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Support for MCP features and SSE (#34)
* Depend on SNAPSHOT version of Helidon. Initial switch to SSE connection to support MCP features. * Add a context object to a session for features to store any relevant state. Refactored logger feature. * Improve tests for logging using SSE and streamable HTTP.
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-97
lines changed

16 files changed

+577
-97
lines changed

‎examples/calendar/pom.xml‎

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@@ -23,7 +23,7 @@
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<parent>
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<groupId>io.helidon.applications</groupId>
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<artifactId>helidon-se</artifactId>
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<version>4.3.0-M1</version>
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<version>4.3.0-SNAPSHOT</version>
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<relativePath/>
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</parent>
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‎examples/weather-application/mcp-client/pom.xml‎

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<parent>
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<groupId>io.helidon.applications</groupId>
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<artifactId>helidon-se</artifactId>
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<version>4.3.0-M1</version>
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<version>4.3.0-SNAPSHOT</version>
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<relativePath/>
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</parent>
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@@ -86,4 +86,24 @@
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</plugin>
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</plugins>
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</build>
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<repositories>
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<repository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</repository>
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</repositories>
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<pluginRepositories>
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<pluginRepository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</pluginRepository>
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</pluginRepositories>
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</project>

‎examples/weather-application/mcp-server-declarative/pom.xml‎

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@@ -23,7 +23,7 @@
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<parent>
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<groupId>io.helidon.applications</groupId>
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<artifactId>helidon-se</artifactId>
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<version>4.3.0-M1</version>
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<version>4.3.0-SNAPSHOT</version>
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<relativePath/>
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</parent>
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@@ -126,4 +126,24 @@
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</plugin>
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</plugins>
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</build>
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<repositories>
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<repository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</repository>
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</repositories>
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<pluginRepositories>
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<pluginRepository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</pluginRepository>
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</pluginRepositories>
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</project>

‎examples/weather-application/mcp-server/pom.xml‎

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@@ -23,7 +23,7 @@
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<parent>
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<groupId>io.helidon.applications</groupId>
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<artifactId>helidon-se</artifactId>
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<version>4.3.0-M1</version>
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<version>4.3.0-SNAPSHOT</version>
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<relativePath/>
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</parent>
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@@ -75,4 +75,24 @@
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</plugin>
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</plugins>
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</build>
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<repositories>
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<repository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</repository>
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</repositories>
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<pluginRepositories>
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<pluginRepository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</pluginRepository>
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</pluginRepositories>
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</project>

‎pom.xml‎

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<properties>
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<version.java>21</version.java>
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<helidon.version>4.3.0-M1</helidon.version>
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<helidon.version>4.3.0-SNAPSHOT</helidon.version>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
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</modules>
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</profile>
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</profiles>
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<repositories>
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<repository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</repository>
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</repositories>
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<pluginRepositories>
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<pluginRepository>
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<id>central-snapshot</id>
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<url>https://central.sonatype.com/repository/maven-snapshots</url>
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<snapshots>
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<enabled>true</enabled>
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</snapshots>
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</pluginRepository>
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</pluginRepositories>
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</project>

‎server/src/main/java/io/helidon/extensions/mcp/server/McpFeature.java‎

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/*
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* Copyright (c) 2025 Oracle and/or its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
8+
* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13+
* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.helidon.extensions.mcp.server;
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import java.util.Objects;
19+
import java.util.Optional;
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import io.helidon.common.context.Context;
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import io.helidon.webserver.sse.SseSink;
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/**
25+
* Base class for all MCP features.
26+
*/
27+
class McpFeature {
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29+
private final McpSession session;
30+
private final SseSink sseSink;
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McpFeature(McpSession session) {
33+
Objects.requireNonNull(session, "session is null");
34+
this.session = session;
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this.sseSink = null;
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}
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McpFeature(McpSession session, SseSink sseSink) {
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Objects.requireNonNull(session, "session is null");
40+
Objects.requireNonNull(sseSink, "sseSink is null");
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this.session = session;
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this.sseSink = sseSink;
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}
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protected McpSession session() {
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return session;
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}
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protected Optional<SseSink> sseSink() {
50+
return Optional.ofNullable(sseSink);
51+
}
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protected Context context() {
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return session.context();
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}
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}

