package ipc

import (
	"fmt"
	"io"
	"math"
	"math/rand"
	"net"
	"strings"
	"sync"
	"time"

	"veyron.io/veyron/veyron2/context"
	"veyron.io/veyron/veyron2/i18n"
	"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"
	"veyron.io/veyron/veyron2/vdl/vdlutil"
	old_verror "veyron.io/veyron/veyron2/verror"
	verror "veyron.io/veyron/veyron2/verror2"
	"veyron.io/veyron/veyron2/vlog"
	"veyron.io/veyron/veyron2/vom"
	"veyron.io/veyron/veyron2/vom2"
	"veyron.io/veyron/veyron2/vtrace"

	"veyron.io/veyron/veyron/runtimes/google/ipc/stream/vc"
	"veyron.io/veyron/veyron/runtimes/google/ipc/version"
	inaming "veyron.io/veyron/veyron/runtimes/google/naming"
	ivtrace "veyron.io/veyron/veyron/runtimes/google/vtrace"
)

const pkgPath = "veyron.io/veyron/veyron/runtimes/google/ipc"

// TODO(cnicolaou): for local errors, automatically assign a new 'id',
// don't use pkgPath etc. Can then move them into being defined on each line
// and not here.
var (
	// Local errs that are used to provide details to the public ones.
	errClientCloseAlreadyCalled = verror.Register(pkgPath+".closeAlreadyCalled", verror.NoRetry,
		"ipc.Client.Close has already been called")

	errClientFinishAlreadyCalled = verror.Register(pkgPath+".finishAlreadyCalled", verror.NoRetry, "ipc.Call.Finish has already been called")

	errNonRootedName = verror.Register(pkgPath+".nonRootedName", verror.NoRetry, "{3} does not appear to contain an address")

	errInvalidEndpoint = verror.Register(pkgPath+".invalidEndpoint", verror.RetryRefetch, "{3} is an invalid endpoint")

	errIncompatibleEndpoint = verror.Register(pkgPath+".invalidEndpoint", verror.RetryRefetch, "{3} is an incompatible endpoint")

	errNotTrusted = verror.Register(pkgPath+".notTrusted", verror.NoRetry, "name {3} not trusted using blessings {4}{:5}")

	errAuthError = verror.Register(pkgPath+".authError", verror.RetryRefetch, "authentication error from server {3}{:4}")

	errSystemRetry = verror.Register(pkgPath+".sysErrorRetryConnection", verror.RetryConnection, "{:3:}")
	errClosingFlow = verror.Register(pkgPath+".errClosingFlow", verror.NoRetry, "{:3:}")

	errVomEncoder = verror.Register(pkgPath+".vomEncoder", verror.NoRetry, "failed to create vom encoder {:3}")
	errVomDecoder = verror.Register(pkgPath+".vomDecoder", verror.NoRetry, "failed to create vom decoder {:3}")

	errRequestEncoding = verror.Register(pkgPath+".requestEncoding", verror.NoRetry, "failed to encode request {3}{:4}")

	errDischargeEncoding = verror.Register(pkgPath+".dischargeEncoding", verror.NoRetry, "failed to encode discharge {3}{:4}")

	errArgEncoding = verror.Register(pkgPath+".argEncoding", verror.NoRetry, "failed to encode arg #{3}{:4:}")

	errMismatchedResults = verror.Register(pkgPath+".mismatchedResults", verror.NoRetry, "expected {3} results, but got {4}")

	errResultDecoding = verror.Register(pkgPath+".resultDecoding", verror.NoRetry, "failed to decode result #{3}{:4}")

	errResponseDecoding = verror.Register(pkgPath+".responseDecoding", verror.NoRetry, "failed to decode response{:3}")

	errRemainingStreamResults = verror.Register(pkgPath+".remaingStreamResults", verror.NoRetry, "stream closed with remaining stream results")

	errNoBlessings = verror.Register(pkgPath+".noBlessings", verror.NoRetry, "server has not presented any blessings")

	errAuthNoPatternMatch = verror.Register(pkgPath+".authNoPatternMatch",
		verror.NoRetry, "server blessings {3} do not match pattern {4}")

	errDefaultAuthDenied = verror.Register(pkgPath+".defaultAuthDenied", verror.NoRetry, "default authorization precludes talking to server with blessings{:3}")

	errBlessingGrant = verror.Register(pkgPath+".blessingGrantFailed", verror.NoRetry, "failed to grant blessing to server with blessings {3}{:4}")

	errBlessingAdd = verror.Register(pkgPath+".blessingAddFailed", verror.NoRetry, "failed to add blessing granted to server {3}{:4}")
)

