add tracing package (forgot to commit)

daemon/job/passive.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 
+	"github.com/golang/protobuf/proto"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 
@@ -180,11 +181,39 @@ func (j *PassiveSide) Run(ctx context.Context) {
 	}
 
 	ctxInterceptor := func(handlerCtx context.Context) context.Context {
-		return logging.WithSubsystemLoggers(handlerCtx, log)
+		reqLog := log.WithField(logging.ReqIDField, rpc.MustGetRequestID(handlerCtx))
+		return logging.WithSubsystemLoggers(handlerCtx, reqLog)
+	}
+
+	// ctxInterceptor already injected request loggers (with request id)
+	pre := func(ctx context.Context, method string, req interface{}) {
+		l := endpoint.GetLogger(ctx).WithField("method", method).WithField("reqT", fmt.Sprintf("%T", req))
+		if p, ok := req.(proto.Message); ok {
+			l = l.WithField("req", proto.CompactTextString(p))
+		}
+		ci, ok := ctx.Value(endpoint.ClientIdentityKey).(string)
+		if !ok {
+			// like endpoint, we must assume that rpc.Server sets it
+			panic(method)
+		}
+		l = l.WithField("clientIdentity", ci)
+		l.Debug("incoming")
+	}
+	post := func(ctx context.Context, res interface{}, err error) {
+		l := endpoint.GetLogger(ctx).
+			WithField("responseT", fmt.Sprintf("%T", res)).
+			WithField("errT", fmt.Sprintf("%T", err))
+		if s, ok := res.(fmt.Stringer); ok {
+			l = l.WithField("response", s.String())
+		}
+		if err != nil {
+			l = l.WithError(err)
+		}
+		l.Debug("handler done")
 	}
 
 	rpcLoggers := rpc.GetLoggersOrPanic(ctx) // WithSubsystemLoggers above
-	server := rpc.NewServer(handler, rpcLoggers, ctxInterceptor)
+	server := rpc.NewServer(handler, rpcLoggers, ctxInterceptor, pre, post)
 
 	listener, err := j.listen()
 	if err != nil {

daemon/logging/build_logging.go

@@ -96,6 +96,11 @@ func WithSubsystemLoggers(ctx context.Context, log logger.Logger) context.Contex
 			Control: log.WithField(SubsysField, SubsysRPCControl),
 			Data:    log.WithField(SubsysField, SubsysRPCData),
 		},
+		// rpc.Loggers{
+		// 	General: logger.NewNullLogger(),
+		// 	Control: logger.NewNullLogger(),
+		// 	Data:    logger.NewNullLogger(),
+		// },
 	)
 	return ctx
 }

daemon/logging/logging_formatters.go

@@ -22,6 +22,7 @@ const (
 const (
 	JobField    string = "job"
 	SubsysField string = "subsystem"
+	ReqIDField  string = "reqid"
 )
 
 type MetadataFlags int64
@@ -85,7 +86,7 @@ func (f *HumanFormatter) Format(e *logger.Entry) (out []byte, err error) {
 		fmt.Fprintf(&line, "[%s]", col.Sprint(e.Level.Short()))
 	}
 
-	prefixFields := []string{JobField, SubsysField}
+	prefixFields := []string{JobField, SubsysField, ReqIDField}
 	prefixed := make(map[string]bool, len(prefixFields)+2)
 	for _, field := range prefixFields {
 		val, ok := e.Fields[field]

endpoint/context.go

@@ -19,6 +19,10 @@ func WithLogger(ctx context.Context, log Logger) context.Context {
 	return context.WithValue(ctx, contextKeyLogger, log)
 }
 
+func GetLogger(ctx context.Context) Logger {
+	return getLogger(ctx)
+}
+
 func getLogger(ctx context.Context) Logger {
 	if l, ok := ctx.Value(contextKeyLogger).(Logger); ok {
 		return l

endpoint/endpoint.go

@@ -159,6 +159,7 @@ func sendArgsFromPDUAndValidateExists(ctx context.Context, fs string, fsv *pdu.F
 }
 
 func (s *Sender) Send(ctx context.Context, r *pdu.SendReq) (*pdu.SendRes, zfs.StreamCopier, error) {
+	getLogger(ctx).WithField("req", r.String()).Debug("incoming Send request")
 
