Run STDIO tests with node instead of npx

Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>

Author: Kehrlann

mcp-test/src/test/java/io/modelcontextprotocol/client/ServerParameterUtils.java

@@ -1,21 +1,188 @@
+/*
+ * Copyright 2024-2026 the original author or authors.
+ */
+
 package io.modelcontextprotocol.client;
 
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardCopyOption;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.Stream;
+
 import io.modelcontextprotocol.client.transport.ServerParameters;
 
+/**
+ * Provides the {@link ServerParameters} used to launch the {@code server-everything} MCP
+ * server for the stdio client tests.
+ *
+ * <p>
+ * Those tests spawn a fresh server process per test, so the launch cost is paid dozens of
+ * times per build. Going through {@code npx} costs roughly 3 seconds per spawn even with
+ * a warm cache, because npx re-resolves the package every time, and it inserts two extra
+ * processes ({@code npx} &rarr; {@code npm exec} &rarr; {@code node}) between the test
+ * and the server. The latter also means the process the transport owns is not the server,
+ * so closing the transport leaves the server behind.
+ *
+ * <p>
+ * Instead, the package is installed once per JVM into a version-keyed directory under the
+ * temporary directory, and the server is launched directly with {@code node}, which
+ * brings the per-spawn cost down to roughly 0.4 seconds.
+ */
 public final class ServerParameterUtils {
 
+	private static final String SERVER_EVERYTHING_VERSION = "2025.12.18";
+
+	private static final boolean IS_WINDOWS = System.getProperty("os.name").toLowerCase().contains("win");
+
+	private static final Path SERVER_SCRIPT = resolveServerScript();
+
+	private static final String NODE_EXECUTABLE = resolveNodeExecutable();
+
 	private ServerParameterUtils() {
 	}
 
 	public static ServerParameters createServerParameters() {
-		if (System.getProperty("os.name").toLowerCase().contains("win")) {
-			return ServerParameters.builder("cmd.exe")
-				.args("/c", "npx.cmd", "-y", "@modelcontextprotocol/server-everything@2025.12.18", "stdio")
-				.build();
-		}
-		return ServerParameters.builder("npx")
-			.args("-y", "@modelcontextprotocol/server-everything@2025.12.18", "stdio")
-			.build();
+		return ServerParameters.builder(NODE_EXECUTABLE).args(SERVER_SCRIPT.toString(), "stdio").build();
+	}
+
+	private static Path resolveServerScript() {
+		Path tmpDir = Paths.get(System.getProperty("java.io.tmpdir"));
+		Path installDir = tmpDir.resolve("mcp-server-everything-" + SERVER_EVERYTHING_VERSION);
+		if (!Files.isRegularFile(serverScriptIn(installDir))) {
+			install(tmpDir, installDir);
+		}
+		Path script = serverScriptIn(installDir);
+		if (!Files.isRegularFile(script)) {
+			throw new IllegalStateException("server-everything was not installed at " + script);
+		}
+		return script;
+	}
+
+	private static Path serverScriptIn(Path installDir) {
+		return installDir
+			.resolve(Paths.get("node_modules", "@modelcontextprotocol", "server-everything", "dist", "index.js"));
+	}
+
+	/**
+	 * Installs into a staging directory and moves it into place atomically, so that
+	 * concurrent builds sharing the temporary directory can never observe a partially
+	 * installed tree.
+	 */
+	private static void install(Path tmpDir, Path installDir) {
+		Path staging;
+		try {
+			staging = Files.createTempDirectory(tmpDir, "mcp-server-everything-staging-");
+		}
+		catch (IOException e) {
+			throw new UncheckedIOException(e);
+		}
+		try {
+			run(npmCommand("install", "--prefix", staging.toString(), "--no-save", "--no-audit", "--no-fund",
+					"--loglevel=error", "@modelcontextprotocol/server-everything@" + SERVER_EVERYTHING_VERSION));
+			try {
+				Files.move(staging, installDir, StandardCopyOption.ATOMIC_MOVE);
+			}
+			catch (IOException e) {
+				// Another build won the race and installed it first, which is fine as
+				// long as the result is usable.
+				if (!Files.isRegularFile(serverScriptIn(installDir))) {
+					throw new UncheckedIOException("Failed to install server-everything to " + installDir, e);
+				}
+			}
+		}
+		finally {
+			deleteRecursively(staging);
+		}
+	}
+
+	private static void deleteRecursively(Path path) {
+		if (!Files.exists(path)) {
+			return;
+		}
+		try (Stream<Path> paths = Files.walk(path)) {
+			paths.sorted(Comparator.reverseOrder()).forEach(p -> {
+				try {
+					Files.deleteIfExists(p);
+				}
+				catch (IOException e) {
+					// Leftovers in the temporary directory are harmless.
+				}
+			});
+		}
+		catch (IOException e) {
+			// Leftovers in the temporary directory are harmless.
+		}
+	}
+
+	/**
+	 * Asks node for its own absolute path, so that spawning the server does not go
+	 * through a {@code node} wrapper script on the {@code PATH} (as installed by nvm and
+	 * friends), which would add an extra shell process per spawn.
+	 */
+	private static String resolveNodeExecutable() {
+		String node = IS_WINDOWS ? "node.exe" : "node";
+		try {
+			return run(List.of(node, "-p", "process.execPath")).trim();
+		}
+		catch (RuntimeException e) {
+			return node;
+		}
+	}
+
+	private static List<String> npmCommand(String... args) {
+		List<String> command = new ArrayList<>();
+		if (IS_WINDOWS) {
+			command.add("cmd.exe");
+			command.add("/c");
+			command.add("npm.cmd");
+		}
+		else {
+			command.add("npm");
+		}
+		command.addAll(List.of(args));
+		return command;
+	}
+
+	private static String run(List<String> command) {
+		try {
+			// Note: the output is redirected to a file rather than inherited, because
+			// writing to the native streams from a forked JVM corrupts the Surefire fork
+			// channel. A file rather than a pipe also keeps the timeout below effective,
+			// which draining the pipe first would not.
+			Path log = Files.createTempFile("mcp-test-", ".log");
+			try {
+				Process process = new ProcessBuilder(command).redirectErrorStream(true)
+					.redirectOutput(log.toFile())
+					.start();
+				if (!process.waitFor(5, TimeUnit.MINUTES)) {
+					process.destroyForcibly();
+					throw new IllegalStateException("Timed out running " + command);
+				}
+				String output = Files.readString(log);
+				if (process.exitValue() != 0) {
+					throw new IllegalStateException(
+							command + " failed with exit code " + process.exitValue() + ":\n" + output);
+				}
+				return output;
+			}
+			finally {
+				Files.deleteIfExists(log);
+			}
+		}
+		catch (IOException e) {
+			throw new UncheckedIOException(e);
+		}
+		catch (InterruptedException e) {
+			Thread.currentThread().interrupt();
+			throw new IllegalStateException(e);
+		}
 	}
 
