Update examples to use copyStream()

Jay Berkenbilt
1 parent 0f0f6010
Showing 3 changed files with 16 additions and 28 deletions
ChangeLog
examples/pdf-custom-filter.cc
examples/pdf-invert-images.cc
 2021-02-25  Jay Berkenbilt  <ejb@ql.org>
+	* Update StreamDataProvider examples to use copyStream() when they
+	want to get to the original stream data from the provider. Prior
+	to 10.2.0, we had to copy the stream to another QPDF, but now we
+	can just use copyStream().
+
 	* Bug fix/behavior change: when QPDF::replaceObject or
 	QPDF::swapObjects is called, existing QPDFObjectHandle instances
 	will now notice the change. This removes a long-standing source of
@@ -198,8 +198,7 @@ class StreamReplacer: public QPDFObjectHandle::StreamDataProvider
     //   original stream data is no longer directly accessible. Trying
     //   to retrieve the stream data would be an infinite loop because
     //   it would just end up calling provideStreamData again. This is
-    //   why maybeReplace uses a stashed copy of the original stream
-    //   from the "other" QPDF object.
+    //   why maybeReplace uses a stashed copy of the original stream.
     // Additional explanation can be found in the method
     // implementations.
@@ -223,11 +222,6 @@ class StreamReplacer: public QPDFObjectHandle::StreamDataProvider
     // we are replacing. We need this to create a new stream.
     QPDF* pdf;
-    // This second QPDF instance gives us a place to copy streams to
-    // so that we can access the original stream data of the streams
-    // whose data we are replacing.
-    QPDF other;
-
     // Map the object/generation in original file to the copied stream
     // in "other". We use this to retrieve the original data.
     std::map<QPDFObjGen, QPDFObjectHandle> copied_streams;
@@ -241,10 +235,6 @@ class StreamReplacer: public QPDFObjectHandle::StreamDataProvider
 StreamReplacer::StreamReplacer(QPDF* pdf) :
     pdf(pdf)
 {
-    // Our "other" QPDF is just a place to stash streams. It doesn't
-    // have to be a valid PDF with pages, etc. We are never going to
-    // write this out.
-    this->other.emptyPDF();
 }
 bool
@@ -375,9 +365,11 @@ StreamReplacer::registerStream(
     if (should_replace)
     {
-        // Copy the stream to another QPDF object so we can get to the
-        // original data from the stream data provider.
-        this->copied_streams[og] = this->other.copyForeignObject(stream);
+        // Copy the stream so we can get to the original data from the
+        // stream data provider. This doesn't actually copy any data,
+        // but the copy retains the original stream data after the
+        // original one is modified.
+        this->copied_streams[og] = stream.copyStream();
         // Update the stream dictionary with any changes.
         auto dict = stream.getDict();
         for (auto const& k: dict_updates.getKeys())
@@ -25,15 +25,13 @@ void usage()
 // allocate memory up front for the objects. We want to replace the
 // stream data with a function of the original stream data. In order
 // to do this without actually holding all the images in memory, we
-// create another QPDF object and copy the streams. Copying the
-// streams doesn't actually copy the data. Internally, the qpdf
-// library is holding onto the location of the stream data in the
-// original file, which makes it possible for the StreamDataProvider
-// to access it when it needs it.
+// create copies of the streams. Copying the streams doesn't actually
+// copy the data. Internally, the qpdf library is holding onto the
+// location of the original stream data, which makes it possible for
+// the StreamDataProvider to access it when it needs it.
 class ImageInverter: public QPDFObjectHandle::StreamDataProvider
 {
   public:
-    ImageInverter();
     virtual ~ImageInverter()
     {
     }
@@ -45,16 +43,9 @@ class ImageInverter: public QPDFObjectHandle::StreamDataProvider
         PointerHolder<QPDFObjectHandle::StreamDataProvider> self);
   private:
-    QPDF other;
-    // Map og in original to copied image
     std::map<QPDFObjGen, QPDFObjectHandle> copied_images;
 };
-ImageInverter::ImageInverter()
-{
-    this->other.emptyPDF();
-}
-
 void
 ImageInverter::registerImage(
     QPDFObjectHandle image,
@@ -77,7 +68,7 @@ ImageInverter::registerImage(
     {
         return;
     }
-    this->copied_images[og] = this->other.copyForeignObject(image);
+    this->copied_images[og] = image.copyStream();
     // Register our stream data provider for this stream. Future calls
     // to getStreamData or pipeStreamData will use the new