Switch to using the dep tool and update all the dependencies

vendor/cloud.google.com/go/trace/apiv1/doc.go

@@ -0,0 +1,38 @@
+// Copyright 2017, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// AUTO-GENERATED CODE. DO NOT EDIT.
+
+// Package trace is an experimental, auto-generated package for the
+// trace API.
+//
+// Send and retrieve trace data from Stackdriver Trace. Data is generated and
+// available by default for all App Engine applications. Data from other
+// applications can be written to Stackdriver Trace for display, reporting,
+// and analysis.
+//
+// Use the client at cloud.google.com/go/trace in preference to this.
+package trace // import "cloud.google.com/go/trace/apiv1"
+
+import (
+	"golang.org/x/net/context"
+	"google.golang.org/grpc/metadata"
+)
+
+func insertXGoog(ctx context.Context, val string) context.Context {
+	md, _ := metadata.FromContext(ctx)
+	md = md.Copy()
+	md["x-goog-api-client"] = []string{val}
+	return metadata.NewContext(ctx, md)
+}

vendor/cloud.google.com/go/trace/apiv1/mock_test.go

@@ -0,0 +1,299 @@
+// Copyright 2017, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// AUTO-GENERATED CODE. DO NOT EDIT.
+
+package trace
+
+import (
+	google_protobuf "github.com/golang/protobuf/ptypes/empty"
+	cloudtracepb "google.golang.org/genproto/googleapis/devtools/cloudtrace/v1"
+)
+
+import (
+	"flag"
+	"io"
+	"log"
+	"net"
+	"os"
+	"testing"
+
+	"github.com/golang/protobuf/proto"
+	"github.com/golang/protobuf/ptypes"
+	"golang.org/x/net/context"
+	"google.golang.org/api/option"
+	status "google.golang.org/genproto/googleapis/rpc/status"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+)
+
+var _ = io.EOF
+var _ = ptypes.MarshalAny
+var _ status.Status
+
+type mockTraceServer struct {
+	// Embed for forward compatibility.
+	// Tests will keep working if more methods are added
+	// in the future.
+	cloudtracepb.TraceServiceServer
+
+	reqs []proto.Message
+
+	// If set, all calls return this error.
+	err error
+
+	// responses to return if err == nil
+	resps []proto.Message
+}
+
+func (s *mockTraceServer) ListTraces(_ context.Context, req *cloudtracepb.ListTracesRequest) (*cloudtracepb.ListTracesResponse, error) {
+	s.reqs = append(s.reqs, req)
+	if s.err != nil {
+		return nil, s.err
+	}
+	return s.resps[0].(*cloudtracepb.ListTracesResponse), nil
+}
+
+func (s *mockTraceServer) GetTrace(_ context.Context, req *cloudtracepb.GetTraceRequest) (*cloudtracepb.Trace, error) {
+	s.reqs = append(s.reqs, req)
+	if s.err != nil {
+		return nil, s.err
+	}
+	return s.resps[0].(*cloudtracepb.Trace), nil
+}
+
+func (s *mockTraceServer) PatchTraces(_ context.Context, req *cloudtracepb.PatchTracesRequest) (*google_protobuf.Empty, error) {
+	s.reqs = append(s.reqs, req)
+	if s.err != nil {
+		return nil, s.err
+	}
+	return s.resps[0].(*google_protobuf.Empty), nil
+}
+
+// clientOpt is the option tests should use to connect to the test server.
+// It is initialized by TestMain.
+var clientOpt option.ClientOption
+
+var (
+	mockTrace mockTraceServer
+)
+
+func TestMain(m *testing.M) {
+	flag.Parse()
+
+	serv := grpc.NewServer()
+	cloudtracepb.RegisterTraceServiceServer(serv, &mockTrace)
+
+	lis, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		log.Fatal(err)
+	}
+	go serv.Serve(lis)
+
+	conn, err := grpc.Dial(lis.Addr().String(), grpc.WithInsecure())
+	if err != nil {
+		log.Fatal(err)
+	}
+	clientOpt = option.WithGRPCConn(conn)
+
+	os.Exit(m.Run())
+}
+
+func TestTraceServicePatchTraces(t *testing.T) {
+	var expectedResponse *google_protobuf.Empty = &google_protobuf.Empty{}
+
+	mockTrace.err = nil
+	mockTrace.reqs = nil
+
+	mockTrace.resps = append(mockTrace.resps[:0], expectedResponse)
+
+	var projectId string = "projectId-1969970175"
+	var traces *cloudtracepb.Traces = &cloudtracepb.Traces{}
+	var request = &cloudtracepb.PatchTracesRequest{
+		ProjectId: projectId,
+		Traces:    traces,
+	}
+
+	c, err := NewClient(context.Background(), clientOpt)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = c.PatchTraces(context.Background(), request)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want, got := request, mockTrace.reqs[0]; !proto.Equal(want, got) {
+		t.Errorf("wrong request %q, want %q", got, want)
+	}
+
+}
+
+func TestTraceServicePatchTracesError(t *testing.T) {
+	errCode := codes.Internal
+	mockTrace.err = grpc.Errorf(errCode, "test error")
+
+	var projectId string = "projectId-1969970175"
+	var traces *cloudtracepb.Traces = &cloudtracepb.Traces{}
+	var request = &cloudtracepb.PatchTracesRequest{
+		ProjectId: projectId,
+		Traces:    traces,
+	}
+
+	c, err := NewClient(context.Background(), clientOpt)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = c.PatchTraces(context.Background(), request)
+
+	if c := grpc.Code(err); c != errCode {
+		t.Errorf("got error code %q, want %q", c, errCode)
+	}
+}
+func TestTraceServiceGetTrace(t *testing.T) {
+	var projectId2 string = "projectId2939242356"
+	var traceId2 string = "traceId2987826376"
+	var expectedResponse = &cloudtracepb.Trace{
+		ProjectId: projectId2,
+		TraceId:   traceId2,
+	}
+
+	mockTrace.err = nil
+	mockTrace.reqs = nil
+
+	mockTrace.resps = append(mockTrace.resps[:0], expectedResponse)
+
+	var projectId string = "projectId-1969970175"
+	var traceId string = "traceId1270300245"
+	var request = &cloudtracepb.GetTraceRequest{
+		ProjectId: projectId,
+		TraceId:   traceId,
+	}
+
+	c, err := NewClient(context.Background(), clientOpt)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	resp, err := c.GetTrace(context.Background(), request)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want, got := request, mockTrace.reqs[0]; !proto.Equal(want, got) {
+		t.Errorf("wrong request %q, want %q", got, want)
+	}
+
+	if want, got := expectedResponse, resp; !proto.Equal(want, got) {
+		t.Errorf("wrong response %q, want %q)", got, want)
+	}
+}
+
+func TestTraceServiceGetTraceError(t *testing.T) {
+	errCode := codes.Internal
+	mockTrace.err = grpc.Errorf(errCode, "test error")
+
+	var projectId string = "projectId-1969970175"
+	var traceId string = "traceId1270300245"
+	var request = &cloudtracepb.GetTraceRequest{
+		ProjectId: projectId,
+		TraceId:   traceId,
+	}
+
+	c, err := NewClient(context.Background(), clientOpt)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	resp, err := c.GetTrace(context.Background(), request)
+
+	if c := grpc.Code(err); c != errCode {
+		t.Errorf("got error code %q, want %q", c, errCode)
+	}
+	_ = resp
+}
+func TestTraceServiceListTraces(t *testing.T) {
+	var nextPageToken string = ""
+	var tracesElement *cloudtracepb.Trace = &cloudtracepb.Trace{}
+	var traces = []*cloudtracepb.Trace{tracesElement}
+	var expectedResponse = &cloudtracepb.ListTracesResponse{
+		NextPageToken: nextPageToken,
+		Traces:        traces,
+	}
+
+	mockTrace.err = nil
+	mockTrace.reqs = nil
+
+	mockTrace.resps = append(mockTrace.resps[:0], expectedResponse)
+
+	var projectId string = "projectId-1969970175"
+	var request = &cloudtracepb.ListTracesRequest{
+		ProjectId: projectId,
+	}
+
+	c, err := NewClient(context.Background(), clientOpt)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	resp, err := c.ListTraces(context.Background(), request).Next()
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want, got := request, mockTrace.reqs[0]; !proto.Equal(want, got) {
+		t.Errorf("wrong request %q, want %q", got, want)
+	}
+
+	want := (interface{})(expectedResponse.Traces[0])
+	got := (interface{})(resp)
+	var ok bool
+
+	switch want := (want).(type) {
+	case proto.Message:
+		ok = proto.Equal(want, got.(proto.Message))
+	default:
+		ok = want == got
+	}
+	if !ok {
+		t.Errorf("wrong response %q, want %q)", got, want)
+	}
+}
+
+func TestTraceServiceListTracesError(t *testing.T) {
+	errCode := codes.Internal
+	mockTrace.err = grpc.Errorf(errCode, "test error")
+
+	var projectId string = "projectId-1969970175"
+	var request = &cloudtracepb.ListTracesRequest{
+		ProjectId: projectId,
+	}
+
+	c, err := NewClient(context.Background(), clientOpt)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	resp, err := c.ListTraces(context.Background(), request).Next()
+
+	if c := grpc.Code(err); c != errCode {
+		t.Errorf("got error code %q, want %q", c, errCode)
+	}
+	_ = resp
+}

vendor/cloud.google.com/go/trace/apiv1/trace_client.go

@@ -0,0 +1,235 @@
+// Copyright 2017, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// AUTO-GENERATED CODE. DO NOT EDIT.
+
+package trace
+
+import (
+	"math"
+	"time"
+
+	"cloud.google.com/go/internal/version"
+	gax "github.com/googleapis/gax-go"
+	"golang.org/x/net/context"
+	"google.golang.org/api/iterator"
+	"google.golang.org/api/option"
+	"google.golang.org/api/transport"
+	cloudtracepb "google.golang.org/genproto/googleapis/devtools/cloudtrace/v1"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+)
+
+// CallOptions contains the retry settings for each method of Client.
