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Don't require stream data provider to know length in advance

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Breaking API change: length parameter has disappeared from the
StreamDataProvider version of QPDFObjectHandle::replaceStreamData
since it is no longer necessary to compute it in advance.  This
breaking change is justified by the fact that removing the length
parameter provides the caller an opportunity to simplify the calling
code.
This commit is contained in:
Jay Berkenbilt 2012-07-07 17:33:45 -04:00
parent 8705e2e8fc
commit e2dedde4bd
12 changed files with 100 additions and 65 deletions
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18
ChangeLog
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@ -1,3 +1,21 @@
2012-07-07 Jay Berkenbilt <ejb@ql.org>
* NOTE: BREAKING API CHANGE. Remove previously required length
parameter from the version QPDFObjectHandle::replaceStreamData
that uses a stream data provider. Prior to qpdf 3.0.0, you had to
compute the stream length in advance so that qpdf could internally
verify that the stream data had the same length every time the
provider was invoked. Now this requirement is enforced a
different way, and the length parameter is no longer required.
Note that I take API-breaking changes very seriously and only did
it in this case since the lack of need to know length in advance
could significantly simplify people's code. If you were
previously going to a lot of trouble to compute the length of the
new stream data in advance, you now no longer have to do that.
You can just drop the length parameter and remove any code that
was previously computing the length. Thanks to Tobias Hoffmann
for pointing out how annoying the original interface was.
2012-07-05 Jay Berkenbilt <ejb@ql.org>
* Add QPDFWriter methods to write to an already open stdio FILE*.

4
TODO
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@ -17,8 +17,8 @@ Next
* Document that your compiler has to support long long.
* Figure out why we have to specify a stream's length in advance when
providing stream data, and remove this restriction if possible.
* Make sure that the release notes call attention to the one API
breaking change: removal of length from replaceStreamData.
* Add a way to create new QPDFObjectHandles with a string
representation of them, such as

10
examples/pdf-create.cc
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@ -17,7 +17,6 @@ class ImageProvider: public QPDFObjectHandle::StreamDataProvider
virtual ~ImageProvider();
virtual void provideStreamData(int objid, int generation,
Pipeline* pipeline);
size_t getLength() const;
private:
int width;
@ -45,12 +44,6 @@ ImageProvider::provideStreamData(int objid, int generation,
pipeline->finish();
}
size_t
ImageProvider::getLength() const
{
return 3 * width * height;
}
void usage()
{
std::cerr << "Usage: " << whoami << " filename" << std::endl
@ -111,8 +104,7 @@ static void create_pdf(char const* filename)
PointerHolder<QPDFObjectHandle::StreamDataProvider> provider(p);
image.replaceStreamData(provider,
QPDFObjectHandle::newNull(),
QPDFObjectHandle::newNull(),
p->getLength());
QPDFObjectHandle::newNull());
// Create direct objects as needed by the page dictionary.
QPDFObjectHandle procset = QPDFObjectHandle::newArray();

3
examples/pdf-invert-images.cc
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@ -141,8 +141,7 @@ int main(int argc, char* argv[])
image.replaceStreamData(
p,
QPDFObjectHandle::newNull(),
QPDFObjectHandle::newNull(),
inv->image_data[objid][gen]->getSize());
QPDFObjectHandle::newNull());
}
}
}

31
include/qpdf/QPDFObjectHandle.hh
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@ -294,18 +294,31 @@ class QPDFObjectHandle
// directly providing a buffer with the stream data, call the
// given provider's provideStreamData method. See comments on the
// StreamDataProvider class (defined above) for details on the
// method. The provider must write the number of bytes as
// indicated by the length parameter, and the data must be
// consistent with filter and decode_parms as provided. Although
// it is more complex to use this form of replaceStreamData than
// the one that takes a buffer, it makes it possible to avoid
// allocating memory for the stream data. Example programs are
// provided that use both forms of replaceStreamData.
// method. The data must be consistent with filter and
// decode_parms as provided. Although it is more complex to use
// this form of replaceStreamData than the one that takes a
// buffer, it makes it possible to avoid allocating memory for the
// stream data. Example programs are provided that use both forms
// of replaceStreamData.
// Note about stream length: for any given stream, the provider
// must provide the same amount of data each time it is called.
// This is critical for making linearization work properly.
// Versions of qpdf before 3.0.0 required a length to be specified
// here. Starting with version 3.0.0, this is no longer necessary
// (or permitted). The first time the stream data provider is
// invoked for a given stream, the actual length is stored.
// Subsequent times, it is enforced that the length be the same as
// the first time.
// If you have gotten a compile error here while building code
// that worked with older versions of qpdf, just omit the length
// parameter. You can also simplify your code by not having to
// compute the length in advance.
QPDF_DLL
void replaceStreamData(PointerHolder<StreamDataProvider> provider,
QPDFObjectHandle const& filter,
QPDFObjectHandle const& decode_parms,
size_t length);
QPDFObjectHandle const& decode_parms);
// return 0 for direct objects
QPDF_DLL

5
libqpdf/QPDFObjectHandle.cc
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@ -414,12 +414,11 @@ QPDFObjectHandle::replaceStreamData(PointerHolder<Buffer> data,
void
QPDFObjectHandle::replaceStreamData(PointerHolder<StreamDataProvider> provider,
QPDFObjectHandle const& filter,
QPDFObjectHandle const& decode_parms,
size_t length)
QPDFObjectHandle const& decode_parms)
{
assertType("Stream", isStream());
dynamic_cast<QPDF_Stream*>(obj.getPointer())->replaceStreamData(
provider, filter, decode_parms, length);
provider, filter, decode_parms);
}
int

