37b01d8edb854b9f605
title: Using DataWeave Expressions
collection: mulesoft
version: current
locale: en-us
portal_url: https://docs.salesforce.com/mulesoft/current/en-us/pdk/1.2/policies-pdk-configure-features-dataweave.md
canonical_url: https://docs.mulesoft.com/pdk/1.2/policies-pdk-configure-features-dataweave
source_site: docs.mulesoft.com
content_type: documentation
content_hash: edcff370378aa1b31e1c6f968c8e87f54e24a766b1186d67e94e6ac4e98b3246
description: MuleSoft Documentation Site
release: "1.2"
latest: false
---
---
product: Omni Gateway Policy Development Kit (PDK)
version: 1.2
---

# Using DataWeave Expressions

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

> [!NOTE] To view an example policy project that uses DataWeave expressions, see
> [Query Policy Example](https://github.com/mulesoft/pdk-custom-policy-examples/blob/1.2.0/query/README.md).

If the input DataWeave expression parameter is valid, the policy parses the expression and
transforms it into a `pdk::script::Script` expression. To obtain the result of the script:

1.  Create an evaluator.

2.  Call the binding function for each parameter defined in the schema definition:

    - `vars`: Call the `bind_vars` method for each of the policy’s `vars`. After all of `vars` are
      bound, the evaluator tries to solve the expression. If the expression contains `vars` other
      than the ones defined in the schema, they resolve to `null`.

    - `attributes`: Call the `bind_attributes` method with an implementation of the
      `AttributesBinding` trait. Flex Gateway Policy Development Kit (PDK) provides an
      implementation of this trait by instantiating a new `HandlerAttributesBinding` for each
      `RequestHeaderState`, `RequestHeaderState`, and response of an
      [HTTP call](https://docs.mulesoft.com/pdk/1.2/policies-pdk-configure-features-http-request).

    - `authentication`: Call the `bind_authentication` method with an implementation of the trait
      `AuthenticationBinding`. PDK provides an implementation of this trait for
      `AuthenticationData`. To inject authentication information into your policy, see
      [Inject Authentication Inforamaion](https://docs.mulesoft.com/pdk/1.2/policies-pdk-configure-features-inject-parameters#authentication).

    - `payload`: Call the `bind_payload` method with an implementation of the trait
      `PayloadBinding`. PDK provides an implementation of this trait for `RequestBodyState`,
      `ResponseBodyState`, and the response of an
      [HTTP call](https://docs.mulesoft.com/pdk/1.2/policies-pdk-configure-features-http-request).

      > [!NOTE] Call only the methods for the bindings defined in the schema definition. For
      > example, if the `attributes` binding is not used, don’t call the `bind_attributes` method.
      >
      > To learn more about defining DataWeave expressions, see
      > [DataWeave Expressions](https://docs.mulesoft.com/pdk/1.2/policies-pdk-create-schema-definition#dataweave-expressions).

3.  After you bind all expression variables, obtain the result by calling the `eval` method.

## Evaluate DataWeave Expressions

For example, to evaluate the `tokenExtractor` DataWeave expression in the following policy schema
definition:

```yaml
apiVersion: gateway.mulesoft.com/v1alpha1
kind: Extension
metadata:
  labels:
    title: jwt-auth
    category: Custom
spec:
  extends:
    - name: extension-definition
      namespace: default
  properties:
    tokenExtractor:
      type: string
      format: dataweave
      default: "#[vars.myVar]"
      bindings:
        payload:
          mimeType: text
        attributes: true
        authentication: true
        vars:
          - myVar
  required:
    - tokenExtractor
```

Use the following Rust snippet:

```rust
// Copyright 2024 Salesforce, Inc. All rights reserved.
mod generated;


use anyhow::Result;


use crate::generated::config::Config;
use pdk::authentication::{Authentication, AuthenticationHandler};
use pdk::logger::info;
use pdk::hl::*;
use pdk::script::{Evaluator, HandlerAttributesBinding, Value};


async fn request_filter(
   state: RequestState,
   stream: StreamProperties,
   auth: Authentication,
   mut evaluator: Evaluator<'_>,
) {
   evaluator.bind_vars("myVar", "myVal");

   evaluator.bind_authentication(&auth.authentication());

   let state = state.into_headers_state().await;
   evaluator.bind_attributes(&HandlerAttributesBinding::new(state.handler(), &stream));

   let state = state.into_body_state().await;
   evaluator.bind_payload(&state);

   if let Ok(value) = evaluator.eval() {
       match value {
           Value::Null => info!("value was null!"),
           Value::Bool(val) => info!("value was Bool: {val}"),
           Value::Number(val) => info!("value was Number: {val}"),
           Value::String(val) => info!("value was String: {val}"),
           Value::Array(val) => info!("value was Array: {val:?}"),
           Value::Object(val) => info!("value was Object: {val:?}"),
       }
   }
}


#[entrypoint]
async fn configure(launcher: Launcher, Configuration(bytes): Configuration) -> Result<()> {
   let config: Config = serde_json::from_slice(&bytes)?;


   launcher
       .launch(on_request(|request, stream, auth| {
           request_filter(request, stream, auth, config.token_extractor.evaluator())
       }))
       .await?;
   Ok(())
}
```

## Validate the Expression was Resolved

You can resolve some expressions before all values are bound. For example, the expression
`#[vars.myVar]` does not require the `attributes`, `payload`, no `authentication` to be resolved.

After one of the binding methods is called, you can confirm the expression was completely resolved
by calling the method:

```rust
evaluator.is_ready()
```

## See Also

- [Implementing Your Custom Policy Features in Rust](https://docs.mulesoft.com/pdk/1.2/policies-pdk-configure-features)