photo storage failures handled: a shot is refused (film kept) while the image folder is not writable, a photo whose png cannot be saved fails like a render error (film back) instead of becoming a vanilla map after the restart, png/index files written atomically (tmp + move, no truncated png after a crash), one-line warnings instead of imageio stack traces, unreadable png warned

src/main/java/eu/mhsl/minecraft/pixelpics/survival/PhotoService.java

@@ -53,6 +53,13 @@ public final class PhotoService {
             return false;
         }
 
+        if (!MapManager.canStore()) {
+            player.sendActionBar(Component.text(
+                    "Fotos können gerade nicht gespeichert werden — bitte einem Admin melden.", NamedTextColor.RED));
+            plugin.getLogger().warning("Photo of " + player.getName() + " refused: the image folder is not writable.");
+            return false;
+        }
+
         RenderManager manager = plugin.getRenderManager();
         UUID user = player.getUniqueId();
         RenderManager.Outcome outcome = manager.tryReserve(user);
@@ -118,7 +125,12 @@ public final class PhotoService {
                     },
                     out -> {
                         chunks.release(); // already released by prepare
-                        MapManager.saveImage(out.image(), id);
+                        if (!MapManager.saveImage(out.image(), id)) {
+                            failed(
+                                    id, user,
+                                    usesFilm); // not stored: it would be lost (or a vanilla map) after a restart
+                            return;
+                        }
                         MapManager.saveIndices(out.indices(), id);
                         plugin.getPendingPhotos().remove(id);
                         mapRenderer.develop(out.indices());

src/main/java/eu/mhsl/minecraft/pixelpics/utils/MapManager.java

@@ -2,9 +2,12 @@ package eu.mhsl.minecraft.pixelpics.utils;
 
 import eu.mhsl.minecraft.pixelpics.Main;
 import java.awt.image.BufferedImage;
+import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;
+import java.nio.file.AtomicMoveNotSupportedException;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -173,28 +176,58 @@ public class MapManager {
                         + backup + ".");
     }
 
-    /** Blank film indices for a photo that has not developed (yet): never a vanilla world map after a restart. */
-    public static void savePlaceholder(int id) {
-        byte[] blank = new byte[INDEX_BYTES];
-        Arrays.fill(blank, ImageMapRenderer.filmColor());
-        saveIndices(blank, id);
+    /** Whether new photos can be stored: the folder exists (or was created) and is writable. */
+    public static boolean canStore() {
+        return ensureFolder() && Files.isWritable(imageFolder().toPath());
     }
 
-    public static void saveImage(BufferedImage image, int id) {
-        if (!ensureFolder()) return;
+    /**
+     * Blank film indices for a photo that has not developed (yet): never a vanilla world map after a restart. False if
+     * they could not be stored.
+     */
+    public static boolean savePlaceholder(int id) {
+        byte[] blank = new byte[INDEX_BYTES];
+        Arrays.fill(blank, ImageMapRenderer.filmColor());
+        return saveIndices(blank, id);
+    }
+
+    /** Stores the PNG (atomically: a crash never leaves a truncated one); false if it could not be written. */
+    public static boolean saveImage(BufferedImage image, int id) {
+        if (!ensureFolder()) return false;
         try {
-            ImageIO.write(image, "png", getImagePath(id));
+            ByteArrayOutputStream png = new ByteArrayOutputStream();
+            if (!ImageIO.write(image, "png", png)) throw new IOException("no PNG writer");
+            writeAtomically(getImagePath(id), png.toByteArray());
+            return true;
         } catch (IOException e) {
-            Main.getInstance().getLogger().warning("Failed to save map image " + id + ": " + e.getMessage());
+            Main.getInstance().getLogger().warning("Failed to save map image " + id + ": " + e);
+            return false;
         }
     }
 
-    public static void saveIndices(byte[] indices, int id) {
-        if (indices == null || indices.length != INDEX_BYTES || !ensureFolder()) return;
+    /** Stores the index cache (atomically); false if it could not be written. */
+    public static boolean saveIndices(byte[] indices, int id) {
+        if (indices == null || indices.length != INDEX_BYTES || !ensureFolder()) return false;
         try {
-            Files.write(getIndexPath(id).toPath(), indices);
+            writeAtomically(getIndexPath(id), indices);
+            return true;
         } catch (IOException e) {
-            Main.getInstance().getLogger().warning("Failed to save map index cache " + id + ": " + e.getMessage());
+            Main.getInstance().getLogger().warning("Failed to save map index cache " + id + ": " + e);
+            return false;
+        }
+    }
+
+    private static void writeAtomically(File target, byte[] data) throws IOException {
+        Path tmp = target.toPath().resolveSibling(target.getName() + ".tmp");
+        try {
+            Files.write(tmp, data);
+            try {
+                Files.move(tmp, target.toPath(), StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
+            } catch (AtomicMoveNotSupportedException e) {
+                Files.move(tmp, target.toPath(), StandardCopyOption.REPLACE_EXISTING);
+            }
+        } finally {
+            Files.deleteIfExists(tmp);
         }
     }
 
@@ -215,8 +248,10 @@ public class MapManager {
         File path = getImagePath(id);
         if (!path.isFile()) return null;
         try {
-            return ImageIO.read(path);
-        } catch (IOException e) {
+            BufferedImage image = ImageIO.read(path);
+            if (image == null) Main.getInstance().getLogger().warning("Map image " + id + " is no readable image.");
+            return image;
+        } catch (IOException | RuntimeException e) {
             Main.getInstance().getLogger().warning("Failed to read map image " + id + ": " + e.getMessage());
             return null;
         }