// TODO(ribrdb): Flip this to true once everything is updated.
const enableSecureServerAuth = false

type client struct {
	streamMgr          stream.Manager
	ns                 naming.Namespace
	vcOpts             []stream.VCOpt // vc opts passed to dial
	preferredProtocols []string

	// We support concurrent calls to StartCall and Close, so we must protect the
	// vcMap.  Everything else is initialized upon client construction, and safe
	// to use concurrently.
	vcMapMu sync.Mutex
	// TODO(ashankar): The key should be a function of the blessings shared with the server?
	vcMap map[string]*vcInfo // map key is endpoint.String

	dc vc.DischargeClient
}

var _ ipc.Client = (*client)(nil)
var _ ipc.BindOpt = (*client)(nil)

type vcInfo struct {
	vc       stream.VC
	remoteEP naming.Endpoint
}

func InternalNewClient(streamMgr stream.Manager, ns naming.Namespace, opts ...ipc.ClientOpt) (ipc.Client, error) {

	c := &client{
		streamMgr: streamMgr,
		ns:        ns,
		vcMap:     make(map[string]*vcInfo),
	}
	for _, opt := range opts {
		if dc, ok := opt.(vc.DischargeClient); ok {
			c.dc = dc
		}
		// Collect all client opts that are also vc opts.
		switch v := opt.(type) {
		case stream.VCOpt:
			c.vcOpts = append(c.vcOpts, v)
		case options.PreferredProtocols:
			c.preferredProtocols = v
		}
	}

	return c, nil
}

func (c *client) createFlow(ctx context.T, ep naming.Endpoint, noDischarges bool) (stream.Flow, verror.E) {
	c.vcMapMu.Lock()
	defer c.vcMapMu.Unlock()
	if c.vcMap == nil {
		return nil, verror.Make(errClientCloseAlreadyCalled, ctx)
	}
	if vcinfo := c.vcMap[ep.String()]; vcinfo != nil {
		if flow, err := vcinfo.vc.Connect(); err == nil {
			return flow, nil
		}
		// If the vc fails to establish a new flow, we assume it's
		// broken, remove it from the map, and proceed to establishing
		// a new vc.
		// TODO(caprita): Should we distinguish errors due to vc being
		// closed from other errors?  If not, should we call vc.Close()
		// before removing the vc from the map?
		delete(c.vcMap, ep.String())
	}
	sm := c.streamMgr
	vcOpts := make([]stream.VCOpt, len(c.vcOpts))
	copy(vcOpts, c.vcOpts)
	c.vcMapMu.Unlock()
	if noDischarges {
		vcOpts = append(vcOpts, vc.NoDischarges{})
	}
	vc, err := sm.Dial(ep, append(vcOpts, vc.DialContext{ctx})...)
	c.vcMapMu.Lock()
	if err != nil {
		if strings.Contains(err.Error(), "authentication failed") {
			return nil, verror.Make(errAuthError, ctx, ep, err)
		} else {
			return nil, verror.Make(errSystemRetry, ctx, err)
		}
	}
	if c.vcMap == nil {
		sm.ShutdownEndpoint(ep)
		return nil, verror.Make(errClientCloseAlreadyCalled, ctx)
	}
	if othervc, exists := c.vcMap[ep.String()]; exists {
		vc = othervc.vc
		// TODO(ashankar,toddw): Figure out how to close up the VC that
		// is discarded. vc.Close?
	} else {
		c.vcMap[ep.String()] = &vcInfo{vc: vc, remoteEP: ep}
	}
	flow, err := vc.Connect()
	if err != nil {

		return nil, verror.Make(errAuthError, ctx, ep, err)
	}
	return flow, nil
}

// connectFlow parses an endpoint and a suffix out of the server and establishes
// a flow to the endpoint, returning the parsed suffix.
// The server name passed in should be a rooted name, of the form "/ep/suffix" or
// "/ep//suffix", or just "/ep".
func (c *client) connectFlow(ctx context.T, server string, noDischarges bool) (stream.Flow, string, verror.E) {
	address, suffix := naming.SplitAddressName(server)
	if len(address) == 0 {
		return nil, "", verror.Make(errNonRootedName, ctx, server)
	}
	ep, err := inaming.NewEndpoint(address)
	if err != nil {
		return nil, "", verror.Make(errInvalidEndpoint, ctx, address)
	}
	if err = version.CheckCompatibility(ep); err != nil {
		return nil, "", verror.Make(errIncompatibleEndpoint, ctx, ep)
	}
	flow, verr := c.createFlow(ctx, ep, noDischarges)
	if verr != nil {
		return nil, "", verr
	}
	return flow, suffix, nil
}

