runtimes/google/ipc/server.go

package ipc

import (
	"fmt"
	"io"
	"net"
	"reflect"
	"strings"
	"sync"
	"time"

	"veyron.io/veyron/veyron2"
	"veyron.io/veyron/veyron2/config"
	"veyron.io/veyron/veyron2/context"
	"veyron.io/veyron/veyron2/ipc"
	"veyron.io/veyron/veyron2/ipc/stream"
	"veyron.io/veyron/veyron2/naming"
	"veyron.io/veyron/veyron2/options"
	"veyron.io/veyron/veyron2/security"
	mttypes "veyron.io/veyron/veyron2/services/mounttable/types"
	"veyron.io/veyron/veyron2/verror"
	"veyron.io/veyron/veyron2/vlog"
	"veyron.io/veyron/veyron2/vom"
	"veyron.io/veyron/veyron2/vtrace"

	"veyron.io/veyron/veyron/lib/glob"
	"veyron.io/veyron/veyron/lib/netstate"
	"veyron.io/veyron/veyron/runtimes/google/lib/publisher"
	inaming "veyron.io/veyron/veyron/runtimes/google/naming"
	ivtrace "veyron.io/veyron/veyron/runtimes/google/vtrace"
)

var (
	errServerStopped = verror.Abortedf("ipc: server is stopped")
)

type server struct {
	sync.Mutex
	ctx              context.T                         // context used by the server to make internal RPCs.
	streamMgr        stream.Manager                    // stream manager to listen for new flows.
	publisher        publisher.Publisher               // publisher to publish mounttable mounts.
	listenerOpts     []stream.ListenerOpt              // listener opts passed to Listen.
	listeners        map[stream.Listener]*dhcpListener // listeners created by Listen.
	disp             ipc.Dispatcher                    // dispatcher to serve RPCs
	active           sync.WaitGroup                    // active goroutines we've spawned.
	stopped          bool                              // whether the server has been stopped.
	stoppedChan      chan struct{}                     // closed when the server has been stopped.
	ns               naming.Namespace
	servesMountTable bool
	// TODO(cnicolaou): remove this when the publisher tracks published names
	// and can return an appropriate error for RemoveName on a name that
	// wasn't 'Added' for this server.
	names       map[string]struct{}
	reservedOpt options.ReservedNameDispatcher
	// TODO(cnicolaou): add roaming stats to ipcStats
	stats *ipcStats // stats for this server.
}

var _ ipc.Server = (*server)(nil)

type dhcpListener struct {
	sync.Mutex
	publisher *config.Publisher // publisher used to fork the stream
	name      string            // name of the publisher stream
	ep        *inaming.Endpoint // endpoint returned after listening and choosing an address to be published
	port      string
	ch        chan config.Setting // channel to receive settings over
}

func InternalNewServer(ctx context.T, streamMgr stream.Manager, ns naming.Namespace, opts ...ipc.ServerOpt) (ipc.Server, error) {
	s := &server{
		ctx:         ctx,
		streamMgr:   streamMgr,
		publisher:   publisher.New(ctx, ns, publishPeriod),
		listeners:   make(map[stream.Listener]*dhcpListener),
		stoppedChan: make(chan struct{}),
		ns:          ns,
		stats:       newIPCStats(naming.Join("ipc", "server", streamMgr.RoutingID().String())),
	}
	for _, opt := range opts {
		switch opt := opt.(type) {
		case stream.ListenerOpt:
			// Collect all ServerOpts that are also ListenerOpts.
			s.listenerOpts = append(s.listenerOpts, opt)
		case options.ServesMountTable:
			s.servesMountTable = bool(opt)
		case options.ReservedNameDispatcher:
			s.reservedOpt = opt
		}
	}
	return s, nil
}

func (s *server) Published() ([]string, error) {
	defer vlog.LogCall()()
	s.Lock()
	defer s.Unlock()
	if s.stopped {
		return nil, errServerStopped
	}
	return s.publisher.Published(), nil
}

// resolveToAddress will try to resolve the input to an address using the
// mount table, if the input is not already an address.
func (s *server) resolveToAddress(address string) (string, error) {
	if _, err := inaming.NewEndpoint(address); err == nil {
		return address, nil
	}
	var names []string
	if s.ns != nil {
		var err error
		if names, err = s.ns.Resolve(s.ctx, address); err != nil {
			return "", err
		}
	} else {
		names = append(names, address)
	}
	for _, n := range names {
		address, suffix := naming.SplitAddressName(n)
		if suffix != "" && suffix != "//" {
			continue
		}
		if _, err := inaming.NewEndpoint(address); err == nil {
			return address, nil
		}
	}
	return "", fmt.Errorf("unable to resolve %q to an endpoint", address)
}

/*
// ipAddressChooser returns the preferred IP address, which is,
// a public IPv4 address, then any non-loopback IPv4, then a public
// IPv6 address and finally any non-loopback/link-local IPv6
// It is replicated here to avoid a circular dependency and will, in any case,
// go away when we transition away from Listen to the ListenX API.
func ipAddressChooser(network string, addrs []ipc.Address) ([]ipc.Address, error) {
	if !netstate.IsIPProtocol(network) {
		return nil, fmt.Errorf("can't support network protocol %q", network)
	}
	accessible := netstate.AddrList(addrs)

