Add Output Schema Validation to next-safe-action

[ReemX]

next-safe-action currently provides robust input validation for server actions using various schema validation libraries. To enhance type safety and consistency, I propose extending this functionality to include output validation as well.

Feature Description

Implement a mechanism to define and validate the output schema of server actions, similar to how input schemas are currently handled. This would allow developers to:

1. Ensure consistency in action responses
2. Catch potential runtime errors early in the development process
3. Improve TypeScript inference for action results

Proposed API

Extend the current API to include an outputSchema option:

const myAction = actionClient
  .schema(inputSchema)
  .outputSchema(outputSchema)
  .action(async ({ parsedInput }) => {
    // Action implementation
    return result; // This would be validated against outputSchema
  });

Benefits

• Increased Type Safety: Ensure that server actions always return data in the expected format.
• Improved Developer Experience: Catch inconsistencies between expected and actual output early in the development process.
• Better Documentation: Output schemas serve as self-documenting code for action results.
• Enhanced Refactoring: Changes to action output structures are caught at compile-time, facilitating safer refactoring.

Implementation Considerations

• Support the same validation libraries as input schemas (Zod, Valibot, Yup, TypeBox)
• Provide clear error messages when output validation fails
• Consider performance implications of additional runtime checks

Discussion Points

• Should output validation be optional or required?
• How should validation errors be handled (e.g., throw an error, return a specific error object)?
• Are there any potential drawbacks or edge cases that should be considered?

I believe this feature would significantly enhance the already powerful next-safe-action library, providing developers with even more tools to create robust and type-safe server actions.

[TheEdoRan]

Hi, this feature is already implemented in the library: outputSchema docs.

[ReemX]

Yep just noticed now :P