Symlinks not supported. `java.nio.file.FileAlreadyExistsException`

[ModestTG]

Minecraft version

1.20.x

Simple Backups version

1.20.1-3.1.7

(Neo)Forge version

1.20.1-47.3.7

The latest.log file

https://pastebin.com/RjrXW5wv

Issue description

I am trying to run backups on my ATM9 server. I want to save my backups onto a NAS folder, so I tried to symlink a folder inside the /data directory to my NAS folder. When I do that, I get a java.nio.file.FileAlreadyExistsException on that directory. Perhaps this isn't an actual issue and I should just reference the NAS folder directly. I've been trying to work through some file permissions to get that to work but in the meantime I thought I would try a symlink.

Steps to reproduce

1. Create a symlink to your backup location

ln -s /path/to/backup/folder /path/inside/minecraft/data/folder

2. ensure the simplebackups-common.toml is configured with outPath pointed to /path/inside/minecraft/data/folder
3. from rcon-cli, run simplebackups backup start.

Other information

No response

[MelanX]

Would you like to test this updated test version?
SimpleBackups-1.20.1-3.1.9-test.zip

Here's what I changed:

Index: src/main/java/de/melanx/simplebackups/config/CommonConfig.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/src/main/java/de/melanx/simplebackups/config/CommonConfig.java b/src/main/java/de/melanx/simplebackups/config/CommonConfig.java
--- a/src/main/java/de/melanx/simplebackups/config/CommonConfig.java	(revision 2489fe982aa691930e04f796411d696108c002f9)
+++ b/src/main/java/de/melanx/simplebackups/config/CommonConfig.java	(date 1727109200454)
@@ -1,10 +1,13 @@
 package de.melanx.simplebackups.config;
 
+import de.melanx.simplebackups.SimpleBackups;
 import de.melanx.simplebackups.StorageSize;
 import net.minecraftforge.common.ForgeConfigSpec;
 
 import javax.annotation.Nullable;
+import java.io.FileInputStream;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.zip.Deflater;
@@ -109,6 +112,15 @@
 
     public static Path getOutputPath(@Nullable String levelId) {
         Path base = Paths.get(outputPath.get());
+        if (Files.isSymbolicLink(base)) {
+            try {
+                base = Files.readSymbolicLink(base);
+            } catch (IOException e) {
+                SimpleBackups.LOGGER.error("Failed to read symbolic link at: {}", base);
+                throw new RuntimeException(e);
+            }
+        }
+
         boolean withSubDir = levelId != null && !levelId.isEmpty() && createSubDirs.get();
         try {
             return withSubDir ? base.toRealPath().resolve(levelId) : base.toRealPath();

It worked on my end, and I hope that it will also fix your issue. I'm not very familiar with symlinks and using them properly.

[ModestTG]

Wow, what a quick update! I was able to test it. I symlinked /data/simplebackups to /tmp/mcback, and set the appropriate config. When I triggered simplebackups backup start, the backup appears to start (I get the chat popup in the MC client), but I don't see any debug message that the backup has started and no actual backup lives on /tmp/mcback. So the code change appears to be evaluating the symlink correctly, but no actual backup seems to be taking place.

Edit: I tried some other directories and I got a lot of java.nio.file.AccessDeniedException errors where I assume my container isn't playing nice with permissions on my filesystem. The only location that worked based on permissions was /tmp/mcback, and I wasn't able to see any backup created or debug message. Thanks again for looking into this! I personally was able to workaround this by just mounting my backup location as a volume inside the MC server container so it worked out that way. But I'll still help you test if you need it!

[MelanX]

Thank you! Since you now have a workaround and it works for you, this issue now has low priority for me. I don't think that I will fix it in the near future. But thank you for offering you as a tester :)
If anyone reads this, it's October - Hacktoberfest and Modtoberfest (or something similar), this may be an easy issue to fix for these events :)

[Reagy]

Tried fixing this in the 1.18.x version but didn't have any luck.
I don't really know java all that well, so I likely did something wrong.

It would be nice if this could be resolved, as I've gotta run symlinks to put the world files on my server's SSD.

[MelanX]

I tried to reproduce this issue multiple times now. I wasn't able to reproduce it sadly. Maybe I'm still doing things wrong. If anyone knows how to fix this issue and is able to test it properly, it would be awesome if this person could help me out here.