// A randomized exponential backoff.  The randomness deters error convoys from forming.
// TODO(cnicolaou): rationalize this and the backoff in ipc.Server. Note
// that rand is not thread safe and may crash.
func backoff(n int, deadline time.Time) bool {
	b := time.Duration(math.Pow(1.5+(rand.Float64()/2.0), float64(n)) * float64(time.Second))
	if b > maxBackoff {
		b = maxBackoff
	}
	r := deadline.Sub(time.Now())
	if b > r {
		// We need to leave a little time for the call to start or
		// we'll just timeout in startCall before we actually do
		// anything.  If we just have a millisecond left, give up.
		if r <= time.Millisecond {
			return false
		}
		b = r - time.Millisecond
	}
	time.Sleep(b)
	return true
}

func getRetryTimeoutOpt(opts []ipc.CallOpt) (time.Duration, bool) {
	for _, o := range opts {
		if r, ok := o.(options.RetryTimeout); ok {
			return time.Duration(r), true
		}
	}
	return 0, false
}

func (c *client) StartCall(ctx context.T, name, method string, args []interface{}, opts ...ipc.CallOpt) (ipc.Call, error) {
	defer vlog.LogCall()()
	return c.startCall(ctx, name, method, args, opts)
}

func getNoResolveOpt(opts []ipc.CallOpt) bool {
	for _, o := range opts {
		if r, ok := o.(options.NoResolve); ok {
			return bool(r)
		}
	}
	return false
}

func shouldNotFetchDischarges(opts []ipc.CallOpt) bool {
	for _, o := range opts {
		if _, ok := o.(vc.NoDischarges); ok {
			return true
		}
	}
	return false
}

func mkDischargeImpetus(serverBlessings []string, method string, args []interface{}) security.DischargeImpetus {
	var impetus security.DischargeImpetus
	if len(serverBlessings) > 0 {
		impetus.Server = make([]security.BlessingPattern, len(serverBlessings))
		for i, b := range serverBlessings {
			impetus.Server[i] = security.BlessingPattern(b)
		}
	}
	impetus.Method = method
	if len(args) > 0 {
		impetus.Arguments = make([]vdlutil.Any, len(args))
		for i, a := range args {
			impetus.Arguments[i] = vdlutil.Any(a)
		}
	}
	return impetus
}

// startCall ensures StartCall always returns verror.E.
func (c *client) startCall(ctx context.T, name, method string, args []interface{}, opts []ipc.CallOpt) (ipc.Call, verror.E) {
	if ctx == nil {
		return nil, verror.ExplicitMake(verror.BadArg, i18n.NoLangID, "ipc.Client", "StartCall")
	}

	ctx, span := ivtrace.WithNewSpan(ctx, fmt.Sprintf("<client>%q.%s", name, method))
	ctx = verror.ContextWithComponentName(ctx, "ipc.Client")

	// Context specified deadline.
	deadline, hasDeadline := ctx.Deadline()
	if !hasDeadline {
		// Default deadline.
		deadline = time.Now().Add(defaultCallTimeout)
	}
	if r, ok := getRetryTimeoutOpt(opts); ok {
		// Caller specified deadline.
		deadline = time.Now().Add(time.Duration(r))
	}

	skipResolve := getNoResolveOpt(opts)

	var lastErr verror.E
	for retries := 0; ; retries++ {
		if retries != 0 {
			if !backoff(retries, deadline) {
				break
			}
		}
		call, action, err := c.tryCall(ctx, name, method, args, skipResolve, opts)
		if err == nil {
			return call, nil
		}
		lastErr = err
		shouldRetry := true
		switch {
		case action != verror.RetryConnection && action != verror.RetryRefetch:
			shouldRetry = false
		case time.Now().After(deadline):
			shouldRetry = false
		case action == verror.RetryRefetch && skipResolve:
			// If we're skipping resolution and there are no servers for
			// this call retrying is not going to help, we can't come up
			// with new servers if there is no resolution.
			shouldRetry = false
		}
		if !shouldRetry {
			span.Annotatef("Cannot retry after error: %s", err)
			break
		}
		span.Annotatef("Retrying due to error: %s", err)
	}
	return nil, lastErr
}

type serverStatus struct {
	index  int
	suffix string
	flow   stream.Flow
	err    verror.E
}

