From 6db714adc4a5925b45582e85890f1fbeb8f2477d Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 13:33:00 -0700
Subject: [PATCH 01/22] Add autoprop module

---
 propagators/autoprop/doc.go        |  23 ++++++
 propagators/autoprop/go.mod        |  11 +++
 propagators/autoprop/go.sum        |  42 ++++++++++
 propagators/autoprop/propagator.go | 121 +++++++++++++++++++++++++++++
 propagators/autoprop/registry.go   |  86 ++++++++++++++++++++
 5 files changed, 283 insertions(+)
 create mode 100644 propagators/autoprop/doc.go
 create mode 100644 propagators/autoprop/go.mod
 create mode 100644 propagators/autoprop/go.sum
 create mode 100644 propagators/autoprop/propagator.go
 create mode 100644 propagators/autoprop/registry.go

diff --git a/propagators/autoprop/doc.go b/propagators/autoprop/doc.go
new file mode 100644
index 00000000000..0f09e745747
--- /dev/null
+++ b/propagators/autoprop/doc.go
@@ -0,0 +1,23 @@
+// 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 autoprop provides an OpenTelemetry TextMapPropagator creation
+// function. The OpenTelemetry specification states that the default
+// TextMapPropagator needs to be a no-operation implementation. The
+// opentelemetry-go project adheres to this requirement. However, for systems
+// that perform propagation this default is not ideal. This package provides a
+// TextMapPropagator with useful defaults (a combined TraceContext and Baggage
+// TextMapPropagator), and supports environment overrides using the
+// OTEL_PROPAGATORS environment variable.
+package autoprop // import "go.opentelemetry.io/contrib/propagators/autoprop"
diff --git a/propagators/autoprop/go.mod b/propagators/autoprop/go.mod
new file mode 100644
index 00000000000..abfdc615345
--- /dev/null
+++ b/propagators/autoprop/go.mod
@@ -0,0 +1,11 @@
+module go.opentelemetry.io/contrib/propagators/autoprop
+
+go 1.16
+
+require (
+	go.opentelemetry.io/contrib/propagators/aws v1.7.0
+	go.opentelemetry.io/contrib/propagators/b3 v1.7.0
+	go.opentelemetry.io/contrib/propagators/jaeger v1.7.0
+	go.opentelemetry.io/contrib/propagators/ot v1.7.0
+	go.opentelemetry.io/otel v1.7.0
+)
diff --git a/propagators/autoprop/go.sum b/propagators/autoprop/go.sum
new file mode 100644
index 00000000000..5e301bccc24
--- /dev/null
+++ b/propagators/autoprop/go.sum
@@ -0,0 +1,42 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/logr v1.2.3 h1:2DntVwHkVopvECVRSlL5PSo9eG+cAkDCuckLubN+rq0=
+github.com/go-logr/logr v1.2.3/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
+github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
+github.com/google/go-cmp v0.5.7 h1:81/ik6ipDQS2aGcBfIN5dHDB36BwrStyeAQquSYCV4o=
+github.com/google/go-cmp v0.5.7/go.mod h1:n+brtR0CgQNWTVd5ZUFpTBC8YFBDLK/h/bpaJ8/DtOE=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.7.1 h1:5TQK59W5E3v0r2duFAb7P95B6hEeOyEnHRa8MjYSMTY=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+go.opentelemetry.io/contrib/propagators/aws v1.7.0 h1:hzLtX+K4YhsrBabA35uBYxCENb5rS/9Z9X8MToTlA3k=
+go.opentelemetry.io/contrib/propagators/aws v1.7.0/go.mod h1:h/ql5T6e1XLRFplWNNdzLHp8eb0dkBu+xYOCYxerh0Q=
+go.opentelemetry.io/contrib/propagators/b3 v1.7.0 h1:oRAenUhj+GFttfIp3gj7HYVzBhPOHgq/dWPDSmLCXSY=
+go.opentelemetry.io/contrib/propagators/b3 v1.7.0/go.mod h1:gXx7AhL4xXCF42gpm9dQvdohoDa2qeyEx4eIIxqK+h4=
+go.opentelemetry.io/contrib/propagators/jaeger v1.7.0 h1:x2mXKtONfOJFfNFSx4QXFx1fms6bKIPVvWvgdiaPdRI=
+go.opentelemetry.io/contrib/propagators/jaeger v1.7.0/go.mod h1:kt2lNImfxV6dETRsDCENd6jU6G0mPRS+P0qlNuvtkTE=
+go.opentelemetry.io/contrib/propagators/ot v1.7.0 h1:KPPToDRxyY/HI3qD4RqwWRbaQ65RIpF8uKWDqWkFHDA=
+go.opentelemetry.io/contrib/propagators/ot v1.7.0/go.mod h1:5qxBZR730yb71uXc3bazxt2Si8o8LQK3iJTnSLca/BU=
+go.opentelemetry.io/otel v1.7.0 h1:Z2lA3Tdch0iDcrhJXDIlC94XE+bxok1F9B+4Lz/lGsM=
+go.opentelemetry.io/otel v1.7.0/go.mod h1:5BdUoMIz5WEs0vt0CUEMtSSaTSHBBVwrhnz7+nrD5xk=
+go.opentelemetry.io/otel/sdk v1.7.0 h1:4OmStpcKVOfvDOgCt7UriAPtKolwIhxpnSNI/yK+1B0=
+go.opentelemetry.io/otel/sdk v1.7.0/go.mod h1:uTEOTwaqIVuTGiJN7ii13Ibp75wJmYUDe374q6cZwUU=
+go.opentelemetry.io/otel/trace v1.7.0 h1:O37Iogk1lEkMRXewVtZ1BBTVn5JEp8GrJvP92bJqC6o=
+go.opentelemetry.io/otel/trace v1.7.0/go.mod h1:fzLSB9nqR2eXzxPXb2JW9IKE+ScyXA48yyE4TNvoHqU=
+go.uber.org/atomic v1.7.0 h1:ADUqmZGgLDDfbSL9ZmPxKTybcoEYHgpYfELNoN+7hsw=
+go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
+go.uber.org/multierr v1.8.0 h1:dg6GjLku4EH+249NNmoIciG9N/jURbDG+pFlTkhzIC8=
+go.uber.org/multierr v1.8.0/go.mod h1:7EAYxJLBy9rStEaz58O2t4Uvip6FSURkq8/ppBp95ak=
+golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7 h1:iGu644GcxtEcrInvDsQRCwJjtCIOlT2V7IRt6ah2Whw=
+golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/propagators/autoprop/propagator.go b/propagators/autoprop/propagator.go
new file mode 100644
index 00000000000..c7074f258c6
--- /dev/null
+++ b/propagators/autoprop/propagator.go
@@ -0,0 +1,121 @@
+// 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 autoprop
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/propagation"
+)
+
+// otelPropagatorsEnvKey is the environment variable name identifying
+// propagators to use.
+const otelPropagatorsEnvKey = "OTEL_PROPAGATORS"
+
+// NewTextMapPropagator returns a new TextMapPropagator composited by props or
+// one defined by the OTEL_PROPAGATORS environment variable. The
+// TextMapPropagator defined by OTEL_PROPAGATORS, if set, will take precedence
