fix: Default basePath to / when server URL has no path (#74)

* fix: Default basePath to / when server URL has no path

URI.create("http://127.0.0.1:4444").getPath() returns an empty
string, not null, so the previous Optional.ofNullable fallback
left basePath empty and HttpServer.createContext rejected it.

* test: Verify handler dispatch when basePath is /

The catch-all 404 context at / collided with the spec context when
the server URL had no path. Skip the catch-all in that case.

Author: thced

src/main/java/com/retailsvc/http/OpenApiServer.java

@@ -93,7 +93,8 @@ record HandlerConfig(
     this.httpServer = HttpServer.create(socketAddress, 0);
     httpServer.setExecutor(newThreadPerTaskExecutor(ofVirtual().name("http-", 0).factory()));
 
-    HttpContext ctx = httpServer.createContext(Optional.ofNullable(spec.basePath()).orElse("/"));
+    String basePath = Optional.ofNullable(spec.basePath()).orElse("/");
+    HttpContext ctx = httpServer.createContext(basePath);
     ctx.getFilters().add(new ExceptionFilter(exceptionHandler));
     ctx.getFilters().add(new RequestPreparationFilter(spec, router, validator, bodyMappers));
     ctx.getFilters()
@@ -117,7 +118,9 @@ record HandlerConfig(
       extraCtx.setHandler(e.getValue());
     }
 
-    httpServer.createContext("/", Handlers.notFoundHandler());
+    if (!"/".equals(basePath)) {
+      httpServer.createContext("/", Handlers.notFoundHandler());
+    }
     httpServer.start();
 
     this.shutdownTimeoutSeconds = shutdownTimeoutSeconds;

src/main/java/com/retailsvc/http/spec/Spec.java

@@ -245,7 +245,8 @@ private static String computeBasePath(List<Server> servers) {
     if (servers.isEmpty()) {
       throw new IllegalStateException("no servers declared");
     }
-    return Optional.ofNullable(URI.create(servers.getFirst().url()).getPath()).orElse("");
+    String path = URI.create(servers.getFirst().url()).getPath();
+    return (path == null || path.isEmpty()) ? "/" : path;
   }
 
   private static <T> Map<String, T> indexByRef(Map<String, T> components, String prefix) {

src/test/java/com/retailsvc/http/OpenApiServerTest.java

@@ -89,6 +89,45 @@ void shouldBindOnlyToLoopbackWhenBindAddressIsLoopback() throws Exception {
     }
   }
 
+  @Test
+  void shouldDispatchHandlerOnRootPathWhenServerUrlHasNoPath() throws Exception {
+    Map<String, Object> raw =
+        Map.of(
+            "openapi", "3.1.0",
+            "info", Map.of("title", "Test API", "version", "1.0"),
+            "servers", List.of(Map.of("url", "http://127.0.0.1:4444")),
+            "paths",
+                Map.of(
+                    "/",
+                    Map.of(
+                        "get",
+                        Map.of(
+                            "operationId",
+                            "root",
+                            "responses",
+                            Map.of("204", Map.of("description", "ok"))))));
+    Spec spec = Spec.from(raw);
+    RequestHandler rootHandler = request -> Response.empty();
+    try (var server =
+        OpenApiServer.builder()
+            .spec(spec)
+            .handlers(Map.of("root", rootHandler))
+            .port(0)
+            .bindAddress(InetAddress.getLoopbackAddress())
+            .build()) {
+      int port = server.listenPort();
+      HttpClient client =
+          HttpClient.newBuilder()
+              .executor(newVirtualThreadPerTaskExecutor())
+              .version(HTTP_1_1)
+              .build();
+      HttpRequest request =
+          HttpRequest.newBuilder().uri(URI.create("http://127.0.0.1:" + port + "/")).GET().build();
+      HttpResponse<Void> response = client.send(request, HttpResponse.BodyHandlers.discarding());
+      assertThat(response.statusCode()).isEqualTo(HttpURLConnection.HTTP_NO_CONTENT);
+    }
+  }
+
   @Test
   void shouldBindToWildcardWhenBindAddressIsUnset() throws IOException {
     try (var server =

src/test/java/com/retailsvc/http/spec/SpecTest.java

@@ -33,6 +33,18 @@ void parsesMinimalSpec() {
     assertThat(spec.operations()).isEmpty();
   }
 
+  @Test
+  void basePathDefaultsToRootWhenServerUrlHasNoPath() {
+    Map<String, Object> raw =
+        Map.of(
+            "openapi", "3.1.0",
+            "info", Map.of("title", "x", "version", "1"),
+            "servers", List.of(Map.of("url", "http://127.0.0.1:4444")),
+            "paths", Map.of());
+    Spec spec = Spec.from(raw);
+    assertThat(spec.basePath()).isEqualTo("/");
+  }
+
   @Test
   void parsesPathsWithMethods() {
     Map<String, Object> raw =