upstream

type CallOptions struct {
	// Timeout is the time to wait on a blocking grpc SendMsg.
	SendTimeout time.Duration

	// StreamTimeout is the time to wait before closing and reopening the gRPC stream.
	// If this is set to the Time.IsZero() value (ex: 0s), no stream timeout will be set unless
	// gRPC is blocked on Send/Recv message. If blocked, the maximum of StreamBlockedTimeout or
	// StreamTimeout is used.
	StreamTimeout time.Duration
	// StreamTimeoutJitter is an upper variance added to StreamTimeout to prevent a thundering
	// herd of streams being reopened.
	StreamTimeoutJitter time.Duration

	// ConnKeepaliveTimeout is the gRPC connection keep-alive timeout.
	// Based on https://github.com/grpc/grpc-go/blob/v1.32.x/keepalive/keepalive.go#L27-L45
	// If unset this defaults to 5 minutes.
	ConnKeepaliveTimeout time.Duration

	// NodeMetadata is an optional node metadata string field. This can be used to send
	// extra information to the management server, possibly on xds-relay specific metadata.
	NodeMetadata string
}

type Client interface {
	// OpenStream creates a stream with the origin server
	//
	// OpenStream should be called once per aggregated key.
	// OpenStream uses one representative node identifier for the entire lifetime of the stream.
	// Therefore, it is not necessary to pass node identifiers on subsequent requests from sidecars.
	// It follows xds protocol https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol
	// to handle the version_info, nonce and error_details and applies the response to the cache.
	//
	// All responses from the origin server are sent back through the callback function.
	//
	// OpenStream uses the retry and timeout configurations to make best effort to get the responses from origin server.
	// If the timeouts are exhausted, receive fails or a irrecoverable error occurs, the response channel is closed.
	// It is the caller's responsibility to send a new request from the last known DiscoveryRequest.
	// The shutdown function should be invoked to signal stream closure.
	// The shutdown function represents the intent that a stream is supposed to be closed.
	// All goroutines that depend on the ctx object should consider ctx.Done to be related to shutdown.
	// All such scenarios need to exit cleanly and are not considered an erroneous situation.
	OpenStream(transport.Request, string) (<-chan transport.Response, func())
}

type UnsupportedResourceError struct {
	TypeURL string
}