 	_, err := s.filterCheckFS(r.Filesystem)
 	if err != nil {
@@ -259,6 +260,7 @@ func (s *Sender) Send(ctx context.Context, r *pdu.SendReq) (*pdu.SendRes, zfs.St
 }
 
 func (p *Sender) SendCompleted(ctx context.Context, r *pdu.SendCompletedReq) (*pdu.SendCompletedRes, error) {
+	getLogger(ctx).WithField("req", r.String()).Debug("incoming SendCompleted request")
 	orig := r.GetOriginalReq() // may be nil, always use proto getters
 	fs := orig.GetFilesystem()
 
@@ -510,7 +512,7 @@ func (s *Receiver) ListFilesystems(ctx context.Context, req *pdu.ListFilesystemR
 	// present filesystem without the root_fs prefix
 	fss := make([]*pdu.Filesystem, 0, len(filtered))
 	for _, a := range filtered {
-		l := getLogger(ctx).WithField("fs", a)
+		l := getLogger(ctx).WithField("fs", a.ToString())
 		ph, err := zfs.ZFSGetFilesystemPlaceholderState(a)
 		if err != nil {
 			l.WithError(err).Error("error getting placeholder state")
@@ -597,7 +599,7 @@ func (s *Receiver) Send(ctx context.Context, req *pdu.SendReq) (*pdu.SendRes, zf
 var maxConcurrentZFSRecvSemaphore = semaphore.New(envconst.Int64("ZREPL_ENDPOINT_MAX_CONCURRENT_RECV", 10))
 
 func (s *Receiver) Receive(ctx context.Context, req *pdu.ReceiveReq, receive zfs.StreamCopier) (*pdu.ReceiveRes, error) {
-	getLogger(ctx).Debug("incoming Receive")
+	getLogger(ctx).WithField("rr", req.String()).Debug("incoming Receive")
 	defer receive.Close()
 
 	root := s.clientRootFromCtx(ctx)

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/gdamore/tcell v1.2.0
 	github.com/go-logfmt/logfmt v0.4.0
 	github.com/go-sql-driver/mysql v1.4.1-0.20190907122137-b2c03bcae3d4
+	github.com/gogo/protobuf v1.1.1
 	github.com/golang/protobuf v1.3.2
 	github.com/google/uuid v1.1.1
 	github.com/jinzhu/copier v0.0.0-20170922082739-db4671f3a9b8

go.sum

@@ -68,6 +68,7 @@ github.com/go-toolsmith/strparse v1.0.0/go.mod h1:YI2nUKP9YGZnL/L1/DLFBfixrcjslW
 github.com/go-toolsmith/typep v0.0.0-20181030061450-d63dc7650676/go.mod h1:JSQCQMUPdRlMZFswiq3TGpNp1GMktqkR2Ns5AIQkATU=
 github.com/go-toolsmith/typep v1.0.0/go.mod h1:JSQCQMUPdRlMZFswiq3TGpNp1GMktqkR2Ns5AIQkATU=
 github.com/gobwas/glob v0.2.3/go.mod h1:d3Ez4x06l9bZtSvzIay5+Yzi0fmZzPgnTbPcKjJAkT8=
+github.com/gogo/protobuf v1.1.1 h1:72R+M5VuhED/KujmZVcIquuo8mBgX4oVda//DQb3PXo=
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=

replication/driver/replication_driver.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"os"
 	"sort"
 	"strings"
 	"sync"
@@ -14,6 +15,7 @@ import (
 	"google.golang.org/grpc/status"
 
 	"github.com/zrepl/zrepl/replication/report"
+	"github.com/zrepl/zrepl/tracing"
 	"github.com/zrepl/zrepl/util/chainlock"
 	"github.com/zrepl/zrepl/util/envconst"
 )
@@ -206,6 +208,7 @@ func Do(ctx context.Context, planner Planner) (ReportFunc, WaitFunc) {
 			}
 			run.attempts = append(run.attempts, cur)
 			run.l.DropWhile(func() {
+				ctx := tracing.Child(ctx, fmt.Sprintf("attempt#%d", ano)) // shadow
 				cur.do(ctx, prev)
 			})
 			prev = cur
@@ -281,7 +284,7 @@ func Do(ctx context.Context, planner Planner) (ReportFunc, WaitFunc) {
 }
 
