fs_storage changes for correctness and efficiency of initial piece ve…

…rification for resuming torrent downloads

lib/fs_storage.js

@@ -12,6 +12,7 @@ var rimraf = require('rimraf')
 var thunky = require('thunky')
 
 var TMP = fs.existsSync('/tmp') ? '/tmp' : os.tmpDir()
+var noop = function () {}
 
 inherits(FSStorage, Storage)
 
@@ -35,19 +36,19 @@ function FSStorage (parsedTorrent, opts) {
   }
 
   self.path = opts.path
-
   self.piecesMap = []
+
+  self.nonExistentError = new Error("Cannot read from non-existent file")
+
   self.files.forEach(function (file) {
     var fileStart   = file.offset
     var fileEnd     = fileStart + file.length
 
-    var firstPiece  = file.pieces[0].index
-    var lastPiece   = file.pieces[file.pieces.length - 1].index
     var pieceLength = file.pieceLength
+    var filePath    = path.join(self.path, file.path)
 
-    var open = thunky(function (cb) {
-      var filePath = path.join(self.path, file.path)
-      var fileDir  = path.dirname(filePath)
+    var openWrite = thunky(function (cb) {
+      var fileDir = path.dirname(filePath)
 
       mkdirp(fileDir, function (err) {
         if (err) return cb(err)
@@ -59,6 +60,13 @@ function FSStorage (parsedTorrent, opts) {
       })
     })
 
+    var openRead = thunky(function (cb) {
+      fs.exists(filePath, function (exists) {
+        if (exists) return openWrite(cb)
+        cb(self.nonExistentError)
+      })
+    })
+
     file.pieces.forEach(function (piece) {
       var index = piece.index
 
@@ -72,10 +80,11 @@ function FSStorage (parsedTorrent, opts) {
       if (!self.piecesMap[index]) self.piecesMap[index] = []
 
       self.piecesMap[index].push({
-        from: from,
-        to: to,
-        offset: offset,
-        open: open
+        from      : from,
+        to        : to,
+        offset    : offset,
+        openWrite : openWrite,
+        openRead  : openRead
       })
     })
   })
@@ -124,8 +133,8 @@ FSStorage.prototype.readBlock = function (index, offset, length, cb) {
       from = rangeFrom
     }
 
-    target.open(function (err, file) {
-      if (err) return cb(err)
+    target.openRead(function (err, file) {
+      if (err) return (err === self.nonExistentError ? readFromNextFile(null, new Buffer(0)) : cb(err))
       file.read(offset, to - from, readFromNextFile)
     })
   }
@@ -147,7 +156,7 @@ FSStorage.prototype._onPieceDone = function (piece) {
     }
 
     var target = targets[i++]
-    target.open(function (err, file) {
+    target.openWrite(function (err, file) {
       if (err) return self.emit('error', err)
       file.write(target.offset, piece.buffer.slice(target.from, target.to), writeToNextFile)
     })