From 5b18bb726c461fefa42890e2477d20c4489b8b3e Mon Sep 17 00:00:00 2001
From: andreatp <andrea.peruffo1982@gmail.com>
Date: Fri, 30 Oct 2026 16:15:08 +0000
Subject: [PATCH] fix: symlink loops throw FileSystemException

The reason matches what the JDK reports for ELOOP, so callers such as a
WASI layer can map it the same way for ZeroFs and the default file system.
---
 .../java/io/roastedroot/zerofs/FileTree.java  |  3 ++-
 .../zerofs/ZeroFsUnixLikeFileSystemTest.java  | 22 +++++++++----------
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/core/src/main/java/io/roastedroot/zerofs/FileTree.java b/core/src/main/java/io/roastedroot/zerofs/FileTree.java
index c9c972230..9b9b8ff4c 100644
--- a/core/src/main/java/io/roastedroot/zerofs/FileTree.java
+++ b/core/src/main/java/io/roastedroot/zerofs/FileTree.java
@@ -1,6 +1,7 @@
 package io.roastedroot.zerofs;
 
 import java.io.IOException;
+import java.nio.file.FileSystemException;
 import java.nio.file.LinkOption;
 import java.nio.file.NoSuchFileException;
 import java.util.Iterator;
@@ -166,7 +167,7 @@ private DirectoryEntry lookUpLast(
     private DirectoryEntry followSymbolicLink(File dir, SymbolicLink link, int linkDepth)
             throws IOException {
         if (linkDepth >= MAX_SYMBOLIC_LINK_DEPTH) {
-            throw new IOException("too many levels of symbolic links");
+            throw new FileSystemException(null, null, "Too many levels of symbolic links");
         }
 
         return lookUp(dir, link.target(), Options.FOLLOW_LINKS, linkDepth + 1);
diff --git a/core/src/test/java/io/roastedroot/zerofs/ZeroFsUnixLikeFileSystemTest.java b/core/src/test/java/io/roastedroot/zerofs/ZeroFsUnixLikeFileSystemTest.java
index 1ba48d1f9..fcb480321 100644
--- a/core/src/test/java/io/roastedroot/zerofs/ZeroFsUnixLikeFileSystemTest.java
+++ b/core/src/test/java/io/roastedroot/zerofs/ZeroFsUnixLikeFileSystemTest.java
@@ -24,6 +24,7 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
 
@@ -1270,19 +1271,16 @@ public void testSymbolicLinks_symlinkCycle() throws IOException {
         Files.createSymbolicLink(path("/foo/bar"), path("baz"));
         Files.createSymbolicLink(path("/foo/baz"), path("bar"));
 
-        try {
-            Files.createFile(path("/foo/bar/file"));
-            fail();
-        } catch (IOException expected) {
-            assertTrue(expected.getMessage().contains("symbolic link"));
-        }
+        FileSystemException expected =
+                assertThrows(
+                        FileSystemException.class, () -> Files.createFile(path("/foo/bar/file")));
+        assertEquals("Too many levels of symbolic links", expected.getReason());
 
-        try {
-            Files.write(path("/foo/bar"), preFilledBytes(10));
-            fail();
-        } catch (IOException expected) {
-            assertTrue(expected.getMessage().contains("symbolic link"));
-        }
+        expected =
+                assertThrows(
+                        FileSystemException.class,
+                        () -> Files.write(path("/foo/bar"), preFilledBytes(10)));
+        assertEquals("Too many levels of symbolic links", expected.getReason());
     }
 
     @Test