Add gRPC client handler.

.gitattributes

@@ -0,0 +1 @@
+* text eol=lf

.gitignore

@@ -22,3 +22,5 @@ _testmain.go
 *.exe
 *.test
 *.prof
+
+.idea

.travis.yml

@@ -3,7 +3,6 @@ language: go
 sudo: false
 
 go:
-  - 1.8.x
   - 1.9.x
   - 1.10.x
   - 1.11.x
@@ -14,7 +13,7 @@ before_install:
 
 install:
   - go get -d -t ./...
-  - if [[ ! $TRAVIS_GO_VERSION = 1.8* ]]; then go get -u golang.org/x/lint/golint ; fi
+  - go get -u golang.org/x/lint/golint
 
 script:
   - make test vet lint bench

Makefile

@@ -12,11 +12,12 @@ bench:
 .PHONY: protoc
 protoc:
 	protoc --go_out=. proto/v2/zipkin.proto
+	protoc --go_out=plugins=grpc:. proto/testing/service.proto
 
 .PHONY: lint
 lint:
 	# Ignore grep's exit code since no match returns 1.
-	-if [[ ! $TRAVIS_GO_VERSION = 1.8* ]]; then echo 'linting...' ; golint ./... ; fi
+	echo 'linting...' ; golint ./...
 
 .PHONY: vet
 vet:

go.mod

@@ -1,15 +1,29 @@
 module github.com/openzipkin/zipkin-go
 
 require (
+	cloud.google.com/go v0.33.1 // indirect
 	github.com/Shopify/sarama v1.19.0
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/eapache/go-resiliency v1.1.0 // indirect
 	github.com/eapache/go-xerial-snappy v0.0.0-20180814174437-776d5712da21 // indirect
 	github.com/eapache/queue v1.1.0 // indirect
+	github.com/golang/lint v0.0.0-20181026193005-c67002cb31c3 // indirect
 	github.com/golang/protobuf v1.2.0
 	github.com/golang/snappy v0.0.0-20180518054509-2e65f85255db // indirect
+	github.com/gorilla/context v1.1.1 // indirect
 	github.com/gorilla/mux v1.6.2
+	github.com/onsi/ginkgo v1.7.0
+	github.com/onsi/gomega v1.4.3
 	github.com/pierrec/lz4 v2.0.5+incompatible // indirect
 	github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a // indirect
+	golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3 // indirect
+	golang.org/x/net v0.0.0-20181114220301-adae6a3d119a
+	golang.org/x/oauth2 v0.0.0-20181120190819-8f65e3013eba // indirect
+	golang.org/x/sync v0.0.0-20181108010431-42b317875d0f // indirect
+	golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b // indirect
+	golang.org/x/tools v0.0.0-20181122213734-04b5d21e00f1 // indirect
+	google.golang.org/appengine v1.3.0 // indirect
+	google.golang.org/genproto v0.0.0-20181109154231-b5d43981345b // indirect
 	google.golang.org/grpc v1.16.0
+	honnef.co/go/tools v0.0.0-20180920025451-e3ad64cb4ed3 // indirect
 )

