2015.07.14 13:19 "[Tiff] TIFFClientOpen when writing... Bug?", by Scott Weber

Hello,

I am implementing the TIFFClientOpen(...) methods for reading a writing in memory.

Reading works fine. The problem is that "writing" is trying to "read".

I set up the call with all the callback functions (they are inside an instantiated class):

    hTif = TIFFClientOpen("OUT","w",
         (thandle_t)this,
        tiff_Read, tiff_Write, tiff_Seek,
        tiff_Close, tiff_Size, NULL,NULL);

And I see that is attempts to read 8 bytes from the beginning of the buffer.

As I step through and debug the lib, I am seeing bizarre things.

Specifically, inside the TIFFClientOpen function, it does the following: Calls "TIFFgetMode(..)" and assigned O_RDWR, O_RDONLY, etc... flags. I see that it tries to decide if it must add the O_TRUNC flag, but the structure of the code is such that it can never happen.

( inside case 'a', if mode[0] == 'w'... which is impossible, because
mode[0] was 'a' )

Later one, there is a peice of code:

     if   (....    !ReadOK( tif...   )

Which tries to do an initial read of the buffer, and verify that the magic header is correct.

So then...

If we are "writing" in what should essentially be a new buffer, why is it trying to read that buffer first to see if it is a valid TIFF?

I could make the alterations I think are correct, but I am reluctant to start messing with the lib because of my unfamiliarity with it's inner workings.

(for example, if I remove that test during "write", does some other portion of the code put the magic bytes there anyway?)

Any advice is appreciated.

Scott Weber