16 files changed, 1555 insertions, 0 deletions

diff --git a/vendor/go.opencensus.io/stats/doc.go b/vendor/go.opencensus.io/stats/doc.go
new file mode 100644
index 0000000..00d473e
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/doc.go
@@ -0,0 +1,69 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 stats contains support for OpenCensus stats recording.
+
+OpenCensus allows users to create typed measures, record measurements,
+aggregate the collected data, and export the aggregated data.
+
+Measures
+
+A measure represents a type of data point to be tracked and recorded.
+For example, latency, request Mb/s, and response Mb/s are measures
+to collect from a server.
+
+Measure constructors such as Int64 and Float64 automatically
+register the measure by the given name. Each registered measure needs
+to be unique by name. Measures also have a description and a unit.
+
+Libraries can define and export measures. Application authors can then
+create views and collect and break down measures by the tags they are
+interested in.
+
+Recording measurements
+
+Measurement is a data point to be collected for a measure. For example,
+for a latency (ms) measure, 100 is a measurement that represents a 100ms
+latency event. Measurements are created from measures with
+the current context. Tags from the current context are recorded with the
+measurements if they are any.
+
+Recorded measurements are dropped immediately if no views are registered for them.
+There is usually no need to conditionally enable and disable
+recording to reduce cost. Recording of measurements is cheap.
+
+Libraries can always record measurements, and applications can later decide
+on which measurements they want to collect by registering views. This allows
+libraries to turn on the instrumentation by default.
+
+Exemplars
+
+For a given recorded measurement, the associated exemplar is a diagnostic map
+that gives more information about the measurement.
+
+When aggregated using a Distribution aggregation, an exemplar is kept for each
+bucket in the Distribution. This allows you to easily find an example of a
+measurement that fell into each bucket.
+
+For example, if you also use the OpenCensus trace package and you
+record a measurement with a context that contains a sampled trace span,
+then the trace span will be added to the exemplar associated with the measurement.
+
+When exported to a supporting back end, you should be able to easily navigate
+to example traces that fell into each bucket in the Distribution.
+
+*/
+package stats // import "go.opencensus.io/stats"
diff --git a/vendor/go.opencensus.io/stats/internal/record.go b/vendor/go.opencensus.io/stats/internal/record.go
new file mode 100644
index 0000000..ed54552
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/internal/record.go
@@ -0,0 +1,25 @@
+// Copyright 2018, OpenCensus Authors
+//
+// 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 internal
+
+import (
+        "go.opencensus.io/tag"
+)
+
+// DefaultRecorder will be called for each Record call.
+var DefaultRecorder func(tags *tag.Map, measurement interface{}, attachments map[string]string)
+
+// SubscriptionReporter reports when a view subscribed with a measure.
+var SubscriptionReporter func(measure string)
diff --git a/vendor/go.opencensus.io/stats/internal/validation.go b/vendor/go.opencensus.io/stats/internal/validation.go
new file mode 100644
index 0000000..b946667
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/internal/validation.go
@@ -0,0 +1,28 @@
+// Copyright 2018, OpenCensus Authors
+//
+// 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 internal // import "go.opencensus.io/stats/internal"
+
+const (
+        MaxNameLength = 255
+)
+
+func IsPrintable(str string) bool {
+        for _, r := range str {
+                if !(r >= ' ' && r <= '~') {
+                        return false
+                }
+        }
+        return true
+}
diff --git a/vendor/go.opencensus.io/stats/measure.go b/vendor/go.opencensus.io/stats/measure.go
new file mode 100644
index 0000000..64d02b1
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/measure.go
@@ -0,0 +1,123 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 stats
+
+import (
+        "sync"
+        "sync/atomic"
+)
+
+// Measure represents a single numeric value to be tracked and recorded.
+// For example, latency, request bytes, and response bytes could be measures
+// to collect from a server.
+//
+// Measures by themselves have no outside effects. In order to be exported,
+// the measure needs to be used in a View. If no Views are defined over a
+// measure, there is very little cost in recording it.
+type Measure interface {
+        // Name returns the name of this measure.
+        //
+        // Measure names are globally unique (among all libraries linked into your program).
+        // We recommend prefixing the measure name with a domain name relevant to your
+        // project or application.
+        //
+        // Measure names are never sent over the wire or exported to backends.
+        // They are only used to create Views.
+        Name() string
+
+        // Description returns the human-readable description of this measure.
+        Description() string
+
+        // Unit returns the units for the values this measure takes on.
+        //
+        // Units are encoded according to the case-sensitive abbreviations from the
+        // Unified Code for Units of Measure: http://unitsofmeasure.org/ucum.html
+        Unit() string
+}
+
+// measureDescriptor is the untyped descriptor associated with each measure.
+// Int64Measure and Float64Measure wrap measureDescriptor to provide typed
+// recording APIs.
+// Two Measures with the same name will have the same measureDescriptor.
+type measureDescriptor struct {
+        subs int32 // access atomically
+
+        name        string
+        description string
+        unit        string
+}
+
+func (m *measureDescriptor) subscribe() {
+        atomic.StoreInt32(&m.subs, 1)
+}
+
+func (m *measureDescriptor) subscribed() bool {
+        return atomic.LoadInt32(&m.subs) == 1
+}
+
+// Name returns the name of the measure.
+func (m *measureDescriptor) Name() string {
+        return m.name
+}
+
+// Description returns the description of the measure.
+func (m *measureDescriptor) Description() string {
+        return m.description
+}
+
+// Unit returns the unit of the measure.