	// Try and find an address on a interface with a default route.
	predicates := []netstate.AddressPredicate{netstate.IsPublicUnicastIPv4,
		netstate.IsUnicastIPv4, netstate.IsPublicUnicastIPv6}
	for _, predicate := range predicates {
		if addrs := accessible.Filter(predicate); len(addrs) > 0 {
			onDefaultRoutes := addrs.Filter(netstate.IsOnDefaultRoute)
			if len(onDefaultRoutes) > 0 {
				return onDefaultRoutes, nil
			}
		}
	}

	// We failed to find any addresses with default routes, try again
	// but without the default route requirement.
	for _, predicate := range predicates {
		if addrs := accessible.Filter(predicate); len(addrs) > 0 {
			return addrs, nil
		}
	}

	return nil, fmt.Errorf("failed to find any usable address for %q", network)
}

func (s *server) Listen(protocol, address string) (naming.Endpoint, error) {
	defer vlog.LogCall()()
	s.Lock()
	// Shortcut if the server is stopped, to avoid needlessly creating a
	// listener.
	if s.stopped {
		s.Unlock()
		return nil, errServerStopped
	}
	s.Unlock()
	var proxyName string
	if protocol == inaming.Network {
		proxyName = address
		var err error
		if address, err = s.resolveToAddress(address); err != nil {
			return nil, err
		}
	}
	// TODO(cnicolaou): pass options.ServesMountTable to streamMgr.Listen so that
	// it can more cleanly set the IsMountTable bit in the endpoint.
	ln, ep, err := s.streamMgr.Listen(protocol, address, s.listenerOpts...)
	if err != nil {
		vlog.Errorf("ipc: Listen on %v %v failed: %v", protocol, address, err)
		return nil, err
	}
	iep, ok := ep.(*inaming.Endpoint)
	if !ok {
		return nil, fmt.Errorf("ipc: Listen on %v %v failed translating internal endpoint data types", protocol, address)
	}

	if protocol != inaming.Network {
		// We know the endpoint format, so we crack it open...
		switch iep.Protocol {
		case "tcp", "tcp4", "tcp6":
			host, port, err := net.SplitHostPort(iep.Address)
			if err != nil {
				return nil, err
			}
			ip := net.ParseIP(host)
			if ip == nil {
				return nil, fmt.Errorf("ipc: Listen(%q, %q) failed to parse IP address from address", protocol, address)
			}
			if ip.IsUnspecified() {
				addrs, err := netstate.GetAccessibleIPs()
				if err == nil {
					if a, err := ipAddressChooser(iep.Protocol, addrs); err == nil && len(a) > 0 {
						iep.Address = net.JoinHostPort(a[0].Address().String(), port)
					}
				}
			}
		}
	}

	s.Lock()
	if s.stopped {
		s.Unlock()
		// Ignore error return since we can't really do much about it.
		ln.Close()
		return nil, errServerStopped
	}
	s.listeners[ln] = nil
	// We have a single goroutine per listener to accept new flows.
	// Each flow is served from its own goroutine.
	s.active.Add(1)
	if protocol == inaming.Network {
		go func(ln stream.Listener, ep *inaming.Endpoint, proxy string) {
			s.proxyListenLoop(ln, ep, proxy)
			s.active.Done()
		}(ln, iep, proxyName)
	} else {
		go func(ln stream.Listener, ep naming.Endpoint) {
			s.listenLoop(ln, ep)
			s.active.Done()
		}(ln, iep)
	}
	s.Unlock()
	s.publisher.AddServer(s.publishEP(iep, s.servesMountTable), s.servesMountTable)
	return ep, nil
}
*/

// externalEndpoint examines the endpoint returned by the stream listen call
// and fills in the address to publish to the mount table. It also returns the
// IP host address that it selected for publishing to the mount table.
func (s *server) externalEndpoint(chooser ipc.AddressChooser, lep naming.Endpoint) (*inaming.Endpoint, *net.IPAddr, error) {
	// We know the endpoint format, so we crack it open...
	iep, ok := lep.(*inaming.Endpoint)
	if !ok {
		return nil, nil, fmt.Errorf("failed translating internal endpoint data types")
	}
	switch iep.Protocol {
	case "tcp", "tcp4", "tcp6":
		host, port, err := net.SplitHostPort(iep.Address)
		if err != nil {
			return nil, nil, err
		}
		ip := net.ParseIP(host)
		if ip == nil {
			return nil, nil, fmt.Errorf("failed to parse %q as an IP host", host)
		}
		if ip.IsUnspecified() && chooser != nil {
			// Need to find a usable IP address since the call to listen
			// didn't specify one.
			addrs, err := netstate.GetAccessibleIPs()
			if err == nil {
				// TODO(cnicolaou): we could return multiple addresses here,
				// all of which can be exported to the mount table. Look at
				// this after we transition fully to ListenX.
				if a, err := chooser(iep.Protocol, addrs); err == nil && len(a) > 0 {
					iep.Address = net.JoinHostPort(a[0].Address().String(), port)
					return iep, a[0].Address().(*net.IPAddr), nil
				}
			}
		} else {
			// Listen used a fixed IP address, which essentially disables
			// roaming.
			return iep, nil, nil
		}
	}
	return iep, nil, nil
}

func (s *server) Listen(listenSpec ipc.ListenSpec) (naming.Endpoint, error) {
	defer vlog.LogCall()()
	s.Lock()
	// Shortcut if the server is stopped, to avoid needlessly creating a
	// listener.
	if s.stopped {
		s.Unlock()
		return nil, errServerStopped
	}
	s.Unlock()

	protocol := listenSpec.Protocol
	address := listenSpec.Address
	proxyAddress := ""
	if len(listenSpec.Proxy) > 0 {
		if address, err := s.resolveToAddress(listenSpec.Proxy); err != nil {
			return nil, err
		} else {
			proxyAddress = address
		}
	}

	ln, lep, err := s.streamMgr.Listen(protocol, address, s.listenerOpts...)
	if err != nil {
		vlog.Errorf("ipc: Listen on %v %v failed: %v", protocol, address, err)
		return nil, err
	}
	ep, ipaddr, err := s.externalEndpoint(listenSpec.AddressChooser, lep)
	if err != nil {
		ln.Close()
		return nil, err
	}

	s.Lock()
	if s.stopped {
		s.Unlock()
		// Ignore error return since we can't really do much about it.
		ln.Close()
		return nil, errServerStopped
	}

	var ip net.IP
	if ipaddr != nil {
		ip = net.ParseIP(ipaddr.String())
	} else {
		vlog.VI(2).Infof("the address %q requested for listening contained a fixed IP address which disables roaming, use :0 instead", address)
	}
	publisher := listenSpec.StreamPublisher
	if ip != nil && !ip.IsLoopback() && publisher != nil {
		streamName := listenSpec.StreamName
		ch := make(chan config.Setting)
		_, err := publisher.ForkStream(streamName, ch)
		if err != nil {
			return nil, fmt.Errorf("failed to fork stream %q: %s", streamName, err)
		}
		_, port, _ := net.SplitHostPort(ep.Address)
		dhcpl := &dhcpListener{ep: ep, port: port, ch: ch, name: streamName, publisher: publisher}

		// We have a goroutine to listen for dhcp changes.
		s.active.Add(1)
		// goroutine to listen for address changes.
		go func(dl *dhcpListener) {
			s.dhcpLoop(dl)
			s.active.Done()
		}(dhcpl)
		s.listeners[ln] = dhcpl
	} else {
		s.listeners[ln] = nil
	}

	// We have a goroutine per listener to accept new flows.
	// Each flow is served from its own goroutine.
	s.active.Add(1)

	//  goroutine to listen for connections
	go func(ln stream.Listener, ep naming.Endpoint) {
		s.listenLoop(ln, ep)
		s.active.Done()
	}(ln, lep)

	if len(proxyAddress) > 0 {
		pln, pep, err := s.streamMgr.Listen(inaming.Network, proxyAddress, s.listenerOpts...)
		if err != nil {
			vlog.Errorf("ipc: Listen on %v %v failed: %v", protocol, address, err)
			return nil, err
		}
		ipep, ok := pep.(*inaming.Endpoint)
		if !ok {
			return nil, fmt.Errorf("failed translating internal endpoint data types")
		}
		// We have a goroutine for listening on proxy connections.
		s.active.Add(1)
		go func(ln stream.Listener, ep *inaming.Endpoint, proxy string) {
			s.proxyListenLoop(ln, ep, proxy)
			s.active.Done()
		}(pln, ipep, listenSpec.Proxy)
		s.listeners[pln] = nil
		// TODO(cnicolaou,p): AddServer no longer needs to take the
		// servesMountTable bool since it can be extracted from the endpoint.
		s.publisher.AddServer(s.publishEP(ipep, s.servesMountTable), s.servesMountTable)
	} else {
		s.publisher.AddServer(s.publishEP(ep, s.servesMountTable), s.servesMountTable)
	}
	s.Unlock()
	return ep, nil
}

func (s *server) publishEP(ep *inaming.Endpoint, servesMountTable bool) string {
	var name string
	if !s.servesMountTable {
		// Make sure that client MountTable code doesn't try and
		// ResolveStep past this final address.
		name = "//"
	}
	ep.IsMountTable = servesMountTable
	return naming.JoinAddressName(ep.String(), name)
}