+type CallOptions struct {
+	PatchTraces []gax.CallOption
+	GetTrace    []gax.CallOption
+	ListTraces  []gax.CallOption
+}
+
+func defaultClientOptions() []option.ClientOption {
+	return []option.ClientOption{
+		option.WithEndpoint("cloudtrace.googleapis.com:443"),
+		option.WithScopes(
+			"https://www.googleapis.com/auth/cloud-platform",
+			"https://www.googleapis.com/auth/trace.append",
+			"https://www.googleapis.com/auth/trace.readonly",
+		),
+	}
+}
+
+func defaultCallOptions() *CallOptions {
+	retry := map[[2]string][]gax.CallOption{
+		{"default", "idempotent"}: {
+			gax.WithRetry(func() gax.Retryer {
+				return gax.OnCodes([]codes.Code{
+					codes.DeadlineExceeded,
+					codes.Unavailable,
+				}, gax.Backoff{
+					Initial:    100 * time.Millisecond,
+					Max:        1000 * time.Millisecond,
+					Multiplier: 1.2,
+				})
+			}),
+		},
+	}
+	return &CallOptions{
+		PatchTraces: retry[[2]string{"default", "idempotent"}],
+		GetTrace:    retry[[2]string{"default", "idempotent"}],
+		ListTraces:  retry[[2]string{"default", "idempotent"}],
+	}
+}
+
+// Client is a client for interacting with Stackdriver Trace API.
+type Client struct {
+	// The connection to the service.
+	conn *grpc.ClientConn
+
+	// The gRPC API client.
+	client cloudtracepb.TraceServiceClient
+
+	// The call options for this service.
+	CallOptions *CallOptions
+
+	// The metadata to be sent with each request.
+	xGoogHeader string
+}
+
+// NewClient creates a new trace service client.
+//
+// This file describes an API for collecting and viewing traces and spans
+// within a trace.  A Trace is a collection of spans corresponding to a single
+// operation or set of operations for an application. A span is an individual
+// timed event which forms a node of the trace tree. Spans for a single trace
+// may span multiple services.
+func NewClient(ctx context.Context, opts ...option.ClientOption) (*Client, error) {
+	conn, err := transport.DialGRPC(ctx, append(defaultClientOptions(), opts...)...)
+	if err != nil {
+		return nil, err
+	}
+	c := &Client{
+		conn:        conn,
+		CallOptions: defaultCallOptions(),
+
+		client: cloudtracepb.NewTraceServiceClient(conn),
+	}
+	c.SetGoogleClientInfo()
+	return c, nil
+}
+
+// Connection returns the client's connection to the API service.
+func (c *Client) Connection() *grpc.ClientConn {
+	return c.conn
+}
+
+// Close closes the connection to the API service. The user should invoke this when
+// the client is no longer required.
+func (c *Client) Close() error {
+	return c.conn.Close()
+}
+
+// SetGoogleClientInfo sets the name and version of the application in
+// the `x-goog-api-client` header passed on each request. Intended for
+// use by Google-written clients.
+func (c *Client) SetGoogleClientInfo(keyval ...string) {
+	kv := append([]string{"gl-go", version.Go()}, keyval...)
+	kv = append(kv, "gapic", version.Repo, "gax", gax.Version, "grpc", "")
+	c.xGoogHeader = gax.XGoogHeader(kv...)
+}
+
+// PatchTraces sends new traces to Stackdriver Trace or updates existing traces. If the ID
+// of a trace that you send matches that of an existing trace, any fields
+// in the existing trace and its spans are overwritten by the provided values,
+// and any new fields provided are merged with the existing trace data. If the
+// ID does not match, a new trace is created.
+func (c *Client) PatchTraces(ctx context.Context, req *cloudtracepb.PatchTracesRequest) error {
+	ctx = insertXGoog(ctx, c.xGoogHeader)
+	err := gax.Invoke(ctx, func(ctx context.Context) error {
+		var err error
+		_, err = c.client.PatchTraces(ctx, req)
+		return err
+	}, c.CallOptions.PatchTraces...)
+	return err
+}
+
+// GetTrace gets a single trace by its ID.
+func (c *Client) GetTrace(ctx context.Context, req *cloudtracepb.GetTraceRequest) (*cloudtracepb.Trace, error) {
+	ctx = insertXGoog(ctx, c.xGoogHeader)
+	var resp *cloudtracepb.Trace
+	err := gax.Invoke(ctx, func(ctx context.Context) error {
+		var err error
+		resp, err = c.client.GetTrace(ctx, req)
+		return err
+	}, c.CallOptions.GetTrace...)
+	if err != nil {
+		return nil, err
+	}
+	return resp, nil
+}
+
+// ListTraces returns of a list of traces that match the specified filter conditions.
+func (c *Client) ListTraces(ctx context.Context, req *cloudtracepb.ListTracesRequest) *TraceIterator {
+	ctx = insertXGoog(ctx, c.xGoogHeader)
+	it := &TraceIterator{}
+	it.InternalFetch = func(pageSize int, pageToken string) ([]*cloudtracepb.Trace, string, error) {
+		var resp *cloudtracepb.ListTracesResponse
+		req.PageToken = pageToken
+		if pageSize > math.MaxInt32 {
+			req.PageSize = math.MaxInt32
+		} else {
+			req.PageSize = int32(pageSize)
+		}
+		err := gax.Invoke(ctx, func(ctx context.Context) error {
+			var err error
+			resp, err = c.client.ListTraces(ctx, req)
+			return err
+		}, c.CallOptions.ListTraces...)
+		if err != nil {
+			return nil, "", err
+		}
+		return resp.Traces, resp.NextPageToken, nil
+	}
+	fetch := func(pageSize int, pageToken string) (string, error) {
+		items, nextPageToken, err := it.InternalFetch(pageSize, pageToken)
+		if err != nil {
+			return "", err
+		}
+		it.items = append(it.items, items...)
+		return nextPageToken, nil
+	}
+	it.pageInfo, it.nextFunc = iterator.NewPageInfo(fetch, it.bufLen, it.takeBuf)
+	return it
+}
+
+// TraceIterator manages a stream of *cloudtracepb.Trace.
+type TraceIterator struct {
+	items    []*cloudtracepb.Trace
+	pageInfo *iterator.PageInfo
+	nextFunc func() error
+
+	// InternalFetch is for use by the Google Cloud Libraries only.
+	// It is not part of the stable interface of this package.
+	//
+	// InternalFetch returns results from a single call to the underlying RPC.
+	// The number of results is no greater than pageSize.
+	// If there are no more results, nextPageToken is empty and err is nil.
+	InternalFetch func(pageSize int, pageToken string) (results []*cloudtracepb.Trace, nextPageToken string, err error)
+}
+
+// PageInfo supports pagination. See the google.golang.org/api/iterator package for details.
+func (it *TraceIterator) PageInfo() *iterator.PageInfo {
+	return it.pageInfo
+}
+
+// Next returns the next result. Its second return value is iterator.Done if there are no more
+// results. Once Next returns Done, all subsequent calls will return Done.
+func (it *TraceIterator) Next() (*cloudtracepb.Trace, error) {
+	var item *cloudtracepb.Trace
+	if err := it.nextFunc(); err != nil {
+		return item, err
+	}
+	item = it.items[0]
+	it.items = it.items[1:]
+	return item, nil
+}
+
+func (it *TraceIterator) bufLen() int {
+	return len(it.items)
+}
+
+func (it *TraceIterator) takeBuf() interface{} {
+	b := it.items
+	it.items = nil
+	return b
+}

vendor/cloud.google.com/go/trace/apiv1/trace_client_example_test.go

@@ -0,0 +1,89 @@
+// Copyright 2017, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// AUTO-GENERATED CODE. DO NOT EDIT.
+
+package trace_test
+
+import (
+	"cloud.google.com/go/trace/apiv1"
+	"golang.org/x/net/context"
+	cloudtracepb "google.golang.org/genproto/googleapis/devtools/cloudtrace/v1"
+)
+
+func ExampleNewClient() {
+	ctx := context.Background()
+	c, err := trace.NewClient(ctx)
+	if err != nil {
+		// TODO: Handle error.
+	}
+	// TODO: Use client.
+	_ = c
+}
+
+func ExampleClient_PatchTraces() {
+	ctx := context.Background()
+	c, err := trace.NewClient(ctx)
+	if err != nil {
+		// TODO: Handle error.
+	}
+
+	req := &cloudtracepb.PatchTracesRequest{
+	// TODO: Fill request struct fields.
+	}
+	err = c.PatchTraces(ctx, req)
+	if err != nil {
+		// TODO: Handle error.
+	}
+}
+
+func ExampleClient_GetTrace() {
+	ctx := context.Background()
+	c, err := trace.NewClient(ctx)
+	if err != nil {
+		// TODO: Handle error.
+	}
+
+	req := &cloudtracepb.GetTraceRequest{
+	// TODO: Fill request struct fields.
+	}
+	resp, err := c.GetTrace(ctx, req)
+	if err != nil {
+		// TODO: Handle error.
+	}
+	// TODO: Use resp.
+	_ = resp
+}
+
+func ExampleClient_ListTraces() {
+	ctx := context.Background()
+	c, err := trace.NewClient(ctx)
+	if err != nil {
+		// TODO: Handle error.
+	}
+
+	req := &cloudtracepb.ListTracesRequest{
+	// TODO: Fill request struct fields.
+	}
+	it := c.ListTraces(ctx, req)
+	for {
+		resp, err := it.Next()
+		if err != nil {
+			// TODO: Handle error.
+			break
+		}
+		// TODO: Use resp.
+		_ = resp
+	}
+}

vendor/cloud.google.com/go/trace/sampling.go

@@ -0,0 +1,117 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package trace
+
+import (
+	crand "crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+
+	"golang.org/x/time/rate"
+)
+
+type SamplingPolicy interface {
+	// Sample returns a Decision.
+	// If Trace is false in the returned Decision, then the Decision should be
+	// the zero value.
+	Sample(p Parameters) Decision
+}
+
+// Parameters contains the values passed to a SamplingPolicy's Sample method.
+type Parameters struct {
+	HasTraceHeader bool // whether the incoming request has a valid X-Cloud-Trace-Context header.
+}
+
+// Decision is the value returned by a call to a SamplingPolicy's Sample method.
