Pipes & Validation

Pipes transform or validate input before it reaches your handler. They run after guards and interceptors (before) but before the handler.

Built-in Pipes

Pipe	Purpose
`NewParseIntPipe("id")`	Convert string param to `int`
`NewParseBoolPipe("active")`	Convert to `bool`
`NewParseFloatPipe("price")`	Convert to `float64`
`NewParseUUIDPipe("id")`	Validate UUID format
`NewDefaultValuePipe("page", 1)`	Provide default for nil/empty
`NewParseArrayPipe("tags")`	Split comma-separated string
`NewValidationPipe()`	Validate struct bodies

Using Pipes

// Route-level
r.Get("/:id", c.findOne).Pipes(gonest.NewParseIntPipe("id"))

// Controller-level
r.UsePipes(gonest.NewValidationPipe())

// Global
app.UseGlobalPipes(gonest.NewValidationPipe())

Validation

The ValidationPipe validates structs using the validate tag:

type CreateCatDto struct {
    Name  string `json:"name"  validate:"required,min=2,max=50"`
    Age   int    `json:"age"   validate:"required,gte=0,lte=30"`
    Email string `json:"email" validate:"required,email"`
}

Supported rules: required, min=N, max=N, gte=N, lte=N, email.

When validation fails, a 400 Bad Request is returned:

{
  "statusCode": 400,
  "message": "validation failed: Name is required; Age must be >= 0"
}

Custom Pipes

type TrimPipe struct{}

func (p *TrimPipe) Transform(value any, meta gonest.ArgumentMetadata) (any, error) {
    if str, ok := value.(string); ok {
        return strings.TrimSpace(str), nil
    }
    return value, nil
}

PipeFunc Shorthand

pipe := gonest.PipeFunc(func(value any, meta gonest.ArgumentMetadata) (any, error) {
    // transform or validate
    return value, nil
})