30
libqpdf/QPDF_Stream.cc
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@ -380,8 +380,10 @@ QPDF_Stream::pipeStreamData(Pipeline* pipeline, bool filter,
this->stream_provider->provideStreamData(
this->objid, this->generation, &count);
qpdf_offset_t actual_length = count.getCount();
qpdf_offset_t desired_length =
this->stream_dict.getKey("/Length").getIntValue();
qpdf_offset_t desired_length = 0;
if (this->stream_dict.hasKey("/Length"))
{
desired_length = this->stream_dict.getKey("/Length").getIntValue();
if (actual_length == desired_length)
{
QTC::TC("qpdf", "QPDF_Stream pipe use stream provider");
@ -399,6 +401,13 @@ QPDF_Stream::pipeStreamData(Pipeline* pipeline, bool filter,
QUtil::int_to_string(desired_length) + " bytes");
}
}
else
{
QTC::TC("qpdf", "QPDF_Stream provider length not provided");
this->stream_dict.replaceKey(
"/Length", QPDFObjectHandle::newInteger(actual_length));
}
}
else if (this->offset == 0)
{
QTC::TC("qpdf", "QPDF_Stream pipe no stream data");
@ -430,12 +439,11 @@ void
QPDF_Stream::replaceStreamData(
PointerHolder<QPDFObjectHandle::StreamDataProvider> provider,
QPDFObjectHandle const& filter,
QPDFObjectHandle const& decode_parms,
size_t length)
QPDFObjectHandle const& decode_parms)
{
this->stream_provider = provider;
this->stream_data = 0;
replaceFilterData(filter, decode_parms, length);
replaceFilterData(filter, decode_parms, 0);
}
void
@ -445,6 +453,14 @@ QPDF_Stream::replaceFilterData(QPDFObjectHandle const& filter,
{
this->stream_dict.replaceOrRemoveKey("/Filter", filter);
this->stream_dict.replaceOrRemoveKey("/DecodeParms", decode_parms);
this->stream_dict.replaceKey("/Length",
QPDFObjectHandle::newInteger((int)length));
if (length == 0)
{
QTC::TC("qpdf", "QPDF_Stream unknown stream length");
this->stream_dict.removeKey("/Length");
}
else
{
this->stream_dict.replaceKey(
"/Length", QPDFObjectHandle::newInteger((int)length));
}
}

3
libqpdf/qpdf/QPDF_Stream.hh
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@ -30,8 +30,7 @@ class QPDF_Stream: public QPDFObject
void replaceStreamData(
PointerHolder<QPDFObjectHandle::StreamDataProvider> provider,
QPDFObjectHandle const& filter,
QPDFObjectHandle const& decode_parms,
size_t length);
QPDFObjectHandle const& decode_parms);
// Replace object ID and generation. This may only be called if
// object ID and generation are 0. It is used by QPDFObjectHandle

2
qpdf/qpdf.testcov
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@ -215,3 +215,5 @@ QPDFObjectHandle shallow copy dictionary 0
QPDFObjectHandle shallow copy scalar 0
QPDFObjectHandle newStream with string 0
QPDF unknown key not inherited 0
QPDF_Stream provider length not provided 0
QPDF_Stream unknown stream length 0

BIN
qpdf/qtest/qpdf/replaced-stream-data-flate.pdf
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Binary file not shown.

17
qpdf/test_driver.cc
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@ -478,7 +478,17 @@ void runtest(int n, char const* filename)
PointerHolder<QPDFObjectHandle::StreamDataProvider> p = provider;
qstream.replaceStreamData(
p, QPDFObjectHandle::newName("/FlateDecode"),
QPDFObjectHandle::newNull(), b->getSize());
QPDFObjectHandle::newNull());
provider->badLength(false);
QPDFWriter w(pdf, "a.pdf");
w.setStaticID(true);
// Linearize to force the provider to be called multiple times.
w.setLinearization(true);
w.setStreamDataMode(qpdf_s_preserve);
w.write();
// Every time a provider pipes stream data, it has to provide
// the same amount of data.
provider->badLength(true);
try
{
@ -489,11 +499,6 @@ void runtest(int n, char const* filename)
{
std::cout << "exception: " << e.what() << std::endl;
}
provider->badLength(false);
QPDFWriter w(pdf, "a.pdf");
w.setStaticID(true);
w.setStreamDataMode(qpdf_s_preserve);
w.write();
}
else if (n == 9)
{

10
qpdf/test_large_file.cc
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@ -109,7 +109,6 @@ class ImageProvider: public QPDFObjectHandle::StreamDataProvider
virtual ~ImageProvider();
virtual void provideStreamData(int objid, int generation,
Pipeline* pipeline);
size_t getLength() const;
private:
int n;
@ -142,12 +141,6 @@ ImageProvider::provideStreamData(int objid, int generation,
pipeline->finish();
}
size_t
ImageProvider::getLength() const
{
return width * height;
}
void usage()
{
std::cerr << "Usage: " << whoami << " {read|write} {large|small} outfile"
@ -229,8 +222,7 @@ static void create_pdf(char const* filename)
PointerHolder<QPDFObjectHandle::StreamDataProvider> provider(p);
image.replaceStreamData(provider,
QPDFObjectHandle::newNull(),
QPDFObjectHandle::newNull(),
p->getLength());
QPDFObjectHandle::newNull());
QPDFObjectHandle xobject = QPDFObjectHandle::newDictionary();
xobject.replaceKey("/Im1", image);