+type Decision struct {
+	Trace  bool    // Whether to trace the request.
+	Sample bool    // Whether the trace is included in the random sample.
+	Policy string  // Name of the sampling policy.
+	Weight float64 // Sample weight to be used in statistical calculations.
+}
+
+type sampler struct {
+	fraction float64
+	skipped  float64
+	*rate.Limiter
+	*rand.Rand
+	sync.Mutex
+}
+
+func (s *sampler) Sample(p Parameters) Decision {
+	s.Lock()
+	x := s.Float64()
+	d := s.sample(p, time.Now(), x)
+	s.Unlock()
+	return d
+}
+
+// sample contains the a deterministic, time-independent logic of Sample.
+func (s *sampler) sample(p Parameters, now time.Time, x float64) (d Decision) {
+	d.Sample = x < s.fraction
+	d.Trace = p.HasTraceHeader || d.Sample
+	if !d.Trace {
+		// We have no reason to trace this request.
+		return Decision{}
+	}
+	// We test separately that the rate limit is not tiny before calling AllowN,
+	// because of overflow problems in x/time/rate.
+	if s.Limit() < 1e-9 || !s.AllowN(now, 1) {
+		// Rejected by the rate limit.
+		if d.Sample {
+			s.skipped++
+		}
+		return Decision{}
+	}
+	if d.Sample {
+		d.Policy, d.Weight = "default", (1.0+s.skipped)/s.fraction
+		s.skipped = 0.0
+	}
+	return
+}
+
+// NewLimitedSampler returns a sampling policy that randomly samples a given
+// fraction of requests.  It also enforces a limit on the number of traces per
+// second.  It tries to trace every request with a trace header, but will not
+// exceed the qps limit to do it.
+func NewLimitedSampler(fraction, maxqps float64) (SamplingPolicy, error) {
+	if !(fraction >= 0) {
+		return nil, fmt.Errorf("invalid fraction %f", fraction)
+	}
+	if !(maxqps >= 0) {
+		return nil, fmt.Errorf("invalid maxqps %f", maxqps)
+	}
+	// Set a limit on the number of accumulated "tokens", to limit bursts of
+	// traced requests.  Use one more than a second's worth of tokens, or 100,
+	// whichever is smaller.
+	// See https://godoc.org/golang.org/x/time/rate#NewLimiter.
+	maxTokens := 100
+	if maxqps < 99.0 {
+		maxTokens = 1 + int(maxqps)
+	}
+	var seed int64
+	if err := binary.Read(crand.Reader, binary.LittleEndian, &seed); err != nil {
+		seed = time.Now().UnixNano()
+	}
+	s := sampler{
+		fraction: fraction,
+		Limiter:  rate.NewLimiter(rate.Limit(maxqps), maxTokens),
+		Rand:     rand.New(rand.NewSource(seed)),
+	}
+	return &s, nil
+}

vendor/cloud.google.com/go/trace/trace.go

@@ -0,0 +1,811 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package trace is a Google Stackdriver Trace library.
+//
+// This package is still experimental and subject to change.
+//
+// See https://cloud.google.com/trace/api/#data_model for a discussion of traces
+// and spans.
+//
+// To initialize a client that connects to the Stackdriver Trace server, use the
+// NewClient function. Generally you will want to do this on program
+// initialization.
+//
+//   import "cloud.google.com/go/trace"
+//   ...
+//   traceClient, err = trace.NewClient(ctx, projectID)
+//
+// Calling SpanFromRequest will create a new trace span for an incoming HTTP
+// request.  If the request contains a trace context header, it is used to
+// determine the trace ID.  Otherwise, a new trace ID is created.
+//
+//   func handler(w http.ResponseWriter, r *http.Request) {
+//     span := traceClient.SpanFromRequest(r)
+//     defer span.Finish()
+//     ...
+//   }
+//
+// SpanFromRequest and NewSpan returns nil if the *Client is nil, so you can disable
+// tracing by not initializing your *Client variable.  All of the exported
+// functions on *Span do nothing when the *Span is nil.
+//
+// If you need to start traces that don't correspond to an incoming HTTP request,
+// you can use NewSpan to create a root-level span.
+//
+//   span := traceClient.NewSpan("span name")
+//   defer span.Finish()
+//
+// Although a trace span object is created for every request, only a subset of
+// traces are uploaded to the server, for efficiency.  By default, the requests
+// that are traced are those with the tracing bit set in the options field of
+// the trace context header.  Ideally, you should override this behaviour by
+// calling SetSamplingPolicy.  NewLimitedSampler returns an implementation of
+// SamplingPolicy which traces requests that have the tracing bit set, and also
+// randomly traces a specified fraction of requests.  Additionally, it sets a
+// limit on the number of requests traced per second.  The following example
+// traces one in every thousand requests, up to a limit of 5 per second.
+//
+//   p, err := trace.NewLimitedSampler(0.001, 5)
+//   traceClient.SetSamplingPolicy(p)
+//
+// You can create a new span as a child of an existing span with NewChild.
+//
+//   childSpan := span.NewChild(name)
+//   ...
+//   childSpan.Finish()
+//
+// When sending an HTTP request to another server, NewRemoteChild will create
+// a span to represent the time the current program waits for the request to
+// complete, and attach a header to the outgoing request so that the trace will
+// be propagated to the destination server.
+//
+//   childSpan := span.NewRemoteChild(&httpRequest)
+//   ...
+//   childSpan.Finish()
+//
+// Alternatively, if you have access to the X-Cloud-Trace-Context header value
+// but not the underlying HTTP request (this can happen if you are using a
+// different transport or messaging protocol, such as gRPC), you can use
+// SpanFromHeader instead of SpanFromRequest. In that case, you will need to
+// specify the span name explicility, since it cannot be constructed from the
+// HTTP request's URL and method.
+//
+//   func handler(r *somepkg.Request) {
+//     span := traceClient.SpanFromHeader("span name", r.TraceContext())
+//     defer span.Finish()
+//     ...
+//   }
+//
+// Spans can contain a map from keys to values that have useful information
+// about the span.  The elements of this map are called labels.  Some labels,
+// whose keys all begin with the string "trace.cloud.google.com/", are set
+// automatically in the following ways:
+//
+// - SpanFromRequest sets some labels to data about the incoming request.
+//
+// - NewRemoteChild sets some labels to data about the outgoing request.
+//
+// - Finish sets a label to a stack trace, if the stack trace option is enabled
+// in the incoming trace header.
+//
+// - The WithResponse option sets some labels to data about a response.
+// You can also set labels using SetLabel.  If a label is given a value
+// automatically and by SetLabel, the automatically-set value is used.
+//
+//   span.SetLabel(key, value)
+//
+// The WithResponse option can be used when Finish is called.
+//
+//   childSpan := span.NewRemoteChild(outgoingReq)
+//   resp, err := http.DefaultClient.Do(outgoingReq)
+//   ...
+//   childSpan.Finish(trace.WithResponse(resp))
+//
+// When a span created by SpanFromRequest or SpamFromHeader is finished, the
+// finished spans in the corresponding trace -- the span itself and its
+// descendants -- are uploaded to the Stackdriver Trace server using the
+// *Client that created the span.  Finish returns immediately, and uploading
+// occurs asynchronously.  You can use the FinishWait function instead to wait
+// until uploading has finished.
+//
+//   err := span.FinishWait()
+//
+// Using contexts to pass *trace.Span objects through your program will often
+// be a better approach than passing them around explicitly.  This allows trace
+// spans, and other request-scoped or part-of-request-scoped values, to be
+// easily passed through API boundaries.  Various Google Cloud libraries will
+// retrieve trace spans from contexts and automatically create child spans for
+// API requests.
+// See https://blog.golang.org/context for more discussion of contexts.
+// A derived context containing a trace span can be created using NewContext.
+//
+//   span := traceClient.SpanFromRequest(r)
+//   ctx = trace.NewContext(ctx, span)
+//
+// The span can be retrieved from a context elsewhere in the program using
+// FromContext.
+//
+//   func foo(ctx context.Context) {
+//     span := trace.FromContext(ctx).NewChild("in foo")
+//     defer span.Finish()
+//     ...
+//   }
+//
+package trace // import "cloud.google.com/go/trace"
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"golang.org/x/net/context"
+	api "google.golang.org/api/cloudtrace/v1"
+	"google.golang.org/api/gensupport"
+	"google.golang.org/api/option"
+	"google.golang.org/api/support/bundler"
+	"google.golang.org/api/transport"
+	"google.golang.org/grpc"
+)
+
+const (
+	httpHeader          = `X-Cloud-Trace-Context`
+	userAgent           = `gcloud-golang-trace/20160501`
+	cloudPlatformScope  = `https://www.googleapis.com/auth/cloud-platform`
+	spanKindClient      = `RPC_CLIENT`
+	spanKindServer      = `RPC_SERVER`
+	spanKindUnspecified = `SPAN_KIND_UNSPECIFIED`
+	maxStackFrames      = 20
+	labelHost           = `trace.cloud.google.com/http/host`
+	labelMethod         = `trace.cloud.google.com/http/method`
+	labelStackTrace     = `trace.cloud.google.com/stacktrace`
+	labelStatusCode     = `trace.cloud.google.com/http/status_code`
+	labelURL            = `trace.cloud.google.com/http/url`
+	labelSamplingPolicy = `trace.cloud.google.com/sampling_policy`
+	labelSamplingWeight = `trace.cloud.google.com/sampling_weight`
+)
+
+const (
+	// ScopeTraceAppend grants permissions to write trace data for a project.
+	ScopeTraceAppend = "https://www.googleapis.com/auth/trace.append"
+
+	// ScopeCloudPlatform grants permissions to view and manage your data
+	// across Google Cloud Platform services.
+	ScopeCloudPlatform = "https://www.googleapis.com/auth/cloud-platform"
+)
+
+type contextKey struct{}
+
+type stackLabelValue struct {
+	Frames []stackFrame `json:"stack_frame"`
+}
+
+type stackFrame struct {
+	Class    string `json:"class_name,omitempty"`
+	Method   string `json:"method_name"`
+	Filename string `json:"file_name"`
+	Line     int64  `json:"line_number"`
+}
+
+var (
+	spanIDCounter   uint64
+	spanIDIncrement uint64
+)
+
+func init() {
+	// Set spanIDCounter and spanIDIncrement to random values.  nextSpanID will
+	// return an arithmetic progression using these values, skipping zero.  We set
+	// the LSB of spanIDIncrement to 1, so that the cycle length is 2^64.