func (s *server) proxyListenLoop(ln stream.Listener, iep *inaming.Endpoint, proxy string) {
	const (
		min = 5 * time.Millisecond
		max = 5 * time.Minute
	)
	for {
		s.listenLoop(ln, iep)
		// The listener is done, so:
		// (1) Unpublish its name
		s.publisher.RemoveServer(s.publishEP(iep, s.servesMountTable))
		// (2) Reconnect to the proxy unless the server has been stopped
		backoff := min
		ln = nil
		// TODO(ashankar,cnicolaou): this code is way too confusing and should
		// be cleaned up.
		for ln == nil {
			select {
			case <-time.After(backoff):
				resolved, err := s.resolveToAddress(proxy)
				if err != nil {
					vlog.VI(1).Infof("Failed to resolve proxy %q (%v), will retry in %v", proxy, err, backoff)
					if backoff = backoff * 2; backoff > max {
						backoff = max
					}
					break
				}
				var ep naming.Endpoint
				ln, ep, err = s.streamMgr.Listen(inaming.Network, resolved, s.listenerOpts...)
				if err == nil {
					var ok bool
					iep, ok = ep.(*inaming.Endpoint)
					if !ok {
						vlog.Errorf("failed translating internal endpoint data types")
						ln = nil
						continue
					}
					vlog.VI(1).Infof("Reconnected to proxy at %q listener: (%v, %v)", proxy, ln, iep)
					break
				}
				if backoff = backoff * 2; backoff > max {
					backoff = max
				}
				vlog.VI(1).Infof("Proxy reconnection failed, will retry in %v", backoff)
			case <-s.stoppedChan:
				return
			}
		}
		// TODO(cnicolaou,ashankar): this won't work when we are both
		// proxying and publishing locally, which is the common case.
		// listenLoop, dhcpLoop and the original publish are all publishing
		// addresses to the same name, but the client is not smart enough
		// to choose sensibly between them.
		// (3) reconnected, publish new address
		s.publisher.AddServer(s.publishEP(iep, s.servesMountTable), s.servesMountTable)
		s.Lock()
		s.listeners[ln] = nil
		s.Unlock()
	}
}

func (s *server) listenLoop(ln stream.Listener, ep naming.Endpoint) {
	defer vlog.VI(1).Infof("ipc: Stopped listening on %v", ep)
	defer func() {
		s.Lock()
		delete(s.listeners, ln)
		s.Unlock()
	}()
	for {
		flow, err := ln.Accept()
		if err != nil {
			vlog.VI(10).Infof("ipc: Accept on %v failed: %v", ln, err)
			return
		}
		s.active.Add(1)
		go func(flow stream.Flow) {
			if err := newFlowServer(flow, s).serve(); err != nil {
				// TODO(caprita): Logging errors here is
				// too spammy. For example, "not
				// authorized" errors shouldn't be
				// logged as server errors.
				vlog.Errorf("Flow serve on %v failed: %v", ln, err)
			}
			s.active.Done()
		}(flow)
	}
}

func (s *server) applyChange(dhcpl *dhcpListener, addrs []net.Addr, fn func(string)) {
	dhcpl.Lock()
	defer dhcpl.Unlock()
	for _, a := range addrs {
		if ip := netstate.AsIP(a); ip != nil {
			dhcpl.ep.Address = net.JoinHostPort(ip.String(), dhcpl.port)
			fn(s.publishEP(dhcpl.ep, s.servesMountTable))
		}
	}
}

func (s *server) dhcpLoop(dhcpl *dhcpListener) {
	defer vlog.VI(1).Infof("ipc: Stopped listen for dhcp changes on %v", dhcpl.ep)
	vlog.VI(2).Infof("ipc: dhcp loop")
	for setting := range dhcpl.ch {
		if setting == nil {
			return
		}
		switch v := setting.Value().(type) {
		case bool:
			return
		case []net.Addr:
			s.Lock()
			if s.stopped {
				s.Unlock()
				return
			}
			// TODO(cnicolaou,ashankar): this won't work when we are both
			// proxying and publishing locally, which is the common case.
			// listenLoop, dhcpLoop and the original publish are all publishing
			// addresses to the same name, but the client is not smart enough
			// to choose sensibly between them.
			publisher := s.publisher
			s.Unlock()
			switch setting.Name() {
			case ipc.NewAddrsSetting:
				vlog.Infof("Added some addresses: %q", v)
				s.applyChange(dhcpl, v, func(name string) { publisher.AddServer(name, s.servesMountTable) })
			case ipc.RmAddrsSetting:
				vlog.Infof("Removed some addresses: %q", v)
				s.applyChange(dhcpl, v, publisher.RemoveServer)
			}

		}
	}
}

func (s *server) Serve(name string, obj interface{}, authorizer security.Authorizer) error {
	if obj == nil {
		// The ReflectInvoker inside the LeafDispatcher will panic
		// if called for a nil value.
		return fmt.Errorf("A nil object is not allowed")
	}
	return s.ServeDispatcher(name, ipc.LeafDispatcher(obj, authorizer))
}

func (s *server) ServeDispatcher(name string, disp ipc.Dispatcher) error {
	s.Lock()
	defer s.Unlock()
	if s.stopped {
		return errServerStopped
	}
	if disp == nil {
		return fmt.Errorf("A nil dispacther is not allowed")
	}
	if s.disp != nil {
		return fmt.Errorf("Serve or ServeDispatcher has already been called")
	}
	s.disp = disp
	s.names = make(map[string]struct{})
	if len(name) > 0 {
		s.publisher.AddName(name)
		s.names[name] = struct{}{}
	}
	return nil
}

