[gdal-dev] GDAL RPC protocol to make GDAL (more) failsafe

[Even Rouault]

Hi,

Just to inform you that I've just commited in trunk a new feature.

See http://trac.osgeo.org/gdal/ticket/4979 :

"""
When dealing with some file formats, particularly the drivers relying on third-
party (potentially closed-source) libraries, it is difficult to ensure that 
those third-party libraries will be robust to hostile/corrupted datasource. 
The implemented solution is to have a fake driver that will expose a 
GDALClientDataset object that will forward all the API calls to another 
process ("server") where the real driver will be run. This way, if the server 
segfaults, the calling process will be unaffected and will report a clean error 
instead of segfaulting itself. 
This is controlled by setting the GDAL_RPC config option to YES. The option can 
also be set to a list of file extensions that must be the only ones to trigger 
this mechanism (e.g. GDAL_RPC=ecw,sid) 
For now, the server launched is the gdalserver executable on Windows. On Unix, 
the default behaviour is to just fork() the current process (the gdalserver 
executable can also be execvp()'ed by forcing GDAL_RPC_SERVER=YES). 
To avoid the cost of forking()/CreateProcess(), a pool of connections is used. 
This is controlled with the GDAL_RPC_RECYCLE config option that is set to YES 
by default. 
Note: the client/server approach can also be used for thread unsafe drivers 
(not actually tested). 
"""
Demo with a corrupted ECW file :
Normal GDAL run :
$ gdalinfo corrupted.ecw -checksum
Driver: ECW/ERDAS Compressed Wavelets (SDK 3.x)
Files: corrupted.ecw
Size is 128, 128
Coordinate System is:
[ ... snip ... ]
Band 1 Block=256x256 Type=Byte, ColorInterp=Gray
Segmentation fault

Under the RPC mechanism :

$ gdalinfo corrupted.ecw -checksum --config GDAL_RPC YES

Driver: ECW/ERDAS Compressed Wavelets (SDK 3.x)
Files: corrupted.ecw
Size is 128, 128
Coordinate System is:
[ ... snip ... ]
Band 1 Block=256x256 Type=Byte, ColorInterp=Gray
ERROR 1: Read from pipe failed
ERROR 3: Checksum value couldn't be computed due to I/O read error.

  Checksum=0
  Mask Flags: 
  Offset: 0,   Scale:0

Of course, there's a small performance cost associated to the RPC round-trips.


Best regards,

Even