// TODO(cnicolaou): implement real, configurable load balancing.
func (c *client) tryServer(ctx context.T, index int, server string, ch chan<- *serverStatus, noDischarges bool) {
	status := &serverStatus{index: index}
	var err verror.E
	var span vtrace.Span
	ctx, span = ivtrace.WithNewSpan(ctx, "<client>connectFlow")
	span.Annotatef("address:%v", server)
	defer span.Finish()
	if status.flow, status.suffix, err = c.connectFlow(ctx, server, noDischarges); err != nil {
		vlog.VI(2).Infof("ipc: err: %s", err)
		status.err = err
		status.flow = nil
	}
	ch <- status
}

// tryCall makes a single attempt at a call, against possibly multiple servers.
func (c *client) tryCall(ctx context.T, name, method string, args []interface{}, skipResolve bool, opts []ipc.CallOpt) (ipc.Call, verror.ActionCode, verror.E) {
	noDischarges := shouldNotFetchDischarges(opts)
	// Resolve name unless told not to.
	var servers []string
	var pattern security.BlessingPattern
	var resolveOpts []naming.ResolveOpt
	if skipResolve {
		resolveOpts = append(resolveOpts, naming.SkipResolveOpt{})
	} else if noDischarges {
		resolveOpts = append(resolveOpts, vc.NoDischarges{})
	}

	if resolved, err := c.ns.ResolveX(ctx, name, resolveOpts...); err != nil {
		vlog.Errorf("ResolveX: %v", err)
		if verror.Is(err, naming.ErrNoSuchName.ID) {
			return nil, verror.RetryRefetch, verror.Make(verror.NoServers, ctx, name)
		}
		return nil, verror.NoRetry, verror.Make(verror.NoExist, ctx, name, err)
	} else {
		pattern = security.BlessingPattern(resolved.Pattern)
		if len(resolved.Servers) == 0 {
			return nil, verror.RetryRefetch, verror.Make(verror.NoServers, ctx, name)
		}
		// An empty set of protocols means all protocols...
		ordered, err := filterAndOrderServers(naming.ToStringSlice(resolved), c.preferredProtocols)
		if err != nil {
			return nil, verror.RetryRefetch, verror.Make(verror.NoServers, ctx, name, err)
		} else if len(ordered) == 0 {
			// sooo annoying....
			r := []interface{}{err}
			r = append(r, name)
			for _, s := range resolved.Servers {
				r = append(r, s)
			}
			return nil, verror.RetryRefetch, verror.Make(verror.NoServers, ctx, r)
		}
		servers = ordered
	}

	// servers is now orderd by the priority heurestic implemented in
	// filterAndOrderServers.
	attempts := len(servers)

	// Try to connect to all servers in parallel.  Provide sufficient buffering
	// for all of the connections to finish instantaneously. This is important
	// because we want to process the responses in priority order; that order is
	// indicated by the order of entries in servers. So, if two respones come in
	// at the same 'instant', we prefer the first in the slice.
	responses := make([]*serverStatus, attempts)
	ch := make(chan *serverStatus, attempts)
	for i, server := range servers {
		go c.tryServer(ctx, i, server, ch, noDischarges)
	}

	delay := time.Duration(ipc.NoTimeout)
	if dl, ok := ctx.Deadline(); ok {
		delay = dl.Sub(time.Now())
	}
	timeoutChan := time.After(delay)

	for {
		// Block for at least one new response from the server, or the timeout.
		select {
		case r := <-ch:
			responses[r.index] = r
			// Read as many more responses as we can without blocking.
		LoopNonBlocking:
			for {
				select {
				default:
					break LoopNonBlocking
				case r := <-ch:
					responses[r.index] = r
				}
			}
		case <-timeoutChan:
			vlog.VI(2).Infof("ipc: timeout on connection to server %v ", name)
			_, _, err := c.failedTryCall(ctx, name, method, servers, responses, ch)
			if !verror.Is(err, verror.Timeout.ID) {
				return nil, verror.NoRetry, verror.Make(verror.Timeout, ctx, err)
			}
			return nil, verror.NoRetry, err
		}

		// Process new responses, in priority order.
		numResponses := 0
		for _, r := range responses {
			if r != nil {
				numResponses++
			}
			if r == nil || r.flow == nil {
				continue
			}
			r.flow.SetDeadline(ctx.Done())

			var (
				serverB  []string
				grantedB security.Blessings
			)

			// LocalPrincipal is nil means that the client wanted to avoid
			// authentication, and thus wanted to skip authorization as well.
			if r.flow.LocalPrincipal() != nil {
				// Validate caveats on the server's identity for the context associated with this call.
				var err error
				if serverB, grantedB, err = c.authorizeServer(ctx, r.flow, name, method, pattern, opts); err != nil {
					r.err = verror.Make(errNotTrusted, ctx,
						name, r.flow.RemoteBlessings(), err)
					vlog.VI(2).Infof("ipc: err: %s", r.err)
					r.flow.Close()
					r.flow = nil
					continue
				}
			}

