Validate User Input for Go Applications

Table of Contents

1. Challenge

   Reusable validation error model

   Input validation is most effective when clients get actionable feedback. In Go, ad-hoc maps and string errors often lead to inconsistent responses and hard-to-test behavior.

   In this step you’ll create a typed validation error model that:

   • Aggregates multiple field failures into a single error
   • Is easy for handlers to detect and translate to HTTP responses
   • Is easy for unit tests to assert on

   This sets the foundation for predictable APIs and reduces duplicated error-building logic across endpoints. info> This lab experience was developed by the Pluralsight team using Forge, an internally developed AI tool utilizing Gemini technology. All sections were verified by human experts for accuracy prior to publication. For issue reporting, please contact us.

2. Challenge

   Reusable validation rules

   Validation rules behave better when inputs are normalized first. Trimming whitespace and canonicalizing values like emails prevents false negatives and reduces downstream surprises.

   You’ll also implement small, reusable validators that are:

   • Composable and request-agnostic
   • Easy to unit test
   • Consistent in how they report failures

   These building blocks will be reused across multiple endpoints, keeping your API behavior uniform.

3. Challenge

   Validate registration endpoint

   Good APIs distinguish between:

   • Malformed syntax (invalid JSON): the server can’t parse the request (HTTP 400)
   • Valid syntax but invalid meaning (failed validation): the server understood the JSON but it breaks business/semantic rules (HTTP 422)

   In this step you’ll validate a registration payload, aggregate all field errors, and wire validation into the HTTP handler with correct status codes and a predictable JSON response shape.

4. Challenge

   Optional field validation

   Many real APIs support partial updates where fields are optional. The tricky part is correctly handling:

   • Missing fields (no change)
   • Present-but-empty fields (often invalid)
   • Conditional validation (rules that apply only when a value is provided)

   You’ll add profile update validation and a handler that reuses the same error conventions established earlier.

5. Challenge

   Consistent error responses

   Consistency is a feature. Centralizing error response formatting prevents endpoints from drifting over time.

   Finally, you’ll add an integration test that validates the complete request path (router → handler → validation → store) to catch wiring mistakes that unit tests may miss.