func (s *server) AddName(name string) error {
	s.Lock()
	defer s.Unlock()
	if s.stopped {
		return errServerStopped
	}
	if len(name) == 0 {
		return fmt.Errorf("empty name")
	}
	s.publisher.AddName(name)
	// TODO(cnicolaou): remove this map when the publisher's RemoveName
	// method returns an error.
	s.names[name] = struct{}{}
	return nil
}

func (s *server) RemoveName(name string) error {
	s.Lock()
	defer s.Unlock()
	if s.stopped {
		return errServerStopped
	}
	if _, present := s.names[name]; !present {
		return fmt.Errorf("%q has not been previously used for this server", name)
	}
	s.publisher.RemoveName(name)
	delete(s.names, name)
	return nil
}

func (s *server) Stop() error {
	defer vlog.LogCall()()
	s.Lock()
	if s.stopped {
		s.Unlock()
		return nil
	}
	s.stopped = true
	close(s.stoppedChan)
	s.Unlock()

	// Delete the stats object.
	s.stats.stop()

	// Note, It's safe to Stop/WaitForStop on the publisher outside of the
	// server lock, since publisher is safe for concurrent access.

	// Stop the publisher, which triggers unmounting of published names.
	s.publisher.Stop()
	// Wait for the publisher to be done unmounting before we can proceed to
	// close the listeners (to minimize the number of mounted names pointing
	// to endpoint that are no longer serving).
	//
	// TODO(caprita): See if make sense to fail fast on rejecting
	// connections once listeners are closed, and parallelize the publisher
	// and listener shutdown.
	s.publisher.WaitForStop()

	s.Lock()
	// Close all listeners.  No new flows will be accepted, while in-flight
	// flows will continue until they terminate naturally.
	nListeners := len(s.listeners)
	errCh := make(chan error, nListeners)

	for ln, dhcpl := range s.listeners {
		go func(ln stream.Listener) {
			errCh <- ln.Close()
		}(ln)
		if dhcpl != nil {
			dhcpl.Lock()
			dhcpl.publisher.CloseFork(dhcpl.name, dhcpl.ch)
			dhcpl.ch <- config.NewBool("EOF", "stop", true)
			dhcpl.Unlock()
		}
	}
	s.Unlock()
	var firstErr error
	for i := 0; i < nListeners; i++ {
		if err := <-errCh; err != nil && firstErr == nil {
			firstErr = err
		}
	}
	// At this point, we are guaranteed that no new requests are going to be
	// accepted.

	// Wait for the publisher and active listener + flows to finish.
	s.active.Wait()
	s.Lock()
	s.disp = nil
	s.Unlock()
	return firstErr
}

// flowServer implements the RPC server-side protocol for a single RPC, over a
// flow that's already connected to the client.
type flowServer struct {
	context.T
	server      *server        // ipc.Server that this flow server belongs to
	disp        ipc.Dispatcher // ipc.Dispatcher that will serve RPCs on this flow
	dec         *vom.Decoder   // to decode requests and args from the client
	enc         *vom.Encoder   // to encode responses and results to the client
	flow        stream.Flow    // underlying flow
	reservedOpt options.ReservedNameDispatcher

	// Fields filled in during the server invocation.
	blessings      security.Blessings
	method, suffix string
	tags           []interface{}
	discharges     map[string]security.Discharge
	starttime      time.Time
	endStreamArgs  bool // are the stream args at EOF?
	allowDebug     bool // true if the caller is permitted to view debug information.
}

var _ ipc.Stream = (*flowServer)(nil)

func newFlowServer(flow stream.Flow, server *server) *flowServer {
	server.Lock()
	disp := server.disp
	runtime := veyron2.RuntimeFromContext(server.ctx)
	server.Unlock()

	return &flowServer{
		T:      InternalNewContext(runtime),
		server: server,
		disp:   disp,
		// TODO(toddw): Support different codecs
		dec:         vom.NewDecoder(flow),
		enc:         vom.NewEncoder(flow),
		flow:        flow,
		reservedOpt: server.reservedOpt,
		discharges:  make(map[string]security.Discharge),
	}
}

// Vom does not encode untyped nils.
// Consequently, the ipc system does not allow nil results with an interface
// type from server methods.  The one exception being errors.
//
// For now, the following hacky assumptions are made, which will be revisited when
// a decision is made on how untyped nils should be encoded/decoded in
// vom/vom2:
//
// - Server methods return 0 or more results
// - Any values returned by the server that have an interface type are either
//   non-nil or of type error.
func result2vom(res interface{}) vom.Value {
	v := vom.ValueOf(res)
	if !v.IsValid() {
		// Untyped nils are assumed to be nil-errors.
		var boxed verror.E
		return vom.ValueOf(&boxed).Elem()
	}
	if err, iserr := res.(error); iserr {
		// Convert errors to verror since errors are often not
		// serializable via vom/gob (errors.New and fmt.Errorf return a
		// type with no exported fields).
		return vom.ValueOf(verror.Convert(err))
	}
	return v
}

func (fs *flowServer) serve() error {
	defer fs.flow.Close()

	results, err := fs.processRequest()

	ivtrace.FromContext(fs).Finish()

	var traceResponse vtrace.Response
	if fs.allowDebug {
		traceResponse = ivtrace.Response(fs)
	}

