Re: [ruby-ffi] FFI check & questions

Subject:

Re: [ruby-ffi] FFI check & questions

From:

Wayne Meissner

Date:

2/27/12 7:13 PM

To:

ruby-ffi@googlegroups.com

There are a couple of problems:

1) The return type of get_pagememsize should be :int, not :size_t - :size_t is 64bit on 64bit platforms, and it will return bogus values from a function that actually returns an int.

2) You're using string ops on binary data. In FFI, anything that is :string, or read_string or write_string treats the string as a NUL terminated C string - i.e. it will stop reading at the first zero byte, and ensures the data written to memory is terminated with a zero byte.

So, in pdf_data_to_pointer(), instead of MemoryPointer.from_string(), use:

@@pointer_data = MemoryPointer.new(:char, data.size)

@@pointer_data.put_bytes(0, data)

And in get_image(), instead of picBuf.read_string, use picBuf.get_bytes(0, image_size)

On Tuesday, 28 February 2012 10:43:07 UTC+10, Jeffrey Jones wrote:

Hi Matjis,
I could have sworn I already checked the header file for a definition
but I obviously missed something
The code is
typedef enum {
EPSoutput,
TIFFoutput,
JPEGoutput,
BMPoutput,
PNGoutput,
RAWoutput,
PDFoutput,
GIFoutput,
} OutputTypeCode;
So 0 would be EPS output I assume, I changed it to 2 (JPEG) out of
curiosity but the allocation is still 4Gb.
Regarding checking if picBuf is null. I added a check immediately after
the malloc and the pointer is indeed null.
If I cheat badly and malloc image_size / 1024 then the picBuf pointer is
not null but them of course the
get_pagemem method fails.
I have no idea why I am getting a return value of 4Gb from the
get_pagememsize(iC) method. I was hoping there
was some obvious mistake (type conversion or something) I was making but
if nothing obvious springs out to
more experienced eyes then I am not sure.
Regards,
Jeff
On 28/02/12 01:14, Matijs van Zuijlen wrote:
> Hi Jeffrey,
>
> On 02/27/2012 02:26 AM, Jeffrey Jones wrote:
>> I am in the process of looking at using the following library from ruby
>> (http://www.datalogics.com/products/pdf2img/) using FFI but have run
>> into a few
>> issues mainly due to my lack of FFI experience and general lack of C++.
>>
>> [...]
>>
>> The following Gist has the example C++ code (Posted with permission)
>> and my Ruby
>> code along side some example output. https://gist.github.com/1920005
>>
>> [...]
>>
>> On line 22 of the ruby file I have defined the second argument as an
>> :int, this
>> is probably wrong but it suffices for the moment I think. I assume
>> the real
>> value is an Enumeration, struct or something along those lines. It is
>> not
>> documented so I will ask the original developers.
>
> You should take a look at the file 'pdf2imglib.h', to see what the
> values of that enumeration are. In particular, what integer value
> corresponds to GIFoutput.
>
>> Questions:
>>
>> 1. On line 40 of the ruby file the required memory is apparently 4Gb,
>> this is
>> obviously wrong, does anyone know why? (I assume I have messed
>> something up
>> somewhere)
>
> Perhaps setting the output type to 0 is wrong. I'm not sure what
> output type would demand 4GB, though.
>
>> 2. Can anyone see any other obvious mistakes on my part?
>
> I'm guessing allocating 4GB is not going very well. Do check the that
> the resulting pointer isn't null, i.e., with picBuf.null?
>
> Regards,

On Tuesday, 28 February 2012 10:43:07 UTC+10, Jeffrey Jones wrote:

