refactor sdk/api logging (open-telemetry#1105)

send errors/warnings/etc by default through PHP's error_log. This gives more control to administrators, since error_log can
be configured to write to any stream (file, stderr, etc). I think it's also less surprising for people trying out otel (particularly
with development PHP settings, where trigger_error often breaks an application).
Adding a configuration value to control where logs go: OTEL_PHP_LOG_DESTINATION.

examples/global_providers.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+use OpenTelemetry\API\Globals;
+use OpenTelemetry\API\Instrumentation\Configurator;
+use OpenTelemetry\SDK\Trace\SpanExporter\ConsoleSpanExporterFactory;
+use OpenTelemetry\SDK\Trace\SpanProcessor\SimpleSpanProcessor;
+use OpenTelemetry\SDK\Trace\TracerProvider;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+/**
+ * Example of globally registering <Signal>Provider instances.
+ * Generally this is hidden inside the SDK builder or SDK autoloading,
+ * but you can also do it manually. The providers are stored in
+ * context, and reset to previous values or defaults when the
+ * scope is detached.
+ */
+
+//before, a no-op provider is provided by default
+echo 'Before: ' . get_class(Globals::tracerProvider()) . PHP_EOL;
+
+$tracerProvider = TracerProvider::builder()->addSpanProcessor(
+    new SimpleSpanProcessor(
+        (new ConsoleSpanExporterFactory())->create()
+    )
+)->build();
+
+$configurator = Configurator::create()
+    ->withTracerProvider($tracerProvider);
+
+$scope = $configurator->activate();
+//activated, now our $tracerProvider is globally available
+echo 'During: ' . get_class(Globals::tracerProvider()) . PHP_EOL;
+
+$scope->detach();
+
+//after scope detached, back to default no-op providers:
+echo 'After: ' . get_class(Globals::tracerProvider()) . PHP_EOL;

examples/logs/exporters/otlp_grpc.php

@@ -4,9 +4,6 @@
 
 namespace OpenTelemetry\Example;
 
-use Monolog\Handler\StreamHandler;
-use Monolog\Logger;
-use OpenTelemetry\API\LoggerHolder;
 use OpenTelemetry\API\Logs\EventLogger;
 use OpenTelemetry\API\Logs\LogRecord;
 use OpenTelemetry\API\Signals;
@@ -19,14 +16,9 @@
 use OpenTelemetry\SDK\Logs\LoggerProvider;
 use OpenTelemetry\SDK\Logs\LogRecordLimitsBuilder;
 use OpenTelemetry\SDK\Logs\Processor\BatchLogRecordProcessor;
-use Psr\Log\LogLevel;
 
 require __DIR__ . '/../../../vendor/autoload.php';
 
-LoggerHolder::set(
-    new Logger('otel-php', [new StreamHandler(STDOUT, LogLevel::DEBUG)])
-);
-
 $transport = (new GrpcTransportFactory())->create('http://collector:4317' . OtlpUtil::method(Signals::LOGS));
 $exporter = new LogsExporter($transport);
 $loggerProvider = new LoggerProvider(

examples/logs/exporters/otlp_http.php

@@ -4,9 +4,6 @@
 
 namespace OpenTelemetry\Example;
 
-use Monolog\Handler\StreamHandler;
-use Monolog\Logger;
-use OpenTelemetry\API\LoggerHolder;
 use OpenTelemetry\API\Logs\EventLogger;
 use OpenTelemetry\API\Logs\LogRecord;
 use OpenTelemetry\Contrib\Otlp\LogsExporter;
@@ -16,14 +13,9 @@
 use OpenTelemetry\SDK\Logs\LoggerProvider;
 use OpenTelemetry\SDK\Logs\LogRecordLimitsBuilder;
 use OpenTelemetry\SDK\Logs\Processor\SimpleLogRecordProcessor;
-use Psr\Log\LogLevel;
 
 require __DIR__ . '/../../../vendor/autoload.php';
 
-LoggerHolder::set(
-    new Logger('otel-php', [new StreamHandler(STDOUT, LogLevel::DEBUG)])
-);
-
 $transport = (new OtlpHttpTransportFactory())->create('http://collector:4318/v1/logs', 'application/json');
 $exporter = new LogsExporter($transport);
 

examples/metrics/exporters/otlp_grpc.php

@@ -13,8 +13,6 @@
 use OpenTelemetry\SDK\Common\Time\ClockFactory;
 use OpenTelemetry\SDK\Metrics\MetricReader\ExportingReader;
 