 func (a *attempt) do(ctx context.Context, prev *attempt) {
-	pfss, err := a.planner.Plan(ctx)
+	pfss, err := a.planner.Plan(tracing.Child(ctx, "plan"))
 	errTime := time.Now()
 	defer a.l.Lock().Unlock()
 	if err != nil {
@@ -361,7 +364,7 @@ func (a *attempt) do(ctx context.Context, prev *attempt) {
 		fssesDone.Add(1)
 		go func(f *fs) {
 			defer fssesDone.Done()
-			f.do(ctx, stepQueue, prevs[f])
+			f.do(tracing.Child(ctx, f.fs.ReportInfo().Name), stepQueue, prevs[f])
 		}(f)
 	}
 	a.l.DropWhile(func() {
@@ -372,6 +375,8 @@ func (a *attempt) do(ctx context.Context, prev *attempt) {
 
 func (fs *fs) do(ctx context.Context, pq *stepQueue, prev *fs) {
 
+	fmt.Fprintf(os.Stderr, "CHILD STACK: %v\n", tracing.GetStack(ctx))
+
 	defer fs.l.Lock().Unlock()
 
 	// get planned steps from replication logic

replication/logic/replication_logic.go

@@ -606,7 +606,7 @@ func (s *Step) doReplication(ctx context.Context) error {
 	log := getLogger(ctx)
 	sr := s.buildSendRequest(false)
 
-	log.Debug("initiate send request")
+	log.WithField("sr", sr.String()).Debug("initiate send request")
 	sres, sstreamCopier, err := s.sender.Send(ctx, sr)
 	if err != nil {
 		log.WithError(err).Error("send request failed")
@@ -633,7 +633,7 @@ func (s *Step) doReplication(ctx context.Context) error {
 		To:               sr.GetTo(),
 		ClearResumeToken: !sres.UsedResumeToken,
 	}
-	log.Debug("initiate receive request")
+	log.WithField("rr", rr.String()).Debug("initiate receive request")
 	_, err = s.receiver.Receive(ctx, rr, byteCountingStream)
 	if err != nil {
 		log.
@@ -649,10 +649,11 @@ func (s *Step) doReplication(ctx context.Context) error {
 	}
 	log.Debug("receive finished")
 
-	log.Debug("tell sender replication completed")
+	scr := &pdu.SendCompletedReq{
-	_, err = s.sender.SendCompleted(ctx, &pdu.SendCompletedReq{
 		OriginalReq: sr,
-	})
+	}
+	log.WithField("scr", scr.String()).Debug("tell sender replication completed")
+	_, err = s.sender.SendCompleted(ctx, scr)
 	if err != nil {
 		log.WithError(err).Error("error telling sender that replication completed successfully")
 		return err

rpc/dataconn/dataconn_client.go

@@ -75,7 +75,7 @@ func (c *Client) recv(ctx context.Context, conn *stream.Conn, res proto.Message)
 	if err != nil {
 		return err
 	}
-	header := string(headerBuf)
+	header := string(headerBuf) // FIXME
 	if strings.HasPrefix(header, responseHeaderHandlerErrorPrefix) {
 		// FIXME distinguishable error type
 		return &RemoteHandlerError{strings.TrimPrefix(header, responseHeaderHandlerErrorPrefix)}

rpc/dataconn/dataconn_server.go

@@ -14,8 +14,8 @@ import (
 	"github.com/zrepl/zrepl/zfs"
 )
 
-// WireInterceptor has a chance to exchange the context and connection on each client connection.
+// ReqInterceptor has a chance to exchange the context and connection on each request.
-type WireInterceptor func(ctx context.Context, rawConn *transport.AuthConn) (context.Context, *transport.AuthConn)
+type ReqInterceptor func(ctx context.Context, rawConn *transport.AuthConn) (context.Context, *transport.AuthConn)
 
 // Handler implements the functionality that is exposed by Server to the Client.
 type Handler interface {
@@ -30,19 +30,27 @@ type Handler interface {
 	PingDataconn(ctx context.Context, r *pdu.PingReq) (*pdu.PingRes, error)
 }
 
+type PreHandlerInspector = func(ctx context.Context, endpoint string, req interface{})
+
+type PostHandlerInspector = func(ctx context.Context, response interface{}, err error)
+
 type Logger = logger.Logger
 
 type Server struct {
 	h    Handler
-	wi  WireInterceptor
+	ri   ReqInterceptor
 	log  Logger
+	pre  PreHandlerInspector
+	post PostHandlerInspector
 }
 