+	binary.Read(rand.Reader, binary.LittleEndian, &spanIDCounter)
+	binary.Read(rand.Reader, binary.LittleEndian, &spanIDIncrement)
+	spanIDIncrement |= 1
+	// Attach hook for autogenerated Google API calls.  This will automatically
+	// create trace spans for API calls if there is a trace in the context.
+	gensupport.RegisterHook(requestHook)
+}
+
+func requestHook(ctx context.Context, req *http.Request) func(resp *http.Response) {
+	span := FromContext(ctx)
+	if span == nil || req == nil {
+		return nil
+	}
+	span = span.NewRemoteChild(req)
+	return func(resp *http.Response) {
+		if resp != nil {
+			span.Finish(WithResponse(resp))
+		} else {
+			span.Finish()
+		}
+	}
+}
+
+// EnableGRPCTracingDialOption traces all outgoing requests from a gRPC client.
+// The calling context should already have a *trace.Span; a child span will be
+// created for the outgoing gRPC call. If the calling context doesn't have a span,
+// the call will not be traced.
+//
+// The functionality in gRPC that this relies on is currently experimental.
+var EnableGRPCTracingDialOption grpc.DialOption = grpc.WithUnaryInterceptor(grpc.UnaryClientInterceptor(grpcUnaryInterceptor))
+
+// EnableGRPCTracing automatically traces all gRPC calls from cloud.google.com/go clients.
+//
+// The functionality in gRPC that this relies on is currently experimental.
+var EnableGRPCTracing option.ClientOption = option.WithGRPCDialOption(EnableGRPCTracingDialOption)
+
+func grpcUnaryInterceptor(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+	// TODO: also intercept streams.
+	span := FromContext(ctx).NewChild(method)
+	err := invoker(ctx, method, req, reply, cc, opts...)
+	if err != nil {
+		// TODO: standardize gRPC label names?
+		span.SetLabel("error", err.Error())
+	}
+	span.Finish()
+	return err
+}
+
+// nextSpanID returns a new span ID.  It will never return zero.
+func nextSpanID() uint64 {
+	var id uint64
+	for id == 0 {
+		id = atomic.AddUint64(&spanIDCounter, spanIDIncrement)
+	}
+	return id
+}
+
+// nextTraceID returns a new trace ID.
+func nextTraceID() string {
+	id1 := nextSpanID()
+	id2 := nextSpanID()
+	return fmt.Sprintf("%016x%016x", id1, id2)
+}
+
+// Client is a client for uploading traces to the Google Stackdriver Trace server.
+type Client struct {
+	service   *api.Service
+	projectID string
+	policy    SamplingPolicy
+	bundler   *bundler.Bundler
+}
+
+// NewClient creates a new Google Stackdriver Trace client.
+func NewClient(ctx context.Context, projectID string, opts ...option.ClientOption) (*Client, error) {
+	o := []option.ClientOption{
+		option.WithScopes(cloudPlatformScope),
+		option.WithUserAgent(userAgent),
+	}
+	o = append(o, opts...)
+	hc, basePath, err := transport.NewHTTPClient(ctx, o...)
+	if err != nil {
+		return nil, fmt.Errorf("creating HTTP client for Google Stackdriver Trace API: %v", err)
+	}
+	apiService, err := api.New(hc)
+	if err != nil {
+		return nil, fmt.Errorf("creating Google Stackdriver Trace API client: %v", err)
+	}
+	if basePath != "" {
+		// An option set a basepath, so override api.New's default.
+		apiService.BasePath = basePath
+	}
+	c := &Client{
+		service:   apiService,
+		projectID: projectID,
+	}
+	bundler := bundler.NewBundler((*api.Trace)(nil), func(bundle interface{}) {
+		traces := bundle.([]*api.Trace)
+		err := c.upload(traces)
+		if err != nil {
+			log.Printf("failed to upload %d traces to the Cloud Trace server.", len(traces))
+		}
+	})
+	bundler.DelayThreshold = 2 * time.Second
+	bundler.BundleCountThreshold = 100
+	// We're not measuring bytes here, we're counting traces and spans as one "byte" each.
+	bundler.BundleByteThreshold = 1000
+	bundler.BundleByteLimit = 1000
+	bundler.BufferedByteLimit = 10000
+	c.bundler = bundler
+	return c, nil
+}
+
+// SetSamplingPolicy sets the SamplingPolicy that determines how often traces
+// are initiated by this client.
+func (c *Client) SetSamplingPolicy(p SamplingPolicy) {
+	if c != nil {
+		c.policy = p
+	}
+}
+
+// SpanFromHeader returns a new trace span, based on a provided request header
+// value. See https://cloud.google.com/trace/docs/faq.
+//
+// It returns nil iff the client is nil.
+//
+// The trace information and identifiers will be read from the header value.
+// Otherwise, a new trace ID is made and the parent span ID is zero.
+//
+// The name of the new span is provided as an argument.
+//
+// If a non-nil sampling policy has been set in the client, it can override
+// the options set in the header and choose whether to trace the request.
+//
+// If the header doesn't have existing tracing information, then a *Span is
+// returned anyway, but it will not be uploaded to the server, just as when
+// calling SpanFromRequest on an untraced request.
+//
+// Most users using HTTP should use SpanFromRequest, rather than
+// SpanFromHeader, since it provides additional functionality for HTTP
+// requests. In particular, it will set various pieces of request information
+// as labels on the *Span, which is not available from the header alone.
+func (c *Client) SpanFromHeader(name string, header string) *Span {
+	if c == nil {
+		return nil
+	}
+	traceID, parentSpanID, options, ok := traceInfoFromHeader(header)
+	if !ok {
+		traceID = nextTraceID()
+	}
+	t := &trace{
+		traceID:       traceID,
+		client:        c,
+		globalOptions: options,
+		localOptions:  options,
+	}
+	span := startNewChild(name, t, parentSpanID)
+	span.span.Kind = spanKindServer
+	span.rootSpan = true
+	configureSpanFromPolicy(span, c.policy, ok)
+	return span
+}
+
+// SpanFromRequest returns a new trace span for an HTTP request.
+//
+// It returns nil iff the client is nil.
+//
+// If the incoming HTTP request contains a trace context header, the trace ID,
+// parent span ID, and tracing options will be read from that header.
+// Otherwise, a new trace ID is made and the parent span ID is zero.
+//
+// If a non-nil sampling policy has been set in the client, it can override the
+// options set in the header and choose whether to trace the request.
+//
+// If the request is not being traced, then a *Span is returned anyway, but it
+// will not be uploaded to the server -- it is only useful for propagating
+// trace context to child requests and for getting the TraceID.  All its
+// methods can still be called -- the Finish, FinishWait, and SetLabel methods
+// do nothing.  NewChild does nothing, and returns the same *Span.  TraceID
+// works as usual.
+func (c *Client) SpanFromRequest(r *http.Request) *Span {
+	if c == nil {
+		return nil
+	}
+	traceID, parentSpanID, options, ok := traceInfoFromHeader(r.Header.Get(httpHeader))
+	if !ok {
+		traceID = nextTraceID()
+	}
+	t := &trace{
+		traceID:       traceID,
+		client:        c,
+		globalOptions: options,
+		localOptions:  options,
+	}
+	span := startNewChildWithRequest(r, t, parentSpanID)
+	span.span.Kind = spanKindServer
+	span.rootSpan = true
+	configureSpanFromPolicy(span, c.policy, ok)
+	return span
+}
+
+// NewSpan returns a new trace span with the given name.
+//
+// A new trace and span ID is generated to trace the span.
+// Returned span need to be finished by calling Finish or FinishWait.
+func (c *Client) NewSpan(name string) *Span {
+	if c == nil {
+		return nil
+	}
+	t := &trace{
+		traceID:       nextTraceID(),
+		client:        c,
+		localOptions:  optionTrace,
+		globalOptions: optionTrace,
+	}
+	span := startNewChild(name, t, 0)
+	span.span.Kind = spanKindServer
+	span.rootSpan = true
+	configureSpanFromPolicy(span, c.policy, false)
+	return span
+}
+
+func configureSpanFromPolicy(s *Span, p SamplingPolicy, ok bool) {
+	if p == nil {
+		return
+	}
+	d := p.Sample(Parameters{HasTraceHeader: ok})
+	if d.Trace {
+		// Turn on tracing locally, and in child requests.
+		s.trace.localOptions |= optionTrace
+		s.trace.globalOptions |= optionTrace
+	} else {
+		// Turn off tracing locally.
+		s.trace.localOptions = 0
+		return
+	}
+	if d.Sample {
+		// This trace is in the random sample, so set the labels.
+		s.SetLabel(labelSamplingPolicy, d.Policy)
+		s.SetLabel(labelSamplingWeight, fmt.Sprint(d.Weight))
+	}
+}
+
+// NewContext returns a derived context containing the span.
+func NewContext(ctx context.Context, s *Span) context.Context {
+	if s == nil {
+		return ctx
+	}
+	return context.WithValue(ctx, contextKey{}, s)
+}
+
+// FromContext returns the span contained in the context, or nil.
+func FromContext(ctx context.Context) *Span {
+	s, _ := ctx.Value(contextKey{}).(*Span)
+	return s
+}
+
+func traceInfoFromHeader(h string) (string, uint64, optionFlags, bool) {
+	// See https://cloud.google.com/trace/docs/faq for the header format.
+	// Return if the header is empty or missing, or if the header is unreasonably
+	// large, to avoid making unnecessary copies of a large string.
+	if h == "" || len(h) > 200 {
+		return "", 0, 0, false
+	}
+
+	// Parse the trace id field.
+	slash := strings.Index(h, `/`)
+	if slash == -1 {
+		return "", 0, 0, false
+	}
+	traceID, h := h[:slash], h[slash+1:]
+
+	// Parse the span id field.
