Fix NullPointerException when accessing arthas-output with MCP disabled

[Copilot]

When arthas.mcpEndpoint is set to empty string (MCP disabled), accessing /arthas-output/ throws NullPointerException at line 79 of HttpRequestHandler.java. The code calls mcpRequestHandler.getMcpEndpoint() without checking if mcpRequestHandler is null.

Changes

• Added null check for mcpRequestHandler before accessing MCP endpoint
• When MCP is disabled, request processing now continues to subsequent handlers (DirectoryBrowser, classpath resources) instead of crashing

// Before
String mcpEndpoint = mcpRequestHandler.getMcpEndpoint();
if (mcpEndpoint.equals(path)) {
    mcpRequestHandler.handle(ctx, request);
    isMcpHandled = true;
    return;
}

// After
if (mcpRequestHandler != null) {
    String mcpEndpoint = mcpRequestHandler.getMcpEndpoint();
    if (mcpEndpoint.equals(path)) {
        mcpRequestHandler.handle(ctx, request);
        isMcpHandled = true;
        return;
    }
}

This aligns with ArthasBootstrap behavior where mcpRequestHandler is only initialized when MCP endpoint is configured (line 479) and explicitly set to null on shutdown (line 538).

Original prompt

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This section details on the original issue you should resolve

<issue_title>Unable to access arthas-output endpoint in tunnel server when mcp is disabled</issue_title>
<issue_description>- [x] I have searched the issues of this repository and believe that this is not a duplicate.

Environment

• Arthas version: 4.1.4
• Operating System version: Linux 5.15 (Ubuntu)
• Java version of target JVM: 21
• Java version of JVM used to attach: 21

Steps to reproduce this issue

1. Turn off mcp in arthas by setting following property:

arthas.mcpEndpoint=

3. Access arthas-output from tunnel server
4. Endpoint results in error

As a workaround, enabling the mcp, by setting the mcp endpoint to /mcp works fine.

Expected Result

Endpoint returns output result

Actual Result

Endpoint fails with an exception

If there is an exception, please attach the exception trace:

2026-01-02 08:48:50 [arthas-TermServer-3-2] ERROR c.t.a.c.s.t.i.h.HttpRequestHandler -arthas process http request error: /arthas-output/
java.lang.NullPointerException: Cannot invoke "com.taobao.arthas.mcp.server.protocol.server.handler.McpHttpRequestHandler.getMcpEndpoint()" because "this.mcpRequestHandler" is null
	at com.taobao.arthas.core.shell.term.impl.http.HttpRequestHandler.channelRead0(HttpRequestHandler.java:79)
	at com.taobao.arthas.core.shell.term.impl.http.HttpRequestHandler.channelRead0(HttpRequestHandler.java:32)
	at com.alibaba.arthas.deps.io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99)
	at com.alibaba.arthas.deps.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at com.alibaba.arthas.deps.io.netty.channel.AbstractChannelHandlerContext.access$600(AbstractChannelHandlerContext.java:61)
	at com.alibaba.arthas.deps.io.netty.channel.AbstractChannelHandlerContext$7.run(AbstractChannelHandlerContext.java:425)
	at com.alibaba.arthas.deps.io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
	at com.alibaba.arthas.deps.io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
	at com.alibaba.arthas.deps.io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
	at com.alibaba.arthas.deps.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:569)
	at com.alibaba.arthas.deps.io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998)
	at com.alibaba.arthas.deps.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at com.alibaba.arthas.deps.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Unknown Source)

Any workarounds to disable mcp without impacting any feature would be helpful.
Thanks.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Unable to access arthas-output endpoint in tunnel server when mcp is disabled #3119

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