Add http/protobuf exporter for metrics (#3440)

* Add OtlpHttpMetricExporter

* Fix test flake by adjusting logging order.

* Drop metric instrumentation of OtlpHttpMetricExporter

* Attempt to fix log tet flake using awaitility

* Rename isCompressionEnabled to compressionEnabled

exporters/otlp-http/metrics/README.md

@@ -0,0 +1,5 @@
+# OpenTelemetry - OTLP Metrics Exporter - HTTP
+
+This is the OpenTelemetry exporter, sending metric data to OpenTelemetry collector via HTTP without gRPC.
+
+// TODO: add javadoc links once published

exporters/otlp-http/metrics/build.gradle.kts

@@ -0,0 +1,23 @@
+plugins {
+    id("otel.java-conventions")
+    id("otel.publish-conventions")
+
+    id("otel.animalsniffer-conventions")
+}
+
+description = "OpenTelemetry Protocol HTTP Metrics Exporter"
+otelJava.moduleName.set("io.opentelemetry.exporter.otlp.http.metrics")
+
+dependencies {
+  api(project(":sdk:metrics"))
+
+  implementation(project(":exporters:otlp:common"))
+
+  implementation("com.squareup.okhttp3:okhttp")
+  implementation("com.squareup.okhttp3:okhttp-tls")
+  implementation("com.squareup.okio:okio")
+
+  testImplementation(project(":sdk:testing"))
+
+  testImplementation("com.linecorp.armeria:armeria-junit5")
+}

exporters/otlp-http/metrics/gradle.properties

@@ -0,0 +1 @@
+otel.release=alpha

exporters/otlp-http/metrics/src/main/java/io/opentelemetry/exporter/otlp/http/metric/OtlpHttpMetricExporter.java