Hi Matjis,
I could have sworn I already checked the header file for a definition
but I obviously missed something
The code is
typedef enum {
EPSoutput,
TIFFoutput,
JPEGoutput,
BMPoutput,
PNGoutput,
RAWoutput,
PDFoutput,
GIFoutput,
} OutputTypeCode;
So 0 would be EPS output I assume, I changed it to 2 (JPEG) out of
curiosity but the allocation is still 4Gb.
Regarding checking if picBuf is null. I added a check immediately after
the malloc and the pointer is indeed null.
If I cheat badly and malloc image_size / 1024 then the picBuf pointer is
not null but them of course the
get_pagemem method fails.
I have no idea why I am getting a return value of 4Gb from the
get_pagememsize(iC) method. I was hoping there
was some obvious mistake (type conversion or something) I was making but
if nothing obvious springs out to
more experienced eyes then I am not sure.
Regards,
Jeff
On 28/02/12 01:14, Matijs van Zuijlen wrote:
> Hi Jeffrey,
>
> On 02/27/2012 02:26 AM, Jeffrey Jones wrote:
>> I am in the process of looking at using the following library from ruby
>> (http://www.datalogics.com/products/pdf2img/) using FFI but have run
>> into a few
>> issues mainly due to my lack of FFI experience and general lack of C++.
>>
>> [...]
>>
>> The following Gist has the example C++ code (Posted with permission)
>> and my Ruby
>> code along side some example output. https://gist.github.com/1920005
>>
>> [...]
>>
>> On line 22 of the ruby file I have defined the second argument as an
>> :int, this
>> is probably wrong but it suffices for the moment I think. I assume
>> the real
>> value is an Enumeration, struct or something along those lines. It is
>> not
>> documented so I will ask the original developers.
>
> You should take a look at the file 'pdf2imglib.h', to see what the
> values of that enumeration are. In particular, what integer value
> corresponds to GIFoutput.
>
>> Questions:
>>
>> 1. On line 40 of the ruby file the required memory is apparently 4Gb,
>> this is
>> obviously wrong, does anyone know why? (I assume I have messed
>> something up
>> somewhere)
>
> Perhaps setting the output type to 0 is wrong. I'm not sure what
> output type would demand 4GB, though.
>
>> 2. Can anyone see any other obvious mistakes on my part?
>
> I'm guessing allocating 4GB is not going very well. Do check the that
> the resulting pointer isn't null, i.e., with picBuf.null?
>
> Regards,

On Tuesday, 28 February 2012 10:43:07 UTC+10, Jeffrey Jones wrote:

Hi Matjis,
I could have sworn I already checked the header file for a definition
but I obviously missed something
The code is
typedef enum {
EPSoutput,
TIFFoutput,
JPEGoutput,
BMPoutput,
PNGoutput,
RAWoutput,
PDFoutput,
GIFoutput,
} OutputTypeCode;
So 0 would be EPS output I assume, I changed it to 2 (JPEG) out of
curiosity but the allocation is still 4Gb.
Regarding checking if picBuf is null. I added a check immediately after
the malloc and the pointer is indeed null.
If I cheat badly and malloc image_size / 1024 then the picBuf pointer is
not null but them of course the
get_pagemem method fails.
I have no idea why I am getting a return value of 4Gb from the
get_pagememsize(iC) method. I was hoping there
was some obvious mistake (type conversion or something) I was making but
if nothing obvious springs out to
more experienced eyes then I am not sure.
Regards,
Jeff
On 28/02/12 01:14, Matijs van Zuijlen wrote:
> Hi Jeffrey,
>
> On 02/27/2012 02:26 AM, Jeffrey Jones wrote:
>> I am in the process of looking at using the following library from ruby
>> (http://www.datalogics.com/products/pdf2img/) using FFI but have run
>> into a few
>> issues mainly due to my lack of FFI experience and general lack of C++.
>>
>> [...]
>>
>> The following Gist has the example C++ code (Posted with permission)
>> and my Ruby
>> code along side some example output. https://gist.github.com/1920005
>>
>> [...]
>>
>> On line 22 of the ruby file I have defined the second argument as an
>> :int, this
>> is probably wrong but it suffices for the moment I think. I assume
>> the real
>> value is an Enumeration, struct or something along those lines. It is
>> not
>> documented so I will ask the original developers.
>
> You should take a look at the file 'pdf2imglib.h', to see what the
> values of that enumeration are. In particular, what integer value
> corresponds to GIFoutput.
>
>> Questions:
>>
>> 1. On line 40 of the ruby file the required memory is apparently 4Gb,
>> this is
>> obviously wrong, does anyone know why? (I assume I have messed
>> something up
>> somewhere)
>
> Perhaps setting the output type to 0 is wrong. I'm not sure what
> output type would demand 4GB, though.
>
>> 2. Can anyone see any other obvious mistakes on my part?
>
> I'm guessing allocating 4GB is not going very well. Do check the that
> the resulting pointer isn't null, i.e., with picBuf.null?
>
> Regards,