	// Respond to the client with the response header and positional results.
	response := ipc.Response{
		Error:            err,
		EndStreamResults: true,
		NumPosResults:    uint64(len(results)),
		TraceResponse:    traceResponse,
	}
	if err := fs.enc.Encode(response); err != nil {
		return verror.BadProtocolf("ipc: response encoding failed: %v", err)
	}
	if response.Error != nil {
		return response.Error
	}
	for ix, res := range results {
		if err := fs.enc.EncodeValue(result2vom(res)); err != nil {
			return verror.BadProtocolf("ipc: result #%d [%T=%v] encoding failed: %v", ix, res, res, err)
		}
	}
	// TODO(ashankar): Should unread data from the flow be drained?
	//
	// Reason to do so:
	// The common stream.Flow implementation (veyron/runtimes/google/ipc/stream/vc/reader.go)
	// uses iobuf.Slices backed by an iobuf.Pool. If the stream is not drained, these
	// slices will not be returned to the pool leading to possibly increased memory usage.
	//
	// Reason to not do so:
	// Draining here will conflict with any Reads on the flow in a separate goroutine
	// (for example, see TestStreamReadTerminatedByServer in full_test.go).
	//
	// For now, go with the reason to not do so as having unread data in the stream
	// should be a rare case.
	return nil
}

func (fs *flowServer) readIPCRequest() (*ipc.Request, verror.E) {
	// Set a default timeout before reading from the flow. Without this timeout,
	// a client that sends no request or a partial request will retain the flow
	// indefinitely (and lock up server resources).
	initTimer := newTimer(defaultCallTimeout)
	defer initTimer.Stop()
	fs.flow.SetDeadline(initTimer.C)

	// Decode the initial request.
	var req ipc.Request
	if err := fs.dec.Decode(&req); err != nil {
		return nil, verror.BadProtocolf("ipc: request decoding failed: %v", err)
	}
	return &req, nil
}

func lookupInvoker(d ipc.Dispatcher, name, method string) (ipc.Invoker, security.Authorizer, error) {
	obj, auth, err := d.Lookup(name, method)
	switch {
	case err != nil:
		return nil, nil, err
	case obj == nil:
		return nil, auth, nil
	}
	if invoker, ok := obj.(ipc.Invoker); ok {
		return invoker, auth, nil
	}
	return ipc.ReflectInvoker(obj), auth, nil
}

func (fs *flowServer) processRequest() ([]interface{}, verror.E) {
	fs.starttime = time.Now()
	req, verr := fs.readIPCRequest()
	if verr != nil {
		// We don't know what the ipc call was supposed to be, but we'll create
		// a placeholder span so we can capture annotations.
		fs.T, _ = ivtrace.WithNewSpan(fs, "Failed IPC Call")
		return nil, verr
	}
	fs.method = req.Method

	// TODO(mattr): Currently this allows users to trigger trace collection
	// on the server even if they will not be allowed to collect the
	// results later.  This might be consider a DOS vector.
	spanName := fmt.Sprintf("Server Call: %s.%s", fs.Name(), fs.Method())
	fs.T, _ = ivtrace.WithContinuedSpan(fs, spanName, req.TraceRequest)

	var cancel context.CancelFunc
	if req.Timeout != ipc.NoTimeout {
		fs.T, cancel = fs.WithDeadline(fs.starttime.Add(time.Duration(req.Timeout)))
	} else {
		fs.T, cancel = fs.WithCancel()
	}
	fs.flow.SetDeadline(fs.Done())

	// Ensure that the context gets cancelled if the flow is closed
	// due to a network error, or client cancellation.
	go func() {
		select {
		case <-fs.flow.Closed():
			// Here we remove the contexts channel as a deadline to the flow.
			// We do this to ensure clients get a consistent error when they read/write
			// after the flow is closed.  Since the flow is already closed, it doesn't
			// matter that the context is also cancelled.
			fs.flow.SetDeadline(nil)
			cancel()
		case <-fs.Done():
		}
	}()