@@ -0,0 +1,196 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.otlp.http.metric;
+
+import com.google.rpc.Code;
+import com.google.rpc.Status;
+import io.opentelemetry.exporter.otlp.internal.MetricAdapter;
+import io.opentelemetry.proto.collector.metrics.v1.ExportMetricsServiceRequest;
+import io.opentelemetry.sdk.common.CompletableResultCode;
+import io.opentelemetry.sdk.internal.ThrottlingLogger;
+import io.opentelemetry.sdk.metrics.data.MetricData;
+import io.opentelemetry.sdk.metrics.export.MetricExporter;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.ThreadSafe;
+import okhttp3.Call;
+import okhttp3.Callback;
+import okhttp3.Headers;
+import okhttp3.MediaType;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.RequestBody;
+import okhttp3.Response;
+import okhttp3.ResponseBody;
+import okio.BufferedSink;
+import okio.GzipSink;
+import okio.Okio;
+
+/** Exports metrics using OTLP via HTTP, using OpenTelemetry's protobuf model. */
+@ThreadSafe
+public final class OtlpHttpMetricExporter implements MetricExporter {
+
+  private static final MediaType PROTOBUF_MEDIA_TYPE = MediaType.parse("application/x-protobuf");
+
+  private final ThrottlingLogger logger =
+      new ThrottlingLogger(Logger.getLogger(OtlpHttpMetricExporter.class.getName()));
+
+  private final OkHttpClient client;
+  private final String endpoint;
+  @Nullable private final Headers headers;
+  private final boolean compressionEnabled;
+
+  OtlpHttpMetricExporter(
+      OkHttpClient client, String endpoint, @Nullable Headers headers, boolean compressionEnabled) {
+    this.client = client;
+    this.endpoint = endpoint;
+    this.headers = headers;
+    this.compressionEnabled = compressionEnabled;
+  }
+
+  /**
+   * Submits all the given metrics in a single batch to the OpenTelemetry collector.
+   *
+   * @param metrics the list of Metrics to be exported.
+   * @return the result of the operation
+   */
+  @Override
+  public CompletableResultCode export(Collection<MetricData> metrics) {
+    ExportMetricsServiceRequest exportMetricsServiceRequest =
+        ExportMetricsServiceRequest.newBuilder()
+            .addAllResourceMetrics(MetricAdapter.toProtoResourceMetrics(metrics))
+            .build();
+
+    Request.Builder requestBuilder = new Request.Builder().url(endpoint);
+    if (headers != null) {
+      requestBuilder.headers(headers);
+    }
+    RequestBody requestBody =
+        RequestBody.create(exportMetricsServiceRequest.toByteArray(), PROTOBUF_MEDIA_TYPE);
+    if (compressionEnabled) {
+      requestBuilder.addHeader("Content-Encoding", "gzip");
+      requestBuilder.post(gzipRequestBody(requestBody));
+    } else {
+      requestBuilder.post(requestBody);
+    }
+
+    CompletableResultCode result = new CompletableResultCode();
+
+    client
+        .newCall(requestBuilder.build())
+        .enqueue(
+            new Callback() {
+              @Override
+              public void onFailure(Call call, IOException e) {
+                logger.log(
+                    Level.SEVERE,
+                    "Failed to export metrics. The request could not be executed. Full error message: "
+                        + e.getMessage());
+                result.fail();
+              }
+
+              @Override
+              public void onResponse(Call call, Response response) {
+                if (response.isSuccessful()) {
+                  result.succeed();
+                  return;
+                }
+
+                int code = response.code();
+
+                Status status = extractErrorStatus(response);
+
+                logger.log(
+                    Level.WARNING,
+                    "Failed to export metrics. Server responded with HTTP status code "
+                        + code
+                        + ". Error message: "
+                        + status.getMessage());
+                result.fail();
+              }
+            });
+
+    return result;
+  }
+
+  private static RequestBody gzipRequestBody(RequestBody requestBody) {
+    return new RequestBody() {
+      @Override
+      public MediaType contentType() {
+        return requestBody.contentType();
+      }
+
+      @Override
+      public long contentLength() {
+        return -1;
+      }
+
+      @Override
+      public void writeTo(BufferedSink bufferedSink) throws IOException {
+        BufferedSink gzipSink = Okio.buffer(new GzipSink(bufferedSink));
+        requestBody.writeTo(gzipSink);
+        gzipSink.close();
+      }
+    };
+  }
+
+  private static Status extractErrorStatus(Response response) {
+    ResponseBody responseBody = response.body();
+    if (responseBody == null) {
+      return Status.newBuilder()
+          .setMessage("Response body missing, HTTP status message: " + response.message())
+          .setCode(Code.UNKNOWN.getNumber())
+          .build();
+    }
+    try {
+      return Status.parseFrom(responseBody.bytes());
+    } catch (IOException e) {
+      return Status.newBuilder()
+          .setMessage("Unable to parse response body, HTTP status message: " + response.message())
+          .setCode(Code.UNKNOWN.getNumber())
+          .build();
+    }
+  }
+
+  /**
+   * The OTLP exporter does not batch metrics, so this method will immediately return with success.
+   *
+   * @return always Success
+   */
+  @Override
+  public CompletableResultCode flush() {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  /**
+   * Returns a new builder instance for this exporter.
+   *
+   * @return a new builder instance for this exporter.
+   */
+  public static OtlpHttpMetricExporterBuilder builder() {
+    return new OtlpHttpMetricExporterBuilder();
+  }
+
+  /**
+   * Returns a new {@link OtlpHttpMetricExporter} using the default values.
+   *
+   * @return a new {@link OtlpHttpMetricExporter} instance.
+   */
+  public static OtlpHttpMetricExporter getDefault() {
+    return builder().build();
+  }
+
+  /** Shutdown the exporter. */
+  @Override
+  public CompletableResultCode shutdown() {
+    final CompletableResultCode result = CompletableResultCode.ofSuccess();
+    client.dispatcher().cancelAll();
+    return result;
+  }
+}

exporters/otlp-http/metrics/src/main/java/io/opentelemetry/exporter/otlp/http/metric/OtlpHttpMetricExporterBuilder.java

