Merge pull request #4553 from VannTen/feat/native_journal_log

log: use native journald protocol for when running as a service

src/main.cpp

@@ -7,6 +7,17 @@
 #include <list>
 #include <mutex>
 
+#ifdef HAVE_LIBSYSTEMD
+#include <spdlog/sinks/systemd_sink.h>
+#include <sys/stat.h>
+
+#include <cassert>
+#include <charconv>
+#include <cstddef>
+#include <cstdlib>
+#include <system_error>
+#endif
+
 #include "bar.hpp"
 #include "client.hpp"
 #include "util/SafeSignal.hpp"
@@ -129,7 +140,7 @@ static void handleSignalMainThread(int signum, bool& reload) {
     return;
   }
 #endif
-  
+
   switch (signum) {
     case SIGUSR1:
       handleUserSignal(SIGUSR1, reload);
@@ -162,7 +173,48 @@ static void handleSignalMainThread(int signum, bool& reload) {
   }
 }
 
+static void logToJournalIfRunAsService() {
+#ifdef HAVE_LIBSYSTEMD
+  /* Implementation of automatic protocol upgrading (from stderr to journal)
+  ** as described in https://systemd.io/JOURNAL_NATIVE_PROTOCOL */
+  char const* journal_stream = std::getenv("JOURNAL_STREAM");
+
+  if (journal_stream != nullptr) {
+    dev_t device;
+    ino_t inode;
+    size_t len = std::strlen(journal_stream);
+
+    auto result = std::from_chars(journal_stream, journal_stream + len, device);
+    if (result.ec == std::errc{})
+      result = std::from_chars(result.ptr + 1, journal_stream + len, inode);
+    if (result.ec != std::errc{}) {
+      spdlog::warn("malformed JOURNAL_STREAM (\"{}\"): {}, logging to console", journal_stream,
+                   std::make_error_condition(result.ec).message());
+    }
+
+    struct stat f_stderr;
+
+    if (fstat(STDERR_FILENO, &f_stderr) != 0) {
+      spdlog::warn("unable to check stderr device and inode numbers: {}", strerror(errno));
+    } else if (device == f_stderr.st_dev && inode == f_stderr.st_ino) {
+      auto journald = spdlog::systemd_logger_st("native_journal", "waybar", false);
+      /* systemd_logger_st is thread-safe with enable_formatter = false
+      ** thanks to underlying sd_journal_send being thread-safe
+      ** https://github.com/gabime/spdlog/issues/2320#issuecomment-1079766037
+      */
+      spdlog::set_default_logger(journald);
+    } else {
+      spdlog::info("JOURNAL_STREAM does not point to stderr, logging to console");
+    }
+  } else {
+    spdlog::info("no JOURNAL_STREAM, logging to console");
+  }
+#endif
+}
+
 int main(int argc, char* argv[]) {
+  logToJournalIfRunAsService();
+
   try {
     auto* client = waybar::Client::inst();