			// This is the 'point of no return'; once the RPC is started (fc.start
			// below) we can't be sure if it makes it to the server or not so, this
			// code will never call fc.start more than once to ensure that we provide
			// 'at-most-once' rpc semantics at this level. Retrying the network
			// connections (i.e. creating flows) is fine since we can cleanup that
			// state if we abort a call (i.e. close the flow).
			//
			// We must ensure that all flows other than r.flow are closed.
			//
			// TODO(cnicolaou): all errors below are marked as NoRetry
			// because we want to provide at-most-once rpc semantics so
			// we only ever attempt an RPC once. In the future, we'll cache
			// responses on the server and then we can retry in-process
			// RPCs.
			go cleanupTryCall(r, responses, ch)
			fc, err := newFlowClient(ctx, serverB, r.flow, c.dc)
			if err != nil {
				return nil, verror.NoRetry, err.(verror.E)
			}

			if doneChan := ctx.Done(); doneChan != nil {
				go func() {
					select {
					case <-ctx.Done():
						fc.Cancel()
					case <-fc.flow.Closed():
					}
				}()
			}

			timeout := time.Duration(ipc.NoTimeout)
			if deadline, hasDeadline := ctx.Deadline(); hasDeadline {
				timeout = deadline.Sub(time.Now())
			}
			if noDischarges {
				fc.dc = nil
			}
			if verr := fc.start(r.suffix, method, args, timeout, grantedB); verr != nil {
				return nil, verror.NoRetry, verr
			}
			return fc, verror.NoRetry, nil
		}
		if numResponses == len(responses) {
			return c.failedTryCall(ctx, name, method, servers, responses, ch)
		}
	}
}

// cleanupTryCall ensures we've waited for every response from the tryServer
// goroutines, and have closed the flow from each one except skip.  This is a
// blocking function; it should be called in its own goroutine.
func cleanupTryCall(skip *serverStatus, responses []*serverStatus, ch chan *serverStatus) {
	numPending := 0
	for _, r := range responses {
		switch {
		case r == nil:
			// The response hasn't arrived yet.
			numPending++
		case r == skip || r.flow == nil:
			// Either we should skip this flow, or we've closed the flow for this
			// response already; nothing more to do.
		default:
			// We received the response, but haven't closed the flow yet.
			r.flow.Close()
		}
	}
	// Now we just need to wait for the pending responses and close their flows.
	for i := 0; i < numPending; i++ {
		if r := <-ch; r.flow != nil {
			r.flow.Close()
		}
	}
}

// failedTryCall performs asynchronous cleanup for tryCall, and returns an
// appropriate error from the responses we've already received.  All parallel
// calls in tryCall failed or we timed out if we get here.
func (c *client) failedTryCall(ctx context.T, name, method string, servers []string, responses []*serverStatus, ch chan *serverStatus) (ipc.Call, verror.ActionCode, verror.E) {
	go cleanupTryCall(nil, responses, ch)
	c.ns.FlushCacheEntry(name)
	noconn, untrusted := []string{}, []string{}
	for i, r := range responses {
		if r != nil && r.err != nil {
			vlog.VI(2).Infof("Server: %s: %s", servers[i], r.err)
			switch {
			case verror.Is(r.err, errNotTrusted.ID) || verror.Is(r.err, errAuthError.ID):
				untrusted = append(untrusted, "("+r.err.Error()+") ")
			default:
				noconn = append(noconn, "("+r.err.Error()+") ")
			}
		}
	}
	// TODO(cnicolaou): we get system errors for things like dialing using
	// the 'ws' protocol which can never succeed even if we retry the connection,
	// hence we return RetryRefetch in all cases below. In the future, we'll
	// pick out this error and then we can retry the connection also. This also
	// plays into the 'at-most-once' rpc semantics change that's needed in order
	// to retry an in-flight RPC.
	switch {
	case len(untrusted) > 0 && len(noconn) > 0:
		return nil, verror.RetryRefetch, verror.Make(verror.NoServersAndAuth, ctx, append(noconn, untrusted...))
	case len(noconn) > 0:
		return nil, verror.RetryRefetch, verror.Make(verror.NoServers, ctx, noconn)
	case len(untrusted) > 0:
		return nil, verror.NoRetry, verror.Make(verror.NotTrusted, ctx, untrusted)
	default:
		return nil, verror.RetryRefetch, verror.Make(verror.Timeout, ctx)
	}
}