@@ -0,0 +1,160 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.otlp.http.metric;
+
+import static io.opentelemetry.api.internal.Utils.checkArgument;
+import static java.util.Objects.requireNonNull;
+
+import com.google.common.base.Preconditions;
+import java.io.ByteArrayInputStream;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.security.cert.CertificateException;
+import java.security.cert.CertificateFactory;
+import java.security.cert.X509Certificate;
+import java.time.Duration;
+import java.util.concurrent.TimeUnit;
+import javax.annotation.Nullable;
+import okhttp3.Headers;
+import okhttp3.OkHttpClient;
+import okhttp3.tls.HandshakeCertificates;
+
+/** Builder utility for {@link OtlpHttpMetricExporter}. */
+public final class OtlpHttpMetricExporterBuilder {
+
+  private static final long DEFAULT_TIMEOUT_SECS = 10;
+  private static final String DEFAULT_ENDPOINT = "http://localhost:4317/v1/metrics";
+
+  private long timeoutNanos = TimeUnit.SECONDS.toNanos(DEFAULT_TIMEOUT_SECS);
+  private String endpoint = DEFAULT_ENDPOINT;
+  private boolean compressionEnabled = false;
+  @Nullable private Headers.Builder headersBuilder;
+  @Nullable private byte[] trustedCertificatesPem;
+
+  /**
+   * Sets the maximum time to wait for the collector to process an exported batch of metrics. If
+   * unset, defaults to {@value DEFAULT_TIMEOUT_SECS}s.
+   */
+  public OtlpHttpMetricExporterBuilder setTimeout(long timeout, TimeUnit unit) {
+    requireNonNull(unit, "unit");
+    checkArgument(timeout >= 0, "timeout must be non-negative");
+    timeoutNanos = unit.toNanos(timeout);
+    return this;
+  }
+
+  /**
+   * Sets the maximum time to wait for the collector to process an exported batch of metrics. If
+   * unset, defaults to {@value DEFAULT_TIMEOUT_SECS}s.
+   */
+  public OtlpHttpMetricExporterBuilder setTimeout(Duration timeout) {
+    requireNonNull(timeout, "timeout");
+    return setTimeout(timeout.toNanos(), TimeUnit.NANOSECONDS);
+  }
+
+  /**
+   * Sets the OTLP endpoint to connect to. If unset, defaults to {@value DEFAULT_ENDPOINT}. The
+   * endpoint must start with either http:// or https://, and include the full HTTP path.
+   */
+  public OtlpHttpMetricExporterBuilder setEndpoint(String endpoint) {
+    requireNonNull(endpoint, "endpoint");
+
+    URI uri;
+    try {
+      uri = new URI(endpoint);
+    } catch (URISyntaxException e) {
+      throw new IllegalArgumentException("Invalid endpoint, must be a URL: " + endpoint, e);
+    }
+
+    if (uri.getScheme() == null
+        || (!uri.getScheme().equals("http") && !uri.getScheme().equals("https"))) {
+      throw new IllegalArgumentException(
+          "Invalid endpoint, must start with http:// or https://: " + uri);
+    }
+
+    this.endpoint = endpoint;
+    return this;
+  }
+
+  /**
+   * Sets the method used to compress payloads. If unset, compression is disabled. Currently the
+   * only supported compression method is "gzip".
+   */
+  public OtlpHttpMetricExporterBuilder setCompression(String compressionMethod) {
+    requireNonNull(compressionMethod, "compressionMethod");
+    Preconditions.checkArgument(
+        compressionMethod.equals("gzip"),
+        "Unsupported compression method. Supported compression methods include: gzip.");
+    this.compressionEnabled = true;
+    return this;
+  }
+
+  /** Add header to requests. */
+  public OtlpHttpMetricExporterBuilder addHeader(String key, String value) {
+    if (headersBuilder == null) {
+      headersBuilder = new Headers.Builder();
+    }
+    headersBuilder.add(key, value);
+    return this;
+  }
+
+  /**
+   * Sets the certificate chain to use for verifying servers when TLS is enabled. The {@code byte[]}
+   * should contain an X.509 certificate collection in PEM format. If not set, TLS connections will
+   * use the system default trusted certificates.
+   */
+  public OtlpHttpMetricExporterBuilder setTrustedCertificates(byte[] trustedCertificatesPem) {
+    this.trustedCertificatesPem = trustedCertificatesPem;
+    return this;
+  }
+
+  /**
+   * Constructs a new instance of the exporter based on the builder's values.
+   *
+   * @return a new exporter's instance
+   */
+  public OtlpHttpMetricExporter build() {
+    OkHttpClient.Builder clientBuilder =
+        new OkHttpClient.Builder().callTimeout(Duration.ofNanos(timeoutNanos));
+
+    if (trustedCertificatesPem != null) {
+      try {
+        HandshakeCertificates handshakeCertificates =
+            toHandshakeCertificates(trustedCertificatesPem);
+        clientBuilder.sslSocketFactory(
+            handshakeCertificates.sslSocketFactory(), handshakeCertificates.trustManager());
+      } catch (CertificateException e) {
+        throw new IllegalStateException(
+            "Could not set trusted certificate for OTLP HTTP connection, are they valid X.509 in PEM format?",
+            e);
+      }
+    }
+
+    Headers headers = headersBuilder == null ? null : headersBuilder.build();
+
+    return new OtlpHttpMetricExporter(clientBuilder.build(), endpoint, headers, compressionEnabled);
+  }
+
+  /**
+   * Extract X.509 certificates from the bytes.
+   *
+   * @param trustedCertificatesPem bytes containing an X.509 certificate collection in PEM format.
+   * @return a HandshakeCertificates with the certificates
+   * @throws CertificateException if an error occurs extracting certificates
+   */
+  private static HandshakeCertificates toHandshakeCertificates(byte[] trustedCertificatesPem)
+      throws CertificateException {
+    ByteArrayInputStream is = new ByteArrayInputStream(trustedCertificatesPem);
+    CertificateFactory factory = CertificateFactory.getInstance("X.509");
+    HandshakeCertificates.Builder certBuilder = new HandshakeCertificates.Builder();
+    while (is.available() > 0) {
+      X509Certificate cert = (X509Certificate) factory.generateCertificate(is);
+      certBuilder.addTrustedCertificate(cert);
+    }
+    return certBuilder.build();
+  }
+
+  OtlpHttpMetricExporterBuilder() {}
+}