go.sum

@@ -1,4 +1,5 @@
 cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+cloud.google.com/go v0.33.1/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
 github.com/Shopify/sarama v1.19.0 h1:9oksLxC6uxVPHPVYUmq6xhr1BOF/hHobWH2UzO67z1s=
 github.com/Shopify/sarama v1.19.0/go.mod h1:FVkBWblsNy7DGZRfXLU0O9RCGt5g3g3yEuWXgklEdEo=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
@@ -10,30 +11,65 @@ github.com/eapache/go-xerial-snappy v0.0.0-20180814174437-776d5712da21 h1:YEetp8
 github.com/eapache/go-xerial-snappy v0.0.0-20180814174437-776d5712da21/go.mod h1:+020luEh2TKB4/GOp8oxxtq0Daoen/Cii55CzbTV6DU=
 github.com/eapache/queue v1.1.0 h1:YOEu7KNc61ntiQlcEeUIoDTJ2o8mQznoNvUhiigpIqc=
 github.com/eapache/queue v1.1.0/go.mod h1:6eCeP0CKFpHLu8blIFXhExK/dRa7WDZfr6jVFPTqq+I=
+github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:tluoj9z5200jBnyusfRPU2LqT6J+DAorxEvtC7LHB+E=
+github.com/golang/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:tluoj9z5200jBnyusfRPU2LqT6J+DAorxEvtC7LHB+E=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/snappy v0.0.0-20180518054509-2e65f85255db h1:woRePGFeVFfLKN/pOkfl+p/TAqKOfFu+7KPlMVpok/w=
 github.com/golang/snappy v0.0.0-20180518054509-2e65f85255db/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
+github.com/gorilla/context v1.1.1 h1:AWwleXJkX/nhcU9bZSnZoi3h/qGYqQAGhq6zZe/aQW8=
+github.com/gorilla/context v1.1.1/go.mod h1:kBGZzfjB9CEq2AlWe17Uuf7NDRt0dE0s8S51q0aT7Yg=
 github.com/gorilla/mux v1.6.2 h1:Pgr17XVTNXAk3q/r4CpKzC5xBM/qW1uVLV+IhRZpIIk=
 github.com/gorilla/mux v1.6.2/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2zaAs=
+github.com/hpcloud/tail v1.0.0 h1:nfCOvKYfkgYP8hkirhJocXT2+zOD8yUNjXaWfTlyFKI=
+github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
+github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
+github.com/onsi/ginkgo v1.7.0 h1:WSHQ+IS43OoUrWtD1/bbclrwK8TTH5hzp+umCiuxHgs=
+github.com/onsi/ginkgo v1.7.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
+github.com/onsi/gomega v1.4.3 h1:RE1xgDvH7imwFD45h+u2SgIfERHlS2yNG4DObb5BSKU=
+github.com/onsi/gomega v1.4.3/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
 github.com/pierrec/lz4 v2.0.5+incompatible h1:2xWsjqPFWcplujydGg4WmhC/6fZqK42wMM8aXeqhl0I=
 github.com/pierrec/lz4 v2.0.5+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=
 github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a h1:9ZKAASQSHhDYGoxY8uLVpewe1GDZ2vu2Tr/vTdVAkFQ=
 github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
+golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
+golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d h1:g9qWBGx4puODJTMVyoPrpoxPFgVGd+z1DZwjfRu4d0I=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20181106065722-10aee1819953/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20181114220301-adae6a3d119a h1:gOpx8G595UYyvj8UK4+OFyY4rx037g3fmfhe5SasG3U=
+golang.org/x/net v0.0.0-20181114220301-adae6a3d119a/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
+golang.org/x/oauth2 v0.0.0-20181120190819-8f65e3013eba/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b h1:MQE+LT/ABUuuvEZ+YQAMSXindAdUh7slEmAkup74op4=
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+golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
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 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
+google.golang.org/appengine v1.3.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
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+google.golang.org/genproto v0.0.0-20181109154231-b5d43981345b/go.mod h1:7Ep/1NZk928CDR8SjdVbjWNpdIf6nzjE3BTgJDr2Atg=
 google.golang.org/grpc v1.16.0 h1:dz5IJGuC2BB7qXR5AyHNwAUBhZscK2xVez7mznh72sY=
 google.golang.org/grpc v1.16.0/go.mod h1:0JHn/cJsOMiMfNA9+DeHDlAU7KAAB5GDlYFpa9MZMio=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/fsnotify.v1 v1.4.7 h1:xOHLXZwVvI9hhs+cLKq5+I5onOuwQLhQwiu63xxlHs4=
+gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
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+gopkg.in/yaml.v2 v2.2.1 h1:mUhvW9EsL+naU5Q3cakzfE91YhliOondGd6ZrsDBHQE=
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 honnef.co/go/tools v0.0.0-20180728063816-88497007e858/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
+honnef.co/go/tools v0.0.0-20180920025451-e3ad64cb4ed3/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=

