fs: fix infinite loop in fs.readFile()

Fix an infinite loop in the case where the file got truncated by a concurrent
writer while fs.readFile() was busy reading in the file.

lib/fs.js

@@ -148,18 +148,18 @@ fs.readFile = function(path, encoding_) {
       });
     }
 
+    if (bytesRead === 0) {
+      return close();
+    }
+
     pos += bytesRead;
     if (size !== 0) {
       if (pos === size) close();
       else read();
     } else {
       // unknown size, just read until we don't get bytes.
-      if (bytesRead > 0) {
-        buffers.push(buffer.slice(0, bytesRead));
-        read();
-      } else {
-        close();
-      }
+      buffers.push(buffer.slice(0, bytesRead));
+      read();
     }
   }
 
@@ -168,6 +168,8 @@ fs.readFile = function(path, encoding_) {
       if (size === 0) {
         // collected the data into the buffers list.
         buffer = Buffer.concat(buffers, pos);
+      } else if (pos < size) {
+        buffer = buffer.slice(0, pos);
       }
 
       if (encoding) buffer = buffer.toString(encoding);