exporters/otlp-http/metrics/src/main/java/io/opentelemetry/exporter/otlp/http/metric/package-info.java

@@ -0,0 +1,10 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/** OpenTelemetry exporter which sends metric data to OpenTelemetry collector via OTLP HTTP. */
+@ParametersAreNonnullByDefault
+package io.opentelemetry.exporter.otlp.http.metric;
+
+import javax.annotation.ParametersAreNonnullByDefault;

exporters/otlp-http/metrics/src/test/java/io/opentelemetry/exporter/otlp/http/metric/OtlpHttpMetricExporterTest.java

@@ -0,0 +1,253 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.otlp.http.metric;
+
+import static io.opentelemetry.api.common.AttributeKey.stringKey;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.awaitility.Awaitility.await;
+
+import com.google.protobuf.InvalidProtocolBufferException;
+import com.google.protobuf.Message;
+import com.google.rpc.Status;
+import com.linecorp.armeria.common.AggregatedHttpRequest;
+import com.linecorp.armeria.common.HttpMethod;
+import com.linecorp.armeria.common.HttpResponse;
+import com.linecorp.armeria.common.HttpStatus;
+import com.linecorp.armeria.common.MediaType;
+import com.linecorp.armeria.server.ServerBuilder;
+import com.linecorp.armeria.testing.junit5.server.mock.MockWebServerExtension;
+import io.github.netmikey.logunit.api.LogCapturer;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.exporter.otlp.internal.MetricAdapter;
+import io.opentelemetry.proto.collector.metrics.v1.ExportMetricsServiceRequest;
+import io.opentelemetry.proto.collector.metrics.v1.ExportMetricsServiceResponse;
+import io.opentelemetry.sdk.common.CompletableResultCode;
+import io.opentelemetry.sdk.common.InstrumentationLibraryInfo;
+import io.opentelemetry.sdk.metrics.data.AggregationTemporality;
+import io.opentelemetry.sdk.metrics.data.LongPointData;
+import io.opentelemetry.sdk.metrics.data.LongSumData;
+import io.opentelemetry.sdk.metrics.data.MetricData;
+import io.opentelemetry.sdk.resources.Resource;
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.nio.charset.StandardCharsets;
+import java.time.Duration;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+import okhttp3.tls.HeldCertificate;
+import okio.Buffer;
+import okio.GzipSource;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.slf4j.event.Level;
+import org.slf4j.event.LoggingEvent;
+
+class OtlpHttpMetricExporterTest {
+
+  private static final MediaType APPLICATION_PROTOBUF =
+      MediaType.create("application", "x-protobuf");
+  private static final HeldCertificate HELD_CERTIFICATE;
+
+  static {
+    try {
+      HELD_CERTIFICATE =
+          new HeldCertificate.Builder()
+              .commonName("localhost")
+              .addSubjectAlternativeName(InetAddress.getByName("localhost").getCanonicalHostName())
+              .build();
+    } catch (UnknownHostException e) {
+      throw new IllegalStateException("Error building certificate.", e);
+    }
+  }
+
+  @RegisterExtension
+  static MockWebServerExtension server =
+      new MockWebServerExtension() {
+        @Override
+        protected void configureServer(ServerBuilder sb) {
+          sb.tls(HELD_CERTIFICATE.keyPair().getPrivate(), HELD_CERTIFICATE.certificate());
+        }
+      };
+
+  @RegisterExtension
+  LogCapturer logs = LogCapturer.create().captureForType(OtlpHttpMetricExporter.class);
+
+  private OtlpHttpMetricExporterBuilder builder;
+
+  @BeforeEach
+  void setup() {
+    builder =
+        OtlpHttpMetricExporter.builder()
+            .setEndpoint("https://localhost:" + server.httpsPort() + "/v1/metrics")