+func (m *measureDescriptor) Unit() string {
+        return m.unit
+}
+
+var (
+        mu       sync.RWMutex
+        measures = make(map[string]*measureDescriptor)
+)
+
+func registerMeasureHandle(name, desc, unit string) *measureDescriptor {
+        mu.Lock()
+        defer mu.Unlock()
+
+        if stored, ok := measures[name]; ok {
+                return stored
+        }
+        m := &measureDescriptor{
+                name:        name,
+                description: desc,
+                unit:        unit,
+        }
+        measures[name] = m
+        return m
+}
+
+// Measurement is the numeric value measured when recording stats. Each measure
+// provides methods to create measurements of their kind. For example, Int64Measure
+// provides M to convert an int64 into a measurement.
+type Measurement struct {
+        v float64
+        m *measureDescriptor
+}
+
+// Value returns the value of the Measurement as a float64.
+func (m Measurement) Value() float64 {
+        return m.v
+}
+
+// Measure returns the Measure from which this Measurement was created.
+func (m Measurement) Measure() Measure {
+        return m.m
+}
diff --git a/vendor/go.opencensus.io/stats/measure_float64.go b/vendor/go.opencensus.io/stats/measure_float64.go
new file mode 100644
index 0000000..acedb21
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/measure_float64.go
@@ -0,0 +1,36 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 stats
+
+// Float64Measure is a measure for float64 values.
+type Float64Measure struct {
+        *measureDescriptor
+}
+
+// M creates a new float64 measurement.
+// Use Record to record measurements.
+func (m *Float64Measure) M(v float64) Measurement {
+        return Measurement{m: m.measureDescriptor, v: v}
+}
+
+// Float64 creates a new measure for float64 values.
+//
+// See the documentation for interface Measure for more guidance on the
+// parameters of this function.
+func Float64(name, description, unit string) *Float64Measure {
+        mi := registerMeasureHandle(name, description, unit)
+        return &Float64Measure{mi}
+}
diff --git a/vendor/go.opencensus.io/stats/measure_int64.go b/vendor/go.opencensus.io/stats/measure_int64.go
new file mode 100644
index 0000000..c4243ba
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/measure_int64.go
@@ -0,0 +1,36 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 stats
+
+// Int64Measure is a measure for int64 values.
+type Int64Measure struct {
+        *measureDescriptor
+}
+
+// M creates a new int64 measurement.
+// Use Record to record measurements.
+func (m *Int64Measure) M(v int64) Measurement {
+        return Measurement{m: m.measureDescriptor, v: float64(v)}
+}
+
+// Int64 creates a new measure for int64 values.
+//
+// See the documentation for interface Measure for more guidance on the
+// parameters of this function.
+func Int64(name, description, unit string) *Int64Measure {
+        mi := registerMeasureHandle(name, description, unit)
+        return &Int64Measure{mi}
+}
diff --git a/vendor/go.opencensus.io/stats/record.go b/vendor/go.opencensus.io/stats/record.go
new file mode 100644
index 0000000..0aced02
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/record.go
@@ -0,0 +1,69 @@
+// Copyright 2018, OpenCensus Authors
+//
+// 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 stats
+
+import (
+        "context"
+
+        "go.opencensus.io/exemplar"
+        "go.opencensus.io/stats/internal"
+        "go.opencensus.io/tag"
+)
+
+func init() {
+        internal.SubscriptionReporter = func(measure string) {
+                mu.Lock()
+                measures[measure].subscribe()
+                mu.Unlock()
+        }
+}
+
+// Record records one or multiple measurements with the same context at once.
+// If there are any tags in the context, measurements will be tagged with them.
+func Record(ctx context.Context, ms ...Measurement) {
+        recorder := internal.DefaultRecorder
+        if recorder == nil {
+                return
+        }
+        if len(ms) == 0 {
+                return
+        }
+        record := false
+        for _, m := range ms {
+                if m.m.subscribed() {
+                        record = true
+                        break
+                }
+        }
+        if !record {
+                return
+        }
+        recorder(tag.FromContext(ctx), ms, exemplar.AttachmentsFromContext(ctx))
+}
+
+// RecordWithTags records one or multiple measurements at once.
+//
+// Measurements will be tagged with the tags in the context mutated by the mutators.
+// RecordWithTags is useful if you want to record with tag mutations but don't want
+// to propagate the mutations in the context.
+func RecordWithTags(ctx context.Context, mutators []tag.Mutator, ms ...Measurement) error {
+        ctx, err := tag.New(ctx, mutators...)
+        if err != nil {
+                return err
+        }
+        Record(ctx, ms...)
+        return nil
+}
diff --git a/vendor/go.opencensus.io/stats/units.go b/vendor/go.opencensus.io/stats/units.go
new file mode 100644
index 0000000..6931a5f
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/units.go
@@ -0,0 +1,25 @@
+// Copyright 2018, OpenCensus Authors
+//
+// 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 stats
+
+// Units are encoded according to the case-sensitive abbreviations from the
+// Unified Code for Units of Measure: http://unitsofmeasure.org/ucum.html
+const (
+        UnitNone          = "1" // Deprecated: Use UnitDimensionless.
+        UnitDimensionless = "1"
+        UnitBytes         = "By"
+        UnitMilliseconds  = "ms"
+)
diff --git a/vendor/go.opencensus.io/stats/view/aggregation.go b/vendor/go.opencensus.io/stats/view/aggregation.go
new file mode 100644
index 0000000..b7f169b
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/aggregation.go
@@ -0,0 +1,120 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view
+
+// AggType represents the type of aggregation function used on a View.
+type AggType int
+
+// All available aggregation types.
+const (
+        AggTypeNone         AggType = iota // no aggregation; reserved for future use.
+        AggTypeCount                       // the count aggregation, see Count.
+        AggTypeSum                         // the sum aggregation, see Sum.
+        AggTypeDistribution                // the distribution aggregation, see Distribution.
+        AggTypeLastValue                   // the last value aggregation, see LastValue.
+)
+
+func (t AggType) String() string {
+        return aggTypeName[t]
+}
+
+var aggTypeName = map[AggType]string{
+        AggTypeNone:         "None",
+        AggTypeCount:        "Count",
+        AggTypeSum:          "Sum",
+        AggTypeDistribution: "Distribution",
+        AggTypeLastValue:    "LastValue",
+}
+
+// Aggregation represents a data aggregation method. Use one of the functions:
+// Count, Sum, or Distribution to construct an Aggregation.
+type Aggregation struct {
+        Type    AggType   // Type is the AggType of this Aggregation.
+        Buckets []float64 // Buckets are the bucket endpoints if this Aggregation represents a distribution, see Distribution.
+
+        newData func() AggregationData
+}
+
+var (
+        aggCount = &Aggregation{
+                Type: AggTypeCount,
+                newData: func() AggregationData {
+                        return &CountData{}
+                },
+        }
+        aggSum = &Aggregation{
+                Type: AggTypeSum,
+                newData: func() AggregationData {
+                        return &SumData{}
+                },
+        }
+)
+
+// Count indicates that data collected and aggregated
+// with this method will be turned into a count value.
+// For example, total number of accepted requests can be
+// aggregated by using Count.
+func Count() *Aggregation {
+        return aggCount
+}
+
+// Sum indicates that data collected and aggregated
+// with this method will be summed up.
+// For example, accumulated request bytes can be aggregated by using
+// Sum.
+func Sum() *Aggregation {
+        return aggSum
+}
+
+// Distribution indicates that the desired aggregation is
+// a histogram distribution.
+//
+// An distribution aggregation may contain a histogram of the values in the
+// population. The bucket boundaries for that histogram are described
+// by the bounds. This defines len(bounds)+1 buckets.
+//
+// If len(bounds) >= 2 then the boundaries for bucket index i are:
+//
+//     [-infinity, bounds[i]) for i = 0
+//     [bounds[i-1], bounds[i]) for 0 < i < length
+//     [bounds[i-1], +infinity) for i = length
+//
+// If len(bounds) is 0 then there is no histogram associated with the
+// distribution. There will be a single bucket with boundaries
+// (-infinity, +infinity).
+//
+// If len(bounds) is 1 then there is no finite buckets, and that single
+// element is the common boundary of the overflow and underflow buckets.
+func Distribution(bounds ...float64) *Aggregation {
+        return &Aggregation{
+                Type:    AggTypeDistribution,
+                Buckets: bounds,
+                newData: func() AggregationData {
+                        return newDistributionData(bounds)
+                },
+        }
+}
+
+// LastValue only reports the last value recorded using this
+// aggregation. All other measurements will be dropped.
+func LastValue() *Aggregation {
+        return &Aggregation{
+                Type: AggTypeLastValue,
+                newData: func() AggregationData {
+                        return &LastValueData{}
+                },
+        }
+}
diff --git a/vendor/go.opencensus.io/stats/view/aggregation_data.go b/vendor/go.opencensus.io/stats/view/aggregation_data.go
new file mode 100644
index 0000000..960b946
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/aggregation_data.go
@@ -0,0 +1,235 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view
+
+import (
+        "math"
+
+        "go.opencensus.io/exemplar"
+)
+
+// AggregationData represents an aggregated value from a collection.
+// They are reported on the view data during exporting.
+// Mosts users won't directly access aggregration data.
+type AggregationData interface {
+        isAggregationData() bool
+        addSample(e *exemplar.Exemplar)
+        clone() AggregationData
+        equal(other AggregationData) bool
+}
+
+const epsilon = 1e-9
+
+// CountData is the aggregated data for the Count aggregation.
+// A count aggregation processes data and counts the recordings.
+//
+// Most users won't directly access count data.
+type CountData struct {
+        Value int64
+}
+
+func (a *CountData) isAggregationData() bool { return true }
+
+func (a *CountData) addSample(_ *exemplar.Exemplar) {
+        a.Value = a.Value + 1
+}
+
+func (a *CountData) clone() AggregationData {
+        return &CountData{Value: a.Value}
+}
+
+func (a *CountData) equal(other AggregationData) bool {
+        a2, ok := other.(*CountData)
+        if !ok {
+                return false
+        }
+
+        return a.Value == a2.Value
+}
+
+// SumData is the aggregated data for the Sum aggregation.
+// A sum aggregation processes data and sums up the recordings.
+//
+// Most users won't directly access sum data.
+type SumData struct {
+        Value float64
+}
+
+func (a *SumData) isAggregationData() bool { return true }
+
+func (a *SumData) addSample(e *exemplar.Exemplar) {
+        a.Value += e.Value
+}
+
+func (a *SumData) clone() AggregationData {
+        return &SumData{Value: a.Value}
+}
+
+func (a *SumData) equal(other AggregationData) bool {
+        a2, ok := other.(*SumData)
+        if !ok {
+                return false
+        }
+        return math.Pow(a.Value-a2.Value, 2) < epsilon
+}
+
+// DistributionData is the aggregated data for the
+// Distribution aggregation.
