From 10077ae7500431816176840be1549cb5a9c8a2a5 Mon Sep 17 00:00:00 2001
From: Nick O'Leary <nick.oleary@gmail.com>
Date: Wed, 21 Aug 2019 16:54:26 +0100
Subject: [PATCH] Use a more atomic process for writing context files Fixes
 #2271

---
 .../runtime/lib/nodes/context/localfilesystem.js   | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/packages/node_modules/@node-red/runtime/lib/nodes/context/localfilesystem.js b/packages/node_modules/@node-red/runtime/lib/nodes/context/localfilesystem.js
index 10b4349b8..0f83573e8 100644
--- a/packages/node_modules/@node-red/runtime/lib/nodes/context/localfilesystem.js
+++ b/packages/node_modules/@node-red/runtime/lib/nodes/context/localfilesystem.js
@@ -137,6 +137,16 @@ function stringify(value) {
     return { json: result, circular: hasCircular };
 }
 
+
+function writeFileAtomic(storagePath, content) {
+    // To protect against file corruption, write to a tmp file first and then
+    // rename to the destination file
+    let finalFile = storagePath + ".json";
+    let tmpFile = finalFile + "."+Date.now()+".tmp";
+    return fs.outputFile(tmpFile, content, "utf8").then(function() {
+        return fs.rename(tmpFile,finalFile);
+    })
+}
 function LocalFileSystem(config){
     this.config = config;
     this.storageBaseDir = getBasePath(this.config);
@@ -202,7 +212,7 @@ LocalFileSystem.prototype.open = function(){
                         delete self.knownCircularRefs[scope];
                     }
                     log.debug("Flushing localfilesystem context scope "+scope);
-                    promises.push(fs.outputFile(storagePath + ".json", stringifiedContext.json, "utf8"));
+                    promises.push(writeFileAtomic(storagePath, stringifiedContext.json))
                 });
                 delete self._pendingWriteTimeout;
                 return Promise.all(promises);
@@ -319,7 +329,7 @@ LocalFileSystem.prototype.set = function(scope, key, value, callback) {
             } else {
                 delete self.knownCircularRefs[scope];
             }
-            return fs.outputFile(storagePath + ".json", stringifiedContext.json, "utf8");
+            return writeFileAtomic(storagePath, stringifiedContext.json);
         }).then(function(){
             if(typeof callback === "function"){
                 callback(null);