Test coverage for ensuring the MessageBodyWriter is used with null Accept header

http/http-advanced-reactive/src/main/java/io/quarkus/ts/http/advanced/reactive/CustomHeaderResponse.java

@@ -0,0 +1,13 @@
+package io.quarkus.ts.http.advanced.reactive;
+
+public class CustomHeaderResponse {
+    private final String content;
+
+    public CustomHeaderResponse(String content) {
+        this.content = content;
+    }
+
+    public String getContent() {
+        return content;
+    }
+}

http/http-advanced-reactive/src/main/java/io/quarkus/ts/http/advanced/reactive/HeadersMessageBodyWriter.java

@@ -0,0 +1,29 @@
+package io.quarkus.ts.http.advanced.reactive;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+
+import jakarta.ws.rs.WebApplicationException;
+import jakarta.ws.rs.core.MediaType;
+import jakarta.ws.rs.core.MultivaluedMap;
+import jakarta.ws.rs.ext.MessageBodyWriter;
+import jakarta.ws.rs.ext.Provider;
+
+@Provider
+public class HeadersMessageBodyWriter implements MessageBodyWriter<CustomHeaderResponse> {
+
+    @Override
+    public boolean isWriteable(Class aClass, Type type, Annotation[] annotations, MediaType mediaType) {
+        return CustomHeaderResponse.class.isAssignableFrom(aClass) && MediaType.TEXT_PLAIN_TYPE.isCompatible(mediaType);
+    }
+
+    @Override
+    public void writeTo(CustomHeaderResponse customHeaderResponse, Class<?> aClass, Type type, Annotation[] annotations,
+            MediaType mediaType, MultivaluedMap<String, Object> multivaluedMap, OutputStream outputStream)
+            throws IOException, WebApplicationException {
+        final String content = "Headers response: " + customHeaderResponse.getContent();
+        outputStream.write(content.getBytes());
+    }
+}

http/http-advanced-reactive/src/main/java/io/quarkus/ts/http/advanced/reactive/HeadersResource.java

@@ -2,6 +2,8 @@
 
 import jakarta.ws.rs.GET;
 import jakarta.ws.rs.Path;
+import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.core.MediaType;
 import jakarta.ws.rs.core.Response;
 
 import io.smallrye.mutiny.Uni;
@@ -28,4 +30,11 @@ public Uni<Response> headersOverride() {
         return Uni.createFrom().item(response);
     }
 
+    @GET
+    @Path("/no-accept")
+    @Produces(MediaType.TEXT_PLAIN)
+    public Uni<Response> noAcceptHeaders() {
+        return Uni.createFrom().item(Response.ok(new CustomHeaderResponse("ok headers")).build());
+    }
+
 }

http/http-advanced-reactive/src/test/java/io/quarkus/ts/http/advanced/reactive/HeadersIT.java

@@ -16,12 +16,15 @@
 import io.quarkus.test.bootstrap.RestService;
 import io.quarkus.test.scenarios.QuarkusScenario;
 import io.quarkus.test.services.QuarkusApplication;
+import io.restassured.http.Header;
 import io.restassured.response.ValidatableResponse;
 
 @QuarkusScenario
 public class HeadersIT {
 
     @QuarkusApplication(classes = { PathSpecificHeadersResource.class,
+            HeadersMessageBodyWriter.class,
+            CustomHeaderResponse.class,
             HeadersResource.class }, properties = "headers.properties")
     static RestService app = new RestService();
 
@@ -100,6 +103,19 @@ private ValidatableResponse whenGet(String path) {
                 .body(is("ok"));
     }
 
+    @Test
+    @Tag("https://github.com/quarkusio/quarkus/pull/41411")
+    void testWithNoAcceptHeader() {
+        Header header = new Header("Accept", null);
+        given()
+                .when()
+                .header(header)
+                .get("/headers/no-accept")
+                .then()
+                .statusCode(200)
+                .body(is("Headers response: ok headers"));
+    }
+
     /**
      * Cache-Control header may be present multiple times in the response, e.g. in an OpenShift deployment. That is why we need
      * to look for a specific value among all headers of the same name, and not just match the last one of them, which is what

http/http-advanced/src/main/java/io/quarkus/ts/http/advanced/CustomHeaderResponse.java