+//
+// Most users won't directly access distribution data.
+//
+// For a distribution with N bounds, the associated DistributionData will have
+// N+1 buckets.
+type DistributionData struct {
+        Count           int64   // number of data points aggregated
+        Min             float64 // minimum value in the distribution
+        Max             float64 // max value in the distribution
+        Mean            float64 // mean of the distribution
+        SumOfSquaredDev float64 // sum of the squared deviation from the mean
+        CountPerBucket  []int64 // number of occurrences per bucket
+        // ExemplarsPerBucket is slice the same length as CountPerBucket containing
+        // an exemplar for the associated bucket, or nil.
+        ExemplarsPerBucket []*exemplar.Exemplar
+        bounds             []float64 // histogram distribution of the values
+}
+
+func newDistributionData(bounds []float64) *DistributionData {
+        bucketCount := len(bounds) + 1
+        return &DistributionData{
+                CountPerBucket:     make([]int64, bucketCount),
+                ExemplarsPerBucket: make([]*exemplar.Exemplar, bucketCount),
+                bounds:             bounds,
+                Min:                math.MaxFloat64,
+                Max:                math.SmallestNonzeroFloat64,
+        }
+}
+
+// Sum returns the sum of all samples collected.
+func (a *DistributionData) Sum() float64 { return a.Mean * float64(a.Count) }
+
+func (a *DistributionData) variance() float64 {
+        if a.Count <= 1 {
+                return 0
+        }
+        return a.SumOfSquaredDev / float64(a.Count-1)
+}
+
+func (a *DistributionData) isAggregationData() bool { return true }
+
+func (a *DistributionData) addSample(e *exemplar.Exemplar) {
+        f := e.Value
+        if f < a.Min {
+                a.Min = f
+        }
+        if f > a.Max {
+                a.Max = f
+        }
+        a.Count++
+        a.addToBucket(e)
+
+        if a.Count == 1 {
+                a.Mean = f
+                return
+        }
+
+        oldMean := a.Mean
+        a.Mean = a.Mean + (f-a.Mean)/float64(a.Count)
+        a.SumOfSquaredDev = a.SumOfSquaredDev + (f-oldMean)*(f-a.Mean)
+}
+
+func (a *DistributionData) addToBucket(e *exemplar.Exemplar) {
+        var count *int64
+        var ex **exemplar.Exemplar
+        for i, b := range a.bounds {
+                if e.Value < b {
+                        count = &a.CountPerBucket[i]
+                        ex = &a.ExemplarsPerBucket[i]
+                        break
+                }
+        }
+        if count == nil {
+                count = &a.CountPerBucket[len(a.bounds)]
+                ex = &a.ExemplarsPerBucket[len(a.bounds)]
+        }
+        *count++
+        *ex = maybeRetainExemplar(*ex, e)
+}
+
+func maybeRetainExemplar(old, cur *exemplar.Exemplar) *exemplar.Exemplar {
+        if old == nil {
+                return cur
+        }
+
+        // Heuristic to pick the "better" exemplar: first keep the one with a
+        // sampled trace attachment, if neither have a trace attachment, pick the
+        // one with more attachments.
+        _, haveTraceID := cur.Attachments[exemplar.KeyTraceID]
+        if haveTraceID || len(cur.Attachments) >= len(old.Attachments) {
+                return cur
+        }
+        return old
+}
+
+func (a *DistributionData) clone() AggregationData {
+        c := *a
+        c.CountPerBucket = append([]int64(nil), a.CountPerBucket...)
+        c.ExemplarsPerBucket = append([]*exemplar.Exemplar(nil), a.ExemplarsPerBucket...)
+        return &c
+}
+
+func (a *DistributionData) equal(other AggregationData) bool {
+        a2, ok := other.(*DistributionData)
+        if !ok {
+                return false
+        }
+        if a2 == nil {
+                return false
+        }
+        if len(a.CountPerBucket) != len(a2.CountPerBucket) {
+                return false
+        }
+        for i := range a.CountPerBucket {
+                if a.CountPerBucket[i] != a2.CountPerBucket[i] {
+                        return false
+                }
+        }
+        return a.Count == a2.Count && a.Min == a2.Min && a.Max == a2.Max && math.Pow(a.Mean-a2.Mean, 2) < epsilon && math.Pow(a.variance()-a2.variance(), 2) < epsilon
+}
+
+// LastValueData returns the last value recorded for LastValue aggregation.
+type LastValueData struct {
+        Value float64
+}
+
+func (l *LastValueData) isAggregationData() bool {
+        return true
+}
+
+func (l *LastValueData) addSample(e *exemplar.Exemplar) {
+        l.Value = e.Value
+}
+
+func (l *LastValueData) clone() AggregationData {
+        return &LastValueData{l.Value}
+}
+
+func (l *LastValueData) equal(other AggregationData) bool {
+        a2, ok := other.(*LastValueData)
+        if !ok {
+                return false
+        }
+        return l.Value == a2.Value
+}
diff --git a/vendor/go.opencensus.io/stats/view/collector.go b/vendor/go.opencensus.io/stats/view/collector.go
new file mode 100644
index 0000000..32415d4
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/collector.go
@@ -0,0 +1,87 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view
+
+import (
+        "sort"
+
+        "go.opencensus.io/exemplar"
+
+        "go.opencensus.io/internal/tagencoding"
+        "go.opencensus.io/tag"
+)
+
+type collector struct {
+        // signatures holds the aggregations values for each unique tag signature
+        // (values for all keys) to its aggregator.
+        signatures map[string]AggregationData
+        // Aggregation is the description of the aggregation to perform for this
+        // view.
+        a *Aggregation
+}
+
+func (c *collector) addSample(s string, e *exemplar.Exemplar) {
+        aggregator, ok := c.signatures[s]
+        if !ok {
+                aggregator = c.a.newData()
+                c.signatures[s] = aggregator
+        }
+        aggregator.addSample(e)
+}
+
+// collectRows returns a snapshot of the collected Row values.
+func (c *collector) collectedRows(keys []tag.Key) []*Row {
+        rows := make([]*Row, 0, len(c.signatures))
+        for sig, aggregator := range c.signatures {
+                tags := decodeTags([]byte(sig), keys)
+                row := &Row{Tags: tags, Data: aggregator.clone()}
+                rows = append(rows, row)
+        }
+        return rows
+}
+
+func (c *collector) clearRows() {
+        c.signatures = make(map[string]AggregationData)
+}
+
+// encodeWithKeys encodes the map by using values
+// only associated with the keys provided.
+func encodeWithKeys(m *tag.Map, keys []tag.Key) []byte {
+        vb := &tagencoding.Values{
+                Buffer: make([]byte, len(keys)),
+        }
+        for _, k := range keys {
+                v, _ := m.Value(k)
+                vb.WriteValue([]byte(v))
+        }
+        return vb.Bytes()
+}
+
+// decodeTags decodes tags from the buffer and
+// orders them by the keys.
+func decodeTags(buf []byte, keys []tag.Key) []tag.Tag {
+        vb := &tagencoding.Values{Buffer: buf}
+        var tags []tag.Tag
+        for _, k := range keys {
+                v := vb.ReadValue()
+                if v != nil {
+                        tags = append(tags, tag.Tag{Key: k, Value: string(v)})
+                }
+        }
+        vb.ReadIndex = 0
+        sort.Slice(tags, func(i, j int) bool { return tags[i].Key.Name() < tags[j].Key.Name() })
+        return tags
+}
diff --git a/vendor/go.opencensus.io/stats/view/doc.go b/vendor/go.opencensus.io/stats/view/doc.go
new file mode 100644
index 0000000..dced225
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/doc.go
@@ -0,0 +1,47 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view contains support for collecting and exposing aggregates over stats.
+//
+// In order to collect measurements, views need to be defined and registered.
+// A view allows recorded measurements to be filtered and aggregated.
+//
+// All recorded measurements can be grouped by a list of tags.
+//
+// OpenCensus provides several aggregation methods: Count, Distribution and Sum.
+//
+// Count only counts the number of measurement points recorded.
+// Distribution provides statistical summary of the aggregated data by counting
+// how many recorded measurements fall into each bucket.
+// Sum adds up the measurement values.
+// LastValue just keeps track of the most recently recorded measurement value.
+// All aggregations are cumulative.
+//
+// Views can be registerd and unregistered at any time during program execution.
+//
+// Libraries can define views but it is recommended that in most cases registering
+// views be left up to applications.
+//
+// Exporting
+//
+// Collected and aggregated data can be exported to a metric collection
+// backend by registering its exporter.
+//
+// Multiple exporters can be registered to upload the data to various
+// different back ends.
+package view // import "go.opencensus.io/stats/view"
+
+// TODO(acetechnologist): Add a link to the language independent OpenCensus
+// spec when it is available.
diff --git a/vendor/go.opencensus.io/stats/view/export.go b/vendor/go.opencensus.io/stats/view/export.go
new file mode 100644
index 0000000..7cb5971
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/export.go
@@ -0,0 +1,58 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view
+
+import "sync"
+
+var (
+        exportersMu sync.RWMutex // guards exporters
+        exporters   = make(map[Exporter]struct{})
+)
+
+// Exporter exports the collected records as view data.
+//
+// The ExportView method should return quickly; if an
+// Exporter takes a significant amount of time to
+// process a Data, that work should be done on another goroutine.
+//
+// It is safe to assume that ExportView will not be called concurrently from
+// multiple goroutines.
+//
+// The Data should not be modified.
+type Exporter interface {
+        ExportView(viewData *Data)
+}
+
+// RegisterExporter registers an exporter.
+// Collected data will be reported via all the
+// registered exporters. Once you no longer
+// want data to be exported, invoke UnregisterExporter
+// with the previously registered exporter.
+//
+// Binaries can register exporters, libraries shouldn't register exporters.
+func RegisterExporter(e Exporter) {
+        exportersMu.Lock()
+        defer exportersMu.Unlock()
+
+        exporters[e] = struct{}{}
+}
+
+// UnregisterExporter unregisters an exporter.
+func UnregisterExporter(e Exporter) {
+        exportersMu.Lock()
+        defer exportersMu.Unlock()
+
+        delete(exporters, e)
+}
diff --git a/vendor/go.opencensus.io/stats/view/view.go b/vendor/go.opencensus.io/stats/view/view.go
new file mode 100644
index 0000000..c2a08af
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/view.go
@@ -0,0 +1,185 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view
+
+import (
+        "bytes"
+        "fmt"
+        "reflect"
+        "sort"
+        "sync/atomic"
+        "time"
+
+        "go.opencensus.io/exemplar"
+
+        "go.opencensus.io/stats"
+        "go.opencensus.io/stats/internal"
+        "go.opencensus.io/tag"
+)
+
+// View allows users to aggregate the recorded stats.Measurements.
