temporality preference from env (#990)

Implement OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE, which controls the temporality of meters when creating from environment vars.
Add OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION to variables, although we do not yet have anything that uses it.

Author: brettmc

Common/Configuration/Defaults.php

@@ -104,6 +104,8 @@ interface Defaults
     public const OTEL_METRICS_EXEMPLAR_FILTER = 'with_sampled_trace';
     public const OTEL_METRIC_EXPORT_INTERVAL = 60000;
     public const OTEL_METRIC_EXPORT_TIMEOUT = 30000;
+    public const OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE = 'cumulative';
+    public const OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION = 'explicit_bucket_histogram';
     /**
      * Language Specific Environment Variables
      * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#language-specific-environment-variables

Common/Configuration/KnownValues.php

@@ -54,6 +54,11 @@ interface KnownValues
     public const VALUE_LOG_NOTICE = LogLevel::NOTICE;
     public const VALUE_LOG_INFO = LogLevel::INFO;
     public const VALUE_LOG_DEBUG = LogLevel::DEBUG;
+    public const VALUE_TEMPORALITY_CUMULATIVE = 'cumulative';
+    public const VALUE_TEMPORALITY_DELTA = 'delta';
+    public const VALUE_TEMPORALITY_LOW_MEMORY = 'lowmemory';
+    public const VALUE_HISTOGRAM_AGGREGATION_EXPLICIT = 'explicit_bucket_histogram';
+    public const VALUE_HISTOGRAM_AGGREGATION_BASE2_EXPONENTIAL = 'base2_exponential_bucket_histogram';
 
     public const VALUES_BOOLEAN = [
         self::VALUE_TRUE,
@@ -71,6 +76,17 @@ interface KnownValues
         self::VALUE_HTTP_JSON,
     ];
 
+    public const VALUES_TEMPORALITY_PREFERENCE = [
+        self::VALUE_TEMPORALITY_CUMULATIVE,
+        self::VALUE_TEMPORALITY_DELTA,
+        self::VALUE_TEMPORALITY_LOW_MEMORY,
+    ];
+
+    public const VALUES_HISTOGRAM_AGGREGATION = [
+        self::VALUE_HISTOGRAM_AGGREGATION_EXPLICIT,
+        self::VALUE_HISTOGRAM_AGGREGATION_BASE2_EXPONENTIAL,
+    ];
+
     /**
      * General SDK Configuration
      * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#general-sdk-configuration

Common/Configuration/ValueTypes.php

@@ -110,6 +110,8 @@ interface ValueTypes
     public const OTEL_METRICS_EXEMPLAR_FILTER = VariableTypes::ENUM;
     public const OTEL_METRIC_EXPORT_INTERVAL = VariableTypes::INTEGER;
     public const OTEL_METRIC_EXPORT_TIMEOUT = VariableTypes::INTEGER;
+    public const OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE = VariableTypes::ENUM;
+    public const OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION = VariableTypes::ENUM;
     /**
      * Language Specific Environment Variables
      * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#language-specific-environment-variables

Common/Configuration/Variables.php

@@ -125,6 +125,8 @@ interface Variables
     public const OTEL_METRICS_EXEMPLAR_FILTER = 'OTEL_METRICS_EXEMPLAR_FILTER';
     public const OTEL_METRIC_EXPORT_INTERVAL = 'OTEL_METRIC_EXPORT_INTERVAL';
     public const OTEL_METRIC_EXPORT_TIMEOUT = 'OTEL_METRIC_EXPORT_TIMEOUT';
+    public const OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE = 'OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE';
+    public const OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION = 'OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION';
     /**
      * Language Specific Environment Variables
      * @see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#language-specific-environment-variables

Metrics/MeterProviderFactory.php

@@ -23,6 +23,11 @@ class MeterProviderFactory
 {
     use LogsMessagesTrait;
 
+    /**
+     * @todo https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk_exporters/otlp.md#general
+     *       - "The exporter MUST configure the default aggregation on the basis of instrument kind using the
+     *         OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION variable as described below if it is implemented."
+     */
     public function create(): MeterProviderInterface
     {
         if (Sdk::isDisabled()) {
@@ -43,6 +48,7 @@ public function create(): MeterProviderInterface
             $exporter = new NoopMetricExporter();
         }
 
+        // @todo "The exporter MUST be paired with a periodic exporting MetricReader"
         $reader = new ExportingReader($exporter);
         $resource = ResourceInfoFactory::defaultResource();
         $exemplarFilter = $this->createExemplarFilter(Configuration::getEnum(Variables::OTEL_METRICS_EXEMPLAR_FILTER));