 }

mcp-test/src/test/java/io/modelcontextprotocol/client/StdioMcpAsyncClientTests.java

@@ -18,16 +18,16 @@
  * Tests for the {@link McpAsyncClient} with {@link StdioClientTransport}.
  *
  * <p>
- * These tests use npx to download and run the MCP "everything" server locally. The first
- * test execution will download the everything server scripts and cache them locally,
- * which can take more than 15 seconds. Subsequent test runs will use the cached version
- * and execute faster.
+ * These tests run the MCP "everything" server locally, spawning a fresh server process
+ * per test. The server package is installed once and launched directly with node, see
+ * {@link ServerParameterUtils}. The first test execution installs the package, which can
+ * take more than 15 seconds; subsequent runs reuse the installed copy.
  *
  * @author Christian Tzolov
  * @author Dariusz Jędrzejczyk
  */
-@Timeout(25) // Giving extra time beyond the client timeout to account for initial server
-				// download
+@Timeout(25) // Giving extra time beyond the client timeout to account for the one-time
+				// install of the server package
 class StdioMcpAsyncClientTests extends AbstractMcpAsyncClientTests {
 
 	@Override

mcp-test/src/test/java/io/modelcontextprotocol/client/StdioMcpSyncClientTests.java

@@ -25,16 +25,16 @@
  * Tests for the {@link McpSyncClient} with {@link StdioClientTransport}.
  *
  * <p>
- * These tests use npx to download and run the MCP "everything" server locally. The first
- * test execution will download the everything server scripts and cache them locally,
- * which can take more than 15 seconds. Subsequent test runs will use the cached version
- * and execute faster.
+ * These tests run the MCP "everything" server locally, spawning a fresh server process
+ * per test. The server package is installed once and launched directly with node, see
+ * {@link ServerParameterUtils}. The first test execution installs the package, which can
+ * take more than 15 seconds; subsequent runs reuse the installed copy.
  *
  * @author Christian Tzolov
  * @author Dariusz Jędrzejczyk
  */
-@Timeout(25) // Giving extra time beyond the client timeout to account for initial server
-				// download
+@Timeout(25) // Giving extra time beyond the client timeout to account for the one-time
+				// install of the server package
 class StdioMcpSyncClientTests extends AbstractMcpSyncClientTests {
 
 	@Override