+// Views need to be passed to the Register function to be before data will be
+// collected and sent to Exporters.
+type View struct {
+        Name        string // Name of View. Must be unique. If unset, will default to the name of the Measure.
+        Description string // Description is a human-readable description for this view.
+
+        // TagKeys are the tag keys describing the grouping of this view.
+        // A single Row will be produced for each combination of associated tag values.
+        TagKeys []tag.Key
+
+        // Measure is a stats.Measure to aggregate in this view.
+        Measure stats.Measure
+
+        // Aggregation is the aggregation function tp apply to the set of Measurements.
+        Aggregation *Aggregation
+}
+
+// WithName returns a copy of the View with a new name. This is useful for
+// renaming views to cope with limitations placed on metric names by various
+// backends.
+func (v *View) WithName(name string) *View {
+        vNew := *v
+        vNew.Name = name
+        return &vNew
+}
+
+// same compares two views and returns true if they represent the same aggregation.
+func (v *View) same(other *View) bool {
+        if v == other {
+                return true
+        }
+        if v == nil {
+                return false
+        }
+        return reflect.DeepEqual(v.Aggregation, other.Aggregation) &&
+                v.Measure.Name() == other.Measure.Name()
+}
+
+// canonicalize canonicalizes v by setting explicit
+// defaults for Name and Description and sorting the TagKeys
+func (v *View) canonicalize() error {
+        if v.Measure == nil {
+                return fmt.Errorf("cannot register view %q: measure not set", v.Name)
+        }
+        if v.Aggregation == nil {
+                return fmt.Errorf("cannot register view %q: aggregation not set", v.Name)
+        }
+        if v.Name == "" {
+                v.Name = v.Measure.Name()
+        }
+        if v.Description == "" {
+                v.Description = v.Measure.Description()
+        }
+        if err := checkViewName(v.Name); err != nil {
+                return err
+        }
+        sort.Slice(v.TagKeys, func(i, j int) bool {
+                return v.TagKeys[i].Name() < v.TagKeys[j].Name()
+        })
+        return nil
+}
+
+// viewInternal is the internal representation of a View.
+type viewInternal struct {
+        view       *View  // view is the canonicalized View definition associated with this view.
+        subscribed uint32 // 1 if someone is subscribed and data need to be exported, use atomic to access
+        collector  *collector
+}
+
+func newViewInternal(v *View) (*viewInternal, error) {
+        return &viewInternal{
+                view:      v,
+                collector: &collector{make(map[string]AggregationData), v.Aggregation},
+        }, nil
+}
+
+func (v *viewInternal) subscribe() {
+        atomic.StoreUint32(&v.subscribed, 1)
+}
+
+func (v *viewInternal) unsubscribe() {
+        atomic.StoreUint32(&v.subscribed, 0)
+}
+
+// isSubscribed returns true if the view is exporting
+// data by subscription.
+func (v *viewInternal) isSubscribed() bool {
+        return atomic.LoadUint32(&v.subscribed) == 1
+}
+
+func (v *viewInternal) clearRows() {
+        v.collector.clearRows()
+}
+
+func (v *viewInternal) collectedRows() []*Row {
+        return v.collector.collectedRows(v.view.TagKeys)
+}
+
+func (v *viewInternal) addSample(m *tag.Map, e *exemplar.Exemplar) {
+        if !v.isSubscribed() {
+                return
+        }
+        sig := string(encodeWithKeys(m, v.view.TagKeys))
+        v.collector.addSample(sig, e)
+}
+
+// A Data is a set of rows about usage of the single measure associated
+// with the given view. Each row is specific to a unique set of tags.
+type Data struct {
+        View       *View
+        Start, End time.Time
+        Rows       []*Row
+}
+
+// Row is the collected value for a specific set of key value pairs a.k.a tags.
+type Row struct {
+        Tags []tag.Tag
+        Data AggregationData
+}
+
+func (r *Row) String() string {
+        var buffer bytes.Buffer
+        buffer.WriteString("{ ")
+        buffer.WriteString("{ ")
+        for _, t := range r.Tags {
+                buffer.WriteString(fmt.Sprintf("{%v %v}", t.Key.Name(), t.Value))
+        }
+        buffer.WriteString(" }")
+        buffer.WriteString(fmt.Sprintf("%v", r.Data))
+        buffer.WriteString(" }")
+        return buffer.String()
+}
+
+// Equal returns true if both rows are equal. Tags are expected to be ordered
+// by the key name. Even both rows have the same tags but the tags appear in
+// different orders it will return false.
+func (r *Row) Equal(other *Row) bool {
+        if r == other {
+                return true
+        }
+        return reflect.DeepEqual(r.Tags, other.Tags) && r.Data.equal(other.Data)
+}
+
+func checkViewName(name string) error {
+        if len(name) > internal.MaxNameLength {
+                return fmt.Errorf("view name cannot be larger than %v", internal.MaxNameLength)
+        }
+        if !internal.IsPrintable(name) {
+                return fmt.Errorf("view name needs to be an ASCII string")
+        }
+        return nil
+}
diff --git a/vendor/go.opencensus.io/stats/view/worker.go b/vendor/go.opencensus.io/stats/view/worker.go
new file mode 100644
index 0000000..63b0ee3
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/worker.go
@@ -0,0 +1,229 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view
+
+import (
+        "fmt"
+        "time"
+
+        "go.opencensus.io/stats"
+        "go.opencensus.io/stats/internal"
+        "go.opencensus.io/tag"
+)
+
+func init() {
+        defaultWorker = newWorker()
+        go defaultWorker.start()
+        internal.DefaultRecorder = record
+}
+
+type measureRef struct {
+        measure string
+        views   map[*viewInternal]struct{}
+}
+
+type worker struct {
+        measures   map[string]*measureRef
+        views      map[string]*viewInternal
+        startTimes map[*viewInternal]time.Time
+
+        timer      *time.Ticker
+        c          chan command
+        quit, done chan bool
+}
+
+var defaultWorker *worker
+
+var defaultReportingDuration = 10 * time.Second
+
+// Find returns a registered view associated with this name.
