Created function ensuring datafile integrity

lib/datastore.js

@@ -542,4 +542,11 @@ Datastore.prototype.remove = function () {
 };
 
 
+var fs = require('fs');
+
+console.log(fs.statSync('workspace/test.db'));
+
+
+
+
 module.exports = Datastore;

lib/persistence.js

@@ -93,6 +93,7 @@ Persistence.getNWAppFilename = function (appName, relativeFilename) {
 Persistence.prototype.persistCachedDatabase = function (cb) {
   var callback = cb || function () {}
     , toPersist = ''
+    , self = this
     ;
 
   if (this.inMemoryOnly) { return callback(null); } 
@@ -101,7 +102,30 @@ Persistence.prototype.persistCachedDatabase = function (cb) {
     toPersist += model.serialize(doc) + '\n';
   });
   
-  fs.writeFile(this.filename, toPersist, function (err) { return callback(err); });
+  async.waterfall([
+    function (cb) {
+      fs.exists(self.tempFilename, function (exists) {
+        if (exists) {
+          fs.unlink(self.tempFilename, function (err) { return cb(err); });
+        } else {
+          return cb();
+        }
+      });
+    }
+  , function (cb) {
+  console.log("==== 3");
+      fs.rename(self.filename, self.tempFilename, function (err) {
+        console.log("==== 4");
+
+        if (err) { return cb(err); }
+        fs.writeFile(self.filename, toPersist, function (err) {
+          console.log("==== 5");
+          if (err) { return cb(err); }
+          fs.unlink(self.tempFilename, function (err) { return cb(err); });
+        });
+      });
+    }
+  ], function (err) { return callback(err); })
 };
 
 
@@ -198,6 +222,52 @@ Persistence.treatRawData = function (rawData) {
 };
 
 
+/**
+ * Ensure that this.filename contains the most up-to-date version of the data
+ * Even if a loadDatabase crashed before
+ */
+Persistence.prototype.ensureDatafileIntegrity = function (callback) {
+  var self = this  ;
+  
+  fs.exists(self.filename, function (filenameExists) {
+    fs.exists(self.tempFilename, function (tempFilenameExists) {
+      // Normal case
+      if (filenameExists && !tempFilenameExists) {
+        return callback();
+      }
+    
+      // Process crashed right after renaming filename
+      if (!filenameExists && tempFilenameExists) {
+        return fs.rename(self.tempFilename, self.filename, function (err) { return callback(err); });
+      }
+      
+      // No file exists, create empty datafile
+      if (!filenameExists && !tempFilenameExists) {
+        return fs.writeFile(self.filename, '', 'utf8', function (err) { callback(err); });      
+      }
+      
+      // Process crashed after or during write to datafile
+      // If datafile is not empty, it means process crashed after the write so we use it
+      // If it is empty, we don't know whether the database was emptied or we had a crash during write. The safest option is to use the temp datafile
+      if (filenameExists && tempFilenameExists) {
+        return fs.stat(self.filename, function (err, stats) {
+          if (err) { return callback(err); }
+          
+          if (stats.size > 0) {
+            fs.unlink(self.tempFilename, function (err) { return callback(err); });
+          } else {
+            fs.unlink(self.tempFilename, function (err) {
+              if (err) { return callback(err); }
+              fs.rename(self.tempFilename, self.filename, function (err) { return callback(err); });
+            });
+          }
+        });
+      }
+    });
+  });
+};
+
+
 /**
  * Load the database
  * This means pulling data out of the data file or creating it if it doesn't exist

test/persistence.test.js

@@ -278,7 +278,9 @@ describe('Persistence', function () {
       cp.on('message', function (msg) {
         // Let the child process enough time to crash
         setTimeout(function () {
-          fs.readFileSync('workspace/lac.db', 'utf8').length.should.not.equal(0);
+//          fs.readFileSync('workspace/lac.db', 'utf8').length.should.not.equal(0);
+          console.log(fs.readFileSync('workspace/lac.db').length);
+          console.log(fs.readFileSync('workspace/lac.db~').length);
           done();
         }, 100);
       });

test_lac/loadAndCrash.test.js

@@ -6,6 +6,6 @@ var Nedb = require('../lib/datastore.js')
 setTimeout(function() {
   process.send('crash');
   process.exit();
-}, 100);
+}, 1880);
   
 db.loadDatabase();