From 7c8a7176d196d4bb3724cfafd41980c16be5f404 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?louiz=E2=80=99?= <louiz@louiz.org>
Date: Fri, 12 Jan 2018 03:59:46 +0100
Subject: Only use sd_journal_* if we really are outputing to journald

We check that the device and inode numbers are actually the same as the
JOURNAL_STREAM value, instead of just checking that the value exists.

This fixes the logger unit tests
---
 src/logger/logger.cpp | 21 ++++++++++++++++++++-
 src/logger/logger.hpp |  1 +
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/logger/logger.cpp b/src/logger/logger.cpp
index 4287794..482cb18 100644
--- a/src/logger/logger.cpp
+++ b/src/logger/logger.cpp
@@ -1,6 +1,10 @@
 #include <logger/logger.hpp>
 #include <config/config.hpp>
 
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
 Logger::Logger(const int log_level):
   log_level(log_level),
   stream(std::cout.rdbuf()),
@@ -8,7 +12,22 @@ Logger::Logger(const int log_level):
   null_stream{&null_buffer}
 {
 #ifdef SYSTEMD_FOUND
-  if (::getenv("JOURNAL_STREAM") != nullptr && this->use_stdout())
+  if (!this->use_stdout())
+    return;
+
+  // See https://www.freedesktop.org/software/systemd/man/systemd.exec.html#%24JOURNAL_STREAM
+  const char* journal_stream = ::getenv("JOURNAL_STREAM");
+  if (journal_stream == nullptr)
+    return;
+
+  struct stat s{};
+  const int res = ::fstat(STDOUT_FILENO, &s);
+  if (res == -1)
+    return;
+
+  const auto stdout_stream = std::to_string(s.st_dev) + ":" + std::to_string(s.st_ino);
+
+  if (stdout_stream == journal_stream)
     this->use_systemd = true;
 #endif
 }
diff --git a/src/logger/logger.hpp b/src/logger/logger.hpp
index a99648c..1689866 100644
--- a/src/logger/logger.hpp
+++ b/src/logger/logger.hpp
@@ -9,6 +9,7 @@
  */
 
 #include <memory>
+#include <string>
 #include <iostream>
 #include <fstream>
 #include <sstream>
-- 
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