@@ -0,0 +1,14 @@
+package io.quarkus.ts.http.advanced;
+
+public class CustomHeaderResponse {
+
+    private final String content;
+
+    public CustomHeaderResponse(String content) {
+        this.content = content;
+    }
+
+    public String getContent() {
+        return content;
+    }
+}

http/http-advanced/src/main/java/io/quarkus/ts/http/advanced/HeadersMessageBodyWriter.java

@@ -0,0 +1,29 @@
+package io.quarkus.ts.http.advanced;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+
+import jakarta.ws.rs.WebApplicationException;
+import jakarta.ws.rs.core.MediaType;
+import jakarta.ws.rs.core.MultivaluedMap;
+import jakarta.ws.rs.ext.MessageBodyWriter;
+import jakarta.ws.rs.ext.Provider;
+
+@Provider
+public class HeadersMessageBodyWriter implements MessageBodyWriter<CustomHeaderResponse> {
+
+    @Override
+    public boolean isWriteable(Class aClass, Type type, Annotation[] annotations, MediaType mediaType) {
+        return CustomHeaderResponse.class.isAssignableFrom(aClass) && MediaType.TEXT_PLAIN_TYPE.isCompatible(mediaType);
+    }
+
+    @Override
+    public void writeTo(CustomHeaderResponse customHeaderResponse, Class<?> aClass, Type type, Annotation[] annotations,
+            MediaType mediaType, MultivaluedMap<String, Object> multivaluedMap, OutputStream outputStream)
+            throws IOException, WebApplicationException {
+        final String content = "Headers response: " + customHeaderResponse.getContent();
+        outputStream.write(content.getBytes());
+    }
+}

http/http-advanced/src/main/java/io/quarkus/ts/http/advanced/HeadersResource.java

@@ -2,6 +2,8 @@
 
 import jakarta.ws.rs.GET;
 import jakarta.ws.rs.Path;
+import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.core.MediaType;
 import jakarta.ws.rs.core.Response;
 
 @Path("/headers")
@@ -25,4 +27,10 @@ public Response headersOverride() {
         return Response.ok("ok").header("foo", "abc").build();
     }
 
+    @GET
+    @Path("/no-accept")
+    @Produces(MediaType.TEXT_PLAIN)
+    public Response noAcceptHeaders() {
+        return Response.ok(new CustomHeaderResponse("ok headers")).build();
+    }
 }

http/http-advanced/src/test/java/io/quarkus/ts/http/advanced/HeadersIT.java

@@ -16,12 +16,15 @@
 import io.quarkus.test.bootstrap.RestService;
 import io.quarkus.test.scenarios.QuarkusScenario;
 import io.quarkus.test.services.QuarkusApplication;
+import io.restassured.http.Header;
 import io.restassured.response.ValidatableResponse;
 
 @QuarkusScenario
 public class HeadersIT {
 
     @QuarkusApplication(classes = { PathSpecificHeadersResource.class,
+            HeadersMessageBodyWriter.class,
+            CustomHeaderResponse.class,
             HeadersResource.class }, properties = "headers.properties")
     static RestService app = new RestService();
 
@@ -93,6 +96,21 @@ void testPathSpecificHeaderRulesOrder() {
         cacheControlMatches(response, "max-age=1");
     }
 
+    /**
+     * Coverage for https://github.com/quarkusio/quarkus/issues/41354 in RESTEasy classic
+     */
+    @Test
+    void testWithNoAcceptHeader() {
+        Header header = new Header("Accept", null);
+        given()
+                .when()
+                .header(header)
+                .get("/headers/no-accept")
+                .then()
+                .statusCode(200)
+                .body(is("Headers response: ok headers"));
+    }
+
     private ValidatableResponse whenGet(String path) {
         return given()
                 .get(path)