On Tuesday, 28 February 2012 10:43:07 UTC+10, Jeffrey Jones wrote:

Hi Matjis,
I could have sworn I already checked the header file for a definition
but I obviously missed something
The code is
typedef enum {
EPSoutput,
TIFFoutput,
JPEGoutput,
BMPoutput,
PNGoutput,
RAWoutput,
PDFoutput,
GIFoutput,
} OutputTypeCode;
So 0 would be EPS output I assume, I changed it to 2 (JPEG) out of
curiosity but the allocation is still 4Gb.
Regarding checking if picBuf is null. I added a check immediately after
the malloc and the pointer is indeed null.
If I cheat badly and malloc image_size / 1024 then the picBuf pointer is
not null but them of course the
get_pagemem method fails.
I have no idea why I am getting a return value of 4Gb from the
get_pagememsize(iC) method. I was hoping there
was some obvious mistake (type conversion or something) I was making but
if nothing obvious springs out to
more experienced eyes then I am not sure.
Regards,
Jeff
On 28/02/12 01:14, Matijs van Zuijlen wrote:
> Hi Jeffrey,
>
> On 02/27/2012 02:26 AM, Jeffrey Jones wrote:
>> I am in the process of looking at using the following library from ruby
>> (http://www.datalogics.com/products/pdf2img/) using FFI but have run
>> into a few
>> issues mainly due to my lack of FFI experience and general lack of C++.
>>
>> [...]
>>
>> The following Gist has the example C++ code (Posted with permission)
>> and my Ruby
>> code along side some example output. https://gist.github.com/1920005
>>
>> [...]
>>
>> On line 22 of the ruby file I have defined the second argument as an
>> :int, this
>> is probably wrong but it suffices for the moment I think. I assume
>> the real
>> value is an Enumeration, struct or something along those lines. It is
>> not
>> documented so I will ask the original developers.
>
> You should take a look at the file 'pdf2imglib.h', to see what the
> values of that enumeration are. In particular, what integer value
> corresponds to GIFoutput.
>
>> Questions:
>>
>> 1. On line 40 of the ruby file the required memory is apparently 4Gb,
>> this is
>> obviously wrong, does anyone know why? (I assume I have messed
>> something up
>> somewhere)
>
> Perhaps setting the output type to 0 is wrong. I'm not sure what
> output type would demand 4GB, though.
>
>> 2. Can anyone see any other obvious mistakes on my part?
>
> I'm guessing allocating 4GB is not going very well. Do check the that
> the resulting pointer isn't null, i.e., with picBuf.null?
>
> Regards,

On Tuesday, 28 February 2012 10:43:07 UTC+10, Jeffrey Jones wrote:

