fix(rest): support application/a2a+json content type

* fix(rest): support application/a2a+json content type

Author: JakubWorek

common/src/main/java/org/a2aproject/sdk/common/MediaType.java

@@ -5,4 +5,7 @@ public interface MediaType {
 
     /** MIME type for JSON content: {@code application/json}. */
     String APPLICATION_JSON = "application/json";
+
+    /** MIME type accepted from HTTP+JSON clients alongside {@code application/json}: {@code application/a2a+json}. */
+    String APPLICATION_A2A_JSON = "application/a2a+json";
 }

reference/rest/src/main/java/org/a2aproject/sdk/server/rest/quarkus/A2AServerRoutes.java

@@ -1,5 +1,6 @@
 package org.a2aproject.sdk.server.rest.quarkus;
 
+import static org.a2aproject.sdk.common.MediaType.APPLICATION_A2A_JSON;
 import static org.a2aproject.sdk.server.ServerCallContext.TRANSPORT_KEY;
 import static org.a2aproject.sdk.spec.A2AMethods.CANCEL_TASK_METHOD;
 import static org.a2aproject.sdk.spec.A2AMethods.SEND_STREAMING_MESSAGE_METHOD;
@@ -774,13 +775,14 @@ private String extractTenant(RoutingContext rc) {
     }
 
     /**
-     * Check if the request content type is application/json.
+     * Check if the request content type is application/json or application/a2a+json.
      * @param rc the routing context
-     * @return true if the content type is application/json - false otherwise.
+     * @return true if the content type is one of those - false otherwise.
      */
     private boolean validateContentType(RoutingContext rc) {
         String contentType = rc.request().getHeader(CONTENT_TYPE);
-        if (contentType == null || !contentType.trim().startsWith(APPLICATION_JSON)) {
+        if (contentType == null || !(contentType.trim().startsWith(APPLICATION_JSON)
+                || contentType.trim().startsWith(APPLICATION_A2A_JSON))) {
             sendResponse(rc, jsonRestHandler.createErrorResponse(new ContentTypeNotSupportedError(null, null, null)));
             return false;
         }