Refactor OTLP exporter env config to be shared across all exporters (#…

…2608)

* setup global envconfig package for otlp exporter

* use envconfig in otlpmetrics package

* fix lint

* add changelog entry

* Update exporters/otlp/internal/envconfig/envconfig.go

Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>

* fix lint

Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>
Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>

CHANGELOG.md

@@ -31,6 +31,7 @@ This update is a breaking change of the unstable Metrics API. Code instrumented
 - The metrics API has been significantly changed. (#2587)
 - Unify path cleaning functionally in the `otlpmetric` and `otlptrace` config. (#2639)
 - Change the debug message from the `sdk/trace.BatchSpanProcessor` to reflect the count is cumulative. (#2640)
+- Introduce new internal envconfig package for OTLP exporters (#2608)
 
 ### Fixed
 

exporters/otlp/internal/envconfig/envconfig.go

@@ -0,0 +1,148 @@
+// 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 envconfig // import "go.opentelemetry.io/otel/exporters/otlp/internal/envconfig"
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"errors"
+	"fmt"
+	"net/url"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// ConfigFn is the generic function used to set a config
+type ConfigFn func(*EnvOptionsReader)
+
+// EnvOptionsReader reads the required environment variables
+type EnvOptionsReader struct {
+	GetEnv    func(string) string
+	ReadFile  func(string) ([]byte, error)
+	Namespace string
+}
+
+// Apply runs every ConfigFn
+func (e *EnvOptionsReader) Apply(opts ...ConfigFn) {
+	for _, o := range opts {
+		o(e)
+	}
+}
+
+// GetEnvValue gets an OTLP environment variable value of the specified key
+// using the GetEnv function.
+// This function prepends the OTLP specified namespace to all key lookups.
+func (e *EnvOptionsReader) GetEnvValue(key string) (string, bool) {
+	v := strings.TrimSpace(e.GetEnv(keyWithNamespace(e.Namespace, key)))
+	return v, v != ""
+}
+
+// WithString retrieves the specified config and passes it to ConfigFn as a string
+func WithString(n string, fn func(string)) func(e *EnvOptionsReader) {
+	return func(e *EnvOptionsReader) {
+		if v, ok := e.GetEnvValue(n); ok {
+			fn(v)
+		}
+	}
+}
+
+// WithDuration retrieves the specified config and passes it to ConfigFn as a duration
+func WithDuration(n string, fn func(time.Duration)) func(e *EnvOptionsReader) {
+	return func(e *EnvOptionsReader) {
+		if v, ok := e.GetEnvValue(n); ok {
+			if d, err := strconv.Atoi(v); err == nil {
+				fn(time.Duration(d) * time.Millisecond)
+			}
+		}
+	}
+}
+
+// WithHeaders retrieves the specified config and passes it to ConfigFn as a map of HTTP headers
+func WithHeaders(n string, fn func(map[string]string)) func(e *EnvOptionsReader) {
+	return func(e *EnvOptionsReader) {
+		if v, ok := e.GetEnvValue(n); ok {
+			fn(stringToHeader(v))
+		}
+	}
+}
+
+// WithURL retrieves the specified config and passes it to ConfigFn as a net/url.URL
+func WithURL(n string, fn func(*url.URL)) func(e *EnvOptionsReader) {
+	return func(e *EnvOptionsReader) {
+		if v, ok := e.GetEnvValue(n); ok {
+			if u, err := url.Parse(v); err == nil {
+				fn(u)
+			}
+		}
+	}
+}
+
+// WithTLSConfig retrieves the specified config and passes it to ConfigFn as a crypto/tls.Config
+func WithTLSConfig(n string, fn func(*tls.Config)) func(e *EnvOptionsReader) {
+	return func(e *EnvOptionsReader) {
+		if v, ok := e.GetEnvValue(n); ok {
+			if b, err := e.ReadFile(v); err == nil {
+				if c, err := createTLSConfig(b); err == nil {
+					fn(c)
+				}
+			}
+		}
+	}
+}
+
+func keyWithNamespace(ns, key string) string {
+	if ns == "" {
+		return key
+	}
+	return fmt.Sprintf("%s_%s", ns, key)
+}
+
+func stringToHeader(value string) map[string]string {
+	headersPairs := strings.Split(value, ",")
+	headers := make(map[string]string)
+
+	for _, header := range headersPairs {
+		nameValue := strings.SplitN(header, "=", 2)
+		if len(nameValue) < 2 {
+			continue
+		}
+		name, err := url.QueryUnescape(nameValue[0])
+		if err != nil {
+			continue
+		}
+		trimmedName := strings.TrimSpace(name)
+		value, err := url.QueryUnescape(nameValue[1])
+		if err != nil {
+			continue
+		}
+		trimmedValue := strings.TrimSpace(value)
+
+		headers[trimmedName] = trimmedValue
+	}
+
+	return headers
+}
+
+func createTLSConfig(certBytes []byte) (*tls.Config, error) {
+	cp := x509.NewCertPool()
+	if ok := cp.AppendCertsFromPEM(certBytes); !ok {
+		return nil, errors.New("failed to append certificate to the cert pool")
+	}
+
+	return &tls.Config{
+		RootCAs: cp,
+	}, nil
+}