+            .addHeader("foo", "bar")
+            .setTrustedCertificates(
+                HELD_CERTIFICATE.certificatePem().getBytes(StandardCharsets.UTF_8));
+  }
+
+  @Test
+  @SuppressWarnings("PreferJavaTimeOverload")
+  void invalidConfig() {
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setTimeout(-1, TimeUnit.MILLISECONDS))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("timeout must be non-negative");
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setTimeout(1, null))
+        .isInstanceOf(NullPointerException.class)
+        .hasMessage("unit");
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setTimeout(null))
+        .isInstanceOf(NullPointerException.class)
+        .hasMessage("timeout");
+
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setEndpoint(null))
+        .isInstanceOf(NullPointerException.class)
+        .hasMessage("endpoint");
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setEndpoint("😺://localhost"))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("Invalid endpoint, must be a URL: 😺://localhost");
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setEndpoint("localhost"))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("Invalid endpoint, must start with http:// or https://: localhost");
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setEndpoint("gopher://localhost"))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("Invalid endpoint, must start with http:// or https://: gopher://localhost");
+
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setCompression(null))
+        .isInstanceOf(NullPointerException.class)
+        .hasMessage("compressionMethod");
+    assertThatThrownBy(() -> OtlpHttpMetricExporter.builder().setCompression("foo"))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("Unsupported compression method. Supported compression methods include: gzip.");
+  }
+
+  @Test
+  void testExportUncompressed() {
+    server.enqueue(successResponse());
+    OtlpHttpMetricExporter exporter = builder.build();
+
+    ExportMetricsServiceRequest payload =
+        exportAndAssertResult(exporter, /* expectedResult= */ true);
+    AggregatedHttpRequest request = server.takeRequest().request();
+    assertRequestCommon(request);
+    assertThat(parseRequestBody(request.content().array())).isEqualTo(payload);
+  }
+
+  @Test
+  void testExportGzipCompressed() {
+    server.enqueue(successResponse());
+    OtlpHttpMetricExporter exporter = builder.setCompression("gzip").build();
+
+    ExportMetricsServiceRequest payload =
+        exportAndAssertResult(exporter, /* expectedResult= */ true);
+    AggregatedHttpRequest request = server.takeRequest().request();
+    assertRequestCommon(request);
+    assertThat(request.headers().get("Content-Encoding")).isEqualTo("gzip");
+    assertThat(parseRequestBody(gzipDecompress(request.content().array()))).isEqualTo(payload);
+  }
+
+  private static void assertRequestCommon(AggregatedHttpRequest request) {
+    assertThat(request.method()).isEqualTo(HttpMethod.POST);
+    assertThat(request.path()).isEqualTo("/v1/metrics");
+    assertThat(request.headers().get("foo")).isEqualTo("bar");
+    assertThat(request.headers().get("Content-Type")).isEqualTo(APPLICATION_PROTOBUF.toString());
+  }
+
+  private static ExportMetricsServiceRequest parseRequestBody(byte[] bytes) {
+    try {
+      return ExportMetricsServiceRequest.parseFrom(bytes);
+    } catch (InvalidProtocolBufferException e) {
+      throw new IllegalStateException("Unable to parse Protobuf request body.", e);
+    }
+  }
+
+  private static byte[] gzipDecompress(byte[] bytes) {
+    try {
+      Buffer result = new Buffer();
+      GzipSource source = new GzipSource(new Buffer().write(bytes));
+      while (source.read(result, Integer.MAX_VALUE) != -1) {}
+      return result.readByteArray();
+    } catch (IOException e) {
+      throw new IllegalStateException("Unable to decompress payload.", e);
+    }
+  }
+
+  @Test
+  void testServerError() {
+    server.enqueue(
+        buildResponse(
+            HttpStatus.INTERNAL_SERVER_ERROR,
+            Status.newBuilder().setMessage("Server error!").build()));
+    OtlpHttpMetricExporter exporter = builder.build();
+
+    exportAndAssertResult(exporter, /* expectedResult= */ false);
+    await()
+        .atMost(Duration.ofSeconds(10))
+        .untilAsserted(
+            () -> {
+              LoggingEvent log =
+                  logs.assertContains(
+                      "Failed to export metrics. Server responded with HTTP status code 500. Error message: Server error!");
+              assertThat(log.getLevel()).isEqualTo(Level.WARN);
+            });
+  }
+
+  @Test
+  void testServerErrorParseError() {
+    server.enqueue(
+        HttpResponse.of(HttpStatus.INTERNAL_SERVER_ERROR, APPLICATION_PROTOBUF, "Server error!"));
+    OtlpHttpMetricExporter exporter = builder.build();
+
+    exportAndAssertResult(exporter, /* expectedResult= */ false);
+    await()
+        .atMost(Duration.ofSeconds(10))
+        .untilAsserted(
+            () -> {
+              LoggingEvent log =
+                  logs.assertContains(
+                      "Failed to export metrics. Server responded with HTTP status code 500. Error message: Unable to parse response body, HTTP status message:");
+              assertThat(log.getLevel()).isEqualTo(Level.WARN);
+            });
+  }
+
+  private static ExportMetricsServiceRequest exportAndAssertResult(
+      OtlpHttpMetricExporter otlpHttpMetricExporter, boolean expectedResult) {
+    List<MetricData> metrics = Collections.singletonList(generateFakeMetric());
+    CompletableResultCode resultCode = otlpHttpMetricExporter.export(metrics);
+    resultCode.join(10, TimeUnit.SECONDS);
+    assertThat(resultCode.isSuccess()).isEqualTo(expectedResult);
+    return ExportMetricsServiceRequest.newBuilder()
+        .addAllResourceMetrics(MetricAdapter.toProtoResourceMetrics(metrics))
+        .build();
+  }
+
+  private static HttpResponse successResponse() {
+    ExportMetricsServiceResponse exportMetricsServiceResponse =
+        ExportMetricsServiceResponse.newBuilder().build();
+    return buildResponse(HttpStatus.OK, exportMetricsServiceResponse);
+  }
+
+  private static <T extends Message> HttpResponse buildResponse(HttpStatus httpStatus, T message) {
+    return HttpResponse.of(httpStatus, APPLICATION_PROTOBUF, message.toByteArray());
+  }
+
+  private static MetricData generateFakeMetric() {
+    long startNs = TimeUnit.MILLISECONDS.toNanos(System.currentTimeMillis());
+    long endNs = startNs + TimeUnit.MILLISECONDS.toNanos(900);
+    return MetricData.createLongSum(
+        Resource.empty(),
+        InstrumentationLibraryInfo.empty(),
+        "name",
+        "description",
+        "1",
+        LongSumData.create(
+            /* isMonotonic= */ true,
+            AggregationTemporality.CUMULATIVE,
+            Collections.singletonList(
+                LongPointData.create(startNs, endNs, Attributes.of(stringKey("k"), "v"), 5))));
+  }
+}

