env.go

// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0

// Package env provides a detector that loads resource information from
// the OTEL_RESOURCE environment variable. A list of labels of the form
// `<key1>=<value1>,<key2>=<value2>,...` is accepted. Domain names and
// paths are accepted as label keys.
package env // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/resourcedetectionprocessor/internal/env"

import (
	"context"
	"fmt"
	"net/url"
	"os"
	"regexp"
	"strings"

	"go.opentelemetry.io/collector/pdata/pcommon"
	"go.opentelemetry.io/collector/processor"

	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/resourcedetectionprocessor/internal"
)

// TypeStr is type of detector.
const TypeStr = "env"

// Environment variable used by "env" to decode a resource.
const envVar = "OTEL_RESOURCE_ATTRIBUTES"

// Deprecated environment variable used by "env" to decode a resource.
// Specification states to use OTEL_RESOURCE_ATTRIBUTES however to avoid
// breaking existing usage, maintain support for OTEL_RESOURCE
// https://github.com/open-telemetry/opentelemetry-specification/blob/1afab39e5658f807315abf2f3256809293bfd421/specification/resource/sdk.md#specifying-resource-information-via-an-environment-variable
const deprecatedEnvVar = "OTEL_RESOURCE"

var _ internal.Detector = (*Detector)(nil)

type Detector struct{}

func NewDetector(processor.Settings, internal.DetectorConfig) (internal.Detector, error) {
	return &Detector{}, nil
}

func (d *Detector) Detect(context.Context) (resource pcommon.Resource, schemaURL string, err error) {
	res := pcommon.NewResource()

	labels := strings.TrimSpace(os.Getenv(envVar))
	if labels == "" {
		labels = strings.TrimSpace(os.Getenv(deprecatedEnvVar))
		if labels == "" {
			return res, "", nil
		}
	}

	err = initializeAttributeMap(res.Attributes(), labels)
	if err != nil {
		res.Attributes().Clear()
		return res, "", err
	}

	return res, "", nil
}

// labelRegex matches any key=value pair including a trailing comma or the end of the
// string. Captures the trimmed key & value parts, and ignores any superfluous spaces.
var labelRegex = regexp.MustCompile(`\s*([[:ascii:]]{1,256}?)\s*=\s*([[:ascii:]]{0,256}?)\s*(?:,|$)`)

func initializeAttributeMap(am pcommon.Map, s string) error {
	matches := labelRegex.FindAllStringSubmatchIndex(s, -1)
	for len(matches) == 0 {
		return fmt.Errorf("invalid resource format: %q", s)
	}

	prevIndex := 0
	for _, match := range matches {
		// if there is any text between matches, raise an error
		if prevIndex != match[0] {
			return fmt.Errorf("invalid resource format, invalid text: %q", s[prevIndex:match[0]])
		}

		key := s[match[2]:match[3]]
		value := s[match[4]:match[5]]

		var err error
		if value, err = url.QueryUnescape(value); err != nil {
			return fmt.Errorf("invalid resource format in attribute: %q, err: %w", s[match[0]:match[1]], err)
		}
		am.PutStr(key, value)

		prevIndex = match[1]
	}

	// if there is any text after the last match, raise an error
	if matches[len(matches)-1][1] != len(s) {
		return fmt.Errorf("invalid resource format, invalid text: %q", s[matches[len(matches)-1][1]:])
	}

	return nil
}