Hi Matjis,
I could have sworn I already checked the header file for a definition
but I obviously missed something
The code is
typedef enum {
EPSoutput,
TIFFoutput,
JPEGoutput,
BMPoutput,
PNGoutput,
RAWoutput,
PDFoutput,
GIFoutput,
} OutputTypeCode;
So 0 would be EPS output I assume, I changed it to 2 (JPEG) out of
curiosity but the allocation is still 4Gb.
Regarding checking if picBuf is null. I added a check immediately after
the malloc and the pointer is indeed null.
If I cheat badly and malloc image_size / 1024 then the picBuf pointer is
not null but them of course the
get_pagemem method fails.
I have no idea why I am getting a return value of 4Gb from the
get_pagememsize(iC) method. I was hoping there
was some obvious mistake (type conversion or something) I was making but
if nothing obvious springs out to
more experienced eyes then I am not sure.
Regards,
Jeff
On 28/02/12 01:14, Matijs van Zuijlen wrote:
> Hi Jeffrey,
>
> On 02/27/2012 02:26 AM, Jeffrey Jones wrote:
>> I am in the process of looking at using the following library from ruby
>> (http://www.datalogics.com/products/pdf2img/) using FFI but have run
>> into a few
>> issues mainly due to my lack of FFI experience and general lack of C++.
>>
>> [...]
>>
>> The following Gist has the example C++ code (Posted with permission)
>> and my Ruby
>> code along side some example output. https://gist.github.com/1920005
>>
>> [...]
>>
>> On line 22 of the ruby file I have defined the second argument as an
>> :int, this
>> is probably wrong but it suffices for the moment I think. I assume
>> the real
>> value is an Enumeration, struct or something along those lines. It is
>> not
>> documented so I will ask the original developers.
>
> You should take a look at the file 'pdf2imglib.h', to see what the
> values of that enumeration are. In particular, what integer value
> corresponds to GIFoutput.
>
>> Questions:
>>
>> 1. On line 40 of the ruby file the required memory is apparently 4Gb,
>> this is
>> obviously wrong, does anyone know why? (I assume I have messed
>> something up
>> somewhere)
>
> Perhaps setting the output type to 0 is wrong. I'm not sure what
> output type would demand 4GB, though.
>
>> 2. Can anyone see any other obvious mistakes on my part?
>
> I'm guessing allocating 4GB is not going very well. Do check the that
> the resulting pointer isn't null, i.e., with picBuf.null?
>
> Regards,

On Tuesday, 28 February 2012 10:43:07 UTC+10, Jeffrey Jones wrote:

Hi Matjis,
I could have sworn I already checked the header file for a definition
but I obviously missed something
The code is
typedef enum {
EPSoutput,
TIFFoutput,
JPEGoutput,
BMPoutput,
PNGoutput,
RAWoutput,
PDFoutput,
GIFoutput,
} OutputTypeCode;
So 0 would be EPS output I assume, I changed it to 2 (JPEG) out of
curiosity but the allocation is still 4Gb.
Regarding checking if picBuf is null. I added a check immediately after
the malloc and the pointer is indeed null.
If I cheat badly and malloc image_size / 1024 then the picBuf pointer is
not null but them of course the
get_pagemem method fails.
I have no idea why I am getting a return value of 4Gb from the
get_pagememsize(iC) method. I was hoping there
was some obvious mistake (type conversion or something) I was making but
if nothing obvious springs out to
more experienced eyes then I am not sure.
Regards,
Jeff
On 28/02/12 01:14, Matijs van Zuijlen wrote:
> Hi Jeffrey,
>
> On 02/27/2012 02:26 AM, Jeffrey Jones wrote:
>> I am in the process of looking at using the following library from ruby
>> (http://www.datalogics.com/products/pdf2img/) using FFI but have run
>> into a few
>> issues mainly due to my lack of FFI experience and general lack of C++.
>>
>> [...]
>>
>> The following Gist has the example C++ code (Posted with permission)
>> and my Ruby
>> code along side some example output. https://gist.github.com/1920005
>>
>> [...]
>>
>> On line 22 of the ruby file I have defined the second argument as an
>> :int, this
>> is probably wrong but it suffices for the moment I think. I assume
>> the real
>> value is an Enumeration, struct or something along those lines. It is
>> not
>> documented so I will ask the original developers.
>
> You should take a look at the file 'pdf2imglib.h', to see what the
> values of that enumeration are. In particular, what integer value
> corresponds to GIFoutput.
>
>> Questions:
>>
>> 1. On line 40 of the ruby file the required memory is apparently 4Gb,
>> this is
>> obviously wrong, does anyone know why? (I assume I have messed
>> something up
>> somewhere)
>
> Perhaps setting the output type to 0 is wrong. I'm not sure what
> output type would demand 4GB, though.
>
>> 2. Can anyone see any other obvious mistakes on my part?
>
> I'm guessing allocating 4GB is not going very well. Do check the that
> the resulting pointer isn't null, i.e., with picBuf.null?
>
> Regards,