// authorizeServer validates that the server (remote end of flow) has the credentials to serve
// the RPC name.method for the client (local end of the flow). It returns the blessings at the
// server that are authorized for this purpose and any blessings that are to be granted to
// the server (via ipc.Granter implementations in opts.)
func (c *client) authorizeServer(ctx context.T, flow stream.Flow, name, method string, serverPattern security.BlessingPattern, opts []ipc.CallOpt) (serverBlessings []string, grantedBlessings security.Blessings, err verror.E) {
	if flow.RemoteBlessings() == nil {
		return nil, nil, verror.Make(errNoBlessings, ctx)
	}
	ctxt := security.NewContext(&security.ContextParams{
		LocalPrincipal:   flow.LocalPrincipal(),
		LocalBlessings:   flow.LocalBlessings(),
		RemoteBlessings:  flow.RemoteBlessings(),
		LocalEndpoint:    flow.LocalEndpoint(),
		RemoteEndpoint:   flow.RemoteEndpoint(),
		RemoteDischarges: flow.RemoteDischarges(),
		Method:           method,
		Suffix:           name})
	serverBlessings = flow.RemoteBlessings().ForContext(ctxt)
	if serverPattern != "" {
		if !serverPattern.MatchedBy(serverBlessings...) {
			return nil, nil, verror.Make(errAuthNoPatternMatch, ctx, serverBlessings, serverPattern)
		}
	} else if enableSecureServerAuth {
		if err := (defaultAuthorizer{}).Authorize(ctxt); err != nil {
			return nil, nil, verror.Make(errDefaultAuthDenied, ctx, serverBlessings)
		}
	}
	for _, o := range opts {
		switch v := o.(type) {
		case ipc.Granter:
			if b, err := v.Grant(flow.RemoteBlessings()); err != nil {
				return nil, nil, verror.Make(errBlessingGrant, ctx, serverBlessings, err)
			} else if grantedBlessings, err = security.UnionOfBlessings(grantedBlessings, b); err != nil {
				return nil, nil, verror.Make(errBlessingAdd, ctx, serverBlessings, err)
			}
		}
	}
	return serverBlessings, grantedBlessings, nil
}

func (c *client) Close() {
	defer vlog.LogCall()()
	c.vcMapMu.Lock()
	for _, v := range c.vcMap {
		c.streamMgr.ShutdownEndpoint(v.remoteEP)
	}
	c.vcMap = nil
	c.vcMapMu.Unlock()
}

// IPCBindOpt makes client implement BindOpt.
func (c *client) IPCBindOpt() {
	//nologcall
}

// flowClient implements the RPC client-side protocol for a single RPC, over a
// flow that's already connected to the server.
type flowClient struct {
	ctx      context.T    // context to annotate with call details
	dec      vomDecoder   // to decode responses and results from the server
	enc      vomEncoder   // to encode requests and args to the server
	server   []string     // Blessings bound to the server that authorize it to receive the IPC request from the client.
	flow     stream.Flow  // the underlying flow
	response ipc.Response // each decoded response message is kept here

	discharges []security.Discharge // discharges used for this request
	dc         vc.DischargeClient   // client-global discharge-client

	sendClosedMu sync.Mutex
	sendClosed   bool // is the send side already closed? GUARDED_BY(sendClosedMu)
	finished     bool // has Finish() already been called?
}

var _ ipc.Call = (*flowClient)(nil)
var _ ipc.Stream = (*flowClient)(nil)

func newFlowClient(ctx context.T, server []string, flow stream.Flow, dc vc.DischargeClient) (*flowClient, error) {
	fc := &flowClient{
		ctx:    ctx,
		dec:    vom.NewDecoder(flow),
		enc:    vom.NewEncoder(flow),
		server: server,
		flow:   flow,
		dc:     dc,
	}
	if vom2.IsEnabled() {
		var err error
		if fc.enc, err = vom2.NewBinaryEncoder(flow); err != nil {
			berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errVomEncoder, fc.ctx, err))
			return nil, fc.close(berr)
		}
		if fc.dec, err = vom2.NewDecoder(flow); err != nil {
			berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errVomDecoder, fc.ctx, err))
			return nil, fc.close(berr)
		}
	} else {
		fc.dec = vom.NewDecoder(flow)
		fc.enc = vom.NewEncoder(flow)
	}
	return fc, nil
}