+// to the once composited by props.
+//
+// The propagators supported with the OTEL_PROPAGATORS environment variable by
+// default are: tracecontext, baggage, b3, b3multi, jaeger, xray, ottrace, and
+// none. Each of these values, and their combination, are supported in
+// conformance with the OpenTelemetry specification. See
+// https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#general-sdk-configuration
+// for more information.
+//
+// The supported environment variable propagators can be extended to include
+// custom 3rd-party TextMapPropagator. See the Register function for more
+// information.
+//
+// If OTEL_PROPAGATORS is not defined and props is no provided, the returned
+// TextMapPropagator will be a composite of the TraceContext and Baggage
+// propagators.
+func NewTextMapPropagator(props ...propagation.TextMapPropagator) propagation.TextMapPropagator {
+	// Environment variable defined propagator has precedence over arguments.
+	envProp, err := parseEnv()
+	if err != nil {
+		// Communicate to the user their supplied value will not be used.
+		otel.Handle(err)
+	}
+	if envProp != nil {
+		return envProp
+	}
+
+	if len(props) != 0 {
+		return propagation.NewCompositeTextMapPropagator(props...)
+	}
+
+	return propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{})
+}
+
+// errUnknownPropagator is returned when an unknown propagator name is used in
+// the OTEL_PROPAGATORS environment variable.
+var errUnknownPropagator = errors.New("unknown propagator")
+
+// parseEnv returns the composite TextMapPropagators defined by the
+// OTEL_PROPAGATORS environment variable. A nil TextMapPropagator is returned
+// if no propagator is defined for the environment variable. A no-op
+// TextMapPropagator will be returned if "none" is defined anywhere in the
+// environment variable.
+func parseEnv() (propagation.TextMapPropagator, error) {
+	propStrs, defined := os.LookupEnv(otelPropagatorsEnvKey)
+	if !defined {
+		return nil, nil
+	}
+
+	const sep = ","
+
+	var (
+		props   []propagation.TextMapPropagator
+		unknown []string
+	)
+
+	for _, pStr := range strings.Split(propStrs, sep) {
+		if pStr == none {
+			// If "none" is passed in combination with any other propagator,
+			// the result still needs to be a no-op propagator. Therefore,
+			// short-circuit here.
+			return propagation.NewCompositeTextMapPropagator(), nil
+		}
+
+		p, ok := envRegistry.load(pStr)
+		if !ok {
+			unknown = append(unknown, pStr)
+			continue
+		}
+		props = append(props, p)
+	}
+
+	var err error
+	if len(unknown) > 0 {
+		joined := strings.Join(unknown, sep)
+		err = fmt.Errorf("%w: %s", errUnknownPropagator, joined)
+	}
+
+	switch len(props) {
+	case 0:
+		return nil, err
+	case 1:
+		// Do not return a composite of a single propagator.
+		return props[0], err
+	default:
+		return propagation.NewCompositeTextMapPropagator(props...), err
+	}
+}
diff --git a/propagators/autoprop/registry.go b/propagators/autoprop/registry.go
new file mode 100644
index 00000000000..4c617c98d42
--- /dev/null
+++ b/propagators/autoprop/registry.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 autoprop
+
+import (
+	"sync"
+
+	"go.opentelemetry.io/contrib/propagators/aws/xray"
+	"go.opentelemetry.io/contrib/propagators/b3"
+	"go.opentelemetry.io/contrib/propagators/jaeger"
+	"go.opentelemetry.io/contrib/propagators/ot"
+	"go.opentelemetry.io/otel/propagation"
+)
+
+// none is the specical "propagator" name that means no propagator shall be
+// configured.
+const none = "none"
+
+// envRegistry is the index of all supported environment variable
+// values and their mapping to a TextMapPropagator.
+var envRegistry = &registry{
+	index: map[string]propagation.TextMapPropagator{
+		// W3C Trace Context.
+		"tracecontext": propagation.TraceContext{},
+		// W3C Baggage.
+		"baggage": propagation.Baggage{},
+		// B3 single-header format.
+		"b3": b3.New(),
+		// B3 multi-header format.
+		"b3multi": b3.New(b3.WithInjectEncoding(b3.B3MultipleHeader)),
+		// Jaeger.
+		"jaeger": jaeger.Jaeger{},
+		// AWS X-Ray.
+		"xray": xray.Propagator{},
+		// OpenTracing Trace.
+		"ottrace": ot.OT{},
+
+		// No-op TextMapPropagator.
+		none: propagation.NewCompositeTextMapPropagator(),
+	},
+}
+
+// registry maintains an index of propagator names to TextMapPropagator
+// implementations that is safe for concurrent use by multiple goroutines
+// without additional locking or coordination.
+type registry struct {
+	mu    sync.Mutex
+	index map[string]propagation.TextMapPropagator
+}
+
+// load returns the value stored in the registry index for a key, or nil if no
+// value is present. The ok result indicates whether value was found in the
+// index.
+func (r *registry) load(key string) (p propagation.TextMapPropagator, ok bool) {
+	r.mu.Lock()
+	p, ok = r.index[key]
+	r.mu.Unlock()
+	return p, ok
+}
+
+// store sets the value for a key.
+func (r *registry) store(key string, value propagation.TextMapPropagator) {
+	r.mu.Lock()
+	r.index[key] = value
+	r.mu.Unlock()
+}
+
+// RegisterTextMapPropagator sets the TextMapPropagator p to be used when the
+// OTEL_PROPAGATORS environment variable contains the propagator name. This
+// allows the default supported environment TextMapPropagators to be extended
+// with 3rd-part implementations.
+func RegisterTextMapPropagator(name string, p propagation.TextMapPropagator) {
+	envRegistry.store(name, p)
+}