exporters/otlp-http/trace/README.md

@@ -1,8 +1,5 @@
 # OpenTelemetry - OTLP Trace Exporter - HTTP
 
-[![Javadocs][javadoc-image]][javadoc-url]
-
 This is the OpenTelemetry exporter, sending span data to OpenTelemetry collector via HTTP without gRPC.
 
-[javadoc-image]: https://www.javadoc.io/badge/io.opentelemetry/opentelemetry-exporters-otlp.svg
-[javadoc-url]: https://www.javadoc.io/doc/io.opentelemetry/opentelemetry-exporters-otlp
+// TODO: add javadoc links once published

exporters/otlp-http/trace/src/main/java/io/opentelemetry/exporter/otlp/http/trace/OtlpHttpSpanExporter.java

@@ -22,6 +22,7 @@ import java.io.IOException;
 import java.util.Collection;
 import java.util.logging.Level;
 import java.util.logging.Logger;
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import okhttp3.Call;
 import okhttp3.Callback;
@@ -59,11 +60,11 @@ public final class OtlpHttpSpanExporter implements SpanExporter {
 
   private final OkHttpClient client;
   private final String endpoint;
-  private final Headers headers;
-  private final boolean isCompressionEnabled;
+  @Nullable private final Headers headers;
+  private final boolean compressionEnabled;
 
   OtlpHttpSpanExporter(
-      OkHttpClient client, String endpoint, Headers headers, boolean isCompressionEnabled) {
+      OkHttpClient client, String endpoint, Headers headers, boolean compressionEnabled) {
     Meter meter = GlobalMeterProvider.get().get("io.opentelemetry.exporters.otlp-http");
     this.spansSeen = meter.counterBuilder("spansSeenByExporter").build().bind(EXPORTER_NAME_LABELS);
     LongCounter spansExportedCounter = meter.counterBuilder("spansExportedByExporter").build();
@@ -73,7 +74,7 @@ public final class OtlpHttpSpanExporter implements SpanExporter {
     this.client = client;
     this.endpoint = endpoint;
     this.headers = headers;
-    this.isCompressionEnabled = isCompressionEnabled;
+    this.compressionEnabled = compressionEnabled;
   }
 
   /**
@@ -96,7 +97,7 @@ public final class OtlpHttpSpanExporter implements SpanExporter {
     }
     RequestBody requestBody =
         RequestBody.create(exportTraceServiceRequest.toByteArray(), PROTOBUF_MEDIA_TYPE);
-    if (isCompressionEnabled) {
+    if (compressionEnabled) {
       requestBuilder.addHeader("Content-Encoding", "gzip");
       requestBuilder.post(gzipRequestBody(requestBody));
     } else {
@@ -112,11 +113,11 @@ public final class OtlpHttpSpanExporter implements SpanExporter {
               @Override
               public void onFailure(Call call, IOException e) {
                 spansExportedFailure.add(spans.size());
-                result.fail();
                 logger.log(
                     Level.SEVERE,
                     "Failed to export spans. The request could not be executed. Full error message: "
                         + e.getMessage());
+                result.fail();
               }
 
