Fixes in pread()

The bug occurs when pread() doesn't return 0 when asked to read an
offset beyond its buffer.

This behavior is explicitly documented at:
http://pubs.opengroup.org/onlinepubs/000095399/functions/read.html

> If the starting position is at or after the end-of-file, 0
> shall be returned

2 files changed, 6 insertions, 0 deletions

diff --git a/src/library_fs.js b/src/library_fs.js
index 8bf0a83a..84a5245b 100644
--- a/src/library_fs.js
+++ b/src/library_fs.js
@@ -1367,7 +1367,10 @@ mergeInto(LibraryManager.library, {
           throw new FS.ErrnoError(ERRNO_CODES.EIO);
         }
         var contents = stream.node.contents;
+        if (position >= contents.length)
+          return 0;
         var size = Math.min(contents.length - position, length);
+        assert(size >= 0);
         if (contents.slice) { // normal array
           for (var i = 0; i < size; i++) {
             buffer[offset + i] = contents[position + i];
diff --git a/src/library_memfs.js b/src/library_memfs.js
index 354f5e95..28178d9f 100644
--- a/src/library_memfs.js
+++ b/src/library_memfs.js
@@ -177,7 +177,10 @@ mergeInto(LibraryManager.library, {
     stream_ops: {
       read: function(stream, buffer, offset, length, position) {
         var contents = stream.node.contents;
+        if (position >= contents.length)
+          return 0;
         var size = Math.min(contents.length - position, length);
+        assert(size >= 0);
 #if USE_TYPED_ARRAYS == 2
         if (size > 8 && contents.subarray) { // non-trivial, and typed array
           buffer.set(contents.subarray(position, position + size), offset);