Implement user-provided stream filters

Refactor QPDF_Stream to use stream filter classes to handle supported
stream filters as well.

2 files changed, 95 insertions, 0 deletions

diff --git a/include/qpdf/QPDF.hh b/include/qpdf/QPDF.hh
index 285ba1e3..b0e9b717 100644
--- a/include/qpdf/QPDF.hh
+++ b/include/qpdf/QPDF.hh
@@ -31,6 +31,8 @@
 #include <list>
 #include <iostream>
 #include <vector>
+#include <functional>
+#include <memory>
 
 #include <qpdf/QIntC.hh>
 #include <qpdf/QPDFExc.hh>
@@ -39,6 +41,7 @@
 #include <qpdf/QPDFXRefEntry.hh>
 #include <qpdf/QPDFObjectHandle.hh>
 #include <qpdf/QPDFTokenizer.hh>
+#include <qpdf/QPDFStreamFilter.hh>
 #include <qpdf/Buffer.hh>
 #include <qpdf/InputSource.hh>
 
@@ -132,6 +135,20 @@ class QPDF
     QPDF_DLL
     void emptyPDF();
 
+    // From 10.1: register a new filter implementation for a specific
+    // stream filter. You can add your own implementations for new
+    // filter types or override existing ones provided by the library.
+    // Registered stream filters are used for decoding only as you can
+    // override encoding with stream data providers. For example, you
+    // could use this method to support for one of the other filter
+    // types by using additional third-party libraries that qpdf does
+    // not presently use. The standard filters are implemented using
+    // QPDFStreamFilter classes.
+    QPDF_DLL
+    static void registerStreamFilter(
+        std::string const& filter_name,
+        std::function<std::shared_ptr<QPDFStreamFilter> ()> factory);
+
     // Parameter settings
 
     // By default, warning messages are issued to std::cerr and output
diff --git a/include/qpdf/QPDFStreamFilter.hh b/include/qpdf/QPDFStreamFilter.hh
new file mode 100644
index 00000000..5fdcf5ca
--- /dev/null
+++ b/include/qpdf/QPDFStreamFilter.hh
@@ -0,0 +1,78 @@
+// Copyright (c) 2005-2020 Jay Berkenbilt
+//
+// This file is part of qpdf.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Versions of qpdf prior to version 7 were released under the terms
+// of version 2.0 of the Artistic License. At your option, you may
+// continue to consider qpdf to be licensed under those terms. Please
+// see the manual for additional information.
+
+#ifndef QPDFSTREAMFILTER_HH
+#define QPDFSTREAMFILTER_HH
+
+#include <qpdf/DLL.h>
+#include <qpdf/QPDFObjectHandle.hh>
+#include <qpdf/Pipeline.hh>
+
+class QPDF_DLL_CLASS QPDFStreamFilter
+{
+  public:
+    QPDF_DLL
+    QPDFStreamFilter() = default;
+
+    QPDF_DLL
+    virtual ~QPDFStreamFilter() = default;
+
+    // A QPDFStreamFilter class must implement, at a minimum,
+    // setDecodeParms() and getDecodePipeline(). QPDF will always call
+    // setDecodeParms() before calling getDecodePipeline(). It is
+    // expected that you will store any needed information from
+    // decode_parms (or the decode_parms object iself) in your
+    // instance so that it can be used to construct the decode
+    // pipeline.
+
+    // Return a boolean indicating whether your filter can proceed
+    // with the given /DecodeParms. The default implementation accepts
+    // a null object and rejects everything else.
+    QPDF_DLL
+    virtual bool setDecodeParms(QPDFObjectHandle decode_parms);
+
+    // Return a pipeline that will decode data encoded with your
+    // filter. Your implementation must ensure that the pipeline is
+    // deleted when the instance of your class is destroyed.
+    QPDF_DLL
+    virtual Pipeline* getDecodePipeline(Pipeline* next) = 0;
+
+    // If your filter implements "specialized" compression or lossy
+    // compression, override one or both of these methods. The default
+    // implementations return false. See comments in QPDFWriter for
+    // details. QPDF defines specialized compression as non-lossy
+    // compression not intended for general-purpose data. qpdf, by
+    // default, doesn't mess with streams that are compressed with
+    // specialized compression, the idea being that the decision to
+    // use that compression scheme would fall outside of what
+    // QPDFWriter would know anything about, so any attempt to decode
+    // and re-encode would probably be undesirable.
+    QPDF_DLL
+    virtual bool isSpecializedCompression();
+    QPDF_DLL
+    virtual bool isLossyCompression();
+
+  private:
+    QPDFStreamFilter(QPDFStreamFilter const&) = delete;
+    QPDFStreamFilter& operator=(QPDFStreamFilter const&) = delete;
+};
+
+#endif // QPDFSTREAMFILTER_HH