OT resource detector (#939)

* first

* all included

* constant

* res keys

* env detector

* Update sdk/detect/env.go

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>

* new test cases and strings operation to handle labels

* solved conflict

* typo

* corrected comments

* deleted env var handling

* push again

* rerun

* restructuring

* new way to aggregate errors

* all in resources package and verbose comments

* solved merge conflicts

* included new error types

* improved error handling

* updated changelog.md

* updated changelog

* updated changelog.md

* updated changelog

* Update CHANGELOG.md

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>
Co-authored-by: Liz Fong-Jones <lizf@honeycomb.io>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -10,6 +10,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ### Added
 
+- Define a general Resources Detector Interface and allow resources to be detected from environment variables. (#939)
 - Github action to generate protobuf Go bindings locally in `internal/opentelemetry-proto-gen`. (#938)
 - OTLP .proto files from `open-telemetry/opentelemetry-proto` imported as a git submodule under `internal/opentelemetry-proto`.
    References to `github.com/open-telemetry/opentelemetry-proto` changed to `go.opentelemetry.io/otel/internal/opentelemetry-proto-gen`. (#942)

sdk/resource/auto.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 resource
+
+import (
+	"context"
+	"errors"
+	"fmt"
+)
+
+var (
+	// ErrMissingResource is returned by a detector when source information
+	// is unavailable for a Resource.
+	ErrMissingResource = errors.New("missing resource")
+	// ErrPartialResource is returned by a detector when complete source
+	// information for a Resource is unavailable or the source information
+	// contains invalid values that are omitted from the returned Resource.
+	ErrPartialResource = errors.New("partial resource")
+)
+
+// Detector detects OpenTelemetry resource information
+type Detector interface {
+	// Detect returns an initialized Resource based on gathered information.
+	// If source information to construct a Resource is inaccessible, an
+	// uninitialized Resource is returned with an appropriately wrapped
+	// ErrMissingResource error is returned. If the source information to
+	// construct a Resource contains invalid values, a Resource is returned
+	// with the valid parts of the source information used for
+	// initialization along with an appropriately wrapped ErrPartialResource
+	// error.
+	Detect(ctx context.Context) (*Resource, error)
+}
+
+// Detect calls all input detectors sequentially and merges each result with the previous one.
+// It returns the merged error too.
+func Detect(ctx context.Context, detectors ...Detector) (*Resource, error) {
+	var autoDetectedRes *Resource
+	var errInfo []string
+	for _, detector := range detectors {
+		res, err := detector.Detect(ctx)
+		if err != nil {
+			errInfo = append(errInfo, err.Error())
+			if !errors.Is(err, ErrPartialResource) {
+				continue
+			}
+		}
+		autoDetectedRes = Merge(autoDetectedRes, res)
+	}
+
+	var aggregatedError error
+	if len(errInfo) > 0 {
+		aggregatedError = fmt.Errorf("detecting resources: %s", errInfo)
+	}
+	return autoDetectedRes, aggregatedError
+}

sdk/resource/doc.go

@@ -0,0 +1,28 @@
+// 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 resource provides detecting and representing resources.
+//
+// The fundamental struct is a Resource which holds identifying information
+// about the entities for which telemetry is exported.
+//
+// To automatically construct Resources from an environment a Detector
+// interface is defined. Implementations of this interface can be passed to
+// the Detect function to generate a Resource from the merged information.
+//
+// To load a user defined Resource from the environment variable
+// OTEL_RESOURCE_LABELS the FromEnv Detector can be used. It will interpret
+// the value as a list of comma delimited key/value pairs
+// (e.g. `<key1>=<value1>,<key2>=<value2>,...`).
+package resource

sdk/resource/env.go

@@ -0,0 +1,69 @@
+// 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 resource
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strings"
+
+	"go.opentelemetry.io/otel/api/kv"
+)
+
+// envVar is the environment variable name OpenTelemetry Resource information can be assigned to.
+const envVar = "OTEL_RESOURCE_LABELS"
+
+var (
+	//errMissingValue is returned when a resource value is missing.
+	errMissingValue = fmt.Errorf("%w: missing value", ErrPartialResource)
+)
+
+// FromEnv is a detector that implements the Detector and collects resources
+// from environment
+type FromEnv struct{}
+
+// compile time assertion that FromEnv implements Detector interface
+var _ Detector = (*FromEnv)(nil)
+
+// Detect collects resources from environment
+func (d *FromEnv) Detect(context.Context) (*Resource, error) {
+	labels := strings.TrimSpace(os.Getenv(envVar))
+
+	if labels == "" {
+		return Empty(), ErrMissingResource
+	}
+	return constructOTResources(labels)
+}
+
+func constructOTResources(s string) (*Resource, error) {
+	pairs := strings.Split(s, ",")
+	labels := []kv.KeyValue{}
+	var invalid []string
+	for _, p := range pairs {
+		field := strings.SplitN(p, "=", 2)
+		if len(field) != 2 {
+			invalid = append(invalid, p)
+			continue
+		}
+		k, v := strings.TrimSpace(field[0]), strings.TrimSpace(field[1])
+		labels = append(labels, kv.String(k, v))
+	}
+	var err error
+	if len(invalid) > 0 {
+		err = fmt.Errorf("%w: %v", errMissingValue, invalid)
+	}
+	return New(labels...), err
+}

sdk/resource/env_test.go

@@ -0,0 +1,73 @@
+// 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 resource
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/otel/api/kv"
+)
+
+func TestDetectOnePair(t *testing.T) {
+	os.Setenv(envVar, "key=value")
+
+	detector := &FromEnv{}
+	res, err := detector.Detect(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, New(kv.String("key", "value")), res)
+}
+
+func TestDetectMultiPairs(t *testing.T) {
+	os.Setenv("x", "1")
+	os.Setenv(envVar, "key=value, k = v , a= x, a=z")
+
+	detector := &FromEnv{}
+	res, err := detector.Detect(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, res, New(
+		kv.String("key", "value"),
+		kv.String("k", "v"),
+		kv.String("a", "x"),
+		kv.String("a", "z"),
+	))
+}
+
+func TestEmpty(t *testing.T) {
+	os.Setenv(envVar, "")
+
+	detector := &FromEnv{}
+	res, err := detector.Detect(context.Background())
+	require.Error(t, err)
+	assert.Equal(t, err, ErrMissingResource)
+	assert.Equal(t, Empty(), res)
+}
+
+func TestMissingKeyError(t *testing.T) {
+	os.Setenv(envVar, "key=value,key")
+
+	detector := &FromEnv{}
+	res, err := detector.Detect(context.Background())
+	assert.Error(t, err)
+	assert.Equal(t, err, fmt.Errorf("%w: %v", errMissingValue, "[key]"))
+	assert.Equal(t, res, New(
+		kv.String("key", "value"),
+	))
+}

sdk/resource/resource.go

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package resource provides functionality for resource, which capture
-// identifying information about the entities for which signals are exported.
 package resource
 
 import (
@@ -34,7 +32,7 @@ type Resource struct {
 
 var emptyResource Resource
 
-// Key creates a resource from a set of attributes.  If there are
+// New creates a resource from a set of attributes.  If there are
 // duplicate keys present in the list of attributes, then the last
 // value found for the key is preserved.
 func New(kvs ...kv.KeyValue) *Resource {