Restore the experimental/streaming SDK implementation (#55)

* Fix streaming - part 1

* Eliminate span{} state

* Eliminate trace/ dir

* Avoid missing AddEvent helpers

experimental/streaming/sdk/span.go

@@ -0,0 +1,122 @@
+// 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 sdk
+
+import (
+	"context"
+
+	"google.golang.org/grpc/codes"
+
+	"go.opentelemetry.io/api/core"
+	"go.opentelemetry.io/api/event"
+	"go.opentelemetry.io/api/tag"
+	apitrace "go.opentelemetry.io/api/trace"
+	"go.opentelemetry.io/experimental/streaming/exporter/observer"
+)
+
+type span struct {
+	tracer  *tracer
+	initial observer.ScopeID
+}
+
+// SpancContext returns span context of the span. Return SpanContext is usable
+// even after the span is finished.
+func (sp *span) SpanContext() core.SpanContext {
+	return sp.initial.SpanContext
+}
+
+// IsRecordingEvents returns true is the span is active and recording events is enabled.
+func (sp *span) IsRecordingEvents() bool {
+	return false
+}
+
+// SetStatus sets the status of the span.
+func (sp *span) SetStatus(status codes.Code) {
+	observer.Record(observer.Event{
+		Type:   observer.SET_STATUS,
+		Scope:  sp.ScopeID(),
+		Status: status,
+	})
+}
+
+func (sp *span) ScopeID() observer.ScopeID {
+	return sp.initial
+}
+
+func (sp *span) SetAttribute(attribute core.KeyValue) {
+	observer.Record(observer.Event{
+		Type:      observer.MODIFY_ATTR,
+		Scope:     sp.ScopeID(),
+		Attribute: attribute,
+	})
+}
+
+func (sp *span) SetAttributes(attributes ...core.KeyValue) {
+	observer.Record(observer.Event{
+		Type:       observer.MODIFY_ATTR,
+		Scope:      sp.ScopeID(),
+		Attributes: attributes,
+	})
+}
+
+func (sp *span) ModifyAttribute(mutator tag.Mutator) {
+	observer.Record(observer.Event{
+		Type:    observer.MODIFY_ATTR,
+		Scope:   sp.ScopeID(),
+		Mutator: mutator,
+	})
+}
+
+func (sp *span) ModifyAttributes(mutators ...tag.Mutator) {
+	observer.Record(observer.Event{
+		Type:     observer.MODIFY_ATTR,
+		Scope:    sp.ScopeID(),
+		Mutators: mutators,
+	})
+}
+
+func (sp *span) Finish() {
+	recovered := recover()
+	observer.Record(observer.Event{
+		Type:      observer.FINISH_SPAN,
+		Scope:     sp.ScopeID(),
+		Recovered: recovered,
+	})
+	if recovered != nil {
+		panic(recovered)
+	}
+}
+
+func (sp *span) Tracer() apitrace.Tracer {
+	return sp.tracer
+}
+
+func (sp *span) AddEvent(ctx context.Context, event event.Event) {
+	observer.Record(observer.Event{
+		Type:       observer.ADD_EVENT,
+		String:     event.Message(),
+		Attributes: event.Attributes(),
+		Context:    ctx,
+	})
+}
+
+func (sp *span) Event(ctx context.Context, msg string, attrs ...core.KeyValue) {
+	observer.Record(observer.Event{
+		Type:       observer.ADD_EVENT,
+		String:     msg,
+		Attributes: attrs,
+		Context:    ctx,
+	})
+}