+// If no registered view is found, nil is returned.
+func Find(name string) (v *View) {
+        req := &getViewByNameReq{
+                name: name,
+                c:    make(chan *getViewByNameResp),
+        }
+        defaultWorker.c <- req
+        resp := <-req.c
+        return resp.v
+}
+
+// Register begins collecting data for the given views.
+// Once a view is registered, it reports data to the registered exporters.
+func Register(views ...*View) error {
+        for _, v := range views {
+                if err := v.canonicalize(); err != nil {
+                        return err
+                }
+        }
+        req := &registerViewReq{
+                views: views,
+                err:   make(chan error),
+        }
+        defaultWorker.c <- req
+        return <-req.err
+}
+
+// Unregister the given views. Data will not longer be exported for these views
+// after Unregister returns.
+// It is not necessary to unregister from views you expect to collect for the
+// duration of your program execution.
+func Unregister(views ...*View) {
+        names := make([]string, len(views))
+        for i := range views {
+                names[i] = views[i].Name
+        }
+        req := &unregisterFromViewReq{
+                views: names,
+                done:  make(chan struct{}),
+        }
+        defaultWorker.c <- req
+        <-req.done
+}
+
+// RetrieveData gets a snapshot of the data collected for the the view registered
+// with the given name. It is intended for testing only.
+func RetrieveData(viewName string) ([]*Row, error) {
+        req := &retrieveDataReq{
+                now: time.Now(),
+                v:   viewName,
+                c:   make(chan *retrieveDataResp),
+        }
+        defaultWorker.c <- req
+        resp := <-req.c
+        return resp.rows, resp.err
+}
+
+func record(tags *tag.Map, ms interface{}, attachments map[string]string) {
+        req := &recordReq{
+                tm:          tags,
+                ms:          ms.([]stats.Measurement),
+                attachments: attachments,
+                t:           time.Now(),
+        }
+        defaultWorker.c <- req
+}
+
+// SetReportingPeriod sets the interval between reporting aggregated views in
+// the program. If duration is less than or equal to zero, it enables the
+// default behavior.
+//
+// Note: each exporter makes different promises about what the lowest supported
+// duration is. For example, the Stackdriver exporter recommends a value no
+// lower than 1 minute. Consult each exporter per your needs.
+func SetReportingPeriod(d time.Duration) {
+        // TODO(acetechnologist): ensure that the duration d is more than a certain
+        // value. e.g. 1s
+        req := &setReportingPeriodReq{
+                d: d,
+                c: make(chan bool),
+        }
+        defaultWorker.c <- req
+        <-req.c // don't return until the timer is set to the new duration.
+}
+
+func newWorker() *worker {
+        return &worker{
+                measures:   make(map[string]*measureRef),
+                views:      make(map[string]*viewInternal),
+                startTimes: make(map[*viewInternal]time.Time),
+                timer:      time.NewTicker(defaultReportingDuration),
+                c:          make(chan command, 1024),
+                quit:       make(chan bool),
+                done:       make(chan bool),
+        }
+}
+
+func (w *worker) start() {
+        for {
+                select {
+                case cmd := <-w.c:
+                        cmd.handleCommand(w)
+                case <-w.timer.C:
+                        w.reportUsage(time.Now())
+                case <-w.quit:
+                        w.timer.Stop()
+                        close(w.c)
+                        w.done <- true
+                        return
+                }
+        }
+}
+
+func (w *worker) stop() {
+        w.quit <- true
+        <-w.done
+}
+
+func (w *worker) getMeasureRef(name string) *measureRef {
+        if mr, ok := w.measures[name]; ok {
+                return mr
+        }
+        mr := &measureRef{
+                measure: name,
+                views:   make(map[*viewInternal]struct{}),
+        }
+        w.measures[name] = mr
+        return mr
+}
+
+func (w *worker) tryRegisterView(v *View) (*viewInternal, error) {
+        vi, err := newViewInternal(v)
+        if err != nil {
+                return nil, err
+        }
+        if x, ok := w.views[vi.view.Name]; ok {
+                if !x.view.same(vi.view) {
+                        return nil, fmt.Errorf("cannot register view %q; a different view with the same name is already registered", v.Name)
+                }
+
+                // the view is already registered so there is nothing to do and the
+                // command is considered successful.