-func NewServer(wi WireInterceptor, logger Logger, handler Handler) *Server {
+func NewServer(ri ReqInterceptor, logger Logger, pre PreHandlerInspector, handler Handler, post PostHandlerInspector) *Server {
 	return &Server{
 		h:   handler,
-		wi:  wi,
+		ri:  ri,
 		log: logger,
+		pre: pre,
+		post: post,
 	}
 }
 
@@ -83,8 +91,8 @@ func (s *Server) serveConn(nc *transport.AuthConn) {
 	defer s.log.Debug("serveConn done")
 
 	ctx := context.Background()
-	if s.wi != nil {
+	if s.ri != nil {
-		ctx, nc = s.wi(ctx, nc)
+		ctx, nc = s.ri(ctx, nc)
 	}
 
 	c := stream.Wrap(nc, HeartbeatInterval, HeartbeatPeerTimeout)
@@ -100,7 +108,7 @@ func (s *Server) serveConn(nc *transport.AuthConn) {
 		s.log.WithError(err).Error("error reading structured part")
 		return
 	}
-	endpoint := string(header)
+	endpoint := string(header) // FIXME
 
 	reqStructured, err := c.ReadStreamedMessage(ctx, RequestStructuredMaxSize, ReqStructured)
 	if err != nil {
@@ -120,6 +128,7 @@ func (s *Server) serveConn(nc *transport.AuthConn) {
 			s.log.WithError(err).Error("cannot unmarshal send request")
 			return
 		}
+		s.pre(ctx, endpoint, &req)
 		res, sendStream, handlerErr = s.h.Send(ctx, &req) // SHADOWING
 	case EndpointRecv:
 		var req pdu.ReceiveReq
@@ -127,6 +136,7 @@ func (s *Server) serveConn(nc *transport.AuthConn) {
 			s.log.WithError(err).Error("cannot unmarshal receive request")
 			return
 		}
+		s.pre(ctx, endpoint, &req)
 		res, handlerErr = s.h.Receive(ctx, &req, &streamCopier{streamConn: c, closeStreamOnClose: false}) // SHADOWING
 	case EndpointPing:
 		var req pdu.PingReq
@@ -134,6 +144,7 @@ func (s *Server) serveConn(nc *transport.AuthConn) {
 			s.log.WithError(err).Error("cannot unmarshal ping request")
 			return
 		}
+		s.pre(ctx, endpoint, &req)
 		res, handlerErr = s.h.PingDataconn(ctx, &req) // SHADOWING
 	default:
 		s.log.WithField("endpoint", endpoint).Error("unknown endpoint")
@@ -142,6 +153,8 @@ func (s *Server) serveConn(nc *transport.AuthConn) {
 
 	s.log.WithField("endpoint", endpoint).WithField("errType", fmt.Sprintf("%T", handlerErr)).Debug("handler returned")
 
+	s.post(ctx, res, handlerErr)
+
 	// prepare protobuf now to return the protobuf error in the header
 	// if marshaling fails. We consider failed marshaling a handler error
 	var protobuf *bytes.Buffer

rpc/grpcclientidentity/authlistener_grpc_adaptor.go

@@ -101,7 +101,11 @@ func (*transportCredentials) OverrideServerName(string) error {
 
 type ContextInterceptor = func(ctx context.Context) context.Context
 
-func NewInterceptors(logger Logger, clientIdentityKey interface{}, ctxInterceptor ContextInterceptor) (unary grpc.UnaryServerInterceptor, stream grpc.StreamServerInterceptor) {
+type PreHandlerInspector func(ctx context.Context, endpoint string, req interface{})
+
+type PostHandlerInspector func(ctx context.Context, response interface{}, err error)
+
+func NewInterceptors(logger Logger, clientIdentityKey interface{}, ctxInterceptor ContextInterceptor, pre PreHandlerInspector, post PostHandlerInspector) (unary grpc.UnaryServerInterceptor, stream grpc.StreamServerInterceptor) {
 	unary = func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
 		logger.WithField("fullMethod", info.FullMethod).Debug("request")
 		p, ok := peer.FromContext(ctx)
@@ -118,7 +122,10 @@ func NewInterceptors(logger Logger, clientIdentityKey interface{}, ctxIntercepto
 		if ctxInterceptor != nil {
 			ctx = ctxInterceptor(ctx)
 		}
-		return handler(ctx, req)
+		pre(ctx, info.FullMethod, req)
+		res, err := handler(ctx, req)
+		post(ctx, res, err)
+		return res, err
 	}
 	stream = func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
 		panic("unimplemented")

rpc/grpcclientidentity/grpchelper/authlistener_grpc_adaptor_wrapper.go

@@ -4,14 +4,18 @@ package grpchelper
 
 import (
 	"context"
+	"fmt"
+	"strings"
 	"time"
 
