[api] Fall back to the HTTP status when the error body omits code

paimon-api/src/main/java/org/apache/paimon/rest/DefaultErrorHandler.java

@@ -42,7 +42,10 @@ public static ErrorHandler getInstance() {
 
     @Override
     public void accept(ErrorResponse error, String requestId) {
-        int code = error.getCode();
+        Integer errorCode = error.getCode();
+        // HttpClient always resolves the code before calling this, but the response may also be
+        // deserialized directly, and then "code" is absent whenever the server omits it.
+        int code = errorCode == null ? 0 : errorCode;
         String message;
         if (DEFAULT_REQUEST_ID.equals(requestId)) {
             message = error.getMessage();

paimon-api/src/main/java/org/apache/paimon/rest/responses/ErrorResponse.java

@@ -71,6 +71,7 @@ public class ErrorResponse implements RESTResponse {
     @JsonProperty(FIELD_MESSAGE)
     private final String message;
 
+    @Nullable
     @JsonProperty(FIELD_CODE)
     private final Integer code;
 
@@ -79,7 +80,7 @@ public ErrorResponse(
             @Nullable @JsonProperty(FIELD_RESOURCE_TYPE) String resourceType,
             @Nullable @JsonProperty(FIELD_RESOURCE_NAME) String resourceName,
             @JsonProperty(FIELD_MESSAGE) String message,
-            @JsonProperty(FIELD_CODE) int code) {
+            @Nullable @JsonProperty(FIELD_CODE) Integer code) {
         this.resourceType = resourceType;
         this.resourceName = resourceName;
         this.message = message;

paimon-core/src/test/java/org/apache/paimon/rest/HttpClientTest.java

@@ -23,6 +23,7 @@
 import org.apache.paimon.rest.auth.RESTAuthFunction;
 import org.apache.paimon.rest.auth.RESTAuthParameter;
 import org.apache.paimon.rest.exceptions.BadRequestException;
+import org.apache.paimon.rest.exceptions.NoSuchResourceException;
 import org.apache.paimon.rest.exceptions.RESTException;
 import org.apache.paimon.rest.responses.ErrorResponse;
 
@@ -45,6 +46,7 @@
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 /** Test for {@link HttpClient}. */
@@ -255,6 +257,17 @@ public void testUrl() {
         assertEquals(restAuthParameter.parameters().get(queryKey), queryParameters.get(queryKey));
     }
 
+    @Test
+    public void testErrorCodeFallsBackToHttpStatus() throws Exception {
+        // "code" is optional in the error schema, so an error body may omit it. The HTTP status
+        // has to be used then, otherwise a 404 no longer maps to NoSuchResourceException.
+        assertNull(RESTApi.fromJson("{\"message\":\"x\"}", ErrorResponse.class).getCode());
+        server.enqueueResponse("{\"message\":\"Table t does not exist\"}", 404);
+        assertThrows(
+                NoSuchResourceException.class,
+                () -> httpClient.get(MOCK_PATH, MockRESTData.class, restAuthFunction));
+    }
+
     private Map<String, String> getParameters(String path) {
         String[] paths = path.split("\\?");
         if (paths.length == 1) {
@@ -293,6 +306,10 @@ public void testGetWithUnparsableJsonErrorResponse() {
             Assertions.assertTrue(
                     e.getMessage().contains("Empty error message"),
                     "Parsed-but-empty message must not be labelled unparseable");
+            Assertions.assertTrue(
+                    e.getMessage().contains("403"),
+                    "The HTTP status must be reported, not the absent body code: "
+                            + e.getMessage());
         }
     }