               @Override

exporters/otlp-http/trace/src/main/java/io/opentelemetry/exporter/otlp/http/trace/OtlpHttpSpanExporterBuilder.java

@@ -30,7 +30,7 @@ public final class OtlpHttpSpanExporterBuilder {
 
   private long timeoutNanos = TimeUnit.SECONDS.toNanos(DEFAULT_TIMEOUT_SECS);
   private String endpoint = DEFAULT_ENDPOINT;
-  private boolean isCompressionEnabled = false;
+  private boolean compressionEnabled = false;
   @Nullable private Headers.Builder headersBuilder;
   @Nullable private byte[] trustedCertificatesPem;
 
@@ -87,7 +87,7 @@ public final class OtlpHttpSpanExporterBuilder {
     Preconditions.checkArgument(
         compressionMethod.equals("gzip"),
         "Unsupported compression method. Supported compression methods include: gzip.");
-    this.isCompressionEnabled = true;
+    this.compressionEnabled = true;
     return this;
   }
 
@@ -134,7 +134,7 @@ public final class OtlpHttpSpanExporterBuilder {
 
     Headers headers = headersBuilder == null ? null : headersBuilder.build();
 
-    return new OtlpHttpSpanExporter(clientBuilder.build(), endpoint, headers, isCompressionEnabled);
+    return new OtlpHttpSpanExporter(clientBuilder.build(), endpoint, headers, compressionEnabled);
   }
 
   /**

exporters/otlp-http/trace/src/test/java/io/opentelemetry/exporter/otlp/http/trace/OtlpHttpSpanExporterTest.java

@@ -7,6 +7,7 @@ package io.opentelemetry.exporter.otlp.http.trace;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.awaitility.Awaitility.await;
 
 import com.google.protobuf.InvalidProtocolBufferException;
 import com.google.protobuf.Message;
@@ -35,6 +36,7 @@ import java.io.IOException;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.nio.charset.StandardCharsets;
+import java.time.Duration;
 import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
@@ -181,10 +183,15 @@ class OtlpHttpSpanExporterTest {
     OtlpHttpSpanExporter exporter = builder.build();
 
     exportAndAssertResult(exporter, /* expectedResult= */ false);
-    LoggingEvent log =
-        logs.assertContains(
-            "Failed to export spans. Server responded with HTTP status code 500. Error message: Server error!");
-    assertThat(log.getLevel()).isEqualTo(Level.WARN);
+    await()
+        .atMost(Duration.ofSeconds(10))
+        .untilAsserted(
+            () -> {
+              LoggingEvent log =
+                  logs.assertContains(
+                      "Failed to export spans. Server responded with HTTP status code 500. Error message: Server error!");
+              assertThat(log.getLevel()).isEqualTo(Level.WARN);
+            });
   }
 
   @Test
@@ -194,10 +201,15 @@ class OtlpHttpSpanExporterTest {
     OtlpHttpSpanExporter exporter = builder.build();
 
     exportAndAssertResult(exporter, /* expectedResult= */ false);
-    LoggingEvent log =
-        logs.assertContains(
-            "Failed to export spans. Server responded with HTTP status code 500. Error message: Unable to parse response body, HTTP status message:");
-    assertThat(log.getLevel()).isEqualTo(Level.WARN);
+    await()
+        .atMost(Duration.ofSeconds(10))
+        .untilAsserted(
+            () -> {
+              LoggingEvent log =
+                  logs.assertContains(
+                      "Failed to export spans. Server responded with HTTP status code 500. Error message: Unable to parse response body, HTTP status message:");
+              assertThat(log.getLevel()).isEqualTo(Level.WARN);
+            });
   }
 
   private static ExportTraceServiceRequest exportAndAssertResult(

settings.gradle.kts

@@ -46,6 +46,7 @@ include(":exporters:otlp:all")
 include(":exporters:otlp:common")
 include(":exporters:otlp:metrics")
 include(":exporters:otlp:trace")
+include(":exporters:otlp-http:metrics")
 include(":exporters:otlp-http:trace")
 include(":exporters:prometheus")
 include(":exporters:zipkin")