feat: enforce MCP request ID validation requirements

mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -218,6 +218,17 @@ public record JSONRPCRequest( // @formatter:off
 		@JsonProperty("method") String method,
 		@JsonProperty("id") Object id,
 		@JsonProperty("params") Object params) implements JSONRPCMessage { // @formatter:on
+
+		/**
+		 * Constructor that validates MCP-specific ID requirements. Unlike base JSON-RPC,
+		 * MCP requires that: (1) Requests MUST include a string or integer ID; (2) The ID
+		 * MUST NOT be null
+		 */
+		public JSONRPCRequest {
+			Assert.notNull(id, "MCP requests MUST include an ID - null IDs are not allowed");
+			Assert.isTrue(id instanceof String || id instanceof Integer || id instanceof Long,
+					"MCP requests MUST have an ID that is either a string or integer");
+		}
 	}
 
 	/**

mcp/src/main/java/io/modelcontextprotocol/util/Assert.java

@@ -76,4 +76,17 @@ public static boolean hasText(@Nullable String str) {
 		return (str != null && !str.isBlank());
 	}
 
+	/**
+	 * Assert a boolean expression, throwing an {@code IllegalArgumentException} if the
+	 * expression evaluates to {@code false}.
+	 * @param expression a boolean expression
+	 * @param message the exception message to use if the assertion fails
+	 * @throws IllegalArgumentException if {@code expression} is {@code false}
+	 */
+	public static void isTrue(boolean expression, String message) {
+		if (!expression) {
+			throw new IllegalArgumentException(message);
+		}
+	}
+
 }

mcp/src/test/java/io/modelcontextprotocol/spec/JSONRPCRequestMcpValidationTest.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2024-2024 the original author or authors.
+ */
+
+package io.modelcontextprotocol.spec;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Tests for MCP-specific validation of JSONRPCRequest ID requirements.
+ *
+ * @author Christian Tzolov
+ */
+public class JSONRPCRequestMcpValidationTest {
+
+	@Test
+	public void testValidStringId() {
+		assertDoesNotThrow(() -> {
+			var request = new McpSchema.JSONRPCRequest("2.0", "test/method", "string-id", null);
+			assertEquals("string-id", request.id());
+		});
+	}
+
+	@Test
+	public void testValidIntegerId() {
+		assertDoesNotThrow(() -> {
+			var request = new McpSchema.JSONRPCRequest("2.0", "test/method", 123, null);
+			assertEquals(123, request.id());
+		});
+	}
+
+	@Test
+	public void testValidLongId() {
+		assertDoesNotThrow(() -> {
+			var request = new McpSchema.JSONRPCRequest("2.0", "test/method", 123L, null);
+			assertEquals(123L, request.id());
+		});
+	}
+
+	@Test
+	public void testNullIdThrowsException() {
+		IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> {
+			new McpSchema.JSONRPCRequest("2.0", "test/method", null, null);
+		});
+
+		assertTrue(exception.getMessage().contains("MCP requests MUST include an ID"));
+		assertTrue(exception.getMessage().contains("null IDs are not allowed"));
+	}
+
+	@Test
+	public void testDoubleIdTypeThrowsException() {
+		IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> {
+			new McpSchema.JSONRPCRequest("2.0", "test/method", 123.45, null);
+		});
+
+		assertTrue(exception.getMessage().contains("MCP requests MUST have an ID that is either a string or integer"));
+		assertTrue(exception.getMessage().contains("Double"));
+	}
+
+	@Test
+	public void testBooleanIdThrowsException() {
+		IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> {
+			new McpSchema.JSONRPCRequest("2.0", "test/method", true, null);
+		});
+
+		assertTrue(exception.getMessage().contains("MCP requests MUST have an ID that is either a string or integer"));
+		assertTrue(exception.getMessage().contains("Boolean"));
+	}
+
+	@Test
+	public void testArrayIdThrowsException() {
+		IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> {
+			new McpSchema.JSONRPCRequest("2.0", "test/method", new String[] { "array" }, null);
+		});
+
+		assertTrue(exception.getMessage().contains("MCP requests MUST have an ID that is either a string or integer"));
+	}
+
+	@Test
+	public void testObjectIdThrowsException() {
+		IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> {
+			new McpSchema.JSONRPCRequest("2.0", "test/method", new Object(), null);
+		});
+
+		assertTrue(exception.getMessage().contains("MCP requests MUST have an ID that is either a string or integer"));
+		assertTrue(exception.getMessage().contains("Object"));
+	}
+
+}