Function initBootstrap

internal/cmd/proxy.go:248–281

initBootstrap initializes the [upstream.Resolver] for bootstrapping upstream servers. It returns the default resolver if no bootstraps were specified. The returned resolver will also use system hosts files first.

(
	ctx context.Context,
	l *slog.Logger,
	bootstraps []string,
	opts *upstream.Options,
)

// servers.  It returns the default resolver if no bootstraps were specified.
// The returned resolver will also use system hosts files first.
func initBootstrap(
	ctx context.Context,
	l *slog.Logger,
	bootstraps []string,
	opts *upstream.Options,
) (r upstream.Resolver, err error) {
	var resolvers []upstream.Resolver

	for i, b := range bootstraps {
		var ur *upstream.UpstreamResolver
		ur, err = upstream.NewUpstreamResolver(b, opts)
		if err != nil {
			return nil, fmt.Errorf("creating bootstrap resolver at index %d: %w", i, err)
		}

		resolvers = append(resolvers, upstream.NewCachingResolver(ur))
	}

	switch len(resolvers) {
	case 0:
		etcHosts, hostsErr := upstream.NewDefaultHostsResolver(ctx, osutil.RootDirFS(), l)
		if hostsErr != nil {
			l.ErrorContext(ctx, "creating default hosts resolver", slogutil.KeyError, hostsErr)

			return net.DefaultResolver, nil
		}

		return upstream.ConsequentResolver{etcHosts, net.DefaultResolver}, nil
	case 1:
		return resolvers[0], nil
	default:
		return upstream.ParallelResolver(resolvers), nil
	}
}

// initEDNS inits EDNS-related config fields.
func (conf *configuration) initEDNS(