Add Baggage API and move Baggage propagator (#1217)

* Move api/baggage to the propagators package

* Create Baggage API to match specification

* Update CHANGELOG.md

* Baggage API unit tests

* Rename and add unit test

* Update unit test value checking

* Update TODO with issue tracking work.

CHANGELOG.md

@@ -11,19 +11,22 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - OTLP Metric exporter supports Histogram aggregation. (#1209)
+- A Baggage API to implement the OpenTelemetry specification. (#1217)
 
 ### Changed
 
 - Set default propagator to no-op propagator. (#1184)
 - The `HTTPSupplier`, `HTTPExtractor`, `HTTPInjector`, and `HTTPPropagator` from the `go.opentelemetry.io/otel/api/propagation` package were replaced with unified `TextMapCarrier` and `TextMapPropagator` in the `go.opentelemetry.io/otel` package. (#1212)
 - The `New` function from the `go.opentelemetry.io/otel/api/propagation` package was replaced with `NewCompositeTextMapPropagator` in the `go.opentelemetry.io/otel` package. (#1212)
+- Move the `go.opentelemetry.io/otel/api/baggage` package into `go.opentelemetry.io/otel/propagators`. (#1217)
 
 ### Removed
 
 - The `ExtractHTTP` and `InjectHTTP` fuctions from the `go.opentelemetry.io/otel/api/propagation` package were removed. (#1212)
 - The `Propagators` interface from the `go.opentelemetry.io/otel/api/propagation` package was removed to conform to the OpenTelemetry specification.
    The explicit `TextMapPropagator` type can be used in its place as this is the `Propagator` type the specification defines. (#1212)
 - The `SetAttribute` method of the `Span` from the `go.opentelemetry.io/otel/api/trace` package was removed given its redundancy with the `SetAttributes` method. (#1216)
+- The internal implementation of Baggage storage is removed in favor of using the new Baggage API functionality. (#1217)
 - Remove duplicate hostname key `HostHostNameKey` in Resource semantic conventions. (#1219)
 
 ## [0.12.0] - 2020-09-24

baggage.go

@@ -0,0 +1,67 @@
+// Copyright The 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 otel
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/internal/baggage"
+	"go.opentelemetry.io/otel/label"
+)
+
+// Baggage returns a copy of the baggage in ctx.
+func Baggage(ctx context.Context) label.Set {
+	// TODO (MrAlias, #1222): The underlying storage, the Map, shares many of
+	// the functional elements of the label.Set. These should be unified so
+	// this conversion is unnecessary and there is no performance hit calling
+	// this.
+	m := baggage.MapFromContext(ctx)
+	values := make([]label.KeyValue, 0, m.Len())
+	m.Foreach(func(kv label.KeyValue) bool {
+		values = append(values, kv)
+		return true
+	})
+	return label.NewSet(values...)
+}
+
+// BaggageValue returns the value related to key in the baggage of ctx. If no
+// value is set, the returned label.Value will be an uninitialized zero-value
+// with type INVALID.
+func BaggageValue(ctx context.Context, key label.Key) label.Value {
+	v, _ := baggage.MapFromContext(ctx).Value(key)
+	return v
+}
+
+// ContextWithBaggageValues returns a copy of parent with pairs updated in the baggage.
+func ContextWithBaggageValues(parent context.Context, pairs ...label.KeyValue) context.Context {
+	m := baggage.MapFromContext(parent).Apply(baggage.MapUpdate{
+		MultiKV: pairs,
+	})
+	return baggage.ContextWithMap(parent, m)
+}
+
+// ContextWithoutBaggageValues returns a copy of parent in which the values related
+// to keys have been removed from the baggage.
+func ContextWithoutBaggageValues(parent context.Context, keys ...label.Key) context.Context {
+	m := baggage.MapFromContext(parent).Apply(baggage.MapUpdate{
+		DropMultiK: keys,
+	})
+	return baggage.ContextWithMap(parent, m)
+}
+
+// ContextWithoutBaggage returns a copy of parent without baggage.
+func ContextWithoutBaggage(parent context.Context) context.Context {
+	return baggage.ContextWithNoCorrelationData(parent)
+}

baggage_test.go

@@ -0,0 +1,86 @@
+// Copyright The 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 otel
+
+import (
+	"context"
+	"testing"
+
+	"go.opentelemetry.io/otel/internal/baggage"
+	"go.opentelemetry.io/otel/label"
+)
+
+func TestBaggage(t *testing.T) {
+	ctx := context.Background()
+	ctx = baggage.ContextWithMap(ctx, baggage.NewEmptyMap())
+
+	b := Baggage(ctx)
+	if b.Len() != 0 {
+		t.Fatalf("empty baggage returned a set with %d elements", b.Len())
+	}
+
+	first, second, third := label.Key("first"), label.Key("second"), label.Key("third")
+	ctx = ContextWithBaggageValues(ctx, first.Bool(true), second.String("2"))
+	m := baggage.MapFromContext(ctx)
+	v, ok := m.Value(first)
+	if !ok {
+		t.Fatal("WithBaggageValues failed to set first value")
+	}
+	if !v.AsBool() {
+		t.Fatal("WithBaggageValues failed to set first correct value")
+	}
+	v, ok = m.Value(second)
+	if !ok {
+		t.Fatal("WithBaggageValues failed to set second value")
+	}
+	if v.AsString() != "2" {
+		t.Fatal("WithBaggageValues failed to set second correct value")
+	}
+	_, ok = m.Value(third)
+	if ok {
+		t.Fatal("WithBaggageValues set an unexpected third value")
+	}
+
+	b = Baggage(ctx)
+	if b.Len() != 2 {
+		t.Fatalf("Baggage returned a set with %d elements, want 2", b.Len())
+	}
+
+	v = BaggageValue(ctx, first)
+	if v.Type() != label.BOOL || !v.AsBool() {
+		t.Fatal("BaggageValue failed to get correct first value")
+	}
+	v = BaggageValue(ctx, second)
+	if v.Type() != label.STRING || v.AsString() != "2" {
+		t.Fatal("BaggageValue failed to get correct second value")
+	}
+
+	ctx = ContextWithoutBaggageValues(ctx, first)
+	m = baggage.MapFromContext(ctx)
+	_, ok = m.Value(first)
+	if ok {
+		t.Fatal("WithoutBaggageValues failed to remove a baggage value")
+	}
+	_, ok = m.Value(second)
+	if !ok {
+		t.Fatal("WithoutBaggageValues removed incorrect value")
+	}
+
+	ctx = ContextWithoutBaggage(ctx)
+	m = baggage.MapFromContext(ctx)
+	if m.Len() != 0 {
+		t.Fatal("WithoutBaggage failed to clear baggage")
+	}
+}