func (fc *flowClient) close(verr verror.E) verror.E {
	if err := fc.flow.Close(); err != nil && verr == nil {
		verr = verror.Make(errClosingFlow, fc.ctx, err)
	}
	return verr
}

func (fc *flowClient) start(suffix, method string, args []interface{}, timeout time.Duration, blessings security.Blessings) verror.E {
	// Fetch any discharges for third-party caveats on the client's blessings
	// if this client owns a discharge-client.
	if self := fc.flow.LocalBlessings(); self != nil && fc.dc != nil {
		fc.discharges = fc.dc.PrepareDischarges(fc.ctx, self.ThirdPartyCaveats(), mkDischargeImpetus(fc.server, method, args))
	}
	req := ipc.Request{
		Suffix:           suffix,
		Method:           method,
		NumPosArgs:       uint64(len(args)),
		Timeout:          int64(timeout),
		GrantedBlessings: security.MarshalBlessings(blessings),
		NumDischarges:    uint64(len(fc.discharges)),
		TraceRequest:     ivtrace.Request(fc.ctx),
	}
	if err := fc.enc.Encode(req); err != nil {
		berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errRequestEncoding, fc.ctx, fmt.Sprintf("%#v", req), err))
		return fc.close(berr)
	}
	for _, d := range fc.discharges {
		if err := fc.enc.Encode(d); err != nil {
			berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errDischargeEncoding, fc.ctx, d.ID(), err))
			return fc.close(berr)
		}
	}
	for ix, arg := range args {
		if err := fc.enc.Encode(arg); err != nil {
			berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errArgEncoding, fc.ctx, ix, err))
			return fc.close(berr)
		}
	}
	return nil
}

func (fc *flowClient) Send(item interface{}) error {
	defer vlog.LogCall()()
	if fc.sendClosed {
		return verror.Make(verror.Aborted, fc.ctx)
	}

	// The empty request header indicates what follows is a streaming arg.
	if err := fc.enc.Encode(ipc.Request{}); err != nil {
		berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errRequestEncoding, fc.ctx, ipc.Request{}, err))
		return fc.close(berr)
	}
	if err := fc.enc.Encode(item); err != nil {
		berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errArgEncoding, fc.ctx, -1, err))
		return fc.close(berr)
	}
	return nil
}

func decodeNetError(ctx context.T, err error) verror.IDAction {
	if neterr, ok := err.(net.Error); ok {
		if neterr.Timeout() || neterr.Temporary() {
			// If a read is cancelled in the lower levels we see
			// a timeout error - see readLocked in vc/reader.go
			if ctx.Err() == context.Canceled {
				return verror.Cancelled
			}
			return verror.Timeout
		}
	}
	return verror.BadProtocol
}

func (fc *flowClient) Recv(itemptr interface{}) error {
	defer vlog.LogCall()()
	switch {
	case fc.response.Error != nil:
		// TODO(cnicolaou): this will become a verror2.E when we convert the
		// server.
		return verror.Make(verror.BadProtocol, fc.ctx, fc.response.Error)
	case fc.response.EndStreamResults:
		return io.EOF
	}

	// Decode the response header and handle errors and EOF.
	if err := fc.dec.Decode(&fc.response); err != nil {
		berr := verror.Make(decodeNetError(fc.ctx, err), fc.ctx, verror.Make(errResponseDecoding, fc.ctx, err))
		return fc.close(berr)
	}
	if fc.response.Error != nil {
		// TODO(cnicolaou): this will become a verror2.E when we convert the
		// server.
		return verror.Make(verror.BadProtocol, fc.ctx, fc.response.Error)
	}
	if fc.response.EndStreamResults {
		// Return EOF to indicate to the caller that there are no more stream
		// results.  Any error sent by the server is kept in fc.response.Error, and
		// returned to the user in Finish.
		return io.EOF
	}
	// Decode the streaming result.
	if err := fc.dec.Decode(itemptr); err != nil {
		berr := verror.Make(decodeNetError(fc.ctx, err), fc.ctx, verror.Make(errResponseDecoding, fc.ctx, err))
		// TODO(cnicolaou): should we be caching this?
		fc.response.Error = berr
		return fc.close(berr)
	}
	return nil
}

func (fc *flowClient) CloseSend() error {
	defer vlog.LogCall()()
	return fc.closeSend()
}

