From 2b6318e14e36b75e85d356e8d50c02c198b465a7 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 28 Jun 2019 14:04:21 +0200
Subject: Use sd_journal_print() for diagnostics when in systemd mode

---
 bbot/buildfile       |  2 ++
 bbot/diagnostics.cxx | 77 +++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 75 insertions(+), 4 deletions(-)

diff --git a/bbot/buildfile b/bbot/buildfile
index 8da2b70..f57edcb 100644
--- a/bbot/buildfile
+++ b/bbot/buildfile
@@ -36,6 +36,8 @@ if ($cxx.target.class == "linux")
                  {hxx ixx cxx}{agent-options}                          \
                  ../libue{bbot}
   }
+
+  cxx.libs += -ldl
 }
 
 ./: exe{bbot-worker}: worker/{hxx ixx txx cxx}{+worker} worker/libue{bbot}
diff --git a/bbot/diagnostics.cxx b/bbot/diagnostics.cxx
index bbdef3b..e5f5747 100644
--- a/bbot/diagnostics.cxx
+++ b/bbot/diagnostics.cxx
@@ -4,6 +4,15 @@
 
 #include <bbot/diagnostics.hxx>
 
+#ifdef __linux__
+#  define BBOT_SYSTEMD
+#endif
+
+#ifdef BBOT_SYSTEMD
+#  include <dlfcn.h>
+#  include <syslog.h> // LOG_*
+#endif
+
 #include <bbot/utility.hxx>
 
 using namespace std;
@@ -51,14 +60,73 @@ namespace bbot
 
   const fail_end endf;
 
-  // We used the right arrow Unicode character to signal line continuation.
-  // It only looked cute when displayed properly.
-  //
-  const char systemd_indent[] = " \\\n";
+#ifndef BBOT_SYSTEMD
+  void
+  systemd_diagnostics (bool)
+  {
+    fail << "systemd mode only supported on Linux";
+  }
+#else
+
+  static const char systemd_indent[] = "\n";
+
+  static const char libsystemd[] = "libsystemd.so.0";
+  static int (*sd_journal_print) (int priority, const char *format, ...);
+
+  static void (*default_writer) (const diag_record&);
+
+  static void
+  systemd_writer (const diag_record& dr)
+  {
+    const string& s (dr.os.str ());
+
+    // Map "<N>..." prefix to priority.
+    //
+    int p (-1);
+    if (s.size () > 2 && s[0] == '<' && s[2] == '>')
+    {
+      char c (s[1]);
+      p = (c == '0' ? LOG_EMERG   :
+           c == '1' ? LOG_ALERT   :
+           c == '2' ? LOG_CRIT    :
+           c == '3' ? LOG_ERR     :
+           c == '4' ? LOG_WARNING :
+           c == '5' ? LOG_NOTICE  :
+           c == '6' ? LOG_INFO    :
+           c == '7' ? LOG_DEBUG   : p);
+    }
+
+    if (p == -1 || sd_journal_print (p, "%s", s.c_str () + 3) != 0)
+      default_writer (dr);
+  }
 
   void
   systemd_diagnostics (bool with_critical)
   {
+    // Using sd_journal_print() allows us to print multi-line records nicely.
+    // However, requiring libsystemd-dev (or equivalent) is a bit of a schlep
+    // so we use the dynamic loading trick.
+    //
+    // Note that we could also fallback to stderr output (which is how it
+    // worked before) if we cannot load the library or resolve the symbol for
+    // some reason. But for now we fail to keep things simple.
+    //
+    void* libsd (dlopen (libsystemd, RTLD_LAZY | RTLD_GLOBAL));
+
+    if (libsd == nullptr)
+      fail << "unable to load " << libsystemd << ": " << dlerror ();
+
+    sd_journal_print =
+      function_cast<decltype(sd_journal_print)> (
+        dlsym (libsd, "sd_journal_print"));
+
+    if (sd_journal_print == nullptr)
+      fail << "unable to lookup sd_journal_print() in " << libsystemd << ": "
+           << dlerror ();
+
+    default_writer = diag_record::writer;
+    diag_record::writer = &systemd_writer;
+
     trace_indent    =
       fail.indent_  =
       error.indent_ =
@@ -74,6 +142,7 @@ namespace bbot
     info.type_  = "<6>";
     trace_type  = "<7>";
   }
+#endif
 
   // tracer
   //
-- 
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