Add propagator interface and W3C propagator (#85)

* add propagation api.

* add http propagator interface and w3c propagator implementation.

* remove Extract api from trace.

* remove Extract interface for tracer.

* fix copyright.

* fix variable names and comments.

* move inject/extract out of trace.

* replace INVALID_SPAN_CONTEXT with EmptySpanContext function.

* fix tag.Map.

* make carrier as interface instead of http.Request.

* rename structs and update doc comments..

* add doc.go

* update doc.

* add noop propagator.

* add new propagation api with Supplier interface.
- added Default Tracer which simply propagates SpanContext.
- added CopyOfRemote option to simply create remote span.

* remove old propagator.

* rename propagator to TextFormatPropagator.

* rename default tracer/span as pass_through tracer/span.

* add test for pass through tracer.

* add missing interface to pass through tracer.

* return SpanContext instead of contex.Context from Extract interface.
- also remove PassThroughTracer

* fix review comments.

* add more test cases for traceContext extraction.

* remove tidy temporarily from circle-ci target to avoid build failure.

* allow header ending in dash '-'.

* add inject test for non-zero value other than 01 for traceoption

* add AddLink and Link interface to MockSpan

* fix running go mod tidy on every build.

internal/trace/mock_span.go

@@ -0,0 +1,96 @@
+// Copyright 2019, OpenTelemetry 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 trace
+
+import (
+	"context"
+
+	"google.golang.org/grpc/codes"
+
+	"go.opentelemetry.io/api/core"
+	"go.opentelemetry.io/api/tag"
+	apitrace "go.opentelemetry.io/api/trace"
+)
+
+// MockSpan is a mock span used in association with MockTracer for testing purpose only.
+type MockSpan struct {
+	sc     core.SpanContext
+	tracer apitrace.Tracer
+}
+
+var _ apitrace.Span = (*MockSpan)(nil)
+
+// SpanContext returns associated core.SpanContext. If the receiver is nil it returns
+// an empty core.SpanContext
+func (ms *MockSpan) SpanContext() core.SpanContext {
+	if ms == nil {
+		core.EmptySpanContext()
+	}
+	return ms.sc
+}
+
+// IsRecordingEvents always returns false for MockSpan.
+func (ms *MockSpan) IsRecordingEvents() bool {
+	return false
+}
+
+// SetStatus does nothing.
+func (ms *MockSpan) SetStatus(status codes.Code) {
+}
+
+// SetError does nothing.
+func (ms *MockSpan) SetError(v bool) {
+}
+
+// SetAttribute does nothing.
+func (ms *MockSpan) SetAttribute(attribute core.KeyValue) {
+}
+
+// SetAttributes does nothing.
+func (ms *MockSpan) SetAttributes(attributes ...core.KeyValue) {
+}
+
+// ModifyAttribute does nothing.
+func (ms *MockSpan) ModifyAttribute(mutator tag.Mutator) {
+}
+
+// ModifyAttributes does nothing.
+func (ms *MockSpan) ModifyAttributes(mutators ...tag.Mutator) {
+}
+
+// Finish does nothing.
+func (ms *MockSpan) Finish(options ...apitrace.FinishOption) {
+}
+
+// SetName does nothing.
+func (ms *MockSpan) SetName(name string) {
+}
+
+// Tracer returns MockTracer implementation of Tracer.
+func (ms *MockSpan) Tracer() apitrace.Tracer {
+	return ms.tracer
+}
+
+// AddEvent does nothing.
+func (ms *MockSpan) AddEvent(ctx context.Context, msg string, attrs ...core.KeyValue) {
+}
+
+// AddLink does nothing.
+func (ms *MockSpan) AddLink(link apitrace.Link) {
+}
+
+// Link does nothing.
+func (ms *MockSpan) Link(sc core.SpanContext, attrs ...core.KeyValue) {
+}

internal/trace/mock_tracer.go

@@ -0,0 +1,91 @@
+// Copyright 2019, OpenTelemetry 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 trace
+
+import (
+	"context"
+	"math/rand"
+	"sync/atomic"
+
+	"go.opentelemetry.io/api/core"
+	apitrace "go.opentelemetry.io/api/trace"
+)
+
+// MockTracer is a simple tracer used for testing purpose only.
+// It only supports ChildOf option. SpanId is atomically increased every time a
+// new span is created.
+type MockTracer struct {
+	// Sampled specifies if the new span should be sampled or not.
+	Sampled bool
+
+	// StartSpanId is used to initialize spanId. It is incremented by one
+	// every time a new span is created.
+	StartSpanId *uint64
+}
+
+var _ apitrace.Tracer = (*MockTracer)(nil)
+
+// WithResources does nothing and returns MockTracer implementation of Tracer.
+func (mt *MockTracer) WithResources(attributes ...core.KeyValue) apitrace.Tracer {
+	return mt
+}
+
+// WithComponent does nothing and returns MockTracer implementation of Tracer.
+func (mt *MockTracer) WithComponent(name string) apitrace.Tracer {
+	return mt
+}
+
+// WithService does nothing and returns MockTracer implementation of Tracer.
+func (mt *MockTracer) WithService(name string) apitrace.Tracer {
+	return mt
+}
+
+// WithSpan does nothing except executing the body.
+func (mt *MockTracer) WithSpan(ctx context.Context, name string, body func(context.Context) error) error {
+	return body(ctx)
+}
+
+// Start starts a MockSpan. It creates a new Span based on Reference SpanContext option.
+// TracdID is used from Reference Span Context and SpanID is assigned.
+// If Reference SpanContext option is not specified then random TraceID is used.
+// No other options are supported.
+func (mt *MockTracer) Start(ctx context.Context, name string, o ...apitrace.SpanOption) (context.Context, apitrace.Span) {
+	var opts apitrace.SpanOptions
+	for _, op := range o {
+		op(&opts)
+	}
+	var span *MockSpan
+	var sc core.SpanContext
+	if !opts.Reference.SpanContext.IsValid() {
+		sc = core.SpanContext{
+			TraceID: core.TraceID{
+				High: rand.Uint64(),
+				Low:  rand.Uint64(),
+			},
+		}
+		if mt.Sampled {
+			sc.TraceOptions = core.TraceOptionSampled
+		}
+	} else {
+		sc = opts.Reference.SpanContext
+	}
+	sc.SpanID = atomic.AddUint64(mt.StartSpanId, 1)
+	span = &MockSpan{
+		sc:     sc,
+		tracer: mt,
+	}
+
+	return apitrace.SetCurrentSpan(ctx, span), span
+}