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/metadata"
 
 	"github.com/zrepl/zrepl/logger"
 	"github.com/zrepl/zrepl/rpc/grpcclientidentity"
 	"github.com/zrepl/zrepl/rpc/netadaptor"
+	"github.com/zrepl/zrepl/tracing"
 	"github.com/zrepl/zrepl/transport"
 )
 
@@ -28,15 +32,40 @@ type Logger = logger.Logger
 
 // ClientConn is an easy-to-use wrapper around the Dialer and TransportCredentials interface
 // to produce a grpc.ClientConn
-func ClientConn(cn transport.Connecter, log Logger) *grpc.ClientConn {
+func ClientConn(cn transport.Connecter, log Logger, genReqID func() string) *grpc.ClientConn {
 	ka := grpc.WithKeepaliveParams(keepalive.ClientParameters{
 		Time:                StartKeepalivesAfterInactivityDuration,
 		Timeout:             KeepalivePeerTimeout,
 		PermitWithoutStream: true,
 	})
+	unaryIntcpt := grpc.WithUnaryInterceptor(func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+
+		traceStack := tracing.GetStack(ctx)
+		if len(traceStack) == 0 {
+			panic("implementation error: expecting trace stack")
+		}
+		reqId := genReqID() + " " + strings.Join(traceStack, " <> ")
+
+		l := log
+		l = l.WithField("reqID", reqId)
+		l = l.WithField("reqT", fmt.Sprintf("%T", req))
+		l = l.WithField("repT", fmt.Sprintf("%T", reply))
+		l = l.WithField("ctxT", fmt.Sprintf("%T", ctx))
+		l.Debug("unary intercepted")
+
+		ctx = metadata.AppendToOutgoingContext(ctx, "zrepl-req-id", reqId)
+
+		err := invoker(ctx, method, req, reply, cc, opts...)
+
+		l = log.WithField("repT", fmt.Sprintf("%T", reply))
+		l = log.WithField("errT", fmt.Sprintf("%T", err))
+		l.Debug("reply intercepted")
+
+		return err
+	})
 	dialerOption := grpc.WithDialer(grpcclientidentity.NewDialer(log, cn))
 	cred := grpc.WithTransportCredentials(grpcclientidentity.NewTransportCredentials(log))
-	cc, err := grpc.DialContext(context.Background(), "doesn't matter done by dialer", dialerOption, cred, ka)
+	cc, err := grpc.DialContext(context.Background(), "doesn't matter done by dialer", dialerOption, cred, ka, unaryIntcpt)
 	if err != nil {
 		log.WithError(err).Error("cannot create gRPC client conn (non-blocking)")
 		// It's ok to panic here: the we call grpc.DialContext without the
@@ -50,7 +79,7 @@ func ClientConn(cn transport.Connecter, log Logger) *grpc.ClientConn {
 }
 