middleware/grpc/client.go

@@ -0,0 +1,105 @@
+// +build go1.9
+
+package grpc
+
+import (
+	"context"
+	"strings"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+
+	"github.com/openzipkin/zipkin-go"
+	"github.com/openzipkin/zipkin-go/model"
+	"github.com/openzipkin/zipkin-go/propagation/b3"
+)
+
+type clientHandler struct {
+	tracer            *zipkin.Tracer
+	rpcHandlers       []RPCHandler
+	remoteServiceName string
+}
+
+// A ClientOption can be passed to NewClientHandler to customize the returned handler.
+type ClientOption func(*clientHandler)
+
+// A RPCHandler can be registered using WithRPCHandler to intercept calls to HandleRPC of a
+// handler for additional span customization.
+type RPCHandler func(span zipkin.Span, rpcStats stats.RPCStats)
+
+// WithRPCHandler allows one to add custom logic for handling a stats.RPCStats, e.g.,
+// to add additional tags.
+func WithRPCHandler(handler RPCHandler) ClientOption {
+	return func(c *clientHandler) {
+		c.rpcHandlers = append(c.rpcHandlers, handler)
+	}
+}
+
+// NewClientHandler returns a stats.Handler which can be used with grpc.WithStatsHandler to add
+// tracing to a gRPC client. The gRPC method name is used as the span name and by default the only
+// tags are the gRPC status code if the call fails. Use WithRPCHandler to add additional tags.
+func NewClientHandler(tracer *zipkin.Tracer, options ...ClientOption) stats.Handler {
+	c := &clientHandler{
+		tracer: tracer,
+	}
+	for _, option := range options {
+		option(c)
+	}
+	return c
+}
+
+// HandleConn exists to satisfy gRPC stats.Handler.
+func (c *clientHandler) HandleConn(ctx context.Context, cs stats.ConnStats) {
+	// no-op
+}
+
+// TagConn exists to satisfy gRPC stats.Handler.
+func (c *clientHandler) TagConn(ctx context.Context, cti *stats.ConnTagInfo) context.Context {
+	// no-op
+	return ctx
+}
+
+// HandleRPC implements per-RPC tracing and stats instrumentation.
+func (c *clientHandler) HandleRPC(ctx context.Context, rs stats.RPCStats) {
+	span := zipkin.SpanFromContext(ctx)
+
+	for _, h := range c.rpcHandlers {
+		h(span, rs)
+	}
+
+	switch rs := rs.(type) {
+	case *stats.End:
+		s, ok := status.FromError(rs.Error)
+		// rs.Error should always be convertable to a status, this is just a defensive check.
+		if ok {
+			if s.Code() != codes.OK {
+				// Uppercase for consistency with Brave
+				c := strings.ToUpper(s.Code().String())
+				span.Tag("grpc.status_code", c)
+				zipkin.TagError.Set(span, c)
+			}
+		} else {
+			zipkin.TagError.Set(span, rs.Error.Error())
+		}
+		span.Finish()
+	}
+}
+
+// TagRPC implements per-RPC context management.
+func (c *clientHandler) TagRPC(ctx context.Context, rti *stats.RPCTagInfo) context.Context {
+	var span zipkin.Span
+
+	name := spanName(rti)
+	span, ctx = c.tracer.StartSpanFromContext(ctx, name, zipkin.Kind(model.Client))
+	md, ok := metadata.FromOutgoingContext(ctx)
+	if ok {
+		md = md.Copy()
+	} else {
+		md = metadata.New(nil)
+	}
+	_ = b3.InjectGRPC(&md)(span.Context())
+	ctx = metadata.NewOutgoingContext(ctx, md)
+	return ctx
+}