From 6f771c364b6fa6d9c91e0b281b20b2cea72ce272 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 13:36:01 -0700
Subject: [PATCH 02/22] Add example tests

---
 propagators/autoprop/example_test.go | 84 ++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 propagators/autoprop/example_test.go

diff --git a/propagators/autoprop/example_test.go b/propagators/autoprop/example_test.go
new file mode 100644
index 00000000000..f43abff28c4
--- /dev/null
+++ b/propagators/autoprop/example_test.go
@@ -0,0 +1,84 @@
+// 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 autoprop_test
+
+import (
+	"fmt"
+	"os"
+	"sort"
+
+	"go.opentelemetry.io/contrib/propagators/autoprop"
+	"go.opentelemetry.io/contrib/propagators/b3"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/propagation"
+)
+
+func ExampleNewTextMapPropagator() {
+	// NewTextMapPropagator returns a TraceContext and Baggage propagator by
+	// default. The response of this function can be directly registered with
+	// the go.opentelemetry.io/otel package.
+	otel.SetTextMapPropagator(autoprop.NewTextMapPropagator())
+
+	fields := otel.GetTextMapPropagator().Fields()
+	sort.Strings(fields)
+	fmt.Println(fields)
+	// Output: [baggage traceparent tracestate]
+}
+
+func ExampleNewTextMapPropagator_arguments() {
+	// NewTextMapPropagator behaves the same as the
+	// NewCompositeTextMapPropagator function in the
+	// go.opentelemetry.io/otel/propagation package when TextMapPropagator are
+	// passed as arguments.
+	fields := autoprop.NewTextMapPropagator(
+		propagation.TraceContext{},
+		propagation.Baggage{},
+		b3.New(),
+	).Fields()
+	sort.Strings(fields)
+	fmt.Println(fields)
+	// Output: [baggage traceparent tracestate x-b3-flags x-b3-sampled x-b3-spanid x-b3-traceid]
+}
+
+func ExampleNewTextMapPropagator_environment() {
+	// Propagators set for the OTEL_PROPAGATORS environment variable take
+	// precedence and will override any arguments passed to
+	// NewTextMapPropagator.
+	os.Setenv("OTEL_PROPAGATORS", "b3,baggage")
+
+	// Returns only a B3 and Baggage TextMapPropagator (i.e. does not include
+	// TraceContext).
+	fields := autoprop.NewTextMapPropagator(propagation.TraceContext{}).Fields()
+	sort.Strings(fields)
+	fmt.Println(fields)
+	// Output: [baggage x-b3-flags x-b3-sampled x-b3-spanid x-b3-traceid]
+}
+
+type myTextMapPropagator struct{ propagation.TextMapPropagator }
+
+func (myTextMapPropagator) Fields() []string {
+	return []string{"my-header-val"}
+}
+
+func ExampleRegisterTextMapPropagator() {
+	// To use your own or a 3rd-party exporter via the OTEL_PROPAGATORS
+	// environment variable, it needs to be registered prior to calling
+	// NewTextMapPropagator.
+	autoprop.RegisterTextMapPropagator("custom-prop", myTextMapPropagator{})
+
+	os.Setenv("OTEL_PROPAGATORS", "custom-prop")
+	fmt.Println(autoprop.NewTextMapPropagator().Fields())
+	// Output: [my-header-val]
+}

From c334328cd48fc6a5212a1175f121e7634f8f8b6c Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 14:17:03 -0700
Subject: [PATCH 03/22] Add unit tests for registry.go

---
 propagators/autoprop/registry.go      |  6 ++-
 propagators/autoprop/registry_test.go | 66 +++++++++++++++++++++++++++
 2 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100644 propagators/autoprop/registry_test.go

diff --git a/propagators/autoprop/registry.go b/propagators/autoprop/registry.go
index 4c617c98d42..4235d1a1825 100644
--- a/propagators/autoprop/registry.go
+++ b/propagators/autoprop/registry.go
@@ -73,8 +73,12 @@ func (r *registry) load(key string) (p propagation.TextMapPropagator, ok bool) {
 // store sets the value for a key.
 func (r *registry) store(key string, value propagation.TextMapPropagator) {
 	r.mu.Lock()
+	defer r.mu.Unlock()
+	if r.index == nil {
+		r.index = map[string]propagation.TextMapPropagator{key: value}
+		return
+	}
 	r.index[key] = value
-	r.mu.Unlock()
 }
 
 // RegisterTextMapPropagator sets the TextMapPropagator p to be used when the
diff --git a/propagators/autoprop/registry_test.go b/propagators/autoprop/registry_test.go
new file mode 100644
index 00000000000..65ef197621f
--- /dev/null
+++ b/propagators/autoprop/registry_test.go
@@ -0,0 +1,66 @@
+// 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 autoprop
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"go.opentelemetry.io/otel/propagation"
+)
+
+var noop = propagation.NewCompositeTextMapPropagator()
+
+func TestRegistryEmptyStore(t *testing.T) {
+	r := registry{}
+	assert.NotPanics(t, func() { r.store("first", noop) })
+}
+
+func TestRegistryEmptyLoad(t *testing.T) {
+	r := registry{}
+	assert.NotPanics(t, func() {
+		v, ok := r.load("non-existent")
+		assert.False(t, ok, "empty registry should hold nothing")
+		assert.Nil(t, v, "non-nil propagator returned")
+	})
+}
+
+func TestRegistryConcurrentSafe(t *testing.T) {
+	const propName = "prop"
+
+	r := registry{}
+	assert.NotPanics(t, func() { r.store(propName, noop) })
+
+	go func() {
+		assert.NotPanics(t, func() { r.store(propName, noop) })
+	}()
+
+	go func() {
+		assert.NotPanics(t, func() {
+			v, ok := r.load(propName)
+			assert.True(t, ok, "missing propagator in registry")
+			assert.Equal(t, noop, v, "wrong propagator retuned")
+		})
+	}()
+}
+
+func TestRegisterTextMapPropagator(t *testing.T) {
+	const propName = "custom"
+	RegisterTextMapPropagator(propName, noop)
+
+	v, ok := envRegistry.load(propName)
+	assert.True(t, ok, "missing propagator in envRegistry")
+	assert.Equal(t, noop, v, "wrong propagator stored")
+}