+	semicolon := strings.Index(h, `;`)
+	if semicolon == -1 {
+		return "", 0, 0, false
+	}
+	spanstr, h := h[:semicolon], h[semicolon+1:]
+	spanID, err := strconv.ParseUint(spanstr, 10, 64)
+	if err != nil {
+		return "", 0, 0, false
+	}
+
+	// Parse the options field.
+	if !strings.HasPrefix(h, "o=") {
+		return "", 0, 0, false
+	}
+	o, err := strconv.ParseUint(h[2:], 10, 64)
+	if err != nil {
+		return "", 0, 0, false
+	}
+	options := optionFlags(o)
+	return traceID, spanID, options, true
+}
+
+type optionFlags uint32
+
+const (
+	optionTrace optionFlags = 1 << iota
+	optionStack
+)
+
+type trace struct {
+	mu            sync.Mutex
+	client        *Client
+	traceID       string
+	globalOptions optionFlags // options that will be passed to any child requests
+	localOptions  optionFlags // options applied in this server
+	spans         []*Span     // finished spans for this trace.
+}
+
+// finish appends s to t.spans.  If s is the root span, uploads the trace to the
+// server.
+func (t *trace) finish(s *Span, wait bool, opts ...FinishOption) error {
+	for _, o := range opts {
+		o.modifySpan(s)
+	}
+	s.end = time.Now()
+	t.mu.Lock()
+	t.spans = append(t.spans, s)
+	spans := t.spans
+	t.mu.Unlock()
+	if s.rootSpan {
+		if wait {
+			return t.client.upload([]*api.Trace{t.constructTrace(spans)})
+		}
+		go func() {
+			tr := t.constructTrace(spans)
+			err := t.client.bundler.Add(tr, 1+len(spans))
+			if err == bundler.ErrOversizedItem {
+				err = t.client.upload([]*api.Trace{tr})
+			}
+			if err != nil {
+				log.Println("error uploading trace:", err)
+			}
+		}()
+	}
+	return nil
+}
+
+func (t *trace) constructTrace(spans []*Span) *api.Trace {
+	apiSpans := make([]*api.TraceSpan, len(spans))
+	for i, sp := range spans {
+		sp.span.StartTime = sp.start.In(time.UTC).Format(time.RFC3339Nano)
+		sp.span.EndTime = sp.end.In(time.UTC).Format(time.RFC3339Nano)
+		if t.localOptions&optionStack != 0 {
+			sp.setStackLabel()
+		}
+		sp.SetLabel(labelHost, sp.host)
+		sp.SetLabel(labelURL, sp.url)
+		sp.SetLabel(labelMethod, sp.method)
+		if sp.statusCode != 0 {
+			sp.SetLabel(labelStatusCode, strconv.Itoa(sp.statusCode))
+		}
+		apiSpans[i] = &sp.span
+	}
+
+	return &api.Trace{
+		ProjectId: t.client.projectID,
+		TraceId:   t.traceID,
+		Spans:     apiSpans,
+	}
+}
+
+func (c *Client) upload(traces []*api.Trace) error {
+	_, err := c.service.Projects.PatchTraces(c.projectID, &api.Traces{Traces: traces}).Do()
+	return err
+}
+
+// Span contains information about one span of a trace.
+type Span struct {
+	trace      *trace
+	span       api.TraceSpan
+	start      time.Time
+	end        time.Time
+	rootSpan   bool
+	stack      [maxStackFrames]uintptr
+	host       string
+	method     string
+	url        string
+	statusCode int
+}
+
+func (s *Span) tracing() bool {
+	return s.trace.localOptions&optionTrace != 0
+}
+
+// NewChild creates a new span with the given name as a child of s.
+// If s is nil, does nothing and returns nil.
+func (s *Span) NewChild(name string) *Span {
+	if s == nil {
+		return nil
+	}
+	if !s.tracing() {
+		return s
+	}
+	return startNewChild(name, s.trace, s.span.SpanId)
+}
+
+// NewRemoteChild creates a new span as a child of s.
+//
+// Some labels in the span are set from the outgoing *http.Request r.
+//
+// A header is set in r so that the trace context is propagated to the
+// destination.  The parent span ID in that header is set as follows:
+// - If the request is being traced, then the ID of s is used.
+// - If the request is not being traced, but there was a trace context header
+//   in the incoming request for this trace (the request passed to
+//   SpanFromRequest), the parent span ID in that header is used.
+// - Otherwise, the parent span ID is zero.
+// The tracing bit in the options is set if tracing is enabled, or if it was
+// set in the incoming request.
+//
+// If s is nil, does nothing and returns nil.
+func (s *Span) NewRemoteChild(r *http.Request) *Span {
+	if s == nil {
+		return nil
+	}
+	if !s.tracing() {
+		r.Header[httpHeader] = []string{spanHeader(s.trace.traceID, s.span.ParentSpanId, s.trace.globalOptions)}
+		return s
+	}
+	newSpan := startNewChildWithRequest(r, s.trace, s.span.SpanId)
+	r.Header[httpHeader] = []string{spanHeader(s.trace.traceID, newSpan.span.SpanId, s.trace.globalOptions)}
+	return newSpan
+}
+
+func startNewChildWithRequest(r *http.Request, trace *trace, parentSpanID uint64) *Span {
+	name := r.URL.Host + r.URL.Path // drop scheme and query params
+	newSpan := startNewChild(name, trace, parentSpanID)
+	if r.Host == "" {
+		newSpan.host = r.URL.Host
+	} else {
+		newSpan.host = r.Host
+	}
+	newSpan.method = r.Method
+	newSpan.url = r.URL.String()
+	return newSpan
+}
+
+func startNewChild(name string, trace *trace, parentSpanID uint64) *Span {
+	spanID := nextSpanID()
+	for spanID == parentSpanID {
+		spanID = nextSpanID()
+	}
+	newSpan := &Span{
+		trace: trace,
+		span: api.TraceSpan{
+			Kind:         spanKindClient,
+			Name:         name,
+			ParentSpanId: parentSpanID,
+			SpanId:       spanID,
+		},
+		start: time.Now(),
+	}
+	if trace.localOptions&optionStack != 0 {
+		_ = runtime.Callers(1, newSpan.stack[:])
+	}
+	return newSpan
+}
+
+// TraceID returns the ID of the trace to which s belongs.
+func (s *Span) TraceID() string {
+	if s == nil {
+		return ""
+	}
+	return s.trace.traceID
+}
+
+// SetLabel sets the label for the given key to the given value.
+// If the value is empty, the label for that key is deleted.
+// If a label is given a value automatically and by SetLabel, the
+// automatically-set value is used.
+// If s is nil, does nothing.
+func (s *Span) SetLabel(key, value string) {
+	if s == nil {
+		return
+	}
+	if !s.tracing() {
+		return
+	}
+	if value == "" {
+		if s.span.Labels != nil {
+			delete(s.span.Labels, key)
+		}
+		return
+	}
+	if s.span.Labels == nil {
+		s.span.Labels = make(map[string]string)
+	}
+	s.span.Labels[key] = value
+}
+
+type FinishOption interface {
+	modifySpan(s *Span)
+}
+
+type withResponse struct {
+	*http.Response
+}
+
+// WithResponse returns an option that can be passed to Finish that indicates
+// that some labels for the span should be set using the given *http.Response.
+func WithResponse(resp *http.Response) FinishOption {
+	return withResponse{resp}
+}
+func (u withResponse) modifySpan(s *Span) {
+	if u.Response != nil {
+		s.statusCode = u.StatusCode
+	}
+}
+
+// Finish declares that the span has finished.
+//
+// If s is nil, Finish does nothing and returns nil.
+//
+// If the option trace.WithResponse(resp) is passed, then some labels are set
+// for s using information in the given *http.Response.  This is useful when the
+// span is for an outgoing http request; s will typically have been created by
+// NewRemoteChild in this case.
+//
+// If s is a root span (one created by SpanFromRequest) then s, and all its
+// descendant spans that have finished, are uploaded to the Google Stackdriver
+// Trace server asynchronously.
+func (s *Span) Finish(opts ...FinishOption) {
+	if s == nil {
+		return
+	}
+	if !s.tracing() {
+		return
+	}
+	s.trace.finish(s, false, opts...)
+}
+
+// FinishWait is like Finish, but if s is a root span, it waits until uploading
+// is finished, then returns an error if one occurred.
+func (s *Span) FinishWait(opts ...FinishOption) error {
+	if s == nil {
+		return nil
+	}
+	if !s.tracing() {
+		return nil
+	}
+	return s.trace.finish(s, true, opts...)
+}
+
+func spanHeader(traceID string, spanID uint64, options optionFlags) string {
+	// See https://cloud.google.com/trace/docs/faq for the header format.
+	return fmt.Sprintf("%s/%d;o=%d", traceID, spanID, options)
+}
+
+func (s *Span) setStackLabel() {
+	var stack stackLabelValue
+	lastSigPanic, inTraceLibrary := false, true
+	for _, pc := range s.stack {
+		if pc == 0 {
+			break
+		}
+		if !lastSigPanic {
+			pc--
+		}
+		fn := runtime.FuncForPC(pc)
+		file, line := fn.FileLine(pc)
+		// Name has one of the following forms:
+		// path/to/package.Foo
+		// path/to/package.(Type).Foo
+		// For the first form, we store the whole name in the Method field of the
+		// stack frame.  For the second form, we set the Method field to "Foo" and
+		// the Class field to "path/to/package.(Type)".