	// If additional credentials are provided, make them available in the context
	var err error
	if fs.blessings, err = security.NewBlessings(req.GrantedBlessings); err != nil {
		return nil, verror.BadProtocolf("ipc: failed to decode granted blessings: %v", err)
	}
	// Detect unusable blessings now, rather then discovering they are unusable on first use.
	// TODO(ashankar,ataly): Potential confused deputy attack: The client provides the
	// server's identity as the blessing. Figure out what we want to do about this -
	// should servers be able to assume that a blessing is something that does not
	// have the authorizations that the server's own identity has?
	if fs.blessings != nil && !reflect.DeepEqual(fs.blessings.PublicKey(), fs.flow.LocalPrincipal().PublicKey()) {
		return nil, verror.BadProtocolf("ipc: blessing granted not bound to this server(%v vs %v)", fs.blessings.PublicKey(), fs.flow.LocalPrincipal().PublicKey())
	}
	// Receive third party caveat discharges the client sent
	for i := uint64(0); i < req.NumDischarges; i++ {
		var d security.Discharge
		if err := fs.dec.Decode(&d); err != nil {
			return nil, verror.BadProtocolf("ipc: decoding discharge %d of %d failed: %v", i, req.NumDischarges, err)
		}
		fs.discharges[d.ID()] = d
	}
	// Lookup the invoker.
	invoker, auth, suffix, verr := fs.lookup(req.Suffix, req.Method)
	fs.suffix = suffix // with leading /'s stripped
	if verr != nil {
		return nil, verr
	}
	// Prepare invoker and decode args.
	numArgs := int(req.NumPosArgs)
	argptrs, tags, err := invoker.Prepare(req.Method, numArgs)
	fs.tags = tags
	if err != nil {
		return nil, verror.Makef(verror.ErrorID(err), "%s: name: %q", err, req.Suffix)
	}
	if len(argptrs) != numArgs {
		return nil, verror.BadProtocolf(fmt.Sprintf("ipc: wrong number of input arguments for method %q, name %q (called with %d args, expected %d)", req.Method, req.Suffix, numArgs, len(argptrs)))
	}
	for ix, argptr := range argptrs {
		if err := fs.dec.Decode(argptr); err != nil {
			return nil, verror.BadProtocolf("ipc: arg %d decoding failed: %v", ix, err)
		}
	}
	fs.allowDebug = fs.LocalPrincipal() == nil
	// Check application's authorization policy and invoke the method.
	// LocalPrincipal is nil means that the server wanted to avoid authentication,
	// and thus wanted to skip authorization as well.
	if fs.LocalPrincipal() != nil {
		// Check if the caller is permitted to view debug information.
		if err := fs.authorize(auth); err != nil {
			return nil, err
		}
		fs.allowDebug = fs.authorizeForDebug(auth) == nil
	}

	results, err := invoker.Invoke(req.Method, fs, argptrs)
	fs.server.stats.record(req.Method, time.Since(fs.starttime))
	return results, verror.Convert(err)
}

// lookup returns the invoker and authorizer responsible for serving the given
// name and method.  The name is stripped of any leading slashes. If it begins
// with ipc.DebugKeyword, we use the internal debug dispatcher to look up the
// invoker. Otherwise, and we use the server's dispatcher. The (stripped) name
// and dispatch suffix are also returned.
func (fs *flowServer) lookup(name, method string) (ipc.Invoker, security.Authorizer, string, verror.E) {
	name = strings.TrimLeft(name, "/")
	if method == "Glob" && len(name) == 0 {
		return ipc.ReflectInvoker(&globInvoker{naming.ReservedNamePrefix, fs}), &acceptAllAuthorizer{}, name, nil
	}
	disp := fs.disp
	if strings.HasPrefix(name, naming.ReservedNamePrefix) {
		parts := strings.SplitN(name, "/", 2)
		if len(parts) > 1 {
			name = parts[1]
		} else {
			name = ""
		}
		disp = fs.reservedOpt.Dispatcher
	}

	if disp != nil {
		invoker, auth, err := lookupInvoker(disp, name, method)
		switch {
		case err != nil:
			return nil, nil, "", verror.Convert(err)
		case invoker != nil:
			return invoker, auth, name, nil
		}
	}
	return nil, nil, "", verror.NoExistf("ipc: invoker not found for %q", name)
}

type acceptAllAuthorizer struct{}

func (acceptAllAuthorizer) Authorize(security.Context) error {
	return nil
}

type globInvoker struct {
	prefix string
	fs     *flowServer
}

// Glob matches the pattern against internal object names if the double-
// underscore prefix is explicitly part of the pattern. Otherwise, it invokes
// the service's Glob method.
func (i *globInvoker) Glob(call ipc.ServerCall, pattern string) error {
	g, err := glob.Parse(pattern)
	if err != nil {
		return err
	}
	if strings.HasPrefix(pattern, naming.ReservedNamePrefix) {
		var err error
		// Match against internal object names.
		if ok, _, left := g.MatchInitialSegment(i.prefix); ok {
			if ierr := i.invokeGlob(call, i.fs.reservedOpt.Dispatcher, i.prefix, left.String()); ierr != nil {
				err = ierr
			}
		}
		return err
	}
	// Invoke the service's method.
	return i.invokeGlob(call, i.fs.disp, "", pattern)
}

func (i *globInvoker) invokeGlob(call ipc.ServerCall, d ipc.Dispatcher, prefix, pattern string) error {
	if d == nil {
		return nil
	}
	obj, auth, err := d.Lookup("", "Glob")
	if err != nil {
		return err
	}
	// TODO(cnicolaou): ipc.Serve TRANSITION
	invoker, ok := obj.(ipc.Invoker)
	if !ok {
		panic(fmt.Errorf("Lookup should have returned an ipc.Invoker, returned %T", obj))
	}
	if obj == nil || !ok {
		return verror.NoExistf("ipc: invoker not found for Glob")
	}

