Bugfix/8199 wfs download size estimation slow

server/src/main/java/au/org/aodn/ogcapi/server/core/service/geoserver/wfs/DownloadWfsDataService.java

@@ -120,6 +120,10 @@ public BigInteger estimateDownloadSize(
                 BigInteger featureCount = BigInteger.valueOf(root.get("totalFeatures").asLong());
                 log.debug("Total record hits {}", featureCount);
 
+                if (featureCount.equals(BigInteger.ZERO)) {
+                    return BigInteger.ZERO;
+                }
+
                 // In case the records we have is smaller than our predefined SAMPLES_SIZE, we use smaller one.
                 long sampleSize = featureCount.longValue() < SAMPLES_SIZE ? featureCount.longValue() : SAMPLES_SIZE;
 

server/src/main/java/au/org/aodn/ogcapi/server/processes/RestServices.java

@@ -321,11 +321,12 @@ public SseEmitter downloadWfsDataWithSse(String uuid,
                                         "timestamp", System.currentTimeMillis()
                                 )));
                     }
-                    catch(IllegalArgumentException iae) {
+                    catch(Exception e) {
+                        log.warn("Unexpected error during size estimation for UUID {}: {}", uuid, e.getMessage());
                         emitter.send(SseEmitter.event()
                                 .name("estimate-failed")
                                 .data(Map.of(
-                                        "message", iae.getMessage(),
+                                        "message", "Size estimation failed: " + e.getMessage(),
                                         "timestamp", System.currentTimeMillis()
                                 )));
                     }

server/src/test/java/au/org/aodn/ogcapi/server/core/service/geoserver/wfs/DownloadWfsDataServiceTest.java

@@ -370,6 +370,48 @@ void shouldReturnEstimatedSizeWhenBothRequestsSucceed() {
         long expected = 227193L * sampleBytes.length / DownloadWfsDataService.SAMPLES_SIZE;
         assertEquals(BigInteger.valueOf(expected), size, "Size match");
     }
+    @Test
+    void shouldReturnZeroWhenTotalFeaturesIsZero() {
+        String uuid = "lyr-123";
+        String layer = "water_bodies";
+        String start = "2024-01-01";
+        String end = "2024-12-31";
+        Object multiPolygon = new Object();
+        List<String> fields = List.of("name", "area");
+        String format = "application/json";
+
+        String countJson = "{\"totalFeatures\": 0, \"features\": []}";
+        ResponseEntity<String> countResponse = new ResponseEntity<>(countJson, HttpStatus.OK);
+
+        doReturn(countResponse)
+                .when(restTemplate).exchange(
+                    argThat((String url) -> url != null && url.contains("maxFeatures=1")),
+                    eq(HttpMethod.GET),
+                    any(HttpEntity.class),
+                    eq(String.class));
+
+        doReturn(Optional.of("http://dummy.com/wfs"))
+                .when(wfsServer).getFeatureServerUrl(eq(uuid), anyString());
+
+        WfsFields fs = WfsFields.builder()
+                .fields(List.of(
+                        WfsField.builder().type("dateTime").name("time").build()
+                ))
+                .build();
+
+        doReturn(fs)
+                .when(wfsServer).getDownloadableFields(eq(uuid), any(WfsServer.WfsFeatureRequest.class));
+
+        BigInteger size = downloadWfsDataService.estimateDownloadSize(
+                uuid, layer, start, end, multiPolygon, fields, format);
+
+        assertEquals(BigInteger.ZERO, size, "Size should be zero when totalFeatures is 0");
+        // No sample download should be made
+        verify(restTemplate, never()).exchange(
+                argThat((String url) -> url != null && url.contains("maxFeatures=0")),
+                eq(HttpMethod.GET), any(), eq(byte[].class));
+    }
+
     /**
      * Expect RuntimeException when GeoServer returns JSON without the totalFeatures field
      * (e.g. GeoServer returned an error JSON or unexpected structure)