From e62f1e4e4457487b3ae7b729b5fb7a78081b0478 Mon Sep 17 00:00:00 2001
From: Jay Berkenbilt <ejb@ql.org>
Date: Sat, 5 Apr 2025 20:52:17 -0400
Subject: [PATCH] Add Pl_DCT::make_compress_config

---
 include/qpdf/Pl_DCT.hh   |  5 +++++
 libqpdf/Pl_DCT.cc        | 24 +++++++++++++++++++++++-
 libqpdf/QPDFJob.cc       |  4 +++-
 libtests/dct_compress.cc |  7 ++++++-
 manual/release-notes.rst |  6 ++++++
 5 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/include/qpdf/Pl_DCT.hh b/include/qpdf/Pl_DCT.hh
index 02f4a34..09a7277 100644
--- a/include/qpdf/Pl_DCT.hh
+++ b/include/qpdf/Pl_DCT.hh
@@ -24,6 +24,7 @@
 
 #include <qpdf/Pl_Buffer.hh>
 #include <cstddef>
+#include <functional>
 
 // jpeglib.h must be included after cstddef or else it messes up the definition of size_t.
 #include <jpeglib.h>
@@ -62,6 +63,10 @@ class QPDF_DLL_CLASS Pl_DCT: public Pipeline
         virtual void apply(jpeg_compress_struct*) = 0;
     };
 
+    QPDF_DLL
+    static std::shared_ptr<CompressConfig>
+        make_compress_config(std::function<void(jpeg_compress_struct*)>);
+
     // Constructor for compressing image data
     QPDF_DLL
     Pl_DCT(
diff --git a/libqpdf/Pl_DCT.cc b/libqpdf/Pl_DCT.cc
index 92af9c9..2e480ec 100644
--- a/libqpdf/Pl_DCT.cc
+++ b/libqpdf/Pl_DCT.cc
@@ -1,6 +1,5 @@
 #include <qpdf/Pl_DCT.hh>
 
-#include "qpdf/QPDFLogger.hh"
 #include <qpdf/QIntC.hh>
 #include <qpdf/QTC.hh>
 
@@ -14,6 +13,23 @@
 
 namespace
 {
+    class FunctionCallbackConfig: public Pl_DCT::CompressConfig
+    {
+      public:
+        explicit FunctionCallbackConfig(std::function<void(jpeg_compress_struct*)> f) :
+            f(std::move(f))
+        {
+        }
+        ~FunctionCallbackConfig() override = default;
+        void
+        apply(jpeg_compress_struct* config) override
+        {
+            f(config);
+        };
+
+        std::function<void(jpeg_compress_struct*)> f;
+    };
+
     struct qpdf_jpeg_error_mgr
     {
         struct jpeg_error_mgr pub;
@@ -407,3 +423,9 @@ Pl_DCT::decompress(void* cinfo_p, Buffer* b)
     (void)jpeg_finish_decompress(cinfo);
     next()->finish();
 }
+
+std::shared_ptr<Pl_DCT::CompressConfig>
+Pl_DCT::make_compress_config(std::function<void(jpeg_compress_struct*)> f)
+{
+    return std::make_shared<FunctionCallbackConfig>(f);
+}
diff --git a/libqpdf/QPDFJob.cc b/libqpdf/QPDFJob.cc
index efa07d3..3077200 100644
--- a/libqpdf/QPDFJob.cc
+++ b/libqpdf/QPDFJob.cc
@@ -57,6 +57,7 @@ namespace
         size_t oi_min_height;
         size_t oi_min_area;
         QPDFObjectHandle image;
+        std::shared_ptr<Pl_DCT::CompressConfig> config;
     };
 
     class DiscardContents: public QPDFObjectHandle::ParserCallbacks
@@ -115,6 +116,7 @@ ImageOptimizer::ImageOptimizer(
     oi_min_area(oi_min_area),
     image(image)
 {
+    config = Pl_DCT::make_compress_config([](jpeg_compress_struct* config) {});
 }
 
 std::shared_ptr<Pipeline>
@@ -195,7 +197,7 @@ ImageOptimizer::makePipeline(std::string const& description, Pipeline* next)
         return result;
     }
 
-    result = std::make_shared<Pl_DCT>("jpg", next, w, h, components, cs);
+    result = std::make_shared<Pl_DCT>("jpg", next, w, h, components, cs, config.get());
     return result;
 }
 
diff --git a/libtests/dct_compress.cc b/libtests/dct_compress.cc
index 0042894..c5f8396 100644
--- a/libtests/dct_compress.cc
+++ b/libtests/dct_compress.cc
@@ -1,6 +1,7 @@
 #include <qpdf/Pl_DCT.hh>
 #include <qpdf/Pl_StdioFile.hh>
 #include <qpdf/QUtil.hh>
+#include <qpdf/assert_test.h>
 
 #include <cstdio>
 #include <cstdlib>
@@ -50,12 +51,16 @@ main(int argc, char* argv[])
     FILE* infile = QUtil::safe_fopen(infilename, "rb");
     FILE* outfile = QUtil::safe_fopen(outfilename, "wb");
     Pl_StdioFile out("stdout", outfile);
+    bool called = false;
+    auto callback = [&called](jpeg_compress_struct*) { called = true; };
+    auto config = Pl_DCT::make_compress_config(callback);
     unsigned char buf[100];
-    Pl_DCT dct("dct", &out, width, height, components, cs);
+    Pl_DCT dct("dct", &out, width, height, components, cs, config.get());
     while (size_t len = fread(buf, 1, sizeof(buf), infile)) {
         dct.write(buf, len);
     }
     dct.finish();
+    assert(called);
 
     fclose(infile);
     fclose(outfile);
diff --git a/manual/release-notes.rst b/manual/release-notes.rst
index 168d40f..cb22412 100644
--- a/manual/release-notes.rst
+++ b/manual/release-notes.rst
@@ -38,6 +38,12 @@ more detail.
       unencrypted. qpdf has always incorrectly handled all
       ``/Metadata`` streams as special with cleartext metadata.
 
+  - Library Enhancements
+
+    - Add function ``Pl_DCT::make_compress_config`` to return a
+      ``Pl_DCT::CompressConfig`` shared pointer from a
+      ``std::function`` for a more modern configuration option.
+
   - CLI Enhancements
 
     - New :qpdf:ref:`--remove-structure` option to exclude the document
--
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