+		name := fn.Name()
+		if inTraceLibrary && !strings.HasPrefix(name, "cloud.google.com/go/trace.") {
+			inTraceLibrary = false
+		}
+		var class string
+		if i := strings.Index(name, ")."); i != -1 {
+			class, name = name[:i+1], name[i+2:]
+		}
+		frame := stackFrame{
+			Class:    class,
+			Method:   name,
+			Filename: file,
+			Line:     int64(line),
+		}
+		if inTraceLibrary && len(stack.Frames) == 1 {
+			stack.Frames[0] = frame
+		} else {
+			stack.Frames = append(stack.Frames, frame)
+		}
+		lastSigPanic = fn.Name() == "runtime.sigpanic"
+	}
+	if label, err := json.Marshal(stack); err == nil {
+		s.SetLabel(labelStackTrace, string(label))
+	}
+}

vendor/cloud.google.com/go/trace/trace_test.go

@@ -0,0 +1,849 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package trace
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"math/rand"
+	"net/http"
+	"reflect"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"cloud.google.com/go/datastore"
+	"cloud.google.com/go/internal/testutil"
+	"cloud.google.com/go/storage"
+	"golang.org/x/net/context"
+	api "google.golang.org/api/cloudtrace/v1"
+	compute "google.golang.org/api/compute/v1"
+	"google.golang.org/api/iterator"
+	"google.golang.org/api/option"
+	dspb "google.golang.org/genproto/googleapis/datastore/v1"
+	"google.golang.org/grpc"
+)
+
+const testProjectID = "testproject"
+
+type fakeRoundTripper struct {
+	reqc chan *http.Request
+}
+
+func newFakeRoundTripper() *fakeRoundTripper {
+	return &fakeRoundTripper{reqc: make(chan *http.Request)}
+}
+
+func (rt *fakeRoundTripper) RoundTrip(r *http.Request) (*http.Response, error) {
+	rt.reqc <- r
+	resp := &http.Response{
+		Status:     "200 OK",
+		StatusCode: 200,
+		Body:       ioutil.NopCloser(strings.NewReader("{}")),
+	}
+	return resp, nil
+}
+
+func newTestClient(rt http.RoundTripper) *Client {
+	t, err := NewClient(context.Background(), testProjectID, option.WithHTTPClient(&http.Client{Transport: rt}))
+	if err != nil {
+		panic(err)
+	}
+	return t
+}
+
+type fakeDatastoreServer struct {
+	dspb.DatastoreServer
+	fail bool
+}
+
+func (f *fakeDatastoreServer) Lookup(ctx context.Context, req *dspb.LookupRequest) (*dspb.LookupResponse, error) {
+	if f.fail {
+		return nil, errors.New("lookup failed")
+	}
+	return &dspb.LookupResponse{}, nil
+}
+
+// makeRequests makes some requests.
+// span is the root span.  rt is the trace client's http client's transport.
+// This is used to retrieve the trace uploaded by the client, if any.  If
+// expectTrace is true, we expect a trace will be uploaded.  If synchronous is
+// true, the call to Finish is expected not to return before the client has
+// uploaded any traces.
+func makeRequests(t *testing.T, span *Span, rt *fakeRoundTripper, synchronous bool, expectTrace bool) *http.Request {
+	ctx := NewContext(context.Background(), span)
+
+	// An HTTP request.
+	{
+		req2, err := http.NewRequest("GET", "http://example.com/bar", nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp := &http.Response{StatusCode: 200}
+		s := span.NewRemoteChild(req2)
+		s.Finish(WithResponse(resp))
+	}
+
+	// An autogenerated API call.
+	{
+		rt := &fakeRoundTripper{reqc: make(chan *http.Request, 1)}
+		hc := &http.Client{Transport: rt}
+		computeClient, err := compute.New(hc)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = computeClient.Zones.List(testProjectID).Context(ctx).Do()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// A cloud library call that uses the autogenerated API.
+	{
+		rt := &fakeRoundTripper{reqc: make(chan *http.Request, 1)}
+		hc := &http.Client{Transport: rt}
+		storageClient, err := storage.NewClient(context.Background(), option.WithHTTPClient(hc))
+		if err != nil {
+			t.Fatal(err)
+		}
+		var objAttrsList []*storage.ObjectAttrs
+		it := storageClient.Bucket("testbucket").Objects(ctx, nil)
+		for {
+			objAttrs, err := it.Next()
+			if err != nil && err != iterator.Done {
+				t.Fatal(err)
+			}
+			if err == iterator.Done {
+				break
+			}
+			objAttrsList = append(objAttrsList, objAttrs)
+		}
+	}
+
+	// A cloud library call that uses grpc internally.
+	for _, fail := range []bool{false, true} {
+		srv, err := testutil.NewServer()
+		if err != nil {
+			t.Fatalf("creating test datastore server: %v", err)
+		}
+		dspb.RegisterDatastoreServer(srv.Gsrv, &fakeDatastoreServer{fail: fail})
+		srv.Start()
+		conn, err := grpc.Dial(srv.Addr, grpc.WithInsecure(), EnableGRPCTracingDialOption)
+		if err != nil {
+			t.Fatalf("connecting to test datastore server: %v", err)
+		}
+		datastoreClient, err := datastore.NewClient(ctx, testProjectID, option.WithGRPCConn(conn))
+		if err != nil {
+			t.Fatalf("creating datastore client: %v", err)
+		}
+		k := datastore.NameKey("Entity", "stringID", nil)
+		e := new(datastore.Entity)
+		datastoreClient.Get(ctx, k, e)
+	}
+
+	done := make(chan struct{})
+	go func() {
+		if synchronous {
+			err := span.FinishWait()
+			if err != nil {
+				t.Errorf("Unexpected error from span.FinishWait: %v", err)
+			}
+		} else {
+			span.Finish()
+		}
+		done <- struct{}{}
+	}()
+	if !expectTrace {
+		<-done
+		select {
+		case <-rt.reqc:
+			t.Errorf("Got a trace, expected none.")
+		case <-time.After(5 * time.Millisecond):
+		}
+		return nil
+	} else if !synchronous {
+		<-done
+		return <-rt.reqc
+	} else {
+		select {
+		case <-done:
+			t.Errorf("Synchronous Finish didn't wait for trace upload.")
+			return <-rt.reqc
+		case <-time.After(5 * time.Millisecond):
+			r := <-rt.reqc
+			<-done
+			return r
+		}
+	}
+}
+
+func TestTrace(t *testing.T) {
+	t.Parallel()
+	testTrace(t, false, true)
+}
+
+func TestTraceWithWait(t *testing.T) {
+	testTrace(t, true, true)
+}
+
+func TestTraceFromHeader(t *testing.T) {
+	t.Parallel()
+	testTrace(t, false, false)
+}
+
+func TestTraceFromHeaderWithWait(t *testing.T) {
+	testTrace(t, false, true)
+}
+
+func TestNewSpan(t *testing.T) {
+	const traceID = "0123456789ABCDEF0123456789ABCDEF"
+
+	rt := newFakeRoundTripper()
+	traceClient := newTestClient(rt)
+	span := traceClient.NewSpan("/foo")
+	span.trace.traceID = traceID
+
+	uploaded := makeRequests(t, span, rt, true, true)
+
+	if uploaded == nil {
+		t.Fatalf("No trace uploaded, expected one.")
+	}
+
+	expected := api.Traces{
+		Traces: []*api.Trace{
+			{
+				ProjectId: testProjectID,
+				Spans: []*api.TraceSpan{
+					{
+						Kind: "RPC_CLIENT",
+						Labels: map[string]string{
+							"trace.cloud.google.com/http/host":        "example.com",
+							"trace.cloud.google.com/http/method":      "GET",
+							"trace.cloud.google.com/http/status_code": "200",
+							"trace.cloud.google.com/http/url":         "http://example.com/bar",
+						},
+						Name: "example.com/bar",
+					},
+					{
+						Kind: "RPC_CLIENT",
+						Labels: map[string]string{
+							"trace.cloud.google.com/http/host":        "www.googleapis.com",
+							"trace.cloud.google.com/http/method":      "GET",
+							"trace.cloud.google.com/http/status_code": "200",
+							"trace.cloud.google.com/http/url":         "https://www.googleapis.com/compute/v1/projects/testproject/zones",
+						},
+						Name: "www.googleapis.com/compute/v1/projects/testproject/zones",
+					},
+					{
+						Kind: "RPC_CLIENT",
+						Labels: map[string]string{
+							"trace.cloud.google.com/http/host":        "www.googleapis.com",
+							"trace.cloud.google.com/http/method":      "GET",
+							"trace.cloud.google.com/http/status_code": "200",
+							"trace.cloud.google.com/http/url":         "https://www.googleapis.com/storage/v1/b/testbucket/o",
+						},
+						Name: "www.googleapis.com/storage/v1/b/testbucket/o",
+					},
+					&api.TraceSpan{
+						Kind:   "RPC_CLIENT",
+						Labels: nil,
+						Name:   "/google.datastore.v1.Datastore/Lookup",
+					},
+					&api.TraceSpan{
+						Kind:   "RPC_CLIENT",
+						Labels: map[string]string{"error": "rpc error: code = Unknown desc = lookup failed"},
+						Name:   "/google.datastore.v1.Datastore/Lookup",
+					},
+					{
+						Kind:   "RPC_SERVER",
+						Labels: map[string]string{},
+						Name:   "/foo",
+					},
+				},
+				TraceId: traceID,
+			},
+		},
+	}
+
+	body, err := ioutil.ReadAll(uploaded.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var patch api.Traces
+	err = json.Unmarshal(body, &patch)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(patch.Traces) != len(expected.Traces) || len(patch.Traces[0].Spans) != len(expected.Traces[0].Spans) {
+		got, _ := json.Marshal(patch)
+		want, _ := json.Marshal(expected)
+		t.Fatalf("PatchTraces request: got %s want %s", got, want)
+	}
+
+	n := len(patch.Traces[0].Spans)
+	rootSpan := patch.Traces[0].Spans[n-1]
+	for i, s := range patch.Traces[0].Spans {
+		if a, b := s.StartTime, s.EndTime; a > b {
+			t.Errorf("span %d start time is later than its end time (%q, %q)", i, a, b)
+		}
+		if a, b := rootSpan.StartTime, s.StartTime; a > b {
+			t.Errorf("trace start time is later than span %d start time (%q, %q)", i, a, b)
+		}
+		if a, b := s.EndTime, rootSpan.EndTime; a > b {
+			t.Errorf("span %d end time is later than trace end time (%q, %q)", i, a, b)
+		}
+		if i > 1 && i < n-1 {
+			if a, b := patch.Traces[0].Spans[i-1].EndTime, s.StartTime; a > b {
+				t.Errorf("span %d end time is later than span %d start time (%q, %q)", i-1, i, a, b)
+			}
+		}
+	}
+
+	if x := rootSpan.ParentSpanId; x != 0 {
+		t.Errorf("Incorrect ParentSpanId: got %d want %d", x, 0)
+	}
+	for i, s := range patch.Traces[0].Spans {
+		if x, y := rootSpan.SpanId, s.ParentSpanId; i < n-1 && x != y {
+			t.Errorf("Incorrect ParentSpanId in span %d: got %d want %d", i, y, x)
+		}
+	}
+	for i, s := range patch.Traces[0].Spans {
+		s.EndTime = ""
+		labels := &expected.Traces[0].Spans[i].Labels
+		for key, value := range *labels {
+			if v, ok := s.Labels[key]; !ok {
+				t.Errorf("Span %d is missing Label %q:%q", i, key, value)
+			} else if key == "trace.cloud.google.com/http/url" {
+				if !strings.HasPrefix(v, value) {
+					t.Errorf("Span %d Label %q: got value %q want prefix %q", i, key, v, value)
+				}
+			} else if v != value {
+				t.Errorf("Span %d Label %q: got value %q want %q", i, key, v, value)
+			}
+		}
+		for key := range s.Labels {
+			if _, ok := (*labels)[key]; key != "trace.cloud.google.com/stacktrace" && !ok {
+				t.Errorf("Span %d: unexpected label %q", i, key)
+			}
+		}
+		*labels = nil
+		s.Labels = nil
+		s.ParentSpanId = 0
+		if s.SpanId == 0 {
+			t.Errorf("Incorrect SpanId: got 0 want nonzero")
+		}
+		s.SpanId = 0
+		s.StartTime = ""
+	}
+	if !reflect.DeepEqual(patch, expected) {
+		got, _ := json.Marshal(patch)
+		want, _ := json.Marshal(expected)
+		t.Errorf("PatchTraces request: got %s want %s", got, want)
+	}
+}
+
+func testTrace(t *testing.T, synchronous bool, fromRequest bool) {
+	const header = `0123456789ABCDEF0123456789ABCDEF/42;o=3`
+	rt := newFakeRoundTripper()
+	traceClient := newTestClient(rt)
+
+	span := traceClient.SpanFromHeader("/foo", header)
+	headerOrReqLabels := map[string]string{}
+	headerOrReqName := "/foo"
+
+	if fromRequest {
+		req, err := http.NewRequest("GET", "http://example.com/foo", nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		req.Header.Set("X-Cloud-Trace-Context", header)
+		span = traceClient.SpanFromRequest(req)
+		headerOrReqLabels = map[string]string{
+			"trace.cloud.google.com/http/host":   "example.com",
+			"trace.cloud.google.com/http/method": "GET",
+			"trace.cloud.google.com/http/url":    "http://example.com/foo",
+		}
+		headerOrReqName = "example.com/foo"
+	}
+
+	uploaded := makeRequests(t, span, rt, synchronous, true)
+	if uploaded == nil {
+		t.Fatalf("No trace uploaded, expected one.")
