core: Backport symlink fix from 4.x

Correctly follow symlinks when writing out files
SpongePowered · Aug 9, 2020 · 5de6e7c · 5de6e7c
1 parent ea961c7
commit 5de6e7c
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diff --git a/configurate-core/src/main/java/ninja/leaping/configurate/loader/AtomicFiles.java b/configurate-core/src/main/java/ninja/leaping/configurate/loader/AtomicFiles.java
@@ -64,9 +64,19 @@ public static Callable<BufferedWriter> createAtomicWriterFactory(@NonNull Path p
      */
     @NonNull
     public static BufferedWriter createAtomicBufferedWriter(@NonNull Path path, @NonNull Charset charset) throws IOException {
+        // absolute
         path = path.toAbsolutePath();
 
-        Path writePath = getTemporaryPath(path.getParent(), path.getFileName().toString());
+        // unwrap any symbolic links
+        try {
+            while (Files.isSymbolicLink(path)) {
+                path = Files.readSymbolicLink(path);
+            }
+        } catch (final UnsupportedOperationException | IOException ex) {
+            // ignore, FS probably doesn't support symlinks
+        }
+
+        final Path writePath = getTemporaryPath(path.getParent(), path.getFileName().toString());
         if (Files.exists(path)) {
             Files.copy(path, writePath, StandardCopyOption.COPY_ATTRIBUTES, StandardCopyOption.REPLACE_EXISTING);
         }

diff --git a/...-core/src/test/java/ninja/leaping/configurate/loader/AbstractConfigurationLoaderTest.java b/...-core/src/test/java/ninja/leaping/configurate/loader/AbstractConfigurationLoaderTest.java
@@ -16,13 +16,21 @@
  */
 package ninja.leaping.configurate.loader;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.junitpioneer.jupiter.TempDirectory;
 
+import java.io.BufferedWriter;
 import java.io.File;
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.stream.Collectors;
 
 @ExtendWith(TempDirectory.class)
 public class AbstractConfigurationLoaderTest {
@@ -40,4 +48,30 @@ public void testLoadNonexistantFile(@TempDirectory.TempDir Path tempDir) throws
         TestConfigurationLoader loader = TestConfigurationLoader.builder().setFile(tempFile).build();
         loader.load();
     }
+
+    @Test
+    public void testSaveFollowsSymbolicLinks(final @TempDirectory.TempDir Path tempDir) throws IOException {
+        final Path actualFile = tempDir.resolve(Paths.get("first", "second", "third.json"));
+        Files.createDirectories(actualFile.getParent());
+        final Path layerOne = tempDir.resolve("general.json");
+        final Path layerTwo = tempDir.resolve("general2.json");
+
+        Files.createFile(actualFile);
+        Files.createSymbolicLink(layerOne, actualFile);
+        Files.createSymbolicLink(layerTwo, layerOne);
+
+        try (BufferedWriter writer = AtomicFiles.createAtomicBufferedWriter(layerTwo, StandardCharsets.UTF_8)) {
+            writer.write("I should follow symlinks!\n");
+        }
+
+        // We expect links are preserved, and the underlying file is written to
+        assertTrue(Files.isSymbolicLink(layerTwo));
+        assertTrue(Files.isSymbolicLink(layerOne));
+        assertEquals(layerOne, Files.readSymbolicLink(layerTwo));
+        assertEquals(actualFile, Files.readSymbolicLink(layerOne));
+        assertEquals("I should follow symlinks!", Files.readAllLines(layerTwo, StandardCharsets.UTF_8).stream()
+                .collect(Collectors.joining("\n")));
+        assertEquals("I should follow symlinks!", Files.readAllLines(actualFile, StandardCharsets.UTF_8).stream()
+                .collect(Collectors.joining("\n")));
+    }
 }