fix(http-client): always provide a fallback URL in A2ACardResolver (a2aproject#1179)

When the user-provided base URL matched the computed card URL, no
fallback was attempted on 404. Now falls back to cleanBase in that
case, and to the original URL otherwise.

This fixes a2aproject#1178

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>

Author: ehsavoie

http-client/src/main/java/org/a2aproject/sdk/client/http/A2ACardResolver.java

@@ -269,7 +269,7 @@ private static ResolvedUrls resolveUrls(String cleanBase, String originalBase, @
             Utils.validateAbsoluteUrl(cleanBase);
             cardUrl = Utils.buildCardUrl(cleanBase, Utils.DEFAULT_AGENT_CARD_PATH);
         }
-        String fallbackUrl = isSameUrl(cardUrl, originalBase) ? null : cleanBase;
+        String fallbackUrl = isSameUrl(cardUrl, originalBase) ? cleanBase : originalBase;
         return new ResolvedUrls(cardUrl, fallbackUrl);
     }
 

http-client/src/test/java/org/a2aproject/sdk/client/http/A2ACardResolverTest.java

@@ -337,14 +337,16 @@ public void testTenantUrl_fullTenantCardUrlProvidedAsBase_withTrailingSlash_notD
     }
 
     @Test
-    public void testTenantUrl_fullTenantCardUrlProvidedAsBase_noFallback() throws Exception {
-        // No fallback when the provided URL already IS the computed card URL.
+    public void testTenantUrl_fullTenantCardUrlProvidedAsBase_fallsBackToCleanBase() throws Exception {
+        // When the provided URL already IS the computed card URL, fall back to the clean base.
         TestHttpClient client = createTestClient();
-        client.status = 404;
+        client.statusSequence.add(404);
+        client.statusSequence.add(200);
         String tenantCardUrl = "http://example.com/.well-known/acme/agent-card.json";
-        A2ACardResolver resolver = A2ACardResolver.builder().httpClient(client).baseUrl(tenantCardUrl).tenant("acme").build();
-        assertThrows(A2AClientHTTPError.class, resolver::getAgentCard);
-        assertEquals(1, client.urlsCalled.size());
+        A2ACardResolver.builder().httpClient(client).baseUrl(tenantCardUrl).tenant("acme").build().getAgentCard();
+        assertEquals(2, client.urlsCalled.size());
+        assertEquals("http://example.com/.well-known/acme/agent-card.json", client.urlsCalled.get(0));
+        assertEquals("http://example.com", client.urlsCalled.get(1));
     }
 
     @Test
@@ -371,16 +373,15 @@ public void testGetAgentCard_httpError_fallsBackToProvidedUrl() throws Exception
     }
 
     @Test
-    public void testGetAgentCard_doubleSlashBaseUrl_fallbackUrlNormalized() throws Exception {
-        // A baseUrl with a double trailing slash must not produce a double-slash fallback URL.
+    public void testGetAgentCard_doubleSlashBaseUrl_fallbackToOriginalUrl() throws Exception {
+        // A baseUrl with a double trailing slash falls back to the originally provided URL.
         TestHttpClient client = createTestClient();
         client.statusSequence.add(404);
         client.statusSequence.add(200);
         A2ACardResolver.builder().httpClient(client).baseUrl("http://example.com//").build().getAgentCard();
         assertEquals(2, client.urlsCalled.size());
         assertEquals("http://example.com" + AGENT_CARD_PATH, client.urlsCalled.get(0));
-        // cleanBase strips one trailing slash from "http://example.com//", yielding "http://example.com/"
-        assertEquals("http://example.com/", client.urlsCalled.get(1));
+        assertEquals("http://example.com//", client.urlsCalled.get(1));
     }
 
     @Test
@@ -448,14 +449,16 @@ public void testGetAgentCard_nonNotFound_noFallback() throws Exception {
     }
 
     @Test
-    public void testGetAgentCard_noFallback_whenUrlAlreadyIsCardUrl() throws Exception {
-        // When the provided URL already equals the computed card URL, no fallback.
+    public void testGetAgentCard_fallbackToCleanBase_whenUrlAlreadyIsCardUrl() throws Exception {
+        // When the provided URL already equals the computed card URL, fall back to the clean base.
         TestHttpClient client = createTestClient();
-        client.status = 404;
+        client.statusSequence.add(404);
+        client.statusSequence.add(200);
         String fullCardUrl = "http://example.com" + AGENT_CARD_PATH;
-        A2ACardResolver resolver = A2ACardResolver.builder().httpClient(client).baseUrl(fullCardUrl).build();
-        assertThrows(A2AClientHTTPError.class, resolver::getAgentCard);
-        assertEquals(1, client.urlsCalled.size());
+        A2ACardResolver.builder().httpClient(client).baseUrl(fullCardUrl).build().getAgentCard();
+        assertEquals(2, client.urlsCalled.size());
+        assertEquals(fullCardUrl, client.urlsCalled.get(0));
+        assertEquals("http://example.com", client.urlsCalled.get(1));
     }
 
     @Test