+	}
+
+	expected := api.Traces{
+		Traces: []*api.Trace{
+			{
+				ProjectId: testProjectID,
+				Spans: []*api.TraceSpan{
+					{
+						Kind: "RPC_CLIENT",
+						Labels: map[string]string{
+							"trace.cloud.google.com/http/host":        "example.com",
+							"trace.cloud.google.com/http/method":      "GET",
+							"trace.cloud.google.com/http/status_code": "200",
+							"trace.cloud.google.com/http/url":         "http://example.com/bar",
+						},
+						Name: "example.com/bar",
+					},
+					{
+						Kind: "RPC_CLIENT",
+						Labels: map[string]string{
+							"trace.cloud.google.com/http/host":        "www.googleapis.com",
+							"trace.cloud.google.com/http/method":      "GET",
+							"trace.cloud.google.com/http/status_code": "200",
+							"trace.cloud.google.com/http/url":         "https://www.googleapis.com/compute/v1/projects/testproject/zones",
+						},
+						Name: "www.googleapis.com/compute/v1/projects/testproject/zones",
+					},
+					{
+						Kind: "RPC_CLIENT",
+						Labels: map[string]string{
+							"trace.cloud.google.com/http/host":        "www.googleapis.com",
+							"trace.cloud.google.com/http/method":      "GET",
+							"trace.cloud.google.com/http/status_code": "200",
+							"trace.cloud.google.com/http/url":         "https://www.googleapis.com/storage/v1/b/testbucket/o",
+						},
+						Name: "www.googleapis.com/storage/v1/b/testbucket/o",
+					},
+					&api.TraceSpan{
+						Kind:   "RPC_CLIENT",
+						Labels: nil,
+						Name:   "/google.datastore.v1.Datastore/Lookup",
+					},
+					&api.TraceSpan{
+						Kind:   "RPC_CLIENT",
+						Labels: map[string]string{"error": "rpc error: code = Unknown desc = lookup failed"},
+						Name:   "/google.datastore.v1.Datastore/Lookup",
+					},
+					{
+						Kind:   "RPC_SERVER",
+						Labels: headerOrReqLabels,
+						Name:   headerOrReqName,
+					},
+				},
+				TraceId: "0123456789ABCDEF0123456789ABCDEF",
+			},
+		},
+	}
+
+	body, err := ioutil.ReadAll(uploaded.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var patch api.Traces
+	err = json.Unmarshal(body, &patch)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if len(patch.Traces) != len(expected.Traces) || len(patch.Traces[0].Spans) != len(expected.Traces[0].Spans) {
+		got, _ := json.Marshal(patch)
+		want, _ := json.Marshal(expected)
+		t.Fatalf("PatchTraces request: got %s want %s", got, want)
+	}
+
+	n := len(patch.Traces[0].Spans)
+	rootSpan := patch.Traces[0].Spans[n-1]
+	for i, s := range patch.Traces[0].Spans {
+		if a, b := s.StartTime, s.EndTime; a > b {
+			t.Errorf("span %d start time is later than its end time (%q, %q)", i, a, b)
+		}
+		if a, b := rootSpan.StartTime, s.StartTime; a > b {
+			t.Errorf("trace start time is later than span %d start time (%q, %q)", i, a, b)
+		}
+		if a, b := s.EndTime, rootSpan.EndTime; a > b {
+			t.Errorf("span %d end time is later than trace end time (%q, %q)", i, a, b)
+		}
+		if i > 1 && i < n-1 {
+			if a, b := patch.Traces[0].Spans[i-1].EndTime, s.StartTime; a > b {
+				t.Errorf("span %d end time is later than span %d start time (%q, %q)", i-1, i, a, b)
+			}
+		}
+	}
+
+	if x := rootSpan.ParentSpanId; x != 42 {
+		t.Errorf("Incorrect ParentSpanId: got %d want %d", x, 42)
+	}
+	for i, s := range patch.Traces[0].Spans {
+		if x, y := rootSpan.SpanId, s.ParentSpanId; i < n-1 && x != y {
+			t.Errorf("Incorrect ParentSpanId in span %d: got %d want %d", i, y, x)
+		}
+	}
+	for i, s := range patch.Traces[0].Spans {
+		s.EndTime = ""
+		labels := &expected.Traces[0].Spans[i].Labels
+		for key, value := range *labels {
+			if v, ok := s.Labels[key]; !ok {
+				t.Errorf("Span %d is missing Label %q:%q", i, key, value)
+			} else if key == "trace.cloud.google.com/http/url" {
+				if !strings.HasPrefix(v, value) {
+					t.Errorf("Span %d Label %q: got value %q want prefix %q", i, key, v, value)
+				}
+			} else if v != value {
+				t.Errorf("Span %d Label %q: got value %q want %q", i, key, v, value)
+			}
+		}
+		for key := range s.Labels {
+			if _, ok := (*labels)[key]; key != "trace.cloud.google.com/stacktrace" && !ok {
+				t.Errorf("Span %d: unexpected label %q", i, key)
+			}
+		}
+		*labels = nil
+		s.Labels = nil
+		s.ParentSpanId = 0
+		if s.SpanId == 0 {
+			t.Errorf("Incorrect SpanId: got 0 want nonzero")
+		}
+		s.SpanId = 0
+		s.StartTime = ""
+	}
+	if !reflect.DeepEqual(patch, expected) {
+		got, _ := json.Marshal(patch)
+		want, _ := json.Marshal(expected)
+		t.Errorf("PatchTraces request: got %s \n\n want %s", got, want)
+	}
+}
+
+func TestNoTrace(t *testing.T) {
+	testNoTrace(t, false, true)
+}
+
+func TestNoTraceWithWait(t *testing.T) {
+	testNoTrace(t, true, true)
+}
+
+func TestNoTraceFromHeader(t *testing.T) {
+	testNoTrace(t, false, false)
+}
+
+func TestNoTraceFromHeaderWithWait(t *testing.T) {
+	testNoTrace(t, true, false)
+}
+
+func testNoTrace(t *testing.T, synchronous bool, fromRequest bool) {
+	for _, header := range []string{
+		`0123456789ABCDEF0123456789ABCDEF/42;o=2`,
+		`0123456789ABCDEF0123456789ABCDEF/42;o=0`,
+		`0123456789ABCDEF0123456789ABCDEF/42`,
+		`0123456789ABCDEF0123456789ABCDEF`,
+		``,
+	} {
+		rt := newFakeRoundTripper()
+		traceClient := newTestClient(rt)
+		var span *Span
+		if fromRequest {
+			req, err := http.NewRequest("GET", "http://example.com/foo", nil)
+			if header != "" {
+				req.Header.Set("X-Cloud-Trace-Context", header)
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			span = traceClient.SpanFromRequest(req)
+		} else {
+			span = traceClient.SpanFromHeader("/foo", header)
+		}
+		uploaded := makeRequests(t, span, rt, synchronous, false)
+		if uploaded != nil {
+			t.Errorf("Got a trace, expected none.")
+		}
+	}
+}
+
+func TestSample(t *testing.T) {
+	// A deterministic test of the sampler logic.