 // NewServer is a convenience interface around the TransportCredentials and Interceptors interface.
-func NewServer(authListener transport.AuthenticatedListener, clientIdentityKey interface{}, logger grpcclientidentity.Logger, ctxInterceptor grpcclientidentity.ContextInterceptor) (srv *grpc.Server, serve func() error) {
+func NewServer(authListener transport.AuthenticatedListener, clientIdentityKey interface{}, logger grpcclientidentity.Logger, interceptor grpcclientidentity.ContextInterceptor, pre grpcclientidentity.PreHandlerInspector, post grpcclientidentity.PostHandlerInspector) (srv *grpc.Server, serve func() error) {
 	ka := grpc.KeepaliveParams(keepalive.ServerParameters{
 		Time:    StartKeepalivesAfterInactivityDuration,
 		Timeout: KeepalivePeerTimeout,
@@ -60,8 +89,17 @@ func NewServer(authListener transport.AuthenticatedListener, clientIdentityKey i
 		PermitWithoutStream: true,
 	})
 	tcs := grpcclientidentity.NewTransportCredentials(logger)
-	unary, stream := grpcclientidentity.NewInterceptors(logger, clientIdentityKey, ctxInterceptor)
+	unary, stream := grpcclientidentity.NewInterceptors(logger, clientIdentityKey, interceptor, pre, post)
-	srv = grpc.NewServer(grpc.Creds(tcs), grpc.UnaryInterceptor(unary), grpc.StreamInterceptor(stream), ka, ep)
+	unary2 := func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (resp interface{}, err error) {
+		md, ok := metadata.FromIncomingContext(ctx)
+		if !ok {
+			logger.Error("no request id in incoming request")
+		} else {
+			logger.Info(fmt.Sprintf("req-id = %v", md.Get("zrepl-req-id")))
+		}
+		return unary(ctx, req, info, handler)
+	}
+	srv = grpc.NewServer(grpc.Creds(tcs), grpc.UnaryInterceptor(unary2), grpc.StreamInterceptor(stream), ka, ep)
 
 	serve = func() error {
 		if err := srv.Serve(netadaptor.New(authListener, logger)); err != nil {

rpc/rpc_client.go

@@ -26,6 +26,7 @@ import (
 // Client implements the active side of a replication setup.
 // It satisfies the Endpoint, Sender and Receiver interface defined by package replication.
 type Client struct {
+	reqIDGen      *requestIDGenerator
 	dataClient    *dataconn.Client
 	controlClient pdu.ReplicationClient // this the grpc client instance, see constructor
 	controlConn   *grpc.ClientConn
@@ -49,8 +50,11 @@ func NewClient(cn transport.Connecter, loggers Loggers) *Client {
 	c := &Client{
 		loggers:  loggers,
 		closed:   make(chan struct{}),
+		reqIDGen: newRequestIDGenerator(),
 	}
-	grpcConn := grpchelper.ClientConn(muxedConnecter.control, loggers.Control)
+	grpcConn := grpchelper.ClientConn(muxedConnecter.control, loggers.Control, func() string {
+		return c.reqIDGen.newID().String()
+	})
 
 	go func() {
 		ctx, cancel := context.WithCancel(context.Background())

rpc/rpc_requestid.go

@@ -0,0 +1,58 @@
+package rpc
+
+import (
+	"context"
+	"encoding/base64"
+	"strings"
+
+	"github.com/google/uuid"
+)
+
+type requestIDGenerator struct{}
+
+func newRequestIDGenerator() *requestIDGenerator {
+	return &requestIDGenerator{}
+}
+
+type RequestID struct{ s string }
+
+func (r RequestID) String() string { return r.s }
+
+type requestIDContextKey int
+
+const (
+	requestIDContextKeyRequestID requestIDContextKey = 1 + iota
+)
+
+func (g *requestIDGenerator) newID() RequestID {
+	id := uuid.New()
+	var buf strings.Builder
+	enc := base64.NewEncoder(base64.RawStdEncoding, &buf)
+	n, err := enc.Write(id[:])
+	if err != nil {
+		panic(err)
+	} else if n != len(id) {
+		panic(n)
+	}
+	if err := enc.Close(); err != nil {
+		panic(err)
+	}
+	return RequestID{buf.String()}
+}
+
+func (g *requestIDGenerator) inject(ctx context.Context) context.Context {
+	return context.WithValue(ctx, requestIDContextKeyRequestID, g.newID())
+}
+
+func GetRequestID(ctx context.Context) (id RequestID, ok bool) {
+	id, ok = ctx.Value(requestIDContextKeyRequestID).(RequestID)
+	return id, ok
+}
+
+func MustGetRequestID(ctx context.Context) (id RequestID) {
+	id, ok := GetRequestID(ctx)
+	if !ok {
+		panic("calling context expectes request id to bet set")
+	}
+	return id
+}

rpc/rpc_server.go

@@ -7,6 +7,7 @@ import (
 	"github.com/zrepl/zrepl/endpoint"
 	"github.com/zrepl/zrepl/replication/logic/pdu"
 	"github.com/zrepl/zrepl/rpc/dataconn"
+	"github.com/zrepl/zrepl/rpc/grpcclientidentity"
 	"github.com/zrepl/zrepl/rpc/grpcclientidentity/grpchelper"
 	"github.com/zrepl/zrepl/rpc/versionhandshake"
 	"github.com/zrepl/zrepl/transport"
@@ -30,15 +31,35 @@ type Server struct {
 	dataServerServe    serveFunc
 }
 
