Rene Nochebuena
328b80c060
Struct validation backed by go-playground/validator/v10 with xerrors integration and pluggable i18n message providers. What's included: - Validator interface with Struct(v any) error method - New(...Option) constructor with WithMessageProvider functional option - MessageProvider interface for i18n; DefaultMessages (EN) and SpanishMessages (ES) built in - ValidationErrors mapped to xerrors.ErrInvalidInput with field and tag context keys - InvalidValidationError (non-struct input) mapped to xerrors.ErrInternal - Full playground.ValidationErrors attached via WithError for callers needing all failures Tested-via: todo-api POC integration Reviewed-against: docs/adr/
28 lines
2.3 KiB
Markdown
28 lines
2.3 KiB
Markdown
# ADR-001: go-playground/validator as Hidden Backend
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**Status:** Accepted
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**Date:** 2026-03-18
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## Context
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Struct validation via struct tags is a well-understood pattern in Go. `github.com/go-playground/validator/v10` is the de-facto standard library for this, supporting a large rule set (`required`, `email`, `min`, `max`, `url`, `uuid`, and hundreds more) and nested struct traversal.
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However, directly using the playground `*validate.Validate` type throughout application code creates a hard dependency: its error types (`ValidationErrors`, `InvalidValidationError`) must be imported wherever errors are inspected, and its configuration API leaks into all call sites.
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## Decision
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`github.com/go-playground/validator/v10` is used as the sole validation backend but is not exposed in the public API.
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The public API is the `Validator` interface, which has one method: `Struct(v any) error`. The concrete type `validator` (unexported) holds a `*playground.Validate` instance. The playground package is imported under the alias `playground` to make it unambiguous at a glance which types originate from it.
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Callers never see `playground.ValidationErrors` or `*playground.InvalidValidationError` directly. The concrete error types are translated to `*xerrors.Err` inside `Struct()` before being returned.
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The playground `*Validate` instance is created once inside `New()` with default options. No custom validators, tag name functions, or struct-level validators are registered. This keeps the API surface small and the behaviour predictable.
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## Consequences
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- **Positive**: The playground library can be upgraded or replaced without changing any call-site code — only the `valid` package internals change.
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- **Positive**: Application code only needs to import `code.nochebuena.dev/go/valid` and `code.nochebuena.dev/go/xerrors`; no direct dependency on `go-playground/validator`.
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- **Negative**: Advanced playground features (custom validators, `RegisterTagNameFunc`, cross-field validation) are not accessible without extending the `valid` package. If a project needs them, it should add `Option` functions or methods to `Validator`.
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- **Note**: The playground alias `playground "github.com/go-playground/validator/v10"` is retained in the source as a readability aid, not a requirement. It prevents confusion with the package name `valid` used in the surrounding code.
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