‎server/src/main/java/io/helidon/extensions/mcp/server/McpFeatures.java‎

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Original file line numberDiff line numberDiff line change
@@ -16,33 +16,86 @@
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package io.helidon.extensions.mcp.server;
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import java.util.Objects;
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import java.util.Optional;
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import io.helidon.webserver.jsonrpc.JsonRpcResponse;
23+
import io.helidon.webserver.sse.SseSink;
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/**
2026
* Support for optional client features like {@link McpProgress} and {@link McpLogger}.
2127
*/
2228
public final class McpFeatures {
23-
private final McpProgress progress;
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private final McpLogger logger;
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private final JsonRpcResponse response;
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private final McpSession session;
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private McpProgress progress;
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private McpLogger logger;
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private SseSink sseSink;
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2636
McpFeatures(McpSession session) {
27-
this.logger = new McpLogger(session);
28-
this.progress = new McpProgress(session);
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Objects.requireNonNull(session, "session is null");
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this.session = session;
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this.response = null;
40+
}
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McpFeatures(McpSession session, JsonRpcResponse response) {
43+
Objects.requireNonNull(response, "response is null");
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Objects.requireNonNull(session, "session is null");
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this.response = response;
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this.session = session;
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}
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/**
3250
* Get a {@link McpProgress} feature.
3351
*
34-
* @return progress
52+
* @return progress the MCP progress
3553
*/
3654
public McpProgress progress() {
55+
if (progress == null) {
56+
if (response != null) {
57+
sseSink = getOrCreateSseSink();
58+
progress = new McpProgress(session, sseSink);
59+
} else {
60+
progress = new McpProgress(session);
61+
}
62+
}
3763
return progress;
3864
}
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4066
/**
4167
* Get a {@link McpLogger} feature.
4268
*
43-
* @return logging
69+
* @return logging the MCP logger
4470
*/
4571
public McpLogger logger() {
72+
if (logger == null) {
73+
if (response != null) {
74+
sseSink = getOrCreateSseSink();
75+
logger = new McpLogger(session, sseSink);
76+
} else {
77+
logger = new McpLogger(session);
78+
}
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}
4680
return logger;
4781
}
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/**
84+
* Get access to underlying SSE sink, if available. This method is package private.
85+
*
86+
* @return optional SSE sink
87+
*/
88+
Optional<SseSink> sseSink() {
89+
return Optional.ofNullable(sseSink);
90+
}
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/**
93+
* Get or create an SSE sink for this instance.
94+
*
95+
* @return the SSE sink
96+
*/
97+
private SseSink getOrCreateSseSink() {
98+
Objects.requireNonNull(response, "response is null");
99+
return sseSink != null ? sseSink : response.sink(SseSink.TYPE);
100+
}
48101
}

‎server/src/main/java/io/helidon/extensions/mcp/server/McpLogger.java‎

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Original file line numberDiff line numberDiff line change
@@ -18,17 +18,23 @@
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import java.util.Objects;
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21+
import io.helidon.http.sse.SseEvent;
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import io.helidon.webserver.sse.SseSink;
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2124
/**
2225
* Mcp logger to send notification to the client.
2326
*/
24-
public final class McpLogger {
27+
public final class McpLogger extends McpFeature {
28+
2529
private final String name;
26-
private final McpSession session;
27-
private Level level;
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2931
McpLogger(McpSession session) {
30-
this.session = session;
31-
this.level = Level.INFO;
32+
super(session);
33+
this.name = "helidon-logger";
34+
}
35+
36+
McpLogger(McpSession session, SseSink sseSink) {
37+
super(session, sseSink);
3238
this.name = "helidon-logger";
3339
}
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@@ -41,8 +47,16 @@ public final class McpLogger {
4147
public void log(Level level, String message) {
4248
Objects.requireNonNull(level, "level must not be null");
4349
Objects.requireNonNull(message, "message must not be null");
44-
if (level.ordinal() >= this.level.ordinal()) {
45-
session.send(McpJsonRpc.createLoggingNotification(level, name, message));
50+
51+
if (level.ordinal() >= level().ordinal()) {
52+
if (sseSink().isPresent()) {
53+
sseSink().get().emit(SseEvent.builder()
54+
.name("message")
55+
.data(McpJsonRpc.createLoggingNotification(level, name, message))
56+
.build());
57+
} else {
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session().send(McpJsonRpc.createLoggingNotification(level, name, message));
59+
}
4660
}
4761
}
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@@ -109,8 +123,23 @@ public void alert(String message) {
109123
log(Level.ALERT, message);
110124
}
111125

126+
/**
127+
* Get level for this logger.
128+
*
129+
* @return the level
130+
*/
131+
McpLogger.Level level() {
132+
return context().get(Level.class).orElse(Level.INFO);
133+
}
134+
135+
/**
136+
* Set level on the session since there could be multiple instances of this
137+
* class with streamable HTTP.
138+
*
139+
* @param level the level
140+
*/
112141
void setLevel(McpLogger.Level level) {
113-
this.level = level;
142+
context().register(level);
114143
}
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116145
/**

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