Fix rewrite of unqualified reference

Signed-off-by: Valentin Delaye <jonesbusy@users.noreply.github.com>

Author: jonesbusy

src/main/java/land/oras/auth/RegistriesConf.java

@@ -295,11 +295,33 @@ public ContainerRef rewrite(ContainerRef ref) {
             }
 
             rewrittenRefString = location + remainder;
-        }
+        } else {
+
+            // For unqualified references, we need to construct the rewritten reference properly
+            // by replacing the registry component and preserving the namespace/repository/tag structure
+            if (ref.isUnqualified()) {
+                // For unqualified references, build the new reference with the location as the new registry
+                String namespace = ref.getNamespace();
+                String repository = ref.getRepository();
+                String tag = ref.getTag();
+                String digest = ref.getDigest();
+
+                StringBuilder rewritten = new StringBuilder(location);
+                if (namespace != null && !namespace.isEmpty()) {
+                    rewritten.append("/").append(namespace);
+                }
+                rewritten.append("/").append(repository);
+                rewritten.append(":").append(tag);
+                if (digest != null && !digest.isEmpty()) {
+                    rewritten.append("@").append(digest);
+                }
+                rewrittenRefString = rewritten.toString();
+            }
 
-        // Just replace the prefix with the location (e.g., docker.io/library → my-registry.com/library)
-        else {
-            rewrittenRefString = location + currentRefString.substring(prefix.length());
+            // For qualified references, use the original string manipulation approach
+            else {
+                rewrittenRefString = location + currentRefString.substring(prefix.length());
+            }
         }
 
         LOG.debug(

src/test/java/land/oras/auth/RegistryConfTest.java

@@ -186,13 +186,23 @@ void shouldRewriteContainerRef() {
         originalRef = ContainerRef.parse("example.com/foo/library/test:latest");
         rewrittenRef = conf.rewrite(originalRef);
         assertEquals("internal-registry-for-example.com/bar/library/test:latest", rewrittenRef.toString());
+    }
+
+    @Test
+    void shouldRewriteUnqualifiedContainerRef() {
 
-        // With tag only
-        // registry = new RegistriesConf.RegistryConfig("example.com/foo:latest", "example.com/foo:othertag", null,
-        // null);
-        // conf = new RegistriesConf(new RegistriesConf.Config(List.of(registry)));
-        // originalRef = ContainerRef.parse("example.com/foo:latest");
-        // rewrittenRef = conf.rewrite(originalRef);
-        // assertEquals("example.com/foo:othertag", rewrittenRef.toString());
+        RegistriesConf.RegistryConfig registry =
+                new RegistriesConf.RegistryConfig("docker.io", "internal-registry-for-example.com", null, null);
+        RegistriesConf conf = new RegistriesConf(new RegistriesConf.Config(List.of(registry)));
+
+        // Without tag
+        ContainerRef originalRef = ContainerRef.parse("alpine");
+        ContainerRef rewrittenRef = conf.rewrite(originalRef);
+        assertEquals("internal-registry-for-example.com/library/alpine:latest", rewrittenRef.toString());
+
+        // Ensure to keep tag
+        originalRef = ContainerRef.parse("alpine:1.0.0");
+        rewrittenRef = conf.rewrite(originalRef);
+        assertEquals("internal-registry-for-example.com/library/alpine:1.0.0", rewrittenRef.toString());
     }
 }