	argptrs, tags, err := invoker.Prepare("Glob", 1)
	i.fs.tags = tags
	if err != nil {
		return verror.Makef(verror.ErrorID(err), "%s", err)
	}
	if err := i.fs.authorize(auth); err != nil {
		return err
	}
	leafCall := &localServerCall{call, prefix}
	argptrs[0] = &pattern
	results, err := invoker.Invoke("Glob", leafCall, argptrs)
	if err != nil {
		return err
	}

	if len(results) != 1 {
		return verror.BadArgf("unexpected number of results. Got %d, want 1", len(results))
	}
	res := results[0]
	if res == nil {
		return nil
	}
	err, ok = res.(error)
	if !ok {
		return verror.BadArgf("unexpected result type. Got %T, want error", res)
	}
	return err
}

// An ipc.ServerCall that prepends a prefix to all the names in the streamed
// MountEntry objects.
type localServerCall struct {
	ipc.ServerCall
	prefix string
}

var _ ipc.ServerCall = (*localServerCall)(nil)
var _ ipc.Stream = (*localServerCall)(nil)
var _ ipc.ServerContext = (*localServerCall)(nil)

func (c *localServerCall) Send(v interface{}) error {
	me, ok := v.(mttypes.MountEntry)
	if !ok {
		return verror.BadArgf("unexpected stream type. Got %T, want MountEntry", v)
	}
	me.Name = naming.Join(c.prefix, me.Name)
	return c.ServerCall.Send(me)
}

func (fs *flowServer) authorize(auth security.Authorizer) verror.E {
	if auth == nil {
		auth = defaultAuthorizer{}
	}
	if err := auth.Authorize(fs); err != nil {
		// TODO(ataly, ashankar): For privacy reasons, should we hide the authorizer error?
		return verror.NoAccessf("ipc: not authorized to call %q.%q (%v)", fs.Name(), fs.Method(), err)
	}
	return nil
}

// debugContext is a context which wraps another context but always returns
// the debug label.
type debugContext struct {
	security.Context
}

func (debugContext) Label() security.Label { return security.DebugLabel }

// TODO(mattr): Is DebugLabel the right thing to check?
func (fs *flowServer) authorizeForDebug(auth security.Authorizer) error {
	dc := debugContext{fs}
	if auth == nil {
		auth = defaultAuthorizer{}
	}
	return auth.Authorize(dc)
}

// Send implements the ipc.Stream method.
func (fs *flowServer) Send(item interface{}) error {
	defer vlog.LogCall()()
	// The empty response header indicates what follows is a streaming result.
	if err := fs.enc.Encode(ipc.Response{}); err != nil {
		return err
	}
	return fs.enc.Encode(item)
}

// Recv implements the ipc.Stream method.
func (fs *flowServer) Recv(itemptr interface{}) error {
	defer vlog.LogCall()()
	var req ipc.Request
	if err := fs.dec.Decode(&req); err != nil {
		return err
	}
	if req.EndStreamArgs {
		fs.endStreamArgs = true
		return io.EOF
	}
	return fs.dec.Decode(itemptr)
}

// Implementations of ipc.ServerContext methods.

func (fs *flowServer) Discharges() map[string]security.Discharge {
	//nologcall
	return fs.discharges
}

func (fs *flowServer) Server() ipc.Server {
	//nologcall
	return fs.server
}
func (fs *flowServer) Timestamp() time.Time {
	//nologcall
	return fs.starttime
}
func (fs *flowServer) Method() string {
	//nologcall
	return fs.method
}
func (fs *flowServer) MethodTags() []interface{} {
	//nologcall
	return fs.tags
}

// TODO(cnicolaou): remove Name from ipc.ServerContext and all of
// its implementations
func (fs *flowServer) Name() string {
	//nologcall
	return fs.suffix
}
func (fs *flowServer) Suffix() string {
	//nologcall
	return fs.suffix
}
func (fs *flowServer) Label() security.Label {
	//nologcall
	for _, t := range fs.tags {
		if l, ok := t.(security.Label); ok {
			return l
		}
	}
	return security.AdminLabel
}
func (fs *flowServer) LocalPrincipal() security.Principal {
	//nologcall
	return fs.flow.LocalPrincipal()
}
func (fs *flowServer) LocalBlessings() security.Blessings {
	//nologcall
	return fs.flow.LocalBlessings()
}
func (fs *flowServer) RemoteBlessings() security.Blessings {
	//nologcall
	return fs.flow.RemoteBlessings()
}
func (fs *flowServer) Blessings() security.Blessings {
	//nologcall
	return fs.blessings
}
func (fs *flowServer) LocalEndpoint() naming.Endpoint {
	//nologcall
	return fs.flow.LocalEndpoint()
}
func (fs *flowServer) RemoteEndpoint() naming.Endpoint {
	//nologcall
	return fs.flow.RemoteEndpoint()
}