+	type testCase struct {
+		rate   float64
+		maxqps float64
+		want   int
+	}
+	const delta = 25 * time.Millisecond
+	for _, test := range []testCase{
+		// qps won't matter, so we will sample half of the 79 calls
+		{0.50, 100, 40},
+		// with 1 qps and a burst of 2, we will sample twice in second #1, once in the partial second #2
+		{0.50, 1, 3},
+	} {
+		sp, err := NewLimitedSampler(test.rate, test.maxqps)
+		if err != nil {
+			t.Fatal(err)
+		}
+		s := sp.(*sampler)
+		sampled := 0
+		tm := time.Now()
+		for i := 0; i < 80; i++ {
+			if s.sample(Parameters{}, tm, float64(i%2)).Sample {
+				sampled++
+			}
+			tm = tm.Add(delta)
+		}
+		if sampled != test.want {
+			t.Errorf("rate=%f, maxqps=%f: got %d samples, want %d", test.rate, test.maxqps, sampled, test.want)
+		}
+	}
+}
+
+func TestSampling(t *testing.T) {
+	t.Parallel()
+	// This scope tests sampling in a larger context, with real time and randomness.
+	wg := sync.WaitGroup{}
+	type testCase struct {
+		rate          float64
+		maxqps        float64
+		expectedRange [2]int
+	}
+	for _, test := range []testCase{
+		{0, 5, [2]int{0, 0}},
+		{5, 0, [2]int{0, 0}},
+		{0.50, 100, [2]int{20, 60}},
+		{0.50, 1, [2]int{3, 4}}, // Windows, with its less precise clock, sometimes gives 4.
+	} {
+		wg.Add(1)
+		go func(test testCase) {
+			rt := newFakeRoundTripper()
+			traceClient := newTestClient(rt)
+			traceClient.bundler.BundleByteLimit = 1
+			p, err := NewLimitedSampler(test.rate, test.maxqps)
+			if err != nil {
+				t.Fatalf("NewLimitedSampler: %v", err)
+			}
+			traceClient.SetSamplingPolicy(p)
+			ticker := time.NewTicker(25 * time.Millisecond)
+			sampled := 0
+			for i := 0; i < 79; i++ {
+				req, err := http.NewRequest("GET", "http://example.com/foo", nil)
+				if err != nil {
+					t.Fatal(err)
+				}
+				span := traceClient.SpanFromRequest(req)
+				span.Finish()
+				select {
+				case <-rt.reqc:
+					<-ticker.C
+					sampled++
+				case <-ticker.C:
+				}
+			}
+			ticker.Stop()
+			if test.expectedRange[0] > sampled || sampled > test.expectedRange[1] {
+				t.Errorf("rate=%f, maxqps=%f: got %d samples want ∈ %v", test.rate, test.maxqps, sampled, test.expectedRange)
+			}
+			wg.Done()
+		}(test)
+	}
+	wg.Wait()
+}
+
+func TestBundling(t *testing.T) {
+	t.Parallel()
+	rt := newFakeRoundTripper()
+	traceClient := newTestClient(rt)
+	traceClient.bundler.DelayThreshold = time.Second / 2
+	traceClient.bundler.BundleCountThreshold = 10
+	p, err := NewLimitedSampler(1, 99) // sample every request.
+	if err != nil {
+		t.Fatalf("NewLimitedSampler: %v", err)
+	}
+	traceClient.SetSamplingPolicy(p)
+
+	for i := 0; i < 35; i++ {
+		go func() {
+			req, err := http.NewRequest("GET", "http://example.com/foo", nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			span := traceClient.SpanFromRequest(req)
+			span.Finish()
+		}()
+	}
+
+	// Read the first three bundles.
+	<-rt.reqc
+	<-rt.reqc
+	<-rt.reqc
+
+	// Test that the fourth bundle isn't sent early.
+	select {
+	case <-rt.reqc:
+		t.Errorf("bundle sent too early")
+	case <-time.After(time.Second / 4):
+		<-rt.reqc
+	}
+
+	// Test that there aren't extra bundles.
+	select {
+	case <-rt.reqc:
+		t.Errorf("too many bundles sent")
+	case <-time.After(time.Second):
+	}
+}
+
+func TestWeights(t *testing.T) {
+	const (
+		expectedNumTraced   = 10100
+		numTracedEpsilon    = 100
+		expectedTotalWeight = 50000
+		totalWeightEpsilon  = 5000
+	)
+	rng := rand.New(rand.NewSource(1))
+	const delta = 2 * time.Millisecond
+	for _, headerRate := range []float64{0.0, 0.5, 1.0} {
+		// Simulate 10 seconds of requests arriving at 500qps.
+		//
+		// The sampling policy tries to sample 25% of them, but has a qps limit of
+		// 100, so it will not be able to.  The returned weight should be higher
+		// for some sampled requests to compensate.
+		//
+		// headerRate is the fraction of incoming requests that have a trace header
+		// set.  The qps limit should not be exceeded, even if headerRate is high.
+		sp, err := NewLimitedSampler(0.25, 100)
+		if err != nil {
+			t.Fatal(err)
+		}
+		s := sp.(*sampler)
+		tm := time.Now()
+		totalWeight := 0.0
+		numTraced := 0
+		seenLargeWeight := false
+		for i := 0; i < 50000; i++ {
+			d := s.sample(Parameters{HasTraceHeader: rng.Float64() < headerRate}, tm, rng.Float64())
+			if d.Trace {
+				numTraced++
+			}
+			if d.Sample {
+				totalWeight += d.Weight
+				if x := int(d.Weight) / 4; x <= 0 || x >= 100 || d.Weight != float64(x)*4.0 {
+					t.Errorf("weight: got %f, want a small positive multiple of 4", d.Weight)
+				}
+				if d.Weight > 4 {
+					seenLargeWeight = true
+				}
+			}
+			tm = tm.Add(delta)
+		}
+		if !seenLargeWeight {
+			t.Errorf("headerRate %f: never saw sample weight higher than 4.", headerRate)
+		}
+		if numTraced < expectedNumTraced-numTracedEpsilon || expectedNumTraced+numTracedEpsilon < numTraced {
+			t.Errorf("headerRate %f: got %d traced requests, want ∈ [%d, %d]", headerRate, numTraced, expectedNumTraced-numTracedEpsilon, expectedNumTraced+numTracedEpsilon)
+		}
+		if totalWeight < expectedTotalWeight-totalWeightEpsilon || expectedTotalWeight+totalWeightEpsilon < totalWeight {
+			t.Errorf("headerRate %f: got total weight %f want ∈ [%d, %d]", headerRate, totalWeight, expectedTotalWeight-totalWeightEpsilon, expectedTotalWeight+totalWeightEpsilon)
+		}
+	}
+}
+
+type alwaysTrace struct{}
+
+func (a alwaysTrace) Sample(p Parameters) Decision {
+	return Decision{Trace: true}
+}
+
+type neverTrace struct{}
+
+func (a neverTrace) Sample(p Parameters) Decision {
+	return Decision{Trace: false}
+}
+
+func TestPropagation(t *testing.T) {
+	rt := newFakeRoundTripper()
+	traceClient := newTestClient(rt)
+	for _, header := range []string{
+		`0123456789ABCDEF0123456789ABCDEF/42;o=0`,
+		`0123456789ABCDEF0123456789ABCDEF/42;o=1`,
+		`0123456789ABCDEF0123456789ABCDEF/42;o=2`,
+		`0123456789ABCDEF0123456789ABCDEF/42;o=3`,
+		`0123456789ABCDEF0123456789ABCDEF/0;o=0`,
+		`0123456789ABCDEF0123456789ABCDEF/0;o=1`,
+		`0123456789ABCDEF0123456789ABCDEF/0;o=2`,
+		`0123456789ABCDEF0123456789ABCDEF/0;o=3`,
+		``,
+	} {
+		for _, policy := range []SamplingPolicy{
+			nil,
+			alwaysTrace{},
+			neverTrace{},
+		} {
+			traceClient.SetSamplingPolicy(policy)
+			req, err := http.NewRequest("GET", "http://example.com/foo", nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if header != "" {
+				req.Header.Set("X-Cloud-Trace-Context", header)
+			}
+
+			span := traceClient.SpanFromRequest(req)
+
+			req2, err := http.NewRequest("GET", "http://example.com/bar", nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			req3, err := http.NewRequest("GET", "http://example.com/baz", nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			span.NewRemoteChild(req2)
+			span.NewRemoteChild(req3)
+
+			var (
+				t1, t2, t3 string
+				s1, s2, s3 uint64
+				o1, o2, o3 uint64
+			)
+			fmt.Sscanf(header, "%32s/%d;o=%d", &t1, &s1, &o1)
+			fmt.Sscanf(req2.Header.Get("X-Cloud-Trace-Context"), "%32s/%d;o=%d", &t2, &s2, &o2)
+			fmt.Sscanf(req3.Header.Get("X-Cloud-Trace-Context"), "%32s/%d;o=%d", &t3, &s3, &o3)
+
+			if header == "" {
+				if t2 != t3 {
+					t.Errorf("expected the same trace ID in child requests, got %q %q", t2, t3)
+				}
+			} else {
+				if t2 != t1 || t3 != t1 {
+					t.Errorf("trace IDs should be passed to child requests")
+				}
+			}
+			trace := policy == alwaysTrace{} || policy == nil && (o1&1) != 0
+			if header == "" {
+				if trace && (s2 == 0 || s3 == 0) {
+					t.Errorf("got span IDs %d %d in child requests, want nonzero", s2, s3)
+				}
+				if trace && s2 == s3 {
+					t.Errorf("got span IDs %d %d in child requests, should be different", s2, s3)
+				}
+				if !trace && (s2 != 0 || s3 != 0) {
+					t.Errorf("got span IDs %d %d in child requests, want zero", s2, s3)
+				}
+			} else {
+				if trace && (s2 == s1 || s3 == s1 || s2 == s3) {
+					t.Errorf("parent span IDs in input and outputs should be all different, got %d %d %d", s1, s2, s3)
+				}
+				if !trace && (s2 != s1 || s3 != s1) {
+					t.Errorf("parent span ID in input, %d, should have been equal to parent span IDs in output: %d %d", s1, s2, s3)
+				}
+			}
+			expectTraceOption := policy == alwaysTrace{} || (o1&1) != 0
+			if expectTraceOption != ((o2&1) != 0) || expectTraceOption != ((o3&1) != 0) {
+				t.Errorf("tracing flag in child requests should be %t, got options %d %d", expectTraceOption, o2, o3)
+			}
+		}
+	}
+}