use random tmpnames

README.md

@@ -3,6 +3,9 @@ safe-replace
 
 A micro-module for safely replacing a file.
 
+This is intended to be generally safe even when a function that writes a file
+is accidentally called twice (as may happen with node cluster).
+
 Commandline Reference
 ---------------------
 
@@ -10,7 +13,7 @@ If I want to safely replace a file with a new version, I would do so like this:
 
 ```bash
 # create the new version
-touch keep.txt.new
+touch keep.txt.RANDOM.tmp
 
 # remove the previous backup
 rm -f keep.txt.bak
@@ -19,7 +22,7 @@ rm -f keep.txt.bak
 mv keep.txt keep.txt.bak
 
 # move the new version to the current
-mv keep.txt.new keep.txt
+mv keep.txt.RANDOM.tmp keep.txt
 ```
 
 If `keep.txt` became corrupt and I wanted to use the backup,
@@ -48,8 +51,8 @@ safeReplace.writeFile('keep.txt', data, 'ascii').then(function () {
   });
 });
 
-// let's say I wrote keep.txt.new with my own mechanism
-safeReplace.commit('keep.txt').then(function () {
+// let's say I wrote keep.txt.x7t7sq926.tmp with my own mechanism
+safeReplace.commit('keep.txt.x7t7sq926.tmp', 'keep.txt').then(function () {
   fs.readdir('.', function (nodes) {
     console.log('file system nodes', nodes);
     // keep.txt
@@ -65,4 +68,14 @@ safeReplace.revert('keep.txt').then(function () {
     // keep.txt.bak
   });
 });
+
+// let's say I want to write a tmp file and not commit it... weird
+safeReplace.stage('keep.txt', data, 'ascii').then(function (tmpname) {
+  fs.readdir('.', function (nodes) {
+    console.log('file system nodes', nodes);
+    // keep.txt
+    // keep.txt.bak
+    // keep.txt.ac71teh8mja.tmp
+  });
+});
 ```

index.js

@@ -2,54 +2,65 @@
 
 var PromiseA = require('bluebird').Promise;
 var fs = PromiseA.promisifyAll(require('fs'));
+var crypto = require('crypto');
 
 function noop() {
 }
 
 function create(options) {
+
   if (!options) {
     options = {};
   }
-  if (!options.new) {
-    options.new = 'new';
+  if (!options.tmp) {
+    options.tmp = 'tmp';
   }
   if (!options.bak) {
     options.bak = 'bak';
   }
-  if (options.new === options.bak) {
-    throw new Error("'new' and 'bak' suffixes cannot be the same... duh");
+  if (options.tmp === options.bak) {
+    throw new Error("'tmp' and 'bak' suffixes cannot be the same... duh");
   }
 
-  var newnamefn = options.newnamefn || function (pathname) {
-    return pathname + '.' + options.new;
+  var tmpnamefn = options.tmpnamefn || function (pathname) {
+    return pathname + '.' + crypto.randomBytes(8).toString('hex') + '.' + options.tmp;
   };
   var baknamefn = options.baknamefn || function (pathname) {
     return pathname + '.' + options.bak;
   };
+  /*
   var namefn = options.namefn || function (pathname) {
     return pathname;
   };
+  */
 
   var sfs = {
     writeFile: function (filename, data, options) {
-      //console.log(newnamefn(filename));
-      return fs.writeFileAsync(newnamefn(filename), data, options).then(function () {
-        //console.log(namefn(filename));
-        return sfs.commit(namefn(filename));
+      return sfs.stage(filename, data, options).then(function (tmpname) {
+        //console.log(filename);
+        return sfs.commit(tmpname, filename);
       });
     }
-  , commit: function (filename) {
+  , stage: function (filename, data, options) {
+      var tmpname = tmpnamefn(filename);
+      //console.log(tmpname);
+      return fs.writeFileAsync(tmpname, data, options).then(function () {
+        return tmpname;
+      });
+    }
+  , commit: function (tmpname, filename) {
+      var bakname = baknamefn(filename);
       // this may not exist
-      return fs.unlinkAsync(baknamefn(filename)).then(noop, noop).then(function () {
+      return fs.unlinkAsync(bakname).then(noop, noop).then(function () {
         // this may not exist
-        //console.log(namefn(filename), '->', baknamefn(filename));
-        return fs.renameAsync(namefn(filename), baknamefn(filename)).then(function () {
+        //console.log(namefn(filename), '->', bakname);
+        return fs.renameAsync(filename, bakname).then(function () {
           //console.log('created bak');
         }, noop);
       }).then(function () {
         // this must be successful
-        //console.log(newnamefn(filename), '->', namefn(filename));
-        return fs.renameAsync(newnamefn(filename), namefn(filename)).then(noop, function (err) {
+        //console.log(filename, '->', filename);
+        return fs.renameAsync(tmpname, filename).then(noop, function (err) {
           //console.error(err);
           return sfs.revert(filename).then(function () {
             return PromiseA.reject(err);
@@ -59,14 +70,19 @@ function create(options) {
     }
   , revert: function (filename) {
       return new PromiseA(function (resolve, reject) {
-        var reader = fs.createReadStream(baknamefn(filename));
-        var writer = fs.createWriteStream(namefn(filename));
+        var bakname = baknamefn(filename);
+        var tmpname = tmpnamefn(filename);
+
+        var reader = fs.createReadStream(bakname);
+        var writer = fs.createWriteStream(tmpname);
 
         reader.on('error', reject);
         writer.on('error', reject);
 
         reader.pipe(writer);
-        writer.on('close', resolve);
+        writer.on('close', function () {
+          sfs.commit(tmpname, filename).then(resolve, reject);
+        });
       });
     }
   };

test.js

@@ -5,7 +5,7 @@ var safeReplace = require('./').create();
 var fs = require('fs');
 
 safeReplace.writeFile('keep.txt', 'my precious').then(function () {
-  fs.readdir('.', function (nodes) {
+  fs.readdir('.', function (err, nodes) {
     console.log('file system nodes', nodes);
   });
 });