Set user agent header in OTLP registry

Co-authored-by: Joao Grassi <5938087+joaopgrassi@users.noreply.github.com>
Co-authored-by: Jonatan Ivanov <jonatan.ivanov@gmail.com>

implementations/micrometer-registry-otlp/build.gradle

@@ -10,6 +10,7 @@ dependencies {
     testImplementation 'io.rest-assured:rest-assured'
     testImplementation 'org.testcontainers:junit-jupiter'
     testImplementation 'org.awaitility:awaitility'
+	testImplementation libs.mockitoCore5
 }
 
 dockerTest {

implementations/micrometer-registry-otlp/src/main/java/io/micrometer/registry/otlp/OtlpMeterRegistry.java

@@ -89,6 +89,8 @@ public class OtlpMeterRegistry extends PushMeterRegistry {
 
     private long deltaAggregationTimeUnixNano = 0L;
 
+    private final String userAgentHeader;
+
     // Time when the last scheduled rollOver has started. Applicable only for delta
     // flavour.
     private volatile long lastMeterRolloverStartTime = -1;
@@ -104,9 +106,10 @@ public OtlpMeterRegistry(OtlpConfig config, Clock clock) {
         this(config, clock, new HttpUrlConnectionSender());
     }
 
+    // VisibleForTesting
     // not public until we decide what we want to expose in public API
     // HttpSender may not be a good idea if we will support a non-HTTP transport
-    private OtlpMeterRegistry(OtlpConfig config, Clock clock, HttpSender httpSender) {
+    OtlpMeterRegistry(OtlpConfig config, Clock clock, HttpSender httpSender) {
         super(config, clock);
         this.config = config;
         this.baseTimeUnit = config.baseTimeUnit();
@@ -115,6 +118,7 @@ private OtlpMeterRegistry(OtlpConfig config, Clock clock, HttpSender httpSender)
         this.otlpAggregationTemporality = AggregationTemporality
             .toOtlpAggregationTemporality(config.aggregationTemporality());
         setDeltaAggregationTimeUnixNano();
+        this.userAgentHeader = getUserAgentHeader();
         config().namingConvention(NamingConvention.dot);
         start(DEFAULT_THREAD_FACTORY);
     }
@@ -163,6 +167,7 @@ protected void publish() {
                         .build())
                     .build();
                 HttpSender.Request.Builder httpRequest = this.httpSender.post(this.config.url())
+                    .withHeader("User-Agent", this.userAgentHeader)
                     .withContent("application/x-protobuf", request.toByteArray());
                 this.config.headers().forEach(httpRequest::withHeader);
                 HttpSender.Response response = httpRequest.send();
@@ -572,4 +577,11 @@ static double[] getSloWithPositiveInf(DistributionStatisticConfig distributionSt
         return sloWithPositiveInf;
     }
 
+    private String getUserAgentHeader() {
+        if (this.getClass().getPackage().getImplementationVersion() == null) {
+            return "Micrometer-OTLP-Exporter-Java";
+        }
+        return "Micrometer-OTLP-Exporter-Java/" + this.getClass().getPackage().getImplementationVersion();
+    }
+
 }

implementations/micrometer-registry-otlp/src/test/java/io/micrometer/registry/otlp/OtlpMeterRegistryTest.java

@@ -15,12 +15,15 @@
  */
 package io.micrometer.registry.otlp;
 
+import io.micrometer.core.Issue;
 import io.micrometer.core.instrument.*;
 import io.micrometer.core.instrument.config.NamingConvention;
 import io.micrometer.core.instrument.distribution.DistributionStatisticConfig;
+import io.micrometer.core.ipc.http.HttpSender;
 import io.opentelemetry.proto.metrics.v1.HistogramDataPoint;
 import io.opentelemetry.proto.metrics.v1.Metric;
 import io.opentelemetry.proto.metrics.v1.NumberDataPoint;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import java.io.IOException;
@@ -31,6 +34,8 @@
 import java.util.concurrent.TimeUnit;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.assertArg;
+import static org.mockito.Mockito.*;
 import static uk.org.webcompere.systemstubs.SystemStubs.withEnvironmentVariables;
 
 /**
@@ -47,12 +52,21 @@ abstract class OtlpMeterRegistryTest {
 
     protected static final Tag meterTag = Tag.of("key", "value");
 
-    protected MockClock clock = new MockClock();
+    protected MockClock clock;
 
-    protected OtlpMeterRegistry registry = new OtlpMeterRegistry(otlpConfig(), clock);
+    protected OtlpMeterRegistry registry;
+
+    private HttpSender mockHttpSender;
 
     abstract OtlpConfig otlpConfig();
 
+    @BeforeEach
+    void setUp() {
+        this.clock = new MockClock();
+        this.mockHttpSender = mock(HttpSender.class);
+        this.registry = new OtlpMeterRegistry(otlpConfig(), this.clock, this.mockHttpSender);
+    }
+
     // If the service.name was not specified, SDKs MUST fallback to 'unknown_service'
     @Test
     void unknownServiceByDefault() {
@@ -106,6 +120,23 @@ void timeGauge() {
                     + "    time_unix_nano: 1000000\n" + "    as_double: 0.024\n" + "  }\n" + "}\n");
     }
 
+    @Issue("#5577")
+    @Test
+    void httpHeaders() throws Throwable {
+        HttpSender.Request.Builder builder = HttpSender.Request.build(otlpConfig().url(), this.mockHttpSender);
+        when(mockHttpSender.post(otlpConfig().url())).thenReturn(builder);
+
+        when(mockHttpSender.send(isA(HttpSender.Request.class))).thenReturn(new HttpSender.Response(200, ""));
+
+        writeToMetric(TimeGauge.builder("gauge.time", this, TimeUnit.MICROSECONDS, o -> 24).register(registry));
+        registry.publish();
+
+        verify(this.mockHttpSender).send(assertArg(request -> {
+            assertThat(request.getRequestHeaders().get("User-Agent")).startsWith("Micrometer-OTLP-Exporter-Java");
+            assertThat(request.getRequestHeaders()).containsEntry("Content-Type", "application/x-protobuf");
+        }));
+    }
+
     @Test
     void distributionWithPercentileShouldWriteSummary() {
         Timer timer = Timer.builder("timer")