Fix timezone portability issue (fixes #515)

ChangeLog

@@ -1,3 +1,10 @@
+2021-04-17  Jay Berkenbilt  <ejb@ql.org>
+
+	* Portability fix: use tm_gmtoff rather than global timezone
+	variable if available to get timezone offset. This fixes
+	compilation on BSD and also results in a daylight saving
+	time-aware offset for Linux or other GNU systems. Fixes #515.
+
 2021-04-05  Jay Berkenbilt  <ejb@ql.org>
 
 	* When adding a page, if the page already exists, make a shallow

autofiles.sums

@@ -1,6 +1,6 @@
-e98dd9c0e2040a128e0bae722821ca1183bd965405d654fb061474a3bddc2327  configure.ac
+04144cd524b4278d6e3c3e0340cf03400daceaf1a241031c1053f8da544d1042  configure.ac
 d3f9ee6f6f0846888d9a10fd3dad2e4b1258be84205426cf04d7cef02d61dad7  aclocal.m4
-3ed561073f0d5c9899e2120e006a7da5ec6bffb80268da1b962cd4f893b89982  libqpdf/qpdf/qpdf-config.h.in
+c12d837479fa9a3fa4c278b6dc7d6b449503d663e0f0d294305595a51ff43f70  libqpdf/qpdf/qpdf-config.h.in
 5297971a0ef90bcd5563eb3f7127a032bb76d3ae2af7258bf13479caf8983a60  m4/ax_cxx_compile_stdcxx.m4
 35bc5c645dc42d47f2daeea06f8f3e767c8a1aee6a35eb2b4854fd2ce66c3413  m4/ax_random_device.m4
 1451e63710701b5f00a668f3a79b435015ef2e63547f0ad0ce8c8c062d53b599  m4/libtool.m4

configure

@@ -17830,6 +17830,78 @@ $as_echo "no" >&6; }
    fi
 fi
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for tm_gmtoff in struct tm" >&5
+$as_echo_n "checking for tm_gmtoff in struct tm... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+      #include <time.h>
+
+int
+main ()
+{
+
+      struct tm tm;
+      tm.tm_gmtoff = 1;
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  qpdf_TM_GMTOFF=1
+else
+  qpdf_TM_GMTOFF=0
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+if test "$qpdf_TM_GMTOFF" = "1"; then
+   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+$as_echo "#define HAVE_TM_GMTOFF 1" >>confdefs.h
+
+else
+   { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for extern long timezone" >&5
+$as_echo_n "checking for extern long timezone... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+      #include <time.h>
+      #include <stdio.h>
+
+int
+main ()
+{
+
+      tzset();
+      printf("%ld\n", timezone);
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  qpdf_EXTERN_LONG_TIMEZONE=1
+else
+  qpdf_EXTERN_LONG_TIMEZONE=0
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+if test "$qpdf_EXTERN_LONG_TIMEZONE" = "1"; then
+   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+
+$as_echo "#define HAVE_EXTERN_LONG_TIMEZONE 1" >>confdefs.h
+
+else
+   { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
 LL_FMT=""
 oCFLAGS=$CFLAGS
 CFLAGS="$WFLAGS $CFLAGS"

configure.ac

@@ -520,6 +520,35 @@ if test "$BUILDRULES" != "msvc"; then
    fi
 fi
 
+AC_MSG_CHECKING(for tm_gmtoff in struct tm)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+      #include <time.h>
+   ]],[[
+      struct tm tm;
+      tm.tm_gmtoff = 1;
+   ]])], [qpdf_TM_GMTOFF=1], [qpdf_TM_GMTOFF=0])
+if test "$qpdf_TM_GMTOFF" = "1"; then
+   AC_MSG_RESULT(yes)
+   AC_DEFINE([HAVE_TM_GMTOFF], [1], [Whether struct tm has tm_gmtoff])
+else
+   AC_MSG_RESULT(no)
+fi
+
+AC_MSG_CHECKING(for extern long timezone)
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+      #include <time.h>
+      #include <stdio.h>
+   ]],[[
+      tzset();
+      printf("%ld\n", timezone);
+   ]])], [qpdf_EXTERN_LONG_TIMEZONE=1], [qpdf_EXTERN_LONG_TIMEZONE=0])
+if test "$qpdf_EXTERN_LONG_TIMEZONE" = "1"; then
+   AC_MSG_RESULT(yes)
+   AC_DEFINE([HAVE_EXTERN_LONG_TIMEZONE], [1], [Whether extern long timezone is available])
+else
+   AC_MSG_RESULT(no)
+fi
+
 LL_FMT=""
 oCFLAGS=$CFLAGS
 CFLAGS="$WFLAGS $CFLAGS"

libqpdf/QUtil.cc

@@ -889,6 +889,7 @@ QUtil::get_current_qpdf_time()
                     static_cast<int>(ltime.wHour),
                     static_cast<int>(ltime.wMinute),
                     static_cast<int>(ltime.wSecond),
+                    // tzinfo.Bias is minutes before UTC
                     static_cast<int>(tzinfo.Bias));
 #else
     struct tm ltime;
@@ -898,6 +899,16 @@ QUtil::get_current_qpdf_time()
     localtime_r(&now, &ltime);
 #else
     ltime = *localtime(&now);
+#endif
+#if HAVE_TM_GMTOFF
+    // tm_gmtoff is seconds after UTC
+    int tzoff = -static_cast<int>(ltime.tm_gmtoff / 60);
+#elif HAVE_EXTERN_LONG_TIMEZONE
+    // timezone is seconds before UTC, not adjusted for daylight saving time
+    int tzoff = static_cast<int>(timezone / 60);
+#else
+    // Don't know how to get timezone on this platform
+    int tzoff = 0;
 #endif
     return QPDFTime(static_cast<int>(ltime.tm_year + 1900),
                     static_cast<int>(ltime.tm_mon + 1),
@@ -905,7 +916,7 @@ QUtil::get_current_qpdf_time()
                     static_cast<int>(ltime.tm_hour),
                     static_cast<int>(ltime.tm_min),
                     static_cast<int>(ltime.tm_sec),
-                    static_cast<int>(timezone / 60));
+                    tzoff);
 #endif
 }
 

libqpdf/qpdf/qpdf-config.h.in

@@ -12,6 +12,9 @@
 /* Define to 1 if you have the <dlfcn.h> header file. */
 #undef HAVE_DLFCN_H
 
+/* Whether extern long timezone is available */
+#undef HAVE_EXTERN_LONG_TIMEZONE
+
 /* Define to 1 if fseeko (and presumably ftello) exists and is declared. */
 #undef HAVE_FSEEKO
 
@@ -51,6 +54,9 @@
 /* Define to 1 if you have the <sys/types.h> header file. */
 #undef HAVE_SYS_TYPES_H
 
+/* Whether struct tm has tm_gmtoff */
+#undef HAVE_TM_GMTOFF
+
 /* Define to 1 if you have the <unistd.h> header file. */
 #undef HAVE_UNISTD_H