From b86fa71806ab52c38004a675f45fa3117d59025f Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 14:30:38 -0700
Subject: [PATCH 04/22] Add unit test for NewTextMapPropagator

---
 propagators/autoprop/propagator.go      | 13 ++++++--
 propagators/autoprop/propagator_test.go | 40 +++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)
 create mode 100644 propagators/autoprop/propagator_test.go

diff --git a/propagators/autoprop/propagator.go b/propagators/autoprop/propagator.go
index c7074f258c6..78c51161aee 100644
--- a/propagators/autoprop/propagator.go
+++ b/propagators/autoprop/propagator.go
@@ -58,11 +58,20 @@ func NewTextMapPropagator(props ...propagation.TextMapPropagator) propagation.Te
 		return envProp
 	}
 
-	if len(props) != 0 {
+	switch len(props) {
+	case 0:
+		// Default to TraceContext and Baggage.
+		return propagation.NewCompositeTextMapPropagator(
+			propagation.TraceContext{}, propagation.Baggage{},
+		)
+	case 1:
+		// Do not add overhead with a composite propagator wrapping a single
+		// propagator, return it directly.
+		return props[0]
+	default:
 		return propagation.NewCompositeTextMapPropagator(props...)
 	}
 
-	return propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{})
 }
 
 // errUnknownPropagator is returned when an unknown propagator name is used in
diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
new file mode 100644
index 00000000000..39f8aa9746c
--- /dev/null
+++ b/propagators/autoprop/propagator_test.go
@@ -0,0 +1,40 @@
+// 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 autoprop
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"go.opentelemetry.io/otel"
+)
+
+type handler struct {
+	err error
+}
+
+var _ otel.ErrorHandler = (*handler)(nil)
+
+func (h *handler) Handle(err error) { h.err = err }
+
+func TestNewTextMapPropagatorInvalidEnvVal(t *testing.T) {
+	h := &handler{}
+	otel.SetErrorHandler(h)
+
+	const name = "invalid-name"
+	t.Setenv(otelPropagatorsEnvKey, name)
+	_ = NewTextMapPropagator()
+	assert.ErrorIs(t, h.err, errUnknownPropagator)
+}

From db7767600c94293d6ea70f8b54b742ecd09e4a42 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 14:40:08 -0700
Subject: [PATCH 05/22] Add NewTextMapPropagator unit tests

---
 propagators/autoprop/propagator_test.go | 30 +++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
index 39f8aa9746c..b5048f6c6ed 100644
--- a/propagators/autoprop/propagator_test.go
+++ b/propagators/autoprop/propagator_test.go
@@ -15,10 +15,12 @@
 package autoprop
 
 import (
+	"context"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/propagation"
 )
 
 type handler struct {
@@ -38,3 +40,31 @@ func TestNewTextMapPropagatorInvalidEnvVal(t *testing.T) {
 	_ = NewTextMapPropagator()
 	assert.ErrorIs(t, h.err, errUnknownPropagator)
 }
+
+func TestNewTextMapPropagatorDefault(t *testing.T) {
+	expect := []string{"traceparent", "tracestate", "baggage"}
+	assert.ElementsMatch(t, expect, NewTextMapPropagator().Fields())
+}
+
+type ptrNoop struct{}
+
+var _ propagation.TextMapPropagator = (*ptrNoop)(nil)
+
+func (*ptrNoop) Inject(context.Context, propagation.TextMapCarrier) {}
+
+func (*ptrNoop) Extract(context.Context, propagation.TextMapCarrier) context.Context {
+	return context.Background()
+}
+func (*ptrNoop) Fields() []string {
+	return nil
+}
+
+func TestNewTextMapPropagatorSingleNoOverhead(t *testing.T) {
+	p := &ptrNoop{}
+	assert.Same(t, p, NewTextMapPropagator(p))
+}
+
+func TestNewTextMapPropagatorMultiEnvNone(t *testing.T) {
+	t.Setenv(otelPropagatorsEnvKey, "b3,none,tracecontext")
+	assert.Equal(t, noop, NewTextMapPropagator())
+}

From 67fb8ec4afdf733ef455269a945cd4e9036bfac3 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 14:44:36 -0700
Subject: [PATCH 06/22] Fix RegisterTextMapPropagator func name

---
 propagators/autoprop/propagator.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/propagators/autoprop/propagator.go b/propagators/autoprop/propagator.go
index 78c51161aee..920176a5d57 100644
--- a/propagators/autoprop/propagator.go
+++ b/propagators/autoprop/propagator.go
@@ -41,8 +41,8 @@ const otelPropagatorsEnvKey = "OTEL_PROPAGATORS"
 // for more information.
 //
 // The supported environment variable propagators can be extended to include
-// custom 3rd-party TextMapPropagator. See the Register function for more
-// information.
+// custom 3rd-party TextMapPropagator. See the RegisterTextMapPropagator
+// function for more information.
 //
 // If OTEL_PROPAGATORS is not defined and props is no provided, the returned
 // TextMapPropagator will be a composite of the TraceContext and Baggage

From 3aab5aa25a2aea084c99a07b864e98102e76f579 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 14:55:24 -0700
Subject: [PATCH 07/22] Fix lint

