Config Passthrough

Some libraries have large config structs with dozens of fields. Rather than mapping every field explicitly in Lakta’s Config struct, you can use the raw passthrough pattern to forward unknown fields directly to the underlying library.

How it works

Declare a Raw field with koanf:",remain" to capture every key not explicitly handled:

type Config struct {
    Host string         `koanf:"host"`
    Port int            `koanf:"port"`
    Raw  map[string]any `koanf:",remain"`
}

Then use mapstructure to decode Raw into the library’s config struct:

import "github.com/mitchellh/mapstructure"

func (c *Config) ToFiberConfig() fiber.Config {
    cfg := fiber.Config{}
    _ = mapstructure.Decode(c.Raw, &cfg)
    return cfg
}

Example config

modules:
  http:
    fiber:
      default:
        host: "0.0.0.0"
        port: 8080
        # These fall into Raw and get decoded into fiber.Config:
        body_limit: 10485760
        read_timeout: "30s"
        write_timeout: "30s"
        enable_trusted_proxy_check: true

When to use this pattern

Use raw passthrough when:

• The underlying library has a large or frequently-changing config struct
• You want users to control library internals without Lakta adding wrapper fields for each one
• The library’s config field names match reasonable YAML keys

Avoid it when you need validation, documentation, or defaults for specific fields — in those cases, declare the field explicitly in your Config struct.