From 36504465587d474e460bdac95ead7c7996970304 Mon Sep 17 00:00:00 2001
From: Michael Vorburger <mike@vorburger.ch>
Date: Tue, 19 Aug 2025 00:25:33 +0200
Subject: [PATCH 1/2] feat: Introduce Slf4jLoggingConsumer

---
 .../client/Slf4jLoggingConsumer.java          | 58 +++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java

diff --git a/mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java b/mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java
new file mode 100644
index 000000000..c5f173595
--- /dev/null
+++ b/mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java
@@ -0,0 +1,58 @@
+/*
+ * Copyright 2025 the original author or authors.
+ */
+package io.modelcontextprotocol.client;
+
+import java.util.function.Consumer;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.slf4j.event.Level;
+
+import io.modelcontextprotocol.client.McpClient.SyncSpec;
+import io.modelcontextprotocol.spec.McpSchema;
+import io.modelcontextprotocol.spec.McpSchema.LoggingMessageNotification;
+
+/**
+ * MCP Client-side consumer which logs received messages from MCP Servers using SLF4J.
+ *
+ * <p>
+ * Use this for {@link SyncSpec#loggingConsumer(Consumer)} to log received MCP messages.
+ *
+ * @author <a href="http://www.vorburger.ch">Michael Vorburger.ch</a>
+ */
+public class Slf4jLoggingConsumer implements Consumer<McpSchema.LoggingMessageNotification> {
+
+	// This class originated in
+	// https://github.com/enola-dev/enola/blob/ffc004666ea7f71357562ef12464d2b9fdbf9dbd/java/dev/enola/ai/mcp/McpServer.java#L29
+	// where it was used for https://docs.enola.dev/concepts/mcp/.
+	//
+	// It then found its way into Google's Agent Development Kit (ADK) in
+	// https://github.com/google/adk-java/pull/370. It's now been moved here to be useful
+	// to others.
+
+	@Override
+	public void accept(LoggingMessageNotification notif) {
+		Logger log = LoggerFactory.getLogger(notif.logger());
+		if (notif.meta().isEmpty()) {
+			// If no meta, then just log the data as a message
+			log.atLevel(convert(notif.level())).log(notif.data());
+		}
+		else {
+			// If there is meta, then log it as a structured log message
+			var builder = log.atLevel(convert(notif.level())).setMessage(notif.data());
+			notif.meta().forEach((key, value) -> builder.addKeyValue(key, value));
+			builder.log();
+		}
+	}
+
+	private Level convert(McpSchema.LoggingLevel level) {
+		return switch (level) {
+			case DEBUG -> Level.DEBUG;
+			case INFO, NOTICE -> Level.INFO;
+			case WARNING -> Level.WARN;
+			case ERROR, CRITICAL, ALERT, EMERGENCY -> Level.ERROR;
+		};
+	}
+
+}

From bea17fba9a247e560b9a1e0652bf60b568d00221 Mon Sep 17 00:00:00 2001
From: Michael Vorburger <mike@vorburger.ch>
Date: Tue, 19 Aug 2025 01:38:04 +0200
Subject: [PATCH 2/2] fix: Slf4jLoggingConsumer use itself as Logger, not the
 server's

---
 .../modelcontextprotocol/client/Slf4jLoggingConsumer.java  | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java b/mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java
index c5f173595..f35ba2329 100644
--- a/mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java
+++ b/mcp/src/main/java/io/modelcontextprotocol/client/Slf4jLoggingConsumer.java
@@ -31,16 +31,17 @@ public class Slf4jLoggingConsumer implements Consumer<McpSchema.LoggingMessageNo
 	// https://github.com/google/adk-java/pull/370. It's now been moved here to be useful
 	// to others.
 
+	private static final Logger LOG = LoggerFactory.getLogger(Slf4jLoggingConsumer.class);
+
 	@Override
 	public void accept(LoggingMessageNotification notif) {
-		Logger log = LoggerFactory.getLogger(notif.logger());
 		if (notif.meta().isEmpty()) {
 			// If no meta, then just log the data as a message
-			log.atLevel(convert(notif.level())).log(notif.data());
+			LOG.atLevel(convert(notif.level())).log(notif.data());
 		}
 		else {
 			// If there is meta, then log it as a structured log message
-			var builder = log.atLevel(convert(notif.level())).setMessage(notif.data());
+			var builder = LOG.atLevel(convert(notif.level())).setMessage(notif.data());
 			notif.meta().forEach((key, value) -> builder.addKeyValue(key, value));
 			builder.log();
 		}