Add ConfigurableMetricReaderProvider SPI

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/internal/PrometheusMetricReaderProvider.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.prometheus.internal;
+
+import io.opentelemetry.exporter.prometheus.PrometheusHttpServer;
+import io.opentelemetry.exporter.prometheus.PrometheusHttpServerBuilder;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import io.opentelemetry.sdk.autoconfigure.spi.internal.ConfigurableMetricReaderProvider;
+import io.opentelemetry.sdk.metrics.export.MetricReader;
+
+/**
+ * SPI implementation for {@link PrometheusHttpServer}.
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ */
+public class PrometheusMetricReaderProvider implements ConfigurableMetricReaderProvider {
+
+  @Override
+  public MetricReader createMetricReader(ConfigProperties config) {
+    PrometheusHttpServerBuilder prometheusBuilder = PrometheusHttpServer.builder();
+
+    Integer port = config.getInt("otel.exporter.prometheus.port");
+    if (port != null) {
+      prometheusBuilder.setPort(port);
+    }
+    String host = config.getString("otel.exporter.prometheus.host");
+    if (host != null) {
+      prometheusBuilder.setHost(host);
+    }
+    return prometheusBuilder.build();
+  }
+
+  @Override
+  public String getName() {
+    return "prometheus";
+  }
+}

exporters/prometheus/src/main/resources/META-INF/services/io.opentelemetry.sdk.autoconfigure.spi.internal.ConfigurableMetricReaderProvider

@@ -0,0 +1 @@
+io.opentelemetry.exporter.prometheus.internal.PrometheusMetricReaderProvider

exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/internal/PrometheusMetricReaderProviderTest.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.prometheus.internal;
+
+import static org.assertj.core.api.Assertions.as;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
+
+import com.sun.net.httpserver.HttpServer;
+import io.opentelemetry.exporter.prometheus.PrometheusHttpServer;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import io.opentelemetry.sdk.autoconfigure.spi.internal.DefaultConfigProperties;
+import io.opentelemetry.sdk.metrics.export.MetricReader;
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.util.HashMap;
+import java.util.Map;
+import org.assertj.core.api.InstanceOfAssertFactories;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.mockito.junit.jupiter.MockitoSettings;
+import org.mockito.quality.Strictness;
+
+@ExtendWith(MockitoExtension.class)
+@MockitoSettings(strictness = Strictness.LENIENT)
+class PrometheusMetricReaderProviderTest {
+
+  private static final PrometheusMetricReaderProvider provider =
+      new PrometheusMetricReaderProvider();
+
+  @Mock private ConfigProperties configProperties;
+
+  @Test
+  void getName() {
+    assertThat(provider.getName()).isEqualTo("prometheus");
+  }
+
+  @Test
+  void createMetricReader_Default() throws IOException {
+    when(configProperties.getInt(any())).thenReturn(null);
+    when(configProperties.getString(any())).thenReturn(null);
+
+    try (MetricReader metricReader = provider.createMetricReader(configProperties)) {
+      assertThat(metricReader)
+          .isInstanceOf(PrometheusHttpServer.class)
+          .extracting("server", as(InstanceOfAssertFactories.type(HttpServer.class)))
+          .satisfies(
+              server -> {
+                assertThat(server.getAddress().getHostName()).isEqualTo("0:0:0:0:0:0:0:0");
+                assertThat(server.getAddress().getPort()).isEqualTo(9464);
+              });
+    }
+  }
+
+  @Test
+  void createMetricReader_WithConfiguration() throws IOException {
+    // Find a random unused port. There's a small race if another process takes it before we
+    // initialize. Consider adding retries to this test if it flakes, presumably it never will on
+    // CI since there's no prometheus there blocking the well-known port.
+    int port;
+    try (ServerSocket socket2 = new ServerSocket(0)) {
+      port = socket2.getLocalPort();
+    }
+
+    Map<String, String> config = new HashMap<>();
+    config.put("otel.exporter.prometheus.host", "localhost");
+    config.put("otel.exporter.prometheus.port", String.valueOf(port));
+
+    when(configProperties.getInt(any())).thenReturn(null);
+    when(configProperties.getString(any())).thenReturn(null);
+
+    try (MetricReader metricReader =
+        provider.createMetricReader(DefaultConfigProperties.createForTest(config))) {
+      assertThat(metricReader)
+          .extracting("server", as(InstanceOfAssertFactories.type(HttpServer.class)))
+          .satisfies(
+              server -> {
+                assertThat(server.getAddress().getHostName()).isEqualTo("localhost");
+                assertThat(server.getAddress().getPort()).isEqualTo(port);
+              });
+    }
+  }
+}

sdk-extensions/autoconfigure-spi/src/main/java/io/opentelemetry/sdk/autoconfigure/spi/internal/ConfigurableMetricReaderProvider.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.autoconfigure.spi.internal;
+
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import io.opentelemetry.sdk.autoconfigure.spi.metrics.ConfigurableMetricExporterProvider;
+import io.opentelemetry.sdk.metrics.export.MetricExporter;
+import io.opentelemetry.sdk.metrics.export.MetricReader;
+import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
+
+/**
+ * A service provider interface (SPI) for providing additional metric readers that can be used with
+ * the autoconfigured SDK. If the {@code otel.metrics.exporter} property contains a value equal to
+ * what is returned by {@link #getName()}, the exporter returned by {@link
+ * #createMetricReader(ConfigProperties)} will be enabled and added to the SDK.
+ *
+ * <p>Where as {@link ConfigurableMetricExporterProvider} provides push-based {@link
+ * MetricExporter}s to be paired with {@link PeriodicMetricReader}, this SPI facilitates pull-based
+ * {@link MetricReader}s.
+ *
+ * <p>This class is internal and is hence not for public use. Its APIs are unstable and can change
+ * at any time.
+ */
+public interface ConfigurableMetricReaderProvider {
+
+  /**
+   * Returns a {@link MetricReader} that can be registered to OpenTelemetry by providing the
+   * property value specified by {@link #getName()}.
+   */
+  MetricReader createMetricReader(ConfigProperties config);
+
+  /**
+   * Returns the name of this reader, which can be specified with the {@code otel.metrics.exporter}
+   * property to enable it. The name returned should NOT be the same as any other reader / exporter
+   * name, either from other implementations of this SPI or {@link
+   * ConfigurableMetricExporterProvider}. If the name does conflict with another reader / exporter
+   * name, the resulting behavior is undefined and it is explicitly unspecified which reader /
+   * exporter will actually be used.
+   */
+  String getName();
+}

sdk-extensions/autoconfigure-spi/src/main/java/io/opentelemetry/sdk/autoconfigure/spi/metrics/ConfigurableMetricExporterProvider.java

@@ -6,14 +6,20 @@
 package io.opentelemetry.sdk.autoconfigure.spi.metrics;
 
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import io.opentelemetry.sdk.autoconfigure.spi.internal.ConfigurableMetricReaderProvider;
 import io.opentelemetry.sdk.metrics.export.MetricExporter;
+import io.opentelemetry.sdk.metrics.export.MetricReader;
 
 /**
  * A service provider interface (SPI) for providing additional exporters that can be used with the
  * autoconfigured SDK. If the {@code otel.metrics.exporter} property contains a value equal to what
  * is returned by {@link #getName()}, the exporter returned by {@link
  * #createExporter(ConfigProperties)} will be enabled and added to the SDK.
  *
+ * <p>The push-based {@link MetricExporter}s supplied by this SPI are paired with a {@link
+ * io.opentelemetry.sdk.metrics.export.PeriodicMetricReader}. See {@link
+ * ConfigurableMetricReaderProvider} for providing pull-based {@link MetricReader}s.
+ *
  * @since 1.15.0
  */
 public interface ConfigurableMetricExporterProvider {
@@ -27,8 +33,10 @@ public interface ConfigurableMetricExporterProvider {
   /**
    * Returns the name of this exporter, which can be specified with the {@code
    * otel.metrics.exporter} property to enable it. The name returned should NOT be the same as any
-   * other exporter name. If the name does conflict with another exporter name, the resulting
-   * behavior is undefined and it is explicitly unspecified which exporter will actually be used.
+   * other exporter / reader name, either from other implementations of this SPI or {@link
+   * ConfigurableMetricReaderProvider}. If the name does conflict with another exporter / reader
+   * name, the resulting behavior is undefined and it is explicitly unspecified which exporter /
+   * reader will actually be used.
    */
   String getName();
 }

sdk-extensions/autoconfigure/src/main/java/io/opentelemetry/sdk/autoconfigure/MeterProviderConfiguration.java

@@ -19,7 +19,6 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
-import java.util.Objects;
 import java.util.Set;
 import java.util.function.BiFunction;
 import java.util.stream.Collectors;
@@ -87,7 +86,6 @@ static List<MetricReader> configureMetricReaders(
             exporterName ->
                 MetricExporterConfiguration.configureReader(
                     exporterName, config, spiHelper, metricExporterCustomizer, closeables))
-        .filter(Objects::nonNull)
         .collect(Collectors.toList());
   }