Add fallback when atomic move not supported

Author: alextwoods

services/signin/src/main/java/software/amazon/awssdk/services/signin/internal/OnDiskTokenManager.java

@@ -20,6 +20,7 @@
 import java.io.OutputStream;
 import java.io.UncheckedIOException;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.AtomicMoveNotSupportedException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
@@ -90,13 +91,13 @@ public Optional<LoginAccessToken> loadToken() {
 
     @Override
     public void storeToken(LoginAccessToken token) {
-        // atomic write (write to a temp file and then move/replace the destination location).
+        // Write to a temp file first, then move to the destination to avoid partial reads.
         try {
             Path temp = createOwnerOnlyTempFile(tokenLocation.getParent(), "token-", ".tmp");
             try (OutputStream os = Files.newOutputStream(temp)) {
                 os.write(marshalToken(token));
             }
-            Files.move(temp, tokenLocation, StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
+            atomicOrFallbackMove(temp, tokenLocation);
         } catch (IOException | UncheckedIOException e) {
             throw SdkClientException.create("Unable to write token to location " + tokenLocation, e);
         }
@@ -118,6 +119,17 @@ private static Path createOwnerOnlyTempFile(Path dir, String prefix, String suff
         }
     }
 
+    /**
+     * Attempts an atomic move, falling back to a non-atomic replace if the file system does not support it.
+     */
+    private static void atomicOrFallbackMove(Path source, Path target) throws IOException {
+        try {
+            Files.move(source, target, StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
+        } catch (AtomicMoveNotSupportedException e) {
+            Files.move(source, target, StandardCopyOption.REPLACE_EXISTING);
+        }
+    }
+
     @Override
     public void close() {
 

services/ssooidc/src/main/java/software/amazon/awssdk/services/ssooidc/internal/OnDiskTokenManager.java

@@ -22,6 +22,7 @@
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.AtomicMoveNotSupportedException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -85,13 +86,13 @@ public Optional<SsoOidcToken> loadToken() {
 
     @Override
     public void storeToken(SsoOidcToken token) {
-        // Atomic write: write to a temp file with restricted permissions, then move to the destination.
+        // Write to a temp file first, then move to the destination to avoid partial reads.
         try {
             Path temp = createOwnerOnlyTempFile(tokenLocation.getParent(), "token-", ".tmp");
             try (OutputStream os = Files.newOutputStream(temp)) {
                 os.write(marshalToken(token));
             }
-            Files.move(temp, tokenLocation, StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
+            atomicOrFallbackMove(temp, tokenLocation);
         } catch (IOException e) {
             throw SdkClientException.create("Unable to write token to location " + tokenLocation, e);
         }
@@ -113,6 +114,17 @@ private static Path createOwnerOnlyTempFile(Path dir, String prefix, String suff
         }
     }
 
+    /**
+     * Attempts an atomic move, falling back to a non-atomic replace if the file system does not support it.
+     */
+    private static void atomicOrFallbackMove(Path source, Path target) throws IOException {
+        try {
+            Files.move(source, target, StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
+        } catch (AtomicMoveNotSupportedException e) {
+            Files.move(source, target, StandardCopyOption.REPLACE_EXISTING);
+        }
+    }
+
     @Override
     public void close() {
     }