middleware/grpc/client_test.go

@@ -0,0 +1,123 @@
+// +build go1.9
+
+package grpc_test
+
+import (
+	"context"
+
+	"github.com/onsi/ginkgo"
+	"github.com/onsi/gomega"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/stats"
+
+	"github.com/openzipkin/zipkin-go"
+	zipkingrpc "github.com/openzipkin/zipkin-go/middleware/grpc"
+	"github.com/openzipkin/zipkin-go/propagation/b3"
+	service "github.com/openzipkin/zipkin-go/proto/testing"
+	"github.com/openzipkin/zipkin-go/reporter/recorder"
+)
+
+var _ = ginkgo.Describe("gRPC Client", func() {
+	var (
+		reporter *recorder.ReporterRecorder
+		tracer   *zipkin.Tracer
+		conn     *grpc.ClientConn
+		client   service.HelloServiceClient
+	)
+
+	ginkgo.BeforeEach(func() {
+		var err error
+
+		reporter = recorder.NewReporter()
+		ep, _ := zipkin.NewEndpoint("grpcClient", "")
+		tracer, err = zipkin.NewTracer(
+			reporter, zipkin.WithLocalEndpoint(ep), zipkin.WithIDGenerator(newSequentialIdGenerator()))
+		gomega.Expect(tracer, err).ToNot(gomega.BeNil())
+	})
+
+	ginkgo.AfterEach(func() {
+		_ = reporter.Close()
+		_ = conn.Close()
+	})
+
+	ginkgo.Context("with defaults", func() {
+		ginkgo.BeforeEach(func() {
+			var err error
+
+			conn, err = grpc.Dial(serverAddr, grpc.WithInsecure(), grpc.WithStatsHandler(zipkingrpc.NewClientHandler(tracer)))
+			gomega.Expect(conn, err).ToNot(gomega.BeNil())
+			client = service.NewHelloServiceClient(conn)
+		})
+
+		ginkgo.It("creates a span", func() {
+			resp, err := client.Hello(context.Background(), &service.HelloRequest{Payload: "Hello"})
+			gomega.Expect(resp, err).ToNot(gomega.BeNil())
+
+			spans := reporter.Flush()
+			gomega.Expect(spans).To(gomega.HaveLen(1))
+			gomega.Expect(spans[0].Name).To(gomega.Equal("zipkin.testing.HelloService.Hello"))
+			gomega.Expect(spans[0].Tags).To(gomega.BeEmpty())
+		})
+
+		ginkgo.It("propagates trace context", func() {
+			resp, err := client.Hello(context.Background(), &service.HelloRequest{Payload: "Hello"})
+			gomega.Expect(resp.GetMetadata(), err).To(gomega.HaveKeyWithValue(b3.TraceID, "0000000000000001"))
+			gomega.Expect(resp.GetMetadata(), err).To(gomega.HaveKeyWithValue(b3.SpanID, "0000000000000001"))
+			gomega.Expect(resp.GetMetadata(), err).ToNot(gomega.HaveKey(b3.ParentSpanID))
+		})
+
+		ginkgo.It("propagates parent span", func() {
+			_, ctx := tracer.StartSpanFromContext(context.Background(), "parent")
+			resp, err := client.Hello(ctx, &service.HelloRequest{Payload: "Hello"})
+			gomega.Expect(resp.GetMetadata(), err).To(gomega.HaveKeyWithValue(b3.TraceID, "0000000000000001"))
+			gomega.Expect(resp.GetMetadata(), err).To(gomega.HaveKeyWithValue(b3.SpanID, "0000000000000002"))
+			gomega.Expect(resp.GetMetadata(), err).To(gomega.HaveKeyWithValue(b3.ParentSpanID, "0000000000000001"))
+		})
+
+		ginkgo.It("tags with error code", func() {
+			_, err := client.Hello(context.Background(), &service.HelloRequest{Payload: "fail"})
+			gomega.Expect(err).To(gomega.HaveOccurred())
+
+			spans := reporter.Flush()
+			gomega.Expect(spans).To(gomega.HaveLen(1))
+			gomega.Expect(spans[0].Tags).To(gomega.HaveLen(2))
+			gomega.Expect(spans[0].Tags).To(gomega.HaveKeyWithValue("grpc.status_code", "ABORTED"))
+			gomega.Expect(spans[0].Tags).To(gomega.HaveKeyWithValue(string(zipkin.TagError), "ABORTED"))
+		})
+
+		ginkgo.It("copies existing metadata", func() {
+			ctx := metadata.AppendToOutgoingContext(context.Background(), "existing", "metadata")
+			resp, err := client.Hello(ctx, &service.HelloRequest{Payload: "Hello"})
+
+			gomega.Expect(resp.GetMetadata(), err).To(gomega.HaveKeyWithValue("existing", "metadata"))
+		})
+	})
+
+	ginkgo.Context("with custom RPCHandler", func() {
+		ginkgo.BeforeEach(func() {
+			var err error
+
+			conn, err = grpc.Dial(
+				serverAddr,
+				grpc.WithInsecure(),
+				grpc.WithStatsHandler(zipkingrpc.NewClientHandler(
+					tracer,
+					zipkingrpc.WithRPCHandler(func(span zipkin.Span, rpcStats stats.RPCStats) {
+						span.Tag("custom", "tag")
+					}))))
+			gomega.Expect(conn, err).ToNot(gomega.BeNil())
+			client = service.NewHelloServiceClient(conn)
+		})
+
+		ginkgo.It("calls custom RPCHandler", func() {
+			resp, err := client.Hello(context.Background(), &service.HelloRequest{Payload: "Hello"})
+			gomega.Expect(resp, err).ToNot(gomega.BeNil())
+
+			spans := reporter.Flush()
+			gomega.Expect(spans).To(gomega.HaveLen(1))
+			gomega.Expect(spans[0].Tags).To(gomega.HaveLen(1))
+			gomega.Expect(spans[0].Tags).To(gomega.HaveKeyWithValue("custom", "tag"))
+		})
+	})
+})

middleware/grpc/doc.go

@@ -0,0 +1,6 @@
+// +build go1.9
+
+/*
+Package grpc contains several gRPC handlers which can be used for instrumenting calls with Zipkin.
+*/
+package grpc