-type HandlerContextInterceptor func(ctx context.Context) context.Context
+type CtxInterceptor = grpcclientidentity.ContextInterceptor
+
+func chainInterceptors(interceptors []CtxInterceptor) CtxInterceptor {
+	return func(ctx context.Context) (_ context.Context) {
+		for _, i := range interceptors {
+			ctx = i(ctx)
+		}
+		return ctx
+	}
+}
+
+type PreHandlerInspector = func(ctx context.Context, endpoint string, req interface{})
+
+type PostHandlerInspector = func(ctx context.Context, response interface{}, err error)
 
 // config must be valid (use its Validate function).
-func NewServer(handler Handler, loggers Loggers, ctxInterceptor HandlerContextInterceptor) *Server {
+func NewServer(handler Handler, loggers Loggers, ctxInterceptor CtxInterceptor, pre PreHandlerInspector, post PostHandlerInspector) *Server {
+
+	reqIdGen := newRequestIDGenerator()
+
+	ctxInterceptor = chainInterceptors([]CtxInterceptor{
+		reqIdGen.inject,
+		ctxInterceptor,
+	})
 
 	// setup control server
 	controlServerServe := func(ctx context.Context, controlListener transport.AuthenticatedListener, errOut chan<- error) {
 
-		controlServer, serve := grpchelper.NewServer(controlListener, endpoint.ClientIdentityKey, loggers.Control, ctxInterceptor)
+		controlServer, serve := grpchelper.NewServer(controlListener, endpoint.ClientIdentityKey, loggers.Control, ctxInterceptor, pre, post)
 		pdu.RegisterReplicationServer(controlServer, handler)
 
 		// give time for graceful stop until deadline expires, then hard stop
@@ -63,7 +84,7 @@ func NewServer(handler Handler, loggers Loggers, ctxInterceptor HandlerContextIn
 		}
 		return ctx, wire
 	}
-	dataServer := dataconn.NewServer(dataServerClientIdentitySetter, loggers.Data, handler)
+	dataServer := dataconn.NewServer(dataServerClientIdentitySetter, loggers.Data, pre, handler, post)
 	dataServerServe := func(ctx context.Context, dataListener transport.AuthenticatedListener, errOut chan<- error) {
 		dataServer.Serve(ctx, dataListener)
 		errOut <- nil // TODO bad design of dataServer?

tracing/tracing.go

@@ -0,0 +1,53 @@
+package tracing
+
+import "context"
+
+type tracingContextKey int
+
+const (
+	CallerContext tracingContextKey = 1 + iota
+)
+
+type jobSubtree struct {
+	jobid string
+}
+
+type ctx struct {
+	parent *ctx
+	job    *jobSubtree
+	ident  string
+}
+
+var root = &ctx{nil, nil, ""}
+
+func getParentOrRoot(c context.Context) *ctx {
+	parent, ok := c.Value(CallerContext).(*ctx)
+	if !ok {
+		parent = root
+	}
+	return parent
+}
+
+func makeChild(c context.Context, child *ctx) context.Context {
+	if child.parent == nil {
+		panic(child)
+	}
+	return context.WithValue(c, CallerContext, child)
+}
+
+func Child(c context.Context, ident string) context.Context {
+	parent := getParentOrRoot(c)
+	return makeChild(c, &ctx{parent: parent, ident: ident})
+}
+
+func GetStack(c context.Context) (idents []string) {
+	ct, ok := c.Value(CallerContext).(*ctx)
+	if !ok {
+		return idents
+	}
+	for ct.parent != nil {
+		idents = append(idents, ct.ident)
+		ct = ct.parent
+	}
+	return idents
+}

tracing/tracing_test.go

@@ -0,0 +1,21 @@
+package tracing
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIt(t *testing.T) {
+	ctx := context.Background()
+
+	ctx = Child(ctx, "a")
+	ctx = Child(ctx, "b")
+	ctx = Child(ctx, "c")
+	ctx = Child(ctx, "d")
+
+	assert.Equal(t, "dcba", strings.Join(GetStack(ctx), ""))
+
+}