// closeSend ensures CloseSend always returns verror.E.
func (fc *flowClient) closeSend() verror.E {
	fc.sendClosedMu.Lock()
	defer fc.sendClosedMu.Unlock()
	if fc.sendClosed {
		return nil
	}
	if err := fc.enc.Encode(ipc.Request{EndStreamArgs: true}); err != nil {
		// TODO(caprita): Indiscriminately closing the flow below causes
		// a race as described in:
		// https://docs.google.com/a/google.com/document/d/1C0kxfYhuOcStdV7tnLZELZpUhfQCZj47B0JrzbE29h8/edit
		//
		// There should be a finer grained way to fix this (for example,
		// encoding errors should probably still result in closing the
		// flow); on the flip side, there may exist other instances
		// where we are closing the flow but should not.
		//
		// For now, commenting out the line below removes the flakiness
		// from our existing unit tests, but this needs to be revisited
		// and fixed correctly.
		//
		//   return fc.close(verror.BadProtocolf("ipc: end stream args encoding failed: %v", err))
	}
	fc.sendClosed = true
	return nil
}

func (fc *flowClient) Finish(resultptrs ...interface{}) error {
	defer vlog.LogCall()()
	err := fc.finish(resultptrs...)
	ivtrace.FromContext(fc.ctx).Finish()
	return err
}

// finish ensures Finish always returns verror.E.
func (fc *flowClient) finish(resultptrs ...interface{}) verror.E {
	if fc.finished {
		err := verror.Make(errClientFinishAlreadyCalled, fc.ctx)
		return fc.close(verror.Make(verror.BadState, fc.ctx, err))
	}
	fc.finished = true

	// Call closeSend implicitly, if the user hasn't already called it.  There are
	// three cases:
	// 1) Server is blocked on Recv waiting for the final request message.
	// 2) Server has already finished processing, the final response message and
	//    out args are queued up on the client, and the flow is closed.
	// 3) Between 1 and 2: the server isn't blocked on Recv, but the final
	//    response and args aren't queued up yet, and the flow isn't closed.
	//
	// We must call closeSend to handle case (1) and unblock the server; otherwise
	// we'll deadlock with both client and server waiting for each other.  We must
	// ignore the error (if any) to handle case (2).  In that case the flow is
	// closed, meaning writes will fail and reads will succeed, and closeSend will
	// always return an error.  But this isn't a "real" error; the client should
	// read the rest of the results and succeed.
	_ = fc.closeSend()

	// Decode the response header, if it hasn't already been decoded by Recv.
	if fc.response.Error == nil && !fc.response.EndStreamResults {
		if err := fc.dec.Decode(&fc.response); err != nil {
			berr := verror.Make(decodeNetError(fc.ctx, err), fc.ctx, verror.Make(errResponseDecoding, fc.ctx, err))
			return fc.close(berr)
		}
		// The response header must indicate the streaming results have ended.
		if fc.response.Error == nil && !fc.response.EndStreamResults {
			berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errRemainingStreamResults, fc.ctx))
			return fc.close(berr)
		}
	}

	// Incorporate any VTrace info that was returned.
	ivtrace.MergeResponse(fc.ctx, &fc.response.TraceResponse)

	if fc.response.Error != nil {
		// TODO(cnicolaou): remove verror.NoAccess with verror version
		// when ipc.Server is converted.
		if verror.Is(fc.response.Error, old_verror.NoAccess) && fc.dc != nil {
			// In case the error was caused by a bad discharge, we do not want to get stuck
			// with retrying again and again with this discharge. As there is no direct way
			// to detect it, we conservatively flush all discharges we used from the cache.
			// TODO(ataly,andreser): add verror.BadDischarge and handle it explicitly?
			vlog.VI(3).Infof("Discarging %d discharges as RPC failed with %v", len(fc.discharges), fc.response.Error)
			fc.dc.Invalidate(fc.discharges...)
		}
		return fc.close(verror.Convert(verror.Internal, fc.ctx, fc.response.Error))
	}
	if got, want := fc.response.NumPosResults, uint64(len(resultptrs)); got != want {
		berr := verror.Make(verror.BadProtocol, fc.ctx, verror.Make(errMismatchedResults, fc.ctx, got, want))
		return fc.close(berr)
	}
	for ix, r := range resultptrs {
		if err := fc.dec.Decode(r); err != nil {
			berr := verror.Make(decodeNetError(fc.ctx, err), fc.ctx, verror.Make(errResultDecoding, fc.ctx, ix, err))
			return fc.close(berr)
		}
	}
	return fc.close(nil)
}

func (fc *flowClient) Cancel() {
	defer vlog.LogCall()()
	ivtrace.FromContext(fc.ctx).Annotate("Cancelled")
	fc.flow.Cancel()
}

func (fc *flowClient) RemoteBlessings() ([]string, security.Blessings) {
	return fc.server, fc.flow.RemoteBlessings()
}