From e42063806c56876523237b5a50285deaa8ba62b6 Mon Sep 17 00:00:00 2001
From: Mike Hearn <hearn@google.com>
Date: Mon, 21 May 2012 15:31:21 +0200
Subject: [PATCH] Write+rename wallet files.

---
 .../java/com/google/bitcoin/core/Wallet.java  | 21 ++++++++++++++++---
 .../com/google/bitcoin/tools/WalletTool.java  | 11 ++--------
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/core/src/main/java/com/google/bitcoin/core/Wallet.java b/core/src/main/java/com/google/bitcoin/core/Wallet.java
index debb21fa..595b2a2e 100644
--- a/core/src/main/java/com/google/bitcoin/core/Wallet.java
+++ b/core/src/main/java/com/google/bitcoin/core/Wallet.java
@@ -19,6 +19,7 @@ package com.google.bitcoin.core;
 import com.google.bitcoin.core.WalletTransaction.Pool;
 import com.google.bitcoin.store.WalletProtobufSerializer;
 import com.google.bitcoin.utils.EventListenerInvoker;
+import com.google.common.base.Preconditions;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -180,15 +181,29 @@ public class Wallet implements Serializable {
 
     /**
      * Uses protobuf serialization to save the wallet to the given file. To learn more about this file format, see
-     * {@link WalletProtobufSerializer}.
+     * {@link WalletProtobufSerializer}. Writes out first to a temporary file in the same directory and then renames
+     * once written.
      */
     public synchronized void saveToFile(File f) throws IOException {
+        Preconditions.checkArgument(f.isFile());
         FileOutputStream stream = null;
+        File temp = null;
         try {
-            stream = new FileOutputStream(f);
+            File directory = f.getParentFile();
+            temp = File.createTempFile("wallet", null, directory);
+            stream = new FileOutputStream(temp);
             saveToFileStream(stream);
         } finally {
-            if (stream != null) stream.close();
+            if (stream != null) {
+                // Attempt to force the bits to hit the disk. In reality the OS or hard disk itself may still decide
+                // to not write through to physical media for at least a few seconds, but this is the best we can do.
+                stream.flush();
+                stream.getFD().sync();
+                stream.close();
+                if (!temp.renameTo(f)) {
+                    throw new IOException("Failed to rename " + temp + " to " + f);
+                }
+            }
         }
     }
 
diff --git a/tools/src/main/java/com/google/bitcoin/tools/WalletTool.java b/tools/src/main/java/com/google/bitcoin/tools/WalletTool.java
index 806b07fe..de42aee3 100644
--- a/tools/src/main/java/com/google/bitcoin/tools/WalletTool.java
+++ b/tools/src/main/java/com/google/bitcoin/tools/WalletTool.java
@@ -524,16 +524,9 @@ public class WalletTool {
     }
 
     private static void saveWallet(File walletFile) {
-        // Save the new state of the wallet to a temp file then rename, in case anything goes wrong.
-        File tmp;
         try {
-            // Create tmp in same directory as wallet to ensure we create on the same drive/volume.
-            tmp = File.createTempFile("wallet", null, walletFile.getParentFile());
-            tmp.deleteOnExit();
-            wallet.saveToFile(tmp);
-            if (!tmp.renameTo(walletFile)) {
-                throw new IOException("Failed to rename wallet");
-            }
+            // This will save the new state of the wallet to a temp file then rename, in case anything goes wrong.
+            wallet.saveToFile(walletFile);
         } catch (IOException e) {
             System.err.println("Failed to save wallet! Old wallet should be left untouched.");
             e.printStackTrace();