From 09df396931c285586eb0335f69de69f0672339bc Mon Sep 17 00:00:00 2001
From: m-holger <m.holger@qpdf.org>
Date: Fri, 4 Jul 2025 14:46:22 +0100
Subject: [PATCH] Refactor `EncryptionParameters` to encapsulate crypt filter interpretation logic, transition `interpretCF` to a class method, and eliminate redundant parameter passing for improved clarity and maintainability.

---
 include/qpdf/QPDF.hh         |  1 -
 libqpdf/QPDF_encryption.cc   | 36 ++++++++++++++++++------------------
 libqpdf/qpdf/QPDF_private.hh |  3 +++
 3 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/include/qpdf/QPDF.hh b/include/qpdf/QPDF.hh
index fb79314..6ec3215 100644
--- a/include/qpdf/QPDF.hh
+++ b/include/qpdf/QPDF.hh
@@ -964,7 +964,6 @@ class QPDF
     void insertPageobjToPage(QPDFObjectHandle const& obj, int pos, bool check_duplicate);
 
     // methods to support encryption -- implemented in QPDF_encryption.cc
-    static encryption_method_e interpretCF(EncryptionParameters& encp, QPDFObjectHandle const& cf);
     void initializeEncryption();
     static std::string
     getKeyForObject(std::shared_ptr<EncryptionParameters> encp, QPDFObjGen og, bool use_aes);
diff --git a/libqpdf/QPDF_encryption.cc b/libqpdf/QPDF_encryption.cc
index 678d079..15690ca 100644
--- a/libqpdf/QPDF_encryption.cc
+++ b/libqpdf/QPDF_encryption.cc
@@ -687,21 +687,21 @@ QPDF::EncryptionData::recover_encryption_key_with_password(
 }
 
 QPDF::encryption_method_e
-QPDF::interpretCF(EncryptionParameters& encp, QPDFObjectHandle const& cf)
+QPDF::EncryptionParameters::interpretCF(QPDFObjectHandle const& cf) const
 {
-    if (cf.isName()) {
-        std::string filter = cf.getName();
-        auto it = encp.crypt_filters.find(filter);
-        if (it != encp.crypt_filters.end()) {
-            return it->second;
-        }
-        if (filter == "/Identity") {
-            return e_none;
-        }
-        return e_unknown;
+    if (!cf.isName()) {
+        // Default: /Identity
+        return e_none;
+    }
+    std::string filter = cf.getName();
+    auto it = crypt_filters.find(filter);
+    if (it != crypt_filters.end()) {
+        return it->second;
+    }
+    if (filter == "/Identity") {
+        return e_none;
     }
-    // Default: /Identity
-    return e_none;
+    return e_unknown;
 }
 
 void
@@ -873,8 +873,8 @@ QPDF::EncryptionParameters::initialize(QPDF& qpdf)
             }
         }
 
-        cf_stream = interpretCF(*this, encryption_dict.getKey("/StmF"));
-        cf_string = interpretCF(*this, encryption_dict.getKey("/StrF"));
+        cf_stream = interpretCF(encryption_dict.getKey("/StmF"));
+        cf_string = interpretCF(encryption_dict.getKey("/StrF"));
         if (auto EFF = encryption_dict.getKey("/EFF"); EFF.isName()) {
             // qpdf does not use this for anything other than informational purposes. This is
             // intended to instruct conforming writers on which crypt filter should be used when new
@@ -885,7 +885,7 @@ QPDF::EncryptionParameters::initialize(QPDF& qpdf)
             // the way I was imagining. Still, providing this information could be useful when
             // looking at a file generated by something else, such as Acrobat when specifying that
             // only attachments should be encrypted.
-            cf_file = interpretCF(*this, EFF);
+            cf_file = interpretCF(EFF);
         } else {
             cf_file = cf_stream;
         }
@@ -1052,7 +1052,7 @@ QPDF::decryptStream(
                 QPDFObjectHandle decode_parms = stream_dict.getKey("/DecodeParms");
                 if (decode_parms.isDictionaryOfType("/CryptFilterDecodeParms")) {
                     QTC::TC("qpdf", "QPDF_encryption stream crypt filter");
-                    method = interpretCF(*encp, decode_parms.getKey("/Name"));
+                    method = encp->interpretCF(decode_parms.getKey("/Name"));
                     method_source = "stream's Crypt decode parameters";
                 }
             } else if (
@@ -1067,7 +1067,7 @@ QPDF::decryptStream(
                             if (crypt_params.isDictionary() &&
                                 crypt_params.getKey("/Name").isName()) {
                                 QTC::TC("qpdf", "QPDF_encrypt crypt array");
-                                method = interpretCF(*encp, crypt_params.getKey("/Name"));
+                                method = encp->interpretCF(crypt_params.getKey("/Name"));
                                 method_source = "stream's Crypt decode parameters (array)";
                             }
                         }
diff --git a/libqpdf/qpdf/QPDF_private.hh b/libqpdf/qpdf/QPDF_private.hh
index 40e3311..f6be303 100644
--- a/libqpdf/qpdf/QPDF_private.hh
+++ b/libqpdf/qpdf/QPDF_private.hh
@@ -187,8 +187,11 @@ class QPDF::EncryptionParameters
   public:
     EncryptionParameters() = default;
 
+    encryption_method_e interpretCF(QPDFObjectHandle const& cf) const;
+
   private:
     void initialize(QPDF& qpdf);
+
     bool encrypted{false};
     bool encryption_initialized{false};
     int encryption_P{0};
--
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