Add a declaration for XSI-compliant strerror_r

- This is to ensure that compilation will not be dependent
  on GNU extensions being enabled.

- A new source file has to be added, because one cannot simply
  undef _GNU_SOURCE in Systemd.cpp - it will cause the a failure
  to compile - something in the logging framework depends
  on GNU extensions.

Author: shenghaoyang

configure.ac

@@ -755,7 +755,8 @@ AC_ARG_ENABLE(
 
 have_libsystemd="no"
 AS_IF([test "x$enable_systemd" != "xno"],
-  [PKG_CHECK_MODULES([libsystemd], [libsystemd >= 38], [have_libsystemd="yes"])
+  [PKG_CHECK_MODULES([libsystemd], [libsystemd >= 38], [have_libsystemd="yes"], 
+                     [AC_MSG_WARN([disabling systemd support: can't find libsystemd])])
    AC_CHECK_HEADER([systemd/sd-daemon.h], [],
                    [have_libsystemd="no"
                     AC_MSG_WARN([disabling systemd support: can't find systemd/sd-daemon.h])])

olad/Makefile.mk

@@ -43,7 +43,8 @@ ola_server_additional_libs += common/http/libolahttp.la
 endif
 
 if HAVE_LIBSYSTEMD
-ola_server_sources += olad/Systemd.cpp olad/Systemd.h
+ola_server_sources += olad/Strerror_r.cpp olad/Strerror_r.h \
+                      olad/Systemd.cpp olad/Systemd.h
 ola_server_additional_libs += $(libsystemd_LIBS)
 endif
 

olad/Strerror_r.cpp

@@ -0,0 +1,49 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Strerror_r.cpp
+ * Definition of strerror_r that is XSI-compliant.
+ * Copyright (C) 2018 Shenghao Yang
+ */
+
+#if HAVE_CONFIG_H
+#include <config.h>
+#endif  // HAVE_CONFIG_H
+
+// Required for string.h to declare the standards-compliant version of
+// strerror_r(), when compiling under glibc. Must come before the inclusion
+// of string.h.
+// These are conditional to avoid errors when not compiling with glibc, or
+// when compiling with a compiler that does not define _POSIX_C_SOURCE.
+#ifdef _GNU_SOURCE
+#undef _GNU_SOURCE
+#endif
+
+#ifdef _POSIX_C_SOURCE
+#undef _POSIX_C_SOURCE
+#endif
+#define _POSIX_C_SOURCE 200112L
+
+#include <string.h>
+
+#include "olad/Strerror_r.h"
+
+namespace ola {
+
+int Strerror_r(int errnum, char* buf, size_t buflen) {
+  return strerror_r(errnum, buf, buflen);
+}
+
+}  // namespace ola

olad/Strerror_r.h

@@ -0,0 +1,35 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Strerror_r.h
+ * Declaration of strerror_r that is XSI-compliant.
+ * Copyright (C) 2018 Shenghao Yang
+ */
+
+#ifndef OLAD_STRERROR_R_H_
+#define OLAD_STRERROR_R_H_
+
+namespace ola {
+
+/*
+ * @brief XSI-compliant version of @ref strerror_r()
+ 
+ * See strerror(3) for more details.
+ */
+int Strerror_r(int errnum, char* buf, size_t buflen);
+
+}  // namespace ola
+
+#endif  // OLAD_STRERROR_R_H_

olad/Systemd.cpp

@@ -24,12 +24,11 @@
 
 #if HAVE_LIBSYSTEMD
 #include <systemd/sd-daemon.h>
-#include <errno.h>
-#include <string.h>
 #endif  // HAVE_LIBSYSTEMD
 
 #include "ola/Logging.h"
 
+#include "olad/Strerror_r.h"
 #include "olad/Systemd.h"
 
 namespace ola {
@@ -38,12 +37,12 @@ int SystemdNotify(int unset_environment, const char *state) {
   int rtn = sd_notify(unset_environment, state);
   if (rtn < 0) {
     char buf[1024];
-    // olad is compiled under GNU extensions: the return value of
-    // strerror_r() is not an error code but a pointer to a character array
-    // containing the error description. The array returned is always NUL
-    // terminated, even in case of errors, so blindly using it is not a problem.
-    OLA_WARN << "Error sending notification to systemd: "
-             << strerror_r(-rtn, buf, sizeof(buf));
+    OLA_WARN << "Error sending notification to systemd: ";
+    if (ola::Strerror_r(-rtn, buf, sizeof(buf))) {
+      OLA_WARN << "errno = " << -rtn;
+    } else {
+      OLA_WARN << buf;
+    }
   }
   return rtn;
 }