-\OpenTelemetry\API\LoggerHolder::set(new \Monolog\Logger('grpc', [new \Monolog\Handler\StreamHandler('php://stderr')]));
-
 $clock = ClockFactory::getDefault();
 
 $reader = new ExportingReader(

examples/sdk_builder.php

@@ -2,10 +2,7 @@
 
 declare(strict_types=1);
 
-use Monolog\Handler\StreamHandler;
-use Monolog\Logger;
 use OpenTelemetry\API\Instrumentation\CachedInstrumentation;
-use OpenTelemetry\API\LoggerHolder;
 use OpenTelemetry\API\Trace\Propagation\TraceContextPropagator;
 use OpenTelemetry\Contrib\Otlp\MetricExporter;
 use OpenTelemetry\SDK\Common\Export\Http\PsrTransportFactory;
@@ -25,8 +22,6 @@
 
 echo 'Starting SDK builder example' . PHP_EOL;
 
-LoggerHolder::set(new Logger('grpc', [new StreamHandler('php://stderr')]));
-
 $resource = ResourceInfoFactory::defaultResource();
 $spanExporter = new InMemoryExporter();
 $logRecordExporter = new \OpenTelemetry\SDK\Logs\Exporter\InMemoryExporter();

examples/traces/exporters/otlp_file.php

@@ -6,18 +6,13 @@
 
 require __DIR__ . '/../../../vendor/autoload.php';
 
-use Monolog\Handler\StreamHandler;
-use Monolog\Logger;
-use OpenTelemetry\API\LoggerHolder;
 use OpenTelemetry\Contrib\Otlp\ContentTypes;
 use OpenTelemetry\Contrib\Otlp\SpanExporter;
 use OpenTelemetry\SDK\Common\Export\Stream\StreamTransportFactory;
 use OpenTelemetry\SDK\Common\Time\ClockFactory;
 use OpenTelemetry\SDK\Trace\SpanProcessor\BatchSpanProcessor;
 use OpenTelemetry\SDK\Trace\TracerProvider;
 
-LoggerHolder::set(new Logger('otlp-example', [new StreamHandler('php://stderr')]));
-
 $filename = sys_get_temp_dir() . '/traces.jsonl';
 $file = fopen($filename, 'a');
 $transport = (new StreamTransportFactory())->create($file, ContentTypes::NDJSON);

examples/traces/exporters/otlp_grpc.php

@@ -13,8 +13,6 @@
 use OpenTelemetry\SDK\Trace\SpanProcessor\SimpleSpanProcessor;
 use OpenTelemetry\SDK\Trace\TracerProvider;
 
-\OpenTelemetry\API\LoggerHolder::set(new \Monolog\Logger('grpc', [new \Monolog\Handler\StreamHandler('php://stderr')]));
-
 $transport = (new GrpcTransportFactory())->create('http://collector:4317' . OtlpUtil::method(Signals::TRACE));
 $exporter = new SpanExporter($transport);
 echo 'Starting OTLP GRPC example';

examples/traces/exporters/otlp_grpc_from_factory.php

@@ -8,8 +8,6 @@
 
 require __DIR__ . '/../../../vendor/autoload.php';
 
-\OpenTelemetry\API\LoggerHolder::set(new \Monolog\Logger('grpc', [new \Monolog\Handler\StreamHandler('php://stderr')]));
-
 /**
  * Create an otlp+grpc tracer provider from TracerProviderFactory, using environment variables as input
  */

examples/traces/exporters/otlp_http.php

@@ -6,16 +6,11 @@
 
 require __DIR__ . '/../../../vendor/autoload.php';
 
-use Monolog\Handler\StreamHandler;
-use Monolog\Logger;
-use OpenTelemetry\API\LoggerHolder;
 use OpenTelemetry\Contrib\Otlp\OtlpHttpTransportFactory;
 use OpenTelemetry\Contrib\Otlp\SpanExporter;
 use OpenTelemetry\SDK\Trace\SpanProcessor\SimpleSpanProcessor;
 use OpenTelemetry\SDK\Trace\TracerProvider;
 
