httputil/response.go

package httputil

import (
	"encoding/json"
	"errors"
	"net/http"

	"code.nochebuena.dev/go/xerrors"
)

// JSON encodes v as JSON and writes it with the given status code.
// Sets Content-Type: application/json.
func JSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// NoContent writes a 204 No Content response.
func NoContent(w http.ResponseWriter) {
	w.WriteHeader(http.StatusNoContent)
}

// Error maps err to the appropriate HTTP status code and writes a JSON error body.
// Understands *xerrors.Err — extracts Code and Message; fields are included if present.
// Falls back to 500 for unknown errors.
func Error(w http.ResponseWriter, err error) {
	if err == nil {
		JSON(w, http.StatusInternalServerError, errorBody("INTERNAL", "internal server error", nil))
		return
	}
	var xe *xerrors.Err
	if errors.As(err, &xe) {
		status := errorCodeToStatus(xe.Code())
		body := errorBody(string(xe.Code()), xe.Message(), xe.Fields())
		JSON(w, status, body)
		return
	}
	JSON(w, http.StatusInternalServerError, errorBody("INTERNAL", "internal server error", nil))
}

func errorBody(code, message string, fields map[string]any) map[string]any {
	m := map[string]any{
		"code":    code,
		"message": message,
	}
	for k, v := range fields {
		m[k] = v
	}
	return m
}

// errorCodeToStatus maps a xerrors.Code to an HTTP status code.
func errorCodeToStatus(code xerrors.Code) int {
	switch code {
	case xerrors.ErrInvalidInput:
		return http.StatusBadRequest
	case xerrors.ErrUnauthorized:
		return http.StatusUnauthorized
	case xerrors.ErrPermissionDenied:
		return http.StatusForbidden
	case xerrors.ErrNotFound:
		return http.StatusNotFound
	case xerrors.ErrAlreadyExists:
		return http.StatusConflict
	case xerrors.ErrGone:
		return http.StatusGone
	case xerrors.ErrPreconditionFailed:
		return http.StatusPreconditionFailed
	case xerrors.ErrRateLimited:
		return http.StatusTooManyRequests
	case xerrors.ErrInternal:
		return http.StatusInternalServerError
	case xerrors.ErrNotImplemented:
		return http.StatusNotImplemented
	case xerrors.ErrUnavailable:
		return http.StatusServiceUnavailable
	case xerrors.ErrDeadlineExceeded:
		return http.StatusGatewayTimeout
	default:
		return http.StatusInternalServerError
	}
}