Add a JournaldLogger

As proposed in #8857, this adds a Logger subclass that writes structured
log messages via journald's native protocol by calling sd_journal_sendv.
The feature therefore depends on the systemd library. sd_journal_sendv is
available since the early days (systemd v38), so a version check is
probably superflous.

We add the following fields to each record:
- MESSAGE: The log message
- PRIORITY (aka severity): Numeric severity as in RFC5424 section 6.2.1
- SYSLOG_FACILITY: Numeric facility as in RFC5424 section 6.2.1
- SYSLOG_IDENTIFIER: If provided, use value from configuration.
  Else use systemd's default behaior, which is to determine the field
  by using libc's program_invocation_short_name, resulting in "icinga2".
- ICINGA2_FACILITY: Facility as in Log::Log(..., String facility, ...),
  e.g. "ApiListener"
- some more fields are added automatically by systemd

Fields are stored indexed, so we can do fast queries for certain field
values. Example:

$ journalctl -t icinga2 ICINGA2_FACILITY=ApiListener -n 5

Syslog compatiblity is ratained because good old tag, severity and facility
is stored along, and systemd can forward to syslog daemons.

See also https://systemd.io/JