feat(mcp): resolve absolute and relative message endpoint URIs (#150)

Improve endpoint URI handling by supporting both relative paths
and properly validated absolute URIs.

- Implement URI resolution in HttpClientSseClientTransport:
- Change baseUri field from String to URI type
- Add Utils.resolveUri method to handle both absolute and relative URIs
- Resolve relative URIs against the base URI
- Validate absolute URIs to ensure they match base URI's scheme, authority, and path
- Add parameterized tests for various URI resolution scenarios
- Add ByteBuddy dependency for HttpClient mocking and update Mockito

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

mcp/src/test/java/io/modelcontextprotocol/client/transport/HttpClientSseClientTransportTests.java

@@ -7,12 +7,13 @@ package io.modelcontextprotocol.client.transport;
 import java.net.URI;
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
 import java.time.Duration;
 import java.util.Map;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
-import java.util.function.Consumer;
 import java.util.function.Function;
 
 import io.modelcontextprotocol.spec.McpSchema;
@@ -21,6 +22,8 @@ import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Mockito;
 import org.testcontainers.containers.GenericContainer;
 import org.testcontainers.containers.wait.strategy.Wait;
 import reactor.core.publisher.Mono;
@@ -31,6 +34,9 @@ import org.springframework.http.codec.ServerSentEvent;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatCode;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 
@@ -364,4 +370,25 @@ class HttpClientSseClientTransportTests {
 		customizedTransport.closeGracefully().block();
 	}
 
+	@Test
+	@SuppressWarnings("unchecked")
+	void testResolvingClientEndpoint() {
+		HttpClient httpClient = Mockito.mock(HttpClient.class);
+		HttpResponse<Void> httpResponse = Mockito.mock(HttpResponse.class);
+		CompletableFuture<HttpResponse<Void>> future = new CompletableFuture<>();
+		future.complete(httpResponse);
+		when(httpClient.sendAsync(any(HttpRequest.class), any(HttpResponse.BodyHandler.class))).thenReturn(future);
+
+		HttpClientSseClientTransport transport = new HttpClientSseClientTransport(httpClient, HttpRequest.newBuilder(),
+				"http://example.com", "http://example.com/sse", new ObjectMapper());
+
+		transport.connect(Function.identity());
+
+		ArgumentCaptor<HttpRequest> httpRequestCaptor = ArgumentCaptor.forClass(HttpRequest.class);
+		verify(httpClient).sendAsync(httpRequestCaptor.capture(), any(HttpResponse.BodyHandler.class));
+		assertThat(httpRequestCaptor.getValue().uri()).isEqualTo(URI.create("http://example.com/sse"));
+
+		transport.closeGracefully().block();
+	}
+
 }

mcp/src/test/java/io/modelcontextprotocol/util/UtilsTests.java

@@ -6,12 +6,17 @@ package io.modelcontextprotocol.util;
 
 import org.junit.jupiter.api.Test;
 
+import java.net.URI;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 class UtilsTests {
 
@@ -37,4 +42,28 @@ class UtilsTests {
 		assertFalse(Utils.isEmpty(Map.of("key", "value")));
 	}
 
+	@ParameterizedTest
+	@CsvSource({
+			// relative endpoints
+			"http://localhost:8080/root, /api/v1, http://localhost:8080/api/v1",
+			"http://localhost:8080/root/, api, http://localhost:8080/root/api",
+			"http://localhost:8080, /api, http://localhost:8080/api",
+			// absolute endpoints matching base
+			"http://localhost:8080/root, http://localhost:8080/root/api/v1, http://localhost:8080/root/api/v1",
+			"http://localhost:8080/root, http://localhost:8080/root, http://localhost:8080/root" })
+	void testValidUriResolution(String baseUrl, String endpoint, String expectedResult) {
+		URI result = Utils.resolveUri(URI.create(baseUrl), endpoint);
+		assertThat(result.toString()).isEqualTo(expectedResult);
+	}
+
+	@ParameterizedTest
+	@CsvSource({ "http://localhost:8080/root, http://localhost:8080/other/api",
+			"http://localhost:8080/root, http://otherhost/api",
+			"http://localhost:8080/root, http://localhost:9090/root/api" })
+	void testAbsoluteUriNotMatchingBase(String baseUrl, String endpoint) {
+		assertThatThrownBy(() -> Utils.resolveUri(URI.create(baseUrl), endpoint))
+			.isInstanceOf(IllegalArgumentException.class)
+			.hasMessageContaining("does not match the base URL");
+	}
+
 }