CdmFileIOImpl: Always SetLength(0) before WriteFile().

CdmFileIOImpl: Always SetLength(0) before WriteFile().

Since Write() takes two (or more) steps to finish, it's possible for
CdmFileIOImpl to be destructed after SetLength() is called but before
WriteFile() is called. In that case, if we SetLength(data_size), we end up with
a corrupted file. If we SetLength(0), we end up with an empty file, which is
relatively better.

BUG=410630
TEST=ECKEncryptedMediaTest.FileIOTest still passes.

[xhwang, 2014-09-11 04:30:58]

xhwang@chromium.org changed reviewers:
+ ddorwin@chromium.org, tzik@chromium.org

[xhwang, 2014-09-11 04:30:59]

ddorwin: PTAL

tzik: Please help make sure this doesn't have any unexpected side effects.

I tested this with existing/new tests and with a real player that users
CdmFileIO and everything seems to be working fine.

[tzik, 2014-09-11 04:45:27]

On 2014/09/11 04:30:59, xhwang wrote:
> ddorwin: PTAL
> 
> tzik: Please help make sure this doesn't have any unexpected side effects.
> 
> I tested this with existing/new tests and with a real player that users
> CdmFileIO and everything seems to be working fine.

LGTM.

Is it possible to avoid overwriting the file by replacing it with a new file
with Rename()?

[xhwang, 2014-09-11 17:49:55]

On 2014/09/11 04:45:27, tzik wrote:
> On 2014/09/11 04:30:59, xhwang wrote:
> > ddorwin: PTAL
> > 
> > tzik: Please help make sure this doesn't have any unexpected side effects.
> > 
> > I tested this with existing/new tests and with a real player that users
> > CdmFileIO and everything seems to be working fine.
> 
> LGTM.
> 
> Is it possible to avoid overwriting the file by replacing it with a new file
> with Rename()?

Yeah, we are investigating using two files to avoid overwriting.

I don't see a Rename() method in the PPB File IO? (ppapi/api/ppb_file_io.idl)

[tzik, 2014-09-12 02:35:46]

On 2014/09/11 17:49:55, xhwang wrote:
> On 2014/09/11 04:45:27, tzik wrote:
> > On 2014/09/11 04:30:59, xhwang wrote:
> > > ddorwin: PTAL
> > > 
> > > tzik: Please help make sure this doesn't have any unexpected side effects.
> > > 
> > > I tested this with existing/new tests and with a real player that users
> > > CdmFileIO and everything seems to be working fine.
> > 
> > LGTM.
> > 
> > Is it possible to avoid overwriting the file by replacing it with a new file
> > with Rename()?
> 
> Yeah, we are investigating using two files to avoid overwriting.
> 
> I don't see a Rename() method in the PPB File IO? (ppapi/api/ppb_file_io.idl)

It's in FileRef, ppapi/api/ppb_file_ref.idl.

[xhwang, 2014-09-15 19:57:47]

On 2014/09/12 02:35:46, tzik wrote:
> On 2014/09/11 17:49:55, xhwang wrote:
> > On 2014/09/11 04:45:27, tzik wrote:
> > > On 2014/09/11 04:30:59, xhwang wrote:
> > > > ddorwin: PTAL
> > > > 
> > > > tzik: Please help make sure this doesn't have any unexpected side
effects.
> > > > 
> > > > I tested this with existing/new tests and with a real player that users
> > > > CdmFileIO and everything seems to be working fine.
> > > 
> > > LGTM.
> > > 
> > > Is it possible to avoid overwriting the file by replacing it with a new
file
> > > with Rename()?
> > 
> > Yeah, we are investigating using two files to avoid overwriting.
> > 
> > I don't see a Rename() method in the PPB File IO?
(ppapi/api/ppb_file_io.idl)
> 
> It's in FileRef, ppapi/api/ppb_file_ref.idl.

I'll do the rename approach as suggested by tzik@ (thanks!). Closing this
issue...