[Backport 3.33] Handle 204 no content for SingleImageLayer

core/src/main/java/org/mapfish/print/map/image/AbstractSingleImageLayer.java

@@ -4,6 +4,7 @@
 
 import com.codahale.metrics.MetricRegistry;
 import com.codahale.metrics.Timer;
+import java.awt.Color;
 import java.awt.Graphics2D;
 import java.awt.Rectangle;
 import java.awt.image.BufferedImage;
@@ -138,6 +139,24 @@ protected BufferedImage createErrorImage(final Rectangle area) {
     }
   }
 
+  /**
+   * Create a transparent image.
+   *
+   * @param area The size of the image
+   */
+  protected BufferedImage createTransparentImage(final Rectangle area) {
+    final BufferedImage bufferedImage =
+        new BufferedImage(area.width, area.height, TYPE_INT_ARGB_PRE);
+    final Graphics2D graphics = bufferedImage.createGraphics();
+    try {
+      graphics.setBackground(new Color(0, 0, 0, 0));
+      graphics.clearRect(0, 0, area.width, area.height);
+      return bufferedImage;
+    } finally {
+      graphics.dispose();
+    }
+  }
+
   /**
    * Fetch the given image from the web.
    *
@@ -152,6 +171,14 @@ protected BufferedImage fetchImage(
     try (Timer.Context ignored = this.registry.timer(baseMetricName).time()) {
       try (ClientHttpResponse httpResponse = request.execute()) {
         final List<String> contentType = httpResponse.getHeaders().get("Content-Type");
+
+        if (httpResponse.getStatusCode() == HttpStatus.NO_CONTENT) {
+          LOGGER.info(
+              "The request {} returns a no content status code, we consider it as an empty tile.",
+              request.getURI());
+          return createTransparentImage(transformer.getPaintArea());
+        }
+
         final String invalidRespBody = getInvalidResponseBody(request, contentType, httpResponse);
 
         if (!isResponseStatusCodeValid(request, httpResponse, invalidRespBody, baseMetricName)) {
@@ -198,13 +225,18 @@ private boolean isResponseStatusCodeValid(
       final String stringBody,
       final String baseMetricName)
       throws IOException {
-    if (httpResponse.getRawStatusCode() != HttpStatus.OK.value()) {
+    if (httpResponse.getStatusCode().value() != HttpStatus.OK.value()) {
       String message =
           String.format(
-              "Invalid status code for %s (%d!=%d), status: %s. With request headers:\n%s\n"
-                  + "The response was: '%s'\nWith response headers:\n%s",
+              """
+              Invalid status code for %s (%d!=%d), status: %s. With request headers:
+              %s
+              The response was: '%s'
+              With response headers:
+              %s\
+              """,
               request.getURI(),
-              httpResponse.getRawStatusCode(),
+              httpResponse.getStatusCode().value(),
               HttpStatus.OK.value(),
               httpResponse.getStatusText(),
               String.join("\n", Utils.getPrintableHeadersList(request.getHeaders())),

core/src/test/java/org/mapfish/print/map/image/AbstractSingleImageLayerTest.java

@@ -1,8 +1,9 @@
 package org.mapfish.print.map.image;
 
-import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.codahale.metrics.MetricRegistry;
+import java.awt.Dimension;
 import java.awt.image.BufferedImage;
 import java.io.IOException;
 import org.junit.Assert;
@@ -36,6 +37,34 @@ public void testFetchImage() throws IOException {
     }
   }
 
+  @Test
+  public void testFetch204NonContent() throws IOException {
+    MapfishMapContext mapContext =
+        new MapfishMapContext(null, new Dimension(10, 10), 100, 100, false, true);
+    MockClientHttpRequest mockClientHttpRequest = new MockClientHttpRequest();
+    final int noContentCode = 204;
+    mockClientHttpRequest.setResponse(new MockClientHttpResponse(new byte[0], noContentCode));
+    AbstractLayerParams layerParams = new AbstractLayerParams();
+    layerParams.failOnError = true;
+    AbstractSingleImageLayer layer = new AbstractSingleImageLayerTestImpl(layerParams);
+    try {
+      BufferedImage bufferedImage = layer.fetchImage(mockClientHttpRequest, mapContext);
+
+      Assert.assertEquals("Image width is not correct", 10, bufferedImage.getWidth());
+      Assert.assertEquals("Image height is not correct", 10, bufferedImage.getHeight());
+
+      // check alpha chanel is equal to 0 for every pixels
+      for (int x = 0; x < bufferedImage.getWidth(); x++) {
+        for (int y = 0; y < bufferedImage.getHeight(); y++) {
+          int argb = bufferedImage.getRGB(x, y);
+          Assert.assertEquals("Pixel (" + x + "," + y + ") is not transparent", 0, (argb >>> 24));
+        }
+      }
+    } catch (Exception e) {
+      Assert.fail("Did throw exception " + e.getMessage());
+    }
+  }
+
   private static class AbstractSingleImageLayerTestImpl extends AbstractSingleImageLayer {
 
     public AbstractSingleImageLayerTestImpl(AbstractLayerParams layerParams) {