---
 propagators/autoprop/example_test.go | 4 ++--
 propagators/autoprop/propagator.go   | 1 -
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/propagators/autoprop/example_test.go b/propagators/autoprop/example_test.go
index f43abff28c4..f98ca9c022f 100644
--- a/propagators/autoprop/example_test.go
+++ b/propagators/autoprop/example_test.go
@@ -56,7 +56,7 @@ func ExampleNewTextMapPropagator_environment() {
 	// Propagators set for the OTEL_PROPAGATORS environment variable take
 	// precedence and will override any arguments passed to
 	// NewTextMapPropagator.
-	os.Setenv("OTEL_PROPAGATORS", "b3,baggage")
+	_ = os.Setenv("OTEL_PROPAGATORS", "b3,baggage")
 
 	// Returns only a B3 and Baggage TextMapPropagator (i.e. does not include
 	// TraceContext).
@@ -78,7 +78,7 @@ func ExampleRegisterTextMapPropagator() {
 	// NewTextMapPropagator.
 	autoprop.RegisterTextMapPropagator("custom-prop", myTextMapPropagator{})
 
-	os.Setenv("OTEL_PROPAGATORS", "custom-prop")
+	_ = os.Setenv("OTEL_PROPAGATORS", "custom-prop")
 	fmt.Println(autoprop.NewTextMapPropagator().Fields())
 	// Output: [my-header-val]
 }
diff --git a/propagators/autoprop/propagator.go b/propagators/autoprop/propagator.go
index 920176a5d57..fed4311ddc3 100644
--- a/propagators/autoprop/propagator.go
+++ b/propagators/autoprop/propagator.go
@@ -71,7 +71,6 @@ func NewTextMapPropagator(props ...propagation.TextMapPropagator) propagation.Te
 	default:
 		return propagation.NewCompositeTextMapPropagator(props...)
 	}
-
 }
 
 // errUnknownPropagator is returned when an unknown propagator name is used in

From 1055a5c94ec7d79d5639e7ba67ece74103318e82 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 15:00:46 -0700
Subject: [PATCH 08/22] Go import lint fix

---
 propagators/autoprop/go.mod             | 1 +
 propagators/autoprop/go.sum             | 1 +
 propagators/autoprop/propagator.go      | 2 +-
 propagators/autoprop/propagator_test.go | 1 +
 propagators/autoprop/registry.go        | 2 +-
 propagators/autoprop/registry_test.go   | 1 +
 6 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/propagators/autoprop/go.mod b/propagators/autoprop/go.mod
index abfdc615345..f2675c663c1 100644
--- a/propagators/autoprop/go.mod
+++ b/propagators/autoprop/go.mod
@@ -3,6 +3,7 @@ module go.opentelemetry.io/contrib/propagators/autoprop
 go 1.16
 
 require (
+	github.com/stretchr/testify v1.7.1
 	go.opentelemetry.io/contrib/propagators/aws v1.7.0
 	go.opentelemetry.io/contrib/propagators/b3 v1.7.0
 	go.opentelemetry.io/contrib/propagators/jaeger v1.7.0
diff --git a/propagators/autoprop/go.sum b/propagators/autoprop/go.sum
index 5e301bccc24..e0001c2d25a 100644
--- a/propagators/autoprop/go.sum
+++ b/propagators/autoprop/go.sum
@@ -36,6 +36,7 @@ go.uber.org/multierr v1.8.0/go.mod h1:7EAYxJLBy9rStEaz58O2t4Uvip6FSURkq8/ppBp95a
 golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7 h1:iGu644GcxtEcrInvDsQRCwJjtCIOlT2V7IRt6ah2Whw=
 golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
diff --git a/propagators/autoprop/propagator.go b/propagators/autoprop/propagator.go
index fed4311ddc3..1fe17781227 100644
--- a/propagators/autoprop/propagator.go
+++ b/propagators/autoprop/propagator.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package autoprop
+package autoprop // import "go.opentelemetry.io/contrib/propagators/autoprop"
 
 import (
 	"errors"
diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
index b5048f6c6ed..0d64ae78ab3 100644
--- a/propagators/autoprop/propagator_test.go
+++ b/propagators/autoprop/propagator_test.go
@@ -19,6 +19,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/propagation"
 )
diff --git a/propagators/autoprop/registry.go b/propagators/autoprop/registry.go
index 4235d1a1825..b8017b80805 100644
--- a/propagators/autoprop/registry.go
+++ b/propagators/autoprop/registry.go
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package autoprop
+package autoprop // import "go.opentelemetry.io/contrib/propagators/autoprop"
 
 import (
 	"sync"
diff --git a/propagators/autoprop/registry_test.go b/propagators/autoprop/registry_test.go
index 65ef197621f..df2b2947315 100644
--- a/propagators/autoprop/registry_test.go
+++ b/propagators/autoprop/registry_test.go
@@ -18,6 +18,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+
 	"go.opentelemetry.io/otel/propagation"
 )
 

From 492a7008a6fa6b39143c1191402c48e31b9540f6 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 15:01:03 -0700
Subject: [PATCH 09/22] Add dependabot entry

---
 .github/dependabot.yml | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index ccf705af38b..a0fb05c3366 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -532,6 +532,15 @@ updates:
     schedule:
       interval: weekly
       day: sunday
+  - package-ecosystem: gomod
+    directory: /propagators/autoprop
+    labels:
+      - dependencies
+      - go
+      - Skip Changelog
+    schedule:
+      interval: weekly
+      day: sunday
   - package-ecosystem: gomod
     directory: /propagators/aws
     labels:

From 9201c4b3c76c8fe0c55670845717f16ec6dcf42f Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 15:02:13 -0700
Subject: [PATCH 10/22] Add change to the changelog

---
 CHANGELOG.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 769e5330467..8e1663c7883 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Added
+
+- The `go.opentelemetry.io/contrib/propagators/autoprop` package to provide configuration of propagators with useful defaults and envar support. (#2258)
+
 ## [1.7.0/0.32.0] - 2022-04-28
 
 ### Added

From 999aa9c929f1cf77a9ecd1e85b3a3bd94509211e Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 15:03:08 -0700
Subject: [PATCH 11/22] Add autoprop to versions

---
 versions.yaml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/versions.yaml b/versions.yaml
index 544be0d0721..382272f6ce6 100644
--- a/versions.yaml
+++ b/versions.yaml
@@ -30,6 +30,7 @@ module-sets:
     version: v0.32.0
     modules:
       - go.opentelemetry.io/contrib/detectors/aws/lambda
+      - go.opentelemetry.io/contrib/propagators/autoprop
       - go.opentelemetry.io/contrib/propagators/opencensus
       - go.opentelemetry.io/contrib/propagators/opencensus/examples
       - go.opentelemetry.io/contrib/instrumentation/gopkg.in/macaron.v1/otelmacaron

From a45b5de33d937c94a74a7b62015e546bc6a355f8 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 15:11:58 -0700
Subject: [PATCH 12/22] Add setenv test func to support Go 1.16

---
 propagators/autoprop/propagator_test.go | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
index 0d64ae78ab3..6ca96abe90e 100644
--- a/propagators/autoprop/propagator_test.go
+++ b/propagators/autoprop/propagator_test.go
@@ -16,6 +16,7 @@ package autoprop
 
 import (
 	"context"
+	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -24,6 +25,22 @@ import (
 	"go.opentelemetry.io/otel/propagation"
 )
 
+// setenv sets and unsets an environment variable in the context of a test
+// run. It is used instead of t.Setenv so as to support Go <1.17. It can be
+// replaced with t.Setenv(key, value) when this support is dropped.
+func setenv(t *testing.T, key, value string) {
+	prevValue, ok := os.LookupEnv(key)
+	if err := os.Setenv(key, value); err != nil {
+		t.Fatalf("cannot set environment variable: %v", err)
+	}
+
+	if ok {
+		t.Cleanup(func() { os.Setenv(key, prevValue) })
+	} else {
+		t.Cleanup(func() { os.Unsetenv(key) })
+	}
+}
+
 type handler struct {
 	err error
 }
@@ -37,7 +54,7 @@ func TestNewTextMapPropagatorInvalidEnvVal(t *testing.T) {
 	otel.SetErrorHandler(h)
 
 	const name = "invalid-name"
-	t.Setenv(otelPropagatorsEnvKey, name)
+	setenv(t, otelPropagatorsEnvKey, name)
 	_ = NewTextMapPropagator()
 	assert.ErrorIs(t, h.err, errUnknownPropagator)
 }
@@ -66,6 +83,6 @@ func TestNewTextMapPropagatorSingleNoOverhead(t *testing.T) {
 }
 
 func TestNewTextMapPropagatorMultiEnvNone(t *testing.T) {
-	t.Setenv(otelPropagatorsEnvKey, "b3,none,tracecontext")
+	setenv(t, otelPropagatorsEnvKey, "b3,none,tracecontext")
 	assert.Equal(t, noop, NewTextMapPropagator())
 }

From 7521e6b52cb1f279b93fca2477ab168a18d5a19c Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 3 May 2022 15:48:56 -0700
Subject: [PATCH 13/22] Fix spelling error in comment

---
 propagators/autoprop/registry.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/propagators/autoprop/registry.go b/propagators/autoprop/registry.go
index b8017b80805..03753e9099e 100644
--- a/propagators/autoprop/registry.go
+++ b/propagators/autoprop/registry.go
@@ -24,7 +24,7 @@ import (
 	"go.opentelemetry.io/otel/propagation"
 )
 
-// none is the specical "propagator" name that means no propagator shall be
+// none is the special "propagator" name that means no propagator shall be
 // configured.
 const none = "none"
 

From 037664e8dd4dd3cfc1d69ffcb2070db16c865558 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Wed, 4 May 2022 13:28:24 -0700
Subject: [PATCH 14/22] Rename registry index field to names

---
 propagators/autoprop/registry.go | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/propagators/autoprop/registry.go b/propagators/autoprop/registry.go
index 03753e9099e..435f7f5ec43 100644
--- a/propagators/autoprop/registry.go
+++ b/propagators/autoprop/registry.go
@@ -31,7 +31,7 @@ const none = "none"
 // envRegistry is the index of all supported environment variable
 // values and their mapping to a TextMapPropagator.
 var envRegistry = &registry{
-	index: map[string]propagation.TextMapPropagator{
+	names: map[string]propagation.TextMapPropagator{
 		// W3C Trace Context.
 		"tracecontext": propagation.TraceContext{},
 		// W3C Baggage.
@@ -52,12 +52,12 @@ var envRegistry = &registry{
 	},
 }
 
-// registry maintains an index of propagator names to TextMapPropagator
+// registry maintains a map of propagator names to TextMapPropagator
 // implementations that is safe for concurrent use by multiple goroutines
 // without additional locking or coordination.
 type registry struct {
 	mu    sync.Mutex
-	index map[string]propagation.TextMapPropagator
+	names map[string]propagation.TextMapPropagator
 }
 
 // load returns the value stored in the registry index for a key, or nil if no
@@ -65,7 +65,7 @@ type registry struct {
 // index.
 func (r *registry) load(key string) (p propagation.TextMapPropagator, ok bool) {
 	r.mu.Lock()
-	p, ok = r.index[key]
+	p, ok = r.names[key]
 	r.mu.Unlock()
 	return p, ok
 }
@@ -74,11 +74,11 @@ func (r *registry) load(key string) (p propagation.TextMapPropagator, ok bool) {
 func (r *registry) store(key string, value propagation.TextMapPropagator) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	if r.index == nil {
-		r.index = map[string]propagation.TextMapPropagator{key: value}
+	if r.names == nil {
+		r.names = map[string]propagation.TextMapPropagator{key: value}
 		return
 	}
-	r.index[key] = value
+	r.names[key] = value
 }
 
 // RegisterTextMapPropagator sets the TextMapPropagator p to be used when the

From a92287d1560e037350785a53dc9e23207a909eee Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Wed, 4 May 2022 13:28:52 -0700
Subject: [PATCH 15/22] Remove interface assertion

---
 propagators/autoprop/propagator_test.go | 2 --
 1 file changed, 2 deletions(-)

diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
index 6ca96abe90e..4f90f39e0b1 100644
--- a/propagators/autoprop/propagator_test.go
+++ b/propagators/autoprop/propagator_test.go
@@ -66,8 +66,6 @@ func TestNewTextMapPropagatorDefault(t *testing.T) {
 
 type ptrNoop struct{}
 
-var _ propagation.TextMapPropagator = (*ptrNoop)(nil)
-
 func (*ptrNoop) Inject(context.Context, propagation.TextMapCarrier) {}
 
 func (*ptrNoop) Extract(context.Context, propagation.TextMapCarrier) context.Context {

