From c3e2a69bd600fa4c4a9d4603094f39ea81c11116 Mon Sep 17 00:00:00 2001
From: Florian Forster <octo@collectd.org>
Date: Sun, 7 May 2017 20:34:09 +0200
Subject: [PATCH] bind plugin: Use timegm() to convert to time_t if available.

FreeBSD doesn't provide the "extern long timezone", presumably because
it's "only" an XSI extension, leading to a portability issue with the
previous approach.

timegm() is a non-standard function available in GNU's and BSD's libc
which is doing exactly what we need. The previous code is left as a
fallback.

Fixes: #1268
---
 configure.ac | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/bind.c   | 32 ++++++++++++++++++++--
 2 files changed, 116 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 5a265c75..98f0a907 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1046,6 +1046,92 @@ then
 fi
 # }}} Check for strptime
 
+# Check for timegm {{{
+
+# These checks need -Werror because implicit function declarations are only a
+# warning ...
+SAVE_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -Werror"
+
+AC_CACHE_CHECK([for timegm],
+  [c_cv_have_timegm],
+  AC_LINK_IFELSE(
+    [AC_LANG_PROGRAM(
+[[[
+#if STRPTIME_NEEDS_STANDARDS
+# ifndef _ISOC99_SOURCE
+#  define _ISOC99_SOURCE 1
+# endif
+# ifndef _POSIX_C_SOURCE
+#  define _POSIX_C_SOURCE 200112L
+# endif
+# ifndef _XOPEN_SOURCE
+#  define _XOPEN_SOURCE 500
+# endif
+#endif
+#include <time.h>
+]]],
+[[[
+ time_t t = timegm(&(struct tm){0});
+ if (t == ((time_t) -1)) {
+   return 1;
+ }
+]]]
+    )],
+    [c_cv_have_timegm="yes"],
+    [c_cv_have_timegm="no"]
+  )
+)
+
+if test "x$c_cv_have_timegm" != "xyes"
+then
+  AC_CACHE_CHECK([for timegm with _BSD_SOURCE],
+    [c_cv_have_timegm_bsd],
+    AC_LINK_IFELSE(
+      [AC_LANG_PROGRAM(
+[[[
+#if STRPTIME_NEEDS_STANDARDS
+# ifndef _ISOC99_SOURCE
+#  define _ISOC99_SOURCE 1
+# endif
+# ifndef _POSIX_C_SOURCE
+#  define _POSIX_C_SOURCE 200112L
+# endif
+# ifndef _XOPEN_SOURCE
+#  define _XOPEN_SOURCE 500
+# endif
+#endif
+#ifndef _BSD_SOURCE
+# define _BSD_SOURCE 1
+#endif
+#include <time.h>
+]]],
+[[[
+ time_t t = timegm(&(struct tm){0});
+ if (t == ((time_t) -1)) {
+   return 1;
+ }
+]]]
+      )],
+      [c_cv_have_timegm_bsd="yes"
+       c_cv_have_timegm="yes"],
+      [c_cv_have_timegm_bsd="no"]
+    )
+  )
+fi
+
+if test "x$c_cv_have_timegm" = "xyes"
+then
+  AC_DEFINE(HAVE_TIMEGM, 1, [Define if the timegm(3) function is available.])
+  if test "x$c_cv_have_timegm_bsd" = "xyes"
+  then
+    AC_DEFINE(TIMEGM_NEEDS_BSD, 1, [Set to true if timegm is only exported in BSD mode.])
+  fi
+fi
+
+CFLAGS="$SAVE_CFLAGS"
+# }}} Check for timegm
+
 AC_CHECK_FUNCS(swapctl, [have_swapctl="yes"], [have_swapctl="no"])
 if test "x$have_swapctl" = "xyes"; then
         AC_CACHE_CHECK([whether swapctl takes two arguments],
diff --git a/src/bind.c b/src/bind.c
index 597b90d3..4860f1b6 100644
--- a/src/bind.c
+++ b/src/bind.c
@@ -35,11 +35,19 @@
 #endif
 #endif /* STRPTIME_NEEDS_STANDARDS */
 
+#if TIMEGM_NEEDS_BSD
+#ifndef _BSD_SOURCE
+#define _BSD_SOURCE 1
+#endif
+#endif /* TIMEGM_NEEDS_BSD */
+
 #include "collectd.h"
 
 #include "common.h"
 #include "plugin.h"
 
+#include <time.h>
+
 /* Some versions of libcurl don't include this themselves and then don't have
  * fd_set available. */
 #if HAVE_SYS_SELECT_H
@@ -433,8 +441,28 @@ static int bind_xml_read_timestamp(const char *xpath_expression, /* {{{ */
     return (-1);
   }
 
-  tzset();
-  *ret_value = mktime(&tm) - timezone;  /* fix strptime() misinterpretation */
+#if HAVE_TIMEGM
+  time_t t = timegm(&tm);
+  if (t == ((time_t)-1)) {
+    char errbuf[1024];
+    ERROR("bind plugin: timegm() failed: %s",
+          sstrerror(errno, errbuf, sizeof(errbuf)));
+    return (-1);
+  }
+  *ret_value = t;
+#else
+  time_t t = mktime(&tm);
+  if (t == ((time_t)-1)) {
+    char errbuf[1024];
+    ERROR("bind plugin: mktime() failed: %s",
+          sstrerror(errno, errbuf, sizeof(errbuf)));
+    return (-1);
+  }
+  /* mktime assumes that tm is local time. Luckily, it also sets timezone to
+   * the offset used for the conversion, and we undo the conversion to convert
+   * back to UTC. */
+  *ret_value = t - timezone;
+#endif
 
   xmlXPathFreeObject(xpathObj);
   return (0);
-- 
2.11.0