+                return x, nil
+        }
+        w.views[vi.view.Name] = vi
+        ref := w.getMeasureRef(vi.view.Measure.Name())
+        ref.views[vi] = struct{}{}
+        return vi, nil
+}
+
+func (w *worker) reportView(v *viewInternal, now time.Time) {
+        if !v.isSubscribed() {
+                return
+        }
+        rows := v.collectedRows()
+        _, ok := w.startTimes[v]
+        if !ok {
+                w.startTimes[v] = now
+        }
+        viewData := &Data{
+                View:  v.view,
+                Start: w.startTimes[v],
+                End:   time.Now(),
+                Rows:  rows,
+        }
+        exportersMu.Lock()
+        for e := range exporters {
+                e.ExportView(viewData)
+        }
+        exportersMu.Unlock()
+}
+
+func (w *worker) reportUsage(now time.Time) {
+        for _, v := range w.views {
+                w.reportView(v, now)
+        }
+}
diff --git a/vendor/go.opencensus.io/stats/view/worker_commands.go b/vendor/go.opencensus.io/stats/view/worker_commands.go
new file mode 100644
index 0000000..b38f26f
--- /dev/null
+++ b/vendor/go.opencensus.io/stats/view/worker_commands.go
@@ -0,0 +1,183 @@
+// Copyright 2017, OpenCensus Authors
+//
+// 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 view
+
+import (
+        "errors"
+        "fmt"
+        "strings"
+        "time"
+
+        "go.opencensus.io/exemplar"
+
+        "go.opencensus.io/stats"
+        "go.opencensus.io/stats/internal"
+        "go.opencensus.io/tag"
+)
+
+type command interface {
+        handleCommand(w *worker)
+}
+
+// getViewByNameReq is the command to get a view given its name.
+type getViewByNameReq struct {
+        name string
+        c    chan *getViewByNameResp
+}
+
+type getViewByNameResp struct {
+        v *View
+}
+
+func (cmd *getViewByNameReq) handleCommand(w *worker) {
+        v := w.views[cmd.name]
+        if v == nil {
+                cmd.c <- &getViewByNameResp{nil}
+                return
+        }
+        cmd.c <- &getViewByNameResp{v.view}
+}
+
+// registerViewReq is the command to register a view.
+type registerViewReq struct {
+        views []*View
+        err   chan error
+}
+
+func (cmd *registerViewReq) handleCommand(w *worker) {
+        var errstr []string
+        for _, view := range cmd.views {
+                vi, err := w.tryRegisterView(view)
+                if err != nil {
+                        errstr = append(errstr, fmt.Sprintf("%s: %v", view.Name, err))
+                        continue
+                }
+                internal.SubscriptionReporter(view.Measure.Name())
+                vi.subscribe()
+        }
+        if len(errstr) > 0 {
+                cmd.err <- errors.New(strings.Join(errstr, "\n"))
+        } else {
+                cmd.err <- nil
+        }
+}
+
+// unregisterFromViewReq is the command to unregister to a view. Has no
+// impact on the data collection for client that are pulling data from the
+// library.
+type unregisterFromViewReq struct {
+        views []string
+        done  chan struct{}
+}
+
+func (cmd *unregisterFromViewReq) handleCommand(w *worker) {
+        for _, name := range cmd.views {
+                vi, ok := w.views[name]
+                if !ok {
+                        continue
+                }
+
+                // Report pending data for this view before removing it.
+                w.reportView(vi, time.Now())
+
+                vi.unsubscribe()
+                if !vi.isSubscribed() {
+                        // this was the last subscription and view is not collecting anymore.
+                        // The collected data can be cleared.
+                        vi.clearRows()
+                }
+                delete(w.views, name)
+        }
+        cmd.done <- struct{}{}
+}
+
+// retrieveDataReq is the command to retrieve data for a view.
+type retrieveDataReq struct {
+        now time.Time
+        v   string
+        c   chan *retrieveDataResp
+}
+
+type retrieveDataResp struct {
+        rows []*Row
+        err  error
+}
+
+func (cmd *retrieveDataReq) handleCommand(w *worker) {
+        vi, ok := w.views[cmd.v]
+        if !ok {
+                cmd.c <- &retrieveDataResp{
+                        nil,
+                        fmt.Errorf("cannot retrieve data; view %q is not registered", cmd.v),
+                }
+                return
+        }
+
+        if !vi.isSubscribed() {
+                cmd.c <- &retrieveDataResp{
+                        nil,
+                        fmt.Errorf("cannot retrieve data; view %q has no subscriptions or collection is not forcibly started", cmd.v),
+                }
+                return
+        }
+        cmd.c <- &retrieveDataResp{
+                vi.collectedRows(),
+                nil,
+        }
+}
+
+// recordReq is the command to record data related to multiple measures
+// at once.
+type recordReq struct {
+        tm          *tag.Map
+        ms          []stats.Measurement
+        attachments map[string]string
+        t           time.Time
+}
+
+func (cmd *recordReq) handleCommand(w *worker) {
+        for _, m := range cmd.ms {
+                if (m == stats.Measurement{}) { // not registered
+                        continue
+                }
+                ref := w.getMeasureRef(m.Measure().Name())
+                for v := range ref.views {
+                        e := &exemplar.Exemplar{
+                                Value:       m.Value(),
+                                Timestamp:   cmd.t,
+                                Attachments: cmd.attachments,
+                        }
+                        v.addSample(cmd.tm, e)
+                }
+        }
+}
+
+// setReportingPeriodReq is the command to modify the duration between
+// reporting the collected data to the registered clients.
+type setReportingPeriodReq struct {
+        d time.Duration
+        c chan bool
+}
+
+func (cmd *setReportingPeriodReq) handleCommand(w *worker) {
+        w.timer.Stop()
+        if cmd.d <= 0 {
+                w.timer = time.NewTicker(defaultReportingDuration)
+        } else {
+                w.timer = time.NewTicker(cmd.d)
+        }
+        cmd.c <- true
+}