mirror of https://github.com/qpdf/qpdf.git
89 lines
3.2 KiB
C++
89 lines
3.2 KiB
C++
// Copyright (c) 2005-2022 Jay Berkenbilt
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//
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// This file is part of qpdf.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Versions of qpdf prior to version 7 were released under the terms
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// of version 2.0 of the Artistic License. At your option, you may
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// continue to consider qpdf to be licensed under those terms. Please
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// see the manual for additional information.
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// Generalized Pipeline interface. By convention, subclasses of
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// Pipeline are called Pl_Something.
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//
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// When an instance of Pipeline is created with a pointer to a next
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// pipeline, that pipeline writes its data to the next one when it
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// finishes with it. In order to make possible a usage style in which
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// a pipeline may be passed to a function which may stick other
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// pipelines in front of it, the allocator of a pipeline is
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// responsible for its destruction. In other words, one pipeline
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// object does not attempt to manage the memory of its successor.
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//
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// The client is required to call finish() before destroying a
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// Pipeline in order to avoid loss of data. A Pipeline class should
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// not throw an exception in the destructor if this hasn't been done
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// though since doing so causes too much trouble when deleting
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// pipelines during error conditions.
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//
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// Some pipelines are reusable (i.e., you can call write() after
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// calling finish() and can call finish() multiple times) while others
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// are not. It is up to the caller to use a pipeline according to its
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// own restrictions.
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#ifndef PIPELINE_HH
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#define PIPELINE_HH
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#include <qpdf/DLL.h>
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#include <qpdf/PointerHolder.hh>
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#include <string>
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class QPDF_DLL_CLASS Pipeline
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{
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public:
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QPDF_DLL
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Pipeline(char const* identifier, Pipeline* next);
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QPDF_DLL
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virtual ~Pipeline();
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// Subclasses should implement write and finish to do their jobs
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// and then, if they are not end-of-line pipelines, call
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// getNext()->write or getNext()->finish. It would be really nice
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// if write could take unsigned char const*, but this would make
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// it much more difficult to write pipelines around legacy
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// interfaces whose calls don't want pointers to const data. As a
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// rule, pipelines should generally not be modifying the data
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// passed to them. They should, instead, create new data to pass
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// downstream.
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QPDF_DLL
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virtual void write(unsigned char* data, size_t len) = 0;
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QPDF_DLL
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virtual void finish() = 0;
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QPDF_DLL
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std::string getIdentifier() const;
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protected:
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QPDF_DLL
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Pipeline* getNext(bool allow_null = false);
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std::string identifier;
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private:
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Pipeline(Pipeline const&) = delete;
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Pipeline& operator=(Pipeline const&) = delete;
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Pipeline* next;
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};
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#endif // PIPELINE_HH
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