From 79ada0bbbaf51d94f9b5cd1140135eaa91d72644 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 24 May 2022 08:31:41 -0700
Subject: [PATCH 16/22] Fix lint

---
 propagators/autoprop/propagator_test.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
index 4f90f39e0b1..8962b43fd36 100644
--- a/propagators/autoprop/propagator_test.go
+++ b/propagators/autoprop/propagator_test.go
@@ -35,9 +35,9 @@ func setenv(t *testing.T, key, value string) {
 	}
 
 	if ok {
-		t.Cleanup(func() { os.Setenv(key, prevValue) })
+		t.Cleanup(func() { _ = os.Setenv(key, prevValue) })
 	} else {
-		t.Cleanup(func() { os.Unsetenv(key) })
+		t.Cleanup(func() { _ = os.Unsetenv(key) })
 	}
 }
 

From f1c9e3de0ab4a8cf6f37241360fed6bee207d96b Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Wed, 25 May 2022 07:53:31 -0700
Subject: [PATCH 17/22] Update RegisterTextMapPropagator docs

---
 propagators/autoprop/registry.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/propagators/autoprop/registry.go b/propagators/autoprop/registry.go
index 435f7f5ec43..112581f039b 100644
--- a/propagators/autoprop/registry.go
+++ b/propagators/autoprop/registry.go
@@ -83,8 +83,8 @@ func (r *registry) store(key string, value propagation.TextMapPropagator) {
 
 // RegisterTextMapPropagator sets the TextMapPropagator p to be used when the
 // OTEL_PROPAGATORS environment variable contains the propagator name. This
-// allows the default supported environment TextMapPropagators to be extended
-// with 3rd-part implementations.
+// allows adding additional environment TextMapPropagators, or replacing the
+// default TextMapPropagators with 3rd-party implementations.
 func RegisterTextMapPropagator(name string, p propagation.TextMapPropagator) {
 	envRegistry.store(name, p)
 }

From dd600fed046af01bfb1bf5245875a4026867344e Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Wed, 25 May 2022 07:54:30 -0700
Subject: [PATCH 18/22] Remove compile time assertion and test of impl

---
 propagators/autoprop/propagator_test.go | 2 --
 1 file changed, 2 deletions(-)

diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
index 8962b43fd36..9753e6ad1bc 100644
--- a/propagators/autoprop/propagator_test.go
+++ b/propagators/autoprop/propagator_test.go
@@ -45,8 +45,6 @@ type handler struct {
 	err error
 }
 
-var _ otel.ErrorHandler = (*handler)(nil)
-
 func (h *handler) Handle(err error) { h.err = err }
 
 func TestNewTextMapPropagatorInvalidEnvVal(t *testing.T) {

From 12a49522bfecc155e1948588c7f30cff8798cf04 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Thu, 26 May 2022 07:59:15 -0700
Subject: [PATCH 19/22] Upgrade to Go 1.17 as min supported version

---
 propagators/autoprop/go.mod | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/propagators/autoprop/go.mod b/propagators/autoprop/go.mod
index f2675c663c1..d5ba5638cef 100644
--- a/propagators/autoprop/go.mod
+++ b/propagators/autoprop/go.mod
@@ -1,6 +1,6 @@
 module go.opentelemetry.io/contrib/propagators/autoprop
 
-go 1.16
+go 1.17
 
 require (
 	github.com/stretchr/testify v1.7.1
@@ -10,3 +10,16 @@ require (
 	go.opentelemetry.io/contrib/propagators/ot v1.7.0
 	go.opentelemetry.io/otel v1.7.0
 )
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/go-logr/logr v1.2.3 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	go.opentelemetry.io/otel/sdk v1.7.0 // indirect
+	go.opentelemetry.io/otel/trace v1.7.0 // indirect
+	go.uber.org/atomic v1.7.0 // indirect
+	go.uber.org/multierr v1.8.0 // indirect
+	golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
+)

From 0b37e5bfaa528deff2ffe6080e755016cb4e60e4 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Thu, 26 May 2022 08:01:11 -0700
Subject: [PATCH 20/22] Use T.Setenv instead of own setenv func

---
 propagators/autoprop/propagator_test.go | 21 ++-------------------
 1 file changed, 2 insertions(+), 19 deletions(-)

diff --git a/propagators/autoprop/propagator_test.go b/propagators/autoprop/propagator_test.go
index 9753e6ad1bc..9eebc1a2f67 100644
--- a/propagators/autoprop/propagator_test.go
+++ b/propagators/autoprop/propagator_test.go
@@ -16,7 +16,6 @@ package autoprop
 
 import (
 	"context"
-	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -25,22 +24,6 @@ import (
 	"go.opentelemetry.io/otel/propagation"
 )
 
-// setenv sets and unsets an environment variable in the context of a test
-// run. It is used instead of t.Setenv so as to support Go <1.17. It can be
-// replaced with t.Setenv(key, value) when this support is dropped.
-func setenv(t *testing.T, key, value string) {
-	prevValue, ok := os.LookupEnv(key)
-	if err := os.Setenv(key, value); err != nil {
-		t.Fatalf("cannot set environment variable: %v", err)
-	}
-
-	if ok {
-		t.Cleanup(func() { _ = os.Setenv(key, prevValue) })
-	} else {
-		t.Cleanup(func() { _ = os.Unsetenv(key) })
-	}
-}
-
 type handler struct {
 	err error
 }
@@ -52,7 +35,7 @@ func TestNewTextMapPropagatorInvalidEnvVal(t *testing.T) {
 	otel.SetErrorHandler(h)
 
 	const name = "invalid-name"
-	setenv(t, otelPropagatorsEnvKey, name)
+	t.Setenv(otelPropagatorsEnvKey, name)
 	_ = NewTextMapPropagator()
 	assert.ErrorIs(t, h.err, errUnknownPropagator)
 }
@@ -79,6 +62,6 @@ func TestNewTextMapPropagatorSingleNoOverhead(t *testing.T) {
 }
 
 func TestNewTextMapPropagatorMultiEnvNone(t *testing.T) {
-	setenv(t, otelPropagatorsEnvKey, "b3,none,tracecontext")
+	t.Setenv(otelPropagatorsEnvKey, "b3,none,tracecontext")
 	assert.Equal(t, noop, NewTextMapPropagator())
 }

