[nginx] Mp4: fixed setting wrong mdat atom size in very rare cases.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/2b2239a1e0d4
branches:  
changeset: 6818:2b2239a1e0d4
user:      hucongcong <hucong.c at foxmail.com>
date:      Tue Nov 22 13:40:08 2016 +0800
description:
Mp4: fixed setting wrong mdat atom size in very rare cases.

Atom size is the sum of atom header size and atom data size. The
specification says that the first 4 bytes are set to one when
the atom size is greater than the maximum unsigned 32-bit value.
Which means atom header size should be considered when the
comparison takes place between atom data size and 0xffffffff.

diffstat:

 src/http/modules/ngx_http_mp4_module.c |  4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diffs (14 lines):

diff --git a/src/http/modules/ngx_http_mp4_module.c b/src/http/modules/ngx_http_mp4_module.c
--- a/src/http/modules/ngx_http_mp4_module.c
+++ b/src/http/modules/ngx_http_mp4_module.c
@@ -1229,7 +1229,9 @@ ngx_http_mp4_update_mdat_atom(ngx_http_m
 
     atom_header = mp4->mdat_atom_header;
 
-    if ((uint64_t) atom_data_size > (uint64_t) 0xffffffff) {
+    if ((uint64_t) atom_data_size
+        > (uint64_t) 0xffffffff - sizeof(ngx_mp4_atom_header_t))
+    {
         atom_size = 1;
         atom_header_size = sizeof(ngx_mp4_atom_header64_t);
         ngx_mp4_set_64value(atom_header + sizeof(ngx_mp4_atom_header_t),