feat: #74 Add OpenTelemetry traces propagation

Signed-off-by: Laurent Broudoux <laurent.broudoux@gmail.com>

Author: lbroudoux

proxy/src/main/java/io/reshapr/proxy/proxy/GrpcProxyService.java

@@ -49,13 +49,11 @@
 import jakarta.enterprise.context.ApplicationScoped;
 import org.jboss.logging.Logger;
 
-import javax.net.ssl.X509TrustManager;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.net.URI;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
-import java.security.cert.X509Certificate;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
@@ -288,6 +286,9 @@ private static Metadata convertHeadersToMetadata(Map<String, List<String>> heade
       // Manage the Forwarded and X-Forwarded-For headers.
       HeadersUtil.addForwardingHeaders(headers);
 
+      // Also inject OpenTelemetry tracing headers.
+      HeadersUtil.injectTracingHeaders(headers);
+
       // Some specific headers must not be included in the gRPC metadata.
       headers.entrySet().stream()
             .filter(entry -> !RESTRICTED_HEADERS.contains(entry.getKey().toLowerCase()))

proxy/src/main/java/io/reshapr/proxy/proxy/HeadersUtil.java

@@ -17,6 +17,12 @@
 
 import io.reshapr.proxy.context.MethodHandlingContext;
 
+import io.opentelemetry.context.Context;
+import io.opentelemetry.context.propagation.TextMapPropagator;
+import io.opentelemetry.context.propagation.TextMapSetter;
+import io.opentelemetry.api.trace.propagation.W3CTraceContextPropagator;
+import io.opentelemetry.api.baggage.propagation.W3CBaggagePropagator;
+
 import java.util.List;
 import java.util.Map;
 
@@ -30,6 +36,10 @@ public class HeadersUtil {
    public static final String X_FORWARDED_FOR = "X-Forwarded-For";
    private static final String FORWARDED_FOR = "for=";
 
+   private static final TextMapPropagator OTEL_PROPAGATOR =
+         TextMapPropagator.composite(W3CTraceContextPropagator.getInstance(),
+               W3CBaggagePropagator.getInstance());
+
    private HeadersUtil () {
       // Utility class
    }
@@ -57,6 +67,14 @@ public static void addForwardingHeaders(Map<String, List<String>> headers) {
       }
    }
 
+   /**
+    * Inject tracing headers into the given map.
+    * @param headers The headers map to inject into.
+    */
+   public static void injectTracingHeaders(Map<String, List<String>> headers) {
+      OTEL_PROPAGATOR.inject(Context.current(), headers, new MapTextMapSetter());
+   }
+
    private static String getForAddress(String remoteAddress) {
       if (!remoteAddress.contains(":")) {
          return remoteAddress;
@@ -65,4 +83,13 @@ private static String getForAddress(String remoteAddress) {
       // See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Forwarded#transitioning_from_x-forwarded-for_to_forwarded
       return "\"[" + remoteAddress + "]\"";
    }
+
+   private static class MapTextMapSetter implements TextMapSetter<Map<String, List<String>>> {
+      @Override
+      public void set(Map<String, List<String>> carrier, String key, String value) {
+         if (carrier != null) {
+            carrier.put(key, List.of(value));
+         }
+      }
+   }
 }

proxy/src/main/java/io/reshapr/proxy/proxy/ProxyService.java

@@ -78,6 +78,9 @@ public BackendResponse callBackend(ConfigurationEntry configuration, URI externa
       // Manage the Forwarded and X-Forwarded-For headers.
       HeadersUtil.addForwardingHeaders(requestHeaders);
 
+      // Also inject OpenTelemetry tracing headers.
+      HeadersUtil.injectTracingHeaders(headers);
+
       // If the configuration has a backend secret, manage security headers.
       if (configuration.backendSecret() != null) {
          manageSecurityHeaders(configuration.backendSecret(), requestHeaders);

proxy/src/main/resources/application.properties

@@ -33,7 +33,7 @@ quarkus.otel.traces.enabled=true
 quarkus.otel.metrics.enabled=true
 quarkus.otel.logs.enabled=true
 #quarkus.otel.exporter.otlp.endpoint=http://localhost:4317
-#quarkus.otel.exporter.otlp.protocol=http/protobuf
+#quarkus.otel.exporter.otlp.protocol=http|grpc
 #quarkus.otel.exporter.otlp.headers=authorization=Bearer my_secret
 
 # Stores configuration.