From 1f54df0cf0647592a19d1159ecd898000b6082b1 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Thu, 26 May 2022 12:41:31 -0700
Subject: [PATCH 21/22] Panic on duplicate prop register

---
 propagators/autoprop/registry.go      | 39 ++++++++++++++++++++++-----
 propagators/autoprop/registry_test.go | 13 +++++++++
 2 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/propagators/autoprop/registry.go b/propagators/autoprop/registry.go
index 112581f039b..499a7da4b75 100644
--- a/propagators/autoprop/registry.go
+++ b/propagators/autoprop/registry.go
@@ -15,6 +15,8 @@
 package autoprop // import "go.opentelemetry.io/contrib/propagators/autoprop"
 
 import (
+	"errors"
+	"fmt"
 	"sync"
 
 	"go.opentelemetry.io/contrib/propagators/aws/xray"
@@ -70,21 +72,46 @@ func (r *registry) load(key string) (p propagation.TextMapPropagator, ok bool) {
 	return p, ok
 }
 
-// store sets the value for a key.
-func (r *registry) store(key string, value propagation.TextMapPropagator) {
+var errDupReg = errors.New("duplicate registration")
+
+// store sets the value for a key if is not already in the registry. errDupReg
+// is returned if the registry already contains key.
+func (r *registry) store(key string, value propagation.TextMapPropagator) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	if r.names == nil {
 		r.names = map[string]propagation.TextMapPropagator{key: value}
-		return
+		return nil
+	}
+	if _, ok := r.names[key]; ok {
+		return fmt.Errorf("%w: %q", errDupReg, key)
 	}
 	r.names[key] = value
+	return nil
+}
+
+// drop removes key from the registry if it exists, otherwise nothing.
+func (r *registry) drop(key string) {
+	r.mu.Lock()
+	delete(r.names, key)
+	r.mu.Unlock()
 }
 
 // RegisterTextMapPropagator sets the TextMapPropagator p to be used when the
 // OTEL_PROPAGATORS environment variable contains the propagator name. This
-// allows adding additional environment TextMapPropagators, or replacing the
-// default TextMapPropagators with 3rd-party implementations.
+// will panic if name has already been registered or is a default
+// (tracecontext, baggage, b3, b3multi, jaeger, xray, or ottrace).
 func RegisterTextMapPropagator(name string, p propagation.TextMapPropagator) {
-	envRegistry.store(name, p)
+	if err := envRegistry.store(name, p); err != nil {
+		// envRegistry.store will return errDupReg if name is already
+		// registered. Panic here so the user is made aware of the duplicate
+		// registration, which could be done by malicious code trying to
+		// intercept cross-cutting concerns.
+		//
+		// Panic for all other errors as well. At this point there should not
+		// be any other errors returned from the store operation. If there
+		// are, alert the developer that adding them as soon as possible that
+		// they need to be handled here.
+		panic(err)
+	}
 }
diff --git a/propagators/autoprop/registry_test.go b/propagators/autoprop/registry_test.go
index df2b2947315..3182a86bd0a 100644
--- a/propagators/autoprop/registry_test.go
+++ b/propagators/autoprop/registry_test.go
@@ -15,6 +15,7 @@
 package autoprop
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -60,8 +61,20 @@ func TestRegistryConcurrentSafe(t *testing.T) {
 func TestRegisterTextMapPropagator(t *testing.T) {
 	const propName = "custom"
 	RegisterTextMapPropagator(propName, noop)
+	t.Cleanup(func() { envRegistry.drop(propName) })
 
 	v, ok := envRegistry.load(propName)
 	assert.True(t, ok, "missing propagator in envRegistry")
 	assert.Equal(t, noop, v, "wrong propagator stored")
 }
+
+func TestDuplicateRegisterTextMapPropagatorPanics(t *testing.T) {
+	const propName = "custom"
+	RegisterTextMapPropagator(propName, noop)
+	t.Cleanup(func() { envRegistry.drop(propName) })
+
+	errString := fmt.Sprintf("%s: %q", errDupReg, propName)
+	assert.PanicsWithError(t, errString, func() {
+		RegisterTextMapPropagator(propName, noop)
+	})
+}

From 0e495e2040c2fa74f9dbbb3e23e17f2538ed2ba4 Mon Sep 17 00:00:00 2001
From: Tyler Yahn <codingalias@gmail.com>
Date: Tue, 31 May 2022 08:26:43 -0700
Subject: [PATCH 22/22] Check errs in registry_test

---
 propagators/autoprop/registry_test.go | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/propagators/autoprop/registry_test.go b/propagators/autoprop/registry_test.go
index 3182a86bd0a..7f284b6a27a 100644
--- a/propagators/autoprop/registry_test.go
+++ b/propagators/autoprop/registry_test.go
@@ -19,6 +19,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"go.opentelemetry.io/otel/propagation"
 )
@@ -27,7 +28,9 @@ var noop = propagation.NewCompositeTextMapPropagator()
 
 func TestRegistryEmptyStore(t *testing.T) {
 	r := registry{}
-	assert.NotPanics(t, func() { r.store("first", noop) })
+	assert.NotPanics(t, func() {
+		require.NoError(t, r.store("first", noop))
+	})
 }
 
 func TestRegistryEmptyLoad(t *testing.T) {
@@ -43,10 +46,14 @@ func TestRegistryConcurrentSafe(t *testing.T) {
 	const propName = "prop"
 
 	r := registry{}
-	assert.NotPanics(t, func() { r.store(propName, noop) })
+	assert.NotPanics(t, func() {
+		require.NoError(t, r.store(propName, noop))
+	})
 
 	go func() {
-		assert.NotPanics(t, func() { r.store(propName, noop) })
+		assert.NotPanics(t, func() {
+			require.ErrorIs(t, r.store(propName, noop), errDupReg)
+		})
 	}()
 
 	go func() {