Move baggage and propagation to separate packages (#1325)

* Move propagation code to propagation package

* Move baggage code to baggage package

* Update changelog

* Make docs of baggage.Set more clear

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

baggage/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 baggage // import "go.opentelemetry.io/otel/baggage"
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/internal/baggage"
+	"go.opentelemetry.io/otel/label"
+)
+
+// Set returns a copy of the set of baggage key-values in ctx.
+func Set(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...)
+}
+
+// Value 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 Value(ctx context.Context, key label.Key) label.Value {
+	v, _ := baggage.MapFromContext(ctx).Value(key)
+	return v
+}
+
+// ContextWithValues returns a copy of parent with pairs updated in the baggage.
+func ContextWithValues(parent context.Context, pairs ...label.KeyValue) context.Context {
+	m := baggage.MapFromContext(parent).Apply(baggage.MapUpdate{
+		MultiKV: pairs,
+	})
+	return baggage.ContextWithMap(parent, m)
+}
+
+// ContextWithoutValues returns a copy of parent in which the values related
+// to keys have been removed from the baggage.
+func ContextWithoutValues(parent context.Context, keys ...label.Key) context.Context {
+	m := baggage.MapFromContext(parent).Apply(baggage.MapUpdate{
+		DropMultiK: keys,
+	})
+	return baggage.ContextWithMap(parent, m)
+}
+
+// ContextWithEmpty returns a copy of parent without baggage.
+func ContextWithEmpty(parent context.Context) context.Context {
+	return baggage.ContextWithNoCorrelationData(parent)
+}

baggage/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 baggage
+
+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 := Set(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 = ContextWithValues(ctx, first.Bool(true), second.String("2"))
+	m := baggage.MapFromContext(ctx)
+	v, ok := m.Value(first)
+	if !ok {
+		t.Fatal("WithValues failed to set first value")
+	}
+	if !v.AsBool() {
+		t.Fatal("WithValues failed to set first correct value")
+	}
+	v, ok = m.Value(second)
+	if !ok {
+		t.Fatal("WithValues failed to set second value")
+	}
+	if v.AsString() != "2" {
+		t.Fatal("WithValues failed to set second correct value")
+	}
+	_, ok = m.Value(third)
+	if ok {
+		t.Fatal("WithValues set an unexpected third value")
+	}
+
+	b = Set(ctx)
+	if b.Len() != 2 {
+		t.Fatalf("Baggage returned a set with %d elements, want 2", b.Len())
+	}
+
+	v = Value(ctx, first)
+	if v.Type() != label.BOOL || !v.AsBool() {
+		t.Fatal("Value failed to get correct first value")
+	}
+	v = Value(ctx, second)
+	if v.Type() != label.STRING || v.AsString() != "2" {
+		t.Fatal("Value failed to get correct second value")
+	}
+
+	ctx = ContextWithoutValues(ctx, first)
+	m = baggage.MapFromContext(ctx)
+	_, ok = m.Value(first)
+	if ok {
+		t.Fatal("WithoutValues failed to remove a baggage value")
+	}
+	_, ok = m.Value(second)
+	if !ok {
+		t.Fatal("WithoutValues removed incorrect value")
+	}
+
+	ctx = ContextWithEmpty(ctx)
+	m = baggage.MapFromContext(ctx)
+	if m.Len() != 0 {
+		t.Fatal("WithoutBaggage failed to clear baggage")
+	}
+}