label_printer/slog_multi.go

package main

import (
	"context"
	"errors"
	"log/slog"
	"slices"
)

// slogMultiHandler is a simple slog.Handler that passes slog.Records on to
// every inner slog.Handler of the slice.
type slogMultiHandler []slog.Handler

func (smh slogMultiHandler) Enabled(ctx context.Context, level slog.Level) bool {
	for _, h := range smh {
		if h.Enabled(ctx, level) {
			return true
		}
	}
	return false
}

func (smh slogMultiHandler) Handle(ctx context.Context, record slog.Record) error {
	retValues := make([]error, len(smh))

	for i, h := range smh {
		if !h.Enabled(ctx, record.Level) {
			continue
		}
		retValues[i] = h.Handle(ctx, record)
	}

	return errors.Join(retValues...)
}

func (smh slogMultiHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	newHandlers := make([]slog.Handler, len(smh))
	for i, h := range smh {
		// From slog.Handler.WithAttrs godoc:
		//  "The Handler owns the slice: it may retain, modify or discard it."
		// Clone the slice so that modifications don't impact other slog.Handlers.
		newHandlers[i] = h.WithAttrs(slices.Clone(attrs))
	}
	return slogMultiHandler(newHandlers)
}

func (smh slogMultiHandler) WithGroup(name string) slog.Handler {
	newHandlers := make([]slog.Handler, len(smh))
	for i, h := range smh {
		newHandlers[i] = h.WithGroup(name)
	}
	return slogMultiHandler(newHandlers)
}