-LoggerHolder::set(new Logger('otlp-example', [new StreamHandler('php://stderr')]));
-
 $transport = (new OtlpHttpTransportFactory())->create('http://collector:4318/v1/traces', 'application/x-protobuf');
 $exporter = new SpanExporter($transport);
 

examples/traces/exporters/otlp_http_from_factory.php

@@ -6,8 +6,6 @@
 
 require __DIR__ . '/../../../vendor/autoload.php';
 
-\OpenTelemetry\API\LoggerHolder::set(new \Monolog\Logger('grpc', [new \Monolog\Handler\StreamHandler('php://stderr')]));
-
 /**
  * Create an otlp+http/protobuf tracer provider from TracerProviderFactory, using environment variables as input
  */

examples/traces/exporters/otlp_http_json.php

@@ -6,16 +6,11 @@
 
 require __DIR__ . '/../../../vendor/autoload.php';
 
-use Monolog\Handler\StreamHandler;
-use Monolog\Logger;
-use OpenTelemetry\API\LoggerHolder;
 use OpenTelemetry\Contrib\Otlp\OtlpHttpTransportFactory;
 use OpenTelemetry\Contrib\Otlp\SpanExporter;
 use OpenTelemetry\SDK\Trace\SpanProcessor\SimpleSpanProcessor;
 use OpenTelemetry\SDK\Trace\TracerProvider;
 
-LoggerHolder::set(new Logger('otlp-example', [new StreamHandler('php://stderr')]));
-
 $transport = (new OtlpHttpTransportFactory())->create('http://collector:4318/v1/traces', 'application/json');
 $exporter = new SpanExporter($transport);
 

examples/traces/troubleshooting/air_gapped_trace_debugging.php → examples/troubleshooting/air_gapped_trace_debugging.php

@@ -4,7 +4,7 @@
 
 namespace OpenTelemetry\Example;
 
-require __DIR__ . '/../../../vendor/autoload.php';
+require __DIR__ . '/../../vendor/autoload.php';
 
 /**
  * If you want/need to test or debug the creation of traces and spans without an instance of an exporter/collector,
@@ -24,7 +24,7 @@
 /**
  * Create the log directory
  */
-$logDir = __DIR__ . '/../var/log';
+$logDir = __DIR__ . '/var/log';
 $logFile = $logDir . '/otel.log';
 if (!is_dir($logDir) && !mkdir($logDir, 0744, true) && !is_dir($logDir)) {
     throw new \RuntimeException(sprintf('Directory "%s" was not created', $logDir));

examples/traces/troubleshooting/logging_of_span_data.php → examples/troubleshooting/logging_of_span_data.php

@@ -4,7 +4,7 @@
 
 namespace OpenTelemetry\Example;
 
-require __DIR__ . '/../../../vendor/autoload.php';
+require __DIR__ . '/../../vendor/autoload.php';
 
 /**
  * If you want to observe or debug the span data, which is sent to an exporter/collector,
@@ -29,7 +29,7 @@
 /**
  * Create the log directory
  */
-$logDir = __DIR__ . '/../var/log';
+$logDir = __DIR__ . '/var/log';
 $logFile = $logDir . '/otel.log';
 if (!is_dir($logDir) && !mkdir($logDir, 0744, true) && !is_dir($logDir)) {
     throw new \RuntimeException(sprintf('Directory "%s" was not created', $logDir));

examples/traces/troubleshooting/setting_up_logging.php → examples/troubleshooting/psr3_logging.php

@@ -4,27 +4,25 @@
 
 namespace OpenTelemetry\Example;
 
-require __DIR__ . '/../../../vendor/autoload.php';
+require __DIR__ . '/../../vendor/autoload.php';
 
-use Monolog\Handler\StreamHandler;
-use Monolog\Logger;
-use OpenTelemetry\API\LoggerHolder;
 use OpenTelemetry\SDK\Trace\TracerProviderFactory;
-use Psr\Log\LogLevel;
 
-echo 'Starting SettingUpLogging example' . PHP_EOL;
+echo 'Starting PSR-3 Logging example' . PHP_EOL;
 
-//By default, opentelemetry's internal logging (errors, warnings, etc) will use `trigger_error`.
-//You can instead provide a psr-3 logger to provide greater control of logging output:
-LoggerHolder::set(
-    new Logger('otel-php', [new StreamHandler(STDOUT, LogLevel::DEBUG)])
-);
+putenv('OTEL_PHP_LOG_DESTINATION=psr3'); //or, do not set this at all.
 putenv('OTEL_EXPORTER_OTLP_ENDPOINT=http://does-not-exist/endpoint'); //invalid endpoint, export will fail
 putenv('OTEL_EXPORTER_OTLP_PROTOCOL=grpc');
+
+$filename = __DIR__ . '/var/otel.log';
+\OpenTelemetry\API\LoggerHolder::set(new \Monolog\Logger('otel', [new \Monolog\Handler\StreamHandler($filename)]));
+
 $factory = new TracerProviderFactory();
 $tracerProvider = $factory->create();
 
 $tracer = $tracerProvider->getTracer('io.opentelemetry.contrib.php');
 $span = $tracer->spanBuilder('root-span')->startSpan();
 $span->end();
 $tracerProvider->shutdown();
+
+echo sprintf("Logs written to: %s\n", $filename);

examples/troubleshooting/setting_up_logging.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\Example;
+
+require __DIR__ . '/../../vendor/autoload.php';
+
+use Monolog\Logger;
+use OpenTelemetry\SDK\Trace\TracerProviderFactory;
+
+echo 'Starting Logging example' . PHP_EOL;
+
+/**
+ * By default errors and warnings from the SDK itself (for example misconfiguration, exporter errors) will be sent to PHP's error_log.
+ * You can change that by setting OTEL_PHP_LOG_DESTINATION.
+ * Valid values for OTEL_PHP_LOG_DESTINATION: error_log, stdout, stderr, none, psr3, default
+ * (default = psr-3 if LoggerHolder::set called, otherwise error_log
+ *
+ * Note that PSR-3 logging will only work if a PSR-3 logger is registered in OpenTelemetry\API\LoggerHolder::set()
+ * If no PSR-3 logger is available, it will fall back to using error_log.
+ */
+
+putenv('OTEL_PHP_LOG_DESTINATION=stderr');
+putenv('OTEL_EXPORTER_OTLP_ENDPOINT=http://does-not-exist/endpoint'); //invalid endpoint, export will fail
+putenv('OTEL_EXPORTER_OTLP_PROTOCOL=grpc');
+
+$factory = new TracerProviderFactory();
+$tracerProvider = $factory->create();
+
+$tracer = $tracerProvider->getTracer('io.opentelemetry.contrib.php');
+$span = $tracer->spanBuilder('root-span')->startSpan();
+$span->end();
+$tracerProvider->shutdown();

src/API/Behavior/Internal/LogWriter/ErrorLogWriter.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\API\Behavior\Internal\LogWriter;
+
+class ErrorLogWriter implements LogWriterInterface
+{
+    public function write($level, string $message, array $context): void
+    {
+        error_log(Formatter::format($level, $message, $context));
+    }
+}

src/API/Behavior/Internal/LogWriter/Formatter.php

@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\API\Behavior\Internal\LogWriter;
+
+class Formatter
+{
+    public static function format($level, string $message, array $context): string
+    {
+        $exception = (array_key_exists('exception', $context) && $context['exception'] instanceof \Throwable)
+            ? $context['exception']
+            : null;
+        if ($exception) {
+            $message = sprintf(
+                'OpenTelemetry: [%s] %s [exception] %s%s%s',
+                $level,
+                $message,
+                $exception->getMessage(),
+                PHP_EOL,
+                $exception->getTraceAsString()
+            );
+        } else {
+            //get calling location, skipping over trait, formatter etc
+            $caller = debug_backtrace()[3];
+            $message = sprintf(
+                'OpenTelemetry: [%s] %s in %s(%s)',
+                $level,
+                $message,
+                $caller['file'],
+                $caller['line'],
+            );
+        }
+
+        return $message;
+    }
+}

src/API/Behavior/Internal/LogWriter/LogWriterInterface.php

@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\API\Behavior\Internal\LogWriter;
+
+interface LogWriterInterface
+{
+    public function write($level, string $message, array $context): void;
+}

src/API/Behavior/Internal/LogWriter/NoopLogWriter.php

@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenTelemetry\API\Behavior\Internal\LogWriter;
+
+class NoopLogWriter implements LogWriterInterface
+{
+    public function write($level, string $message, array $context): void
+    {
+        //do nothing
+    }
+}