First POC for external extension loading

examples/extension/build.gradle

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+group 'io.opentelemetry.example'
+version '1.0-SNAPSHOT'
+
+subprojects {
+  version = rootProject.version
+
+  apply plugin: "java"
+
+  ext {
+    versions = [
+      opentelemetry         : "1.1.0",
+      opentelemetryJavaagent: "1.2.0-SNAPSHOT",
+      bytebuddy             : "1.10.18",
+      guava                 : "30.1-jre"
+    ]
+    versions.opentelemetryAlpha = "${versions.opentelemetry}-alpha"
+    versions.opentelemetryJavaagentAlpha = "1.2.0-alpha-SNAPSHOT"
+
+    deps = [
+      bytebuddy           : dependencies.create(group: 'net.bytebuddy', name: 'byte-buddy', version: versions.bytebuddy),
+      bytebuddyagent      : dependencies.create(group: 'net.bytebuddy', name: 'byte-buddy-agent', version: versions.bytebuddy),
+      autoservice         : [
+        dependencies.create(group: 'com.google.auto.service', name: 'auto-service', version: '1.0-rc7'),
+        dependencies.create(group: 'com.google.auto', name: 'auto-common', version: '0.8'),
+        dependencies.create(group: 'com.google.guava', name: 'guava', version: "${versions.guava}"),
+      ],
+      autoValueAnnotations: "com.google.auto.value:auto-value-annotations:${versions.autoValue}",
+    ]
+  }
+
+  repositories {
+    mavenLocal()
+    mavenCentral()
+  }
+
+  dependencies {
+    testImplementation("org.mockito:mockito-core:3.3.3")
+    testImplementation("org.junit.jupiter:junit-jupiter-api:5.6.2")
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.6.2")
+  }
+
+  tasks {
+    test {
+      useJUnitPlatform()
+    }
+
+    compileJava {
+      options.release.set(11)
+    }
+  }
+}

examples/extension/custom/build.gradle

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+plugins {
+  id "java"
+}
+
+dependencies {
+  compileOnly("io.opentelemetry:opentelemetry-sdk:${versions.opentelemetry}")
+  compileOnly("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure:${versions.opentelemetryAlpha}")
+
+  compileOnly("io.opentelemetry.javaagent:opentelemetry-javaagent-spi:${versions.opentelemetryJavaagentAlpha}")
+  compileOnly("io.opentelemetry.javaagent:opentelemetry-javaagent-api:${versions.opentelemetryJavaagentAlpha}")
+  compileOnly("io.opentelemetry.javaagent:opentelemetry-javaagent-tooling:${versions.opentelemetryJavaagentAlpha}")
+
+  compileOnly deps.bytebuddy
+  compileOnly deps.bytebuddyagent
+  annotationProcessor deps.autoservice
+  compileOnly deps.autoservice
+
+  compileOnly group: 'javax.servlet', name: 'javax.servlet-api', version: '3.0.1'
+
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoIdGenerator.java

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+package com.example.javaagent;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.sdk.trace.IdGenerator;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * Custom {@link IdGenerator} which provides span and trace ids.
+ *
+ * @see io.opentelemetry.sdk.trace.SdkTracerProvider
+ * @see DemoSdkTracerProviderConfigurer
+ */
+public class DemoIdGenerator implements IdGenerator {
+  private static final AtomicLong traceId = new AtomicLong(0);
+  private static final AtomicLong spanId = new AtomicLong(0);
+
+  @Override
+  public String generateSpanId() {
+    return String.format("%016d", spanId.incrementAndGet());
+  }
+
+  @Override
+  public String generateTraceId() {
+    return String.format("%032d", traceId.incrementAndGet());
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoPropagator.java

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+package com.example.javaagent;
+
+import io.opentelemetry.context.Context;
+import io.opentelemetry.context.ContextKey;
+import io.opentelemetry.context.propagation.TextMapGetter;
+import io.opentelemetry.context.propagation.TextMapPropagator;
+import io.opentelemetry.context.propagation.TextMapSetter;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * See <a href="https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/context/api-propagators.md">
+ * OpenTelemetry Specification</a> for more information about Propagators.
+ *
+ * @see DemoPropagatorProvider
+ */
+public class DemoPropagator implements TextMapPropagator {
+  private static final String FIELD = "X-demo-field";
+  private static final ContextKey<Long> PROPAGATION_START_KEY = ContextKey.named("propagation.start");
+
+  @Override
+  public List<String> fields() {
+    return Collections.singletonList(FIELD);
+  }
+
+  @Override
+  public <C> void inject(Context context, C carrier, TextMapSetter<C> setter) {
+    Long propagationStart = context.get(PROPAGATION_START_KEY);
+    if (propagationStart == null) {
+      propagationStart = System.currentTimeMillis();
+    }
+    setter.set(carrier, FIELD, String.valueOf(propagationStart));
+  }
+
+  @Override
+  public <C> Context extract(Context context, C carrier, TextMapGetter<C> getter) {
+    String propagationStart = getter.get(carrier, FIELD);
+    if (propagationStart != null) {
+      return context.with(PROPAGATION_START_KEY, Long.valueOf(propagationStart));
+    } else {
+      return context;
+    }
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoPropagatorProvider.java

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+package com.example.javaagent;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.context.propagation.TextMapPropagator;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigurablePropagatorProvider;
+
+/**
+ * Registers the custom propagator used by this example.
+ *
+ * @see ConfigurablePropagatorProvider
+ * @see DemoPropagator
+ */
+@AutoService(ConfigurablePropagatorProvider.class)
+public class DemoPropagatorProvider implements ConfigurablePropagatorProvider {
+  @Override
+  public TextMapPropagator getPropagator() {
+    return new DemoPropagator();
+  }
+
+  @Override
+  public String getName() {
+    return "demo";
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoPropertySource.java

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+package com.example.javaagent;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.javaagent.spi.config.PropertySource;
+import java.util.Map;
+
+/**
+ * {@link PropertySource} is an SPI provided by OpenTelemetry Java instrumentation agent.
+ * By implementing it custom distributions can supply their own default configuration.
+ * The configuration priority, from highest to lowest is:
+ * system properties -> environment variables -> configuration file -> PropertySource SPI -> hard-coded defaults
+ */
+@AutoService(PropertySource.class)
+public class DemoPropertySource implements PropertySource {
+
+  @Override
+  public Map<String, String> getProperties() {
+    return Map.of(
+        "otel.exporter.otlp.endpoint", "http://collector:55680",
+        "otel.exporter.otlp.insecure", "true",
+        "otel.config.max.attrs", "16"
+    );
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoResourceProvider.java

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+package com.example.javaagent;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.sdk.autoconfigure.ConfigProperties;
+import io.opentelemetry.sdk.autoconfigure.spi.ResourceProvider;
+import io.opentelemetry.sdk.resources.Resource;
+
+@AutoService(ResourceProvider.class)
+public class DemoResourceProvider implements ResourceProvider {
+  @Override
+  public Resource createResource(ConfigProperties config) {
+    Attributes attributes = Attributes.builder().put("custom.resource", "demo").build();
+    return Resource.create(attributes);
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoSampler.java

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+package com.example.javaagent;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.trace.SpanKind;
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.data.LinkData;
+import io.opentelemetry.sdk.trace.samplers.Sampler;
+import io.opentelemetry.sdk.trace.samplers.SamplingDecision;
+import io.opentelemetry.sdk.trace.samplers.SamplingResult;
+import java.util.List;
+
+/**
+ * This demo sampler filters out all internal spans whose name contains string "greeting".
+ * <p>
+ * See <a href="https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/sdk.md#sampling">
+ * OpenTelemetry Specification</a> for more information about span sampling.
+ *
+ * @see DemoSdkTracerProviderConfigurer
+ */
+public class DemoSampler implements Sampler {
+  @Override
+  public SamplingResult shouldSample(Context parentContext, String traceId, String name,
+      SpanKind spanKind, Attributes attributes, List<LinkData> parentLinks) {
+    if (spanKind == SpanKind.INTERNAL && name.contains("greeting")) {
+      return SamplingResult.create(SamplingDecision.DROP);
+    } else {
+      return SamplingResult.create(SamplingDecision.RECORD_AND_SAMPLE);
+    }
+  }
+
+  @Override
+  public String getDescription() {
+    return "DemoSampler";
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoSdkTracerProviderConfigurer.java

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+package com.example.javaagent;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.sdk.autoconfigure.spi.SdkTracerProviderConfigurer;
+import io.opentelemetry.sdk.trace.SdkTracerProviderBuilder;
+import io.opentelemetry.sdk.trace.SpanLimits;
+import io.opentelemetry.sdk.trace.export.SimpleSpanProcessor;
+
+/**
+ * This is one of the main entry points for Instrumentation Agent's customizations.
+ * It allows configuring {@link SdkTracerProviderBuilder}.
+ * See the {@link #configure(SdkTracerProviderBuilder)} method below.
+ * <p>
+ * Also see https://github.com/open-telemetry/opentelemetry-java/issues/2022
+ *
+ * @see SdkTracerProviderConfigurer
+ * @see DemoPropagatorProvider
+ */
+@AutoService(SdkTracerProviderConfigurer.class)
+public class DemoSdkTracerProviderConfigurer implements SdkTracerProviderConfigurer {
+  @Override
+  public void configure(SdkTracerProviderBuilder tracerProvider) {
+    tracerProvider
+        .setIdGenerator(new DemoIdGenerator())
+        .setSpanLimits(SpanLimits.builder().setMaxNumberOfAttributes(1024).build())
+        .setSampler(new DemoSampler())
+        .addSpanProcessor(new DemoSpanProcessor())
+        .addSpanProcessor(SimpleSpanProcessor.create(new DemoSpanExporter()));
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoSpanExporter.java

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+package com.example.javaagent;
+
+import io.opentelemetry.sdk.common.CompletableResultCode;
+import io.opentelemetry.sdk.trace.data.SpanData;
+import io.opentelemetry.sdk.trace.export.SpanExporter;
+import java.util.Collection;
+
+/**
+ * See <a href="https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/sdk.md#span-exporter">
+ * OpenTelemetry Specification</a> for more information about {@link SpanExporter}.
+ *
+ * @see DemoSdkTracerProviderConfigurer
+ */
+public class DemoSpanExporter implements SpanExporter {
+  @Override
+  public CompletableResultCode export(Collection<SpanData> spans) {
+    System.out.printf("%d spans exported%n", spans.size());
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode flush() {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode shutdown() {
+    return CompletableResultCode.ofSuccess();
+  }
+}

examples/extension/custom/src/main/java/com/example/javaagent/DemoSpanProcessor.java

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+package com.example.javaagent;
+
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.common.CompletableResultCode;
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import io.opentelemetry.sdk.trace.ReadableSpan;
+import io.opentelemetry.sdk.trace.SpanProcessor;
+
+/**
+ * See <a href="https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/sdk.md#span-processor">
+ * OpenTelemetry Specification</a> for more information about {@link SpanProcessor}.
+ *
+ * @see DemoSdkTracerProviderConfigurer
+ */
+public class DemoSpanProcessor implements SpanProcessor {
+  @Override
+  public void onStart(Context parentContext, ReadWriteSpan span) {
+    span.setAttribute("custom", "demo");
+  }
+
+  @Override
+  public boolean isStartRequired() {
+    return true;
+  }
+
+  @Override
+  public void onEnd(ReadableSpan span) {
+
+  }
+
+  @Override
+  public boolean isEndRequired() {
+    return false;
+  }
+
+  @Override
+  public CompletableResultCode shutdown() {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode forceFlush() {
+    return CompletableResultCode.ofSuccess();
+  }
+}