From a2c0ebd3b54ef036759f6b230a4bc55848c094f9 Mon Sep 17 00:00:00 2001
From: Friedel Ziegelmayer <dignifiedquire@gmail.com>
Date: Sat, 10 Sep 2016 13:09:46 +0200
Subject: [PATCH] fix: lock source to ensure no double reads happen

When the source is read very fast while the file descriptor is still
being opened it can come to double reads of chunks of the file. This
introduces a lock to avoid this issue.
---
 index.js          | 17 +++++++++++++----
 package.json      |  3 ++-
 test/largefile.js | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/index.js b/index.js
index 62fbcc5..113053e 100644
--- a/index.js
+++ b/index.js
@@ -4,6 +4,7 @@
 
 var fs = require('fs');
 var Decoder = require('pull-utf8-decoder')
+var Lock = require('lock')
 /**
   # pull-file
 
@@ -25,6 +26,7 @@ module.exports = function(filename, opts) {
 
   var ended, closeNext, busy;
   var _buffer = new Buffer(bufferSize)
+  var lock = Lock()
   var live = opts && !!opts.live
   var liveCb, closeCb
   var watcher
@@ -78,10 +80,12 @@ module.exports = function(filename, opts) {
           return cb(err);
         }
 
-        if(count === buffer.length) {
+        if(count === toRead && count === buffer.length) {
           cb(null, buffer);
         } else if(count === 0 && live) {
           liveCb = cb; closeNext = true
+        } else if (count === 0) {
+          cb(ended = true)
         } else {
           closeNext = true;
           cb(null, buffer.slice(0, count));
@@ -161,11 +165,16 @@ module.exports = function(filename, opts) {
       readNext(cb);
   };
 
+  var lockedSource = function (end, cb) {
+    lock('source', function (release) {
+      source(end, release(cb))
+    })
+  }
+
   //read directly to text
   if(opts && opts.encoding)
-    return Decoder(opts.encoding)(source)
+    return Decoder(opts.encoding)(lockedSource)
 
-  return source
+  return lockedSource
 
 };
-
diff --git a/package.json b/package.json
index 7fd0a2d..361a8c9 100644
--- a/package.json
+++ b/package.json
@@ -34,6 +34,7 @@
   },
   "homepage": "https://github.com/DamonOehlman/pull-file",
   "dependencies": {
+    "lock": "^0.1.3",
     "pull-utf8-decoder": "^1.0.2"
   }
-}
\ No newline at end of file
+}
diff --git a/test/largefile.js b/test/largefile.js
index 1ac116e..a10988a 100644
--- a/test/largefile.js
+++ b/test/largefile.js
@@ -43,8 +43,43 @@ test('large file as ascii strings', function(t) {
   );
 });
 
+test('large file fast reads', function(t) {
+  var big = crypto.pseudoRandomBytes(10*1024*1024)
+  fs.writeFileSync(tmpfile, big)
 
+  var read = file(tmpfile, {bufferSize: 1024 * 1024})
+  var items = []
 
+  read(null, checkRead)
+  read(null, checkRead)
+  read(null, checkRead)
+  read(null, checkRead)
+  read(null, checkRead)
 
+  setTimeout(function () {
+    read(null, checkRead)
+    read(null, checkRead)
+    read(null, checkRead)
+    read(null, checkRead)
+    read(null, checkRead)
+    read(null, function (err, data) {
+      t.equal(err, true)
+      t.equal(data, undefined)
+      next()
+    })
+  }, 10)
 
+  function checkRead (err, data) {
+    t.equal(data.length, 1024 * 1024)
+    items.push(data)
+    next()
+  }
 
+  var i = 0
+  function next () {
+    if (++i === 11) {
+      t.equal(hash(big), hash(Buffer.concat(items)))
+      t.end()
+    }
+  }
+})