From 8cf7f2bfb542b1583aa525611179d1a545f945d5 Mon Sep 17 00:00:00 2001
From: Jay Berkenbilt <ejb@ql.org>
Date: Sat, 5 Feb 2022 08:26:32 -0500
Subject: [PATCH] API contract: qpdf_get_qpdf_version() returns a static

---
 ChangeLog             | 3 +++
 include/qpdf/QPDF.hh  | 2 +-
 include/qpdf/qpdf-c.h | 4 +++-
 libqpdf/QPDF.cc       | 5 ++++-
 libqpdf/qpdf-c.cc     | 1 +
 5 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index db2faa7f..3bc733e0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2022-02-05  Jay Berkenbilt  <ejb@ql.org>
 
+	* Add comments letting people know that the version string
+	returned by QPDF::QPDFVersion and qpdf_get_qpdf_version is static.
+
 	* Add QUtil::make_unique_cstr to return a std::unique_ptr<char[]>
 	as an alternative to QUtil::copy_string and
 	QUtil::make_shared_cstr.
diff --git a/include/qpdf/QPDF.hh b/include/qpdf/QPDF.hh
index b26fc805..5d3fd651 100644
--- a/include/qpdf/QPDF.hh
+++ b/include/qpdf/QPDF.hh
@@ -773,7 +773,7 @@ class QPDF
     friend class Pipe;
 
   private:
-    static std::string qpdf_version;
+    static std::string const qpdf_version;
 
     class ObjCache
     {
diff --git a/include/qpdf/qpdf-c.h b/include/qpdf/qpdf-c.h
index a6fc82ae..5a0595b2 100644
--- a/include/qpdf/qpdf-c.h
+++ b/include/qpdf/qpdf-c.h
@@ -171,7 +171,9 @@ extern "C" {
     QPDF_DLL
     void qpdf_silence_errors(qpdf_data qpdf);
 
-    /* Returns the version of the qpdf software */
+    /* Returns the version of the qpdf software. This is guaranteed to
+     * be a static value.
+     */
     QPDF_DLL
     char const* qpdf_get_qpdf_version();
 
diff --git a/libqpdf/QPDF.cc b/libqpdf/QPDF.cc
index ce534d6e..565c73f6 100644
--- a/libqpdf/QPDF.cc
+++ b/libqpdf/QPDF.cc
@@ -26,7 +26,9 @@
 #include <qpdf/QPDF_Stream.hh>
 #include <qpdf/QPDF_Array.hh>
 
-std::string QPDF::qpdf_version(QPDF_VERSION);
+// This must be a fixed value. This API returns a const reference to
+// it, and the C API relies on its being static as well.
+std::string const QPDF::qpdf_version(QPDF_VERSION);
 
 static char const* EMPTY_PDF =
     "%PDF-1.3\n"
@@ -178,6 +180,7 @@ QPDF::StringDecrypter::decryptString(std::string& val)
 std::string const&
 QPDF::QPDFVersion()
 {
+    // The C API relies on this being a static value.
     return QPDF::qpdf_version;
 }
 
diff --git a/libqpdf/qpdf-c.cc b/libqpdf/qpdf-c.cc
index 6f03a315..f03ed845 100644
--- a/libqpdf/qpdf-c.cc
+++ b/libqpdf/qpdf-c.cc
@@ -161,6 +161,7 @@ static QPDF_ERROR_CODE trap_errors(
 char const* qpdf_get_qpdf_version()
 {
     QTC::TC("qpdf", "qpdf-c called qpdf_get_qpdf_version");
+    // The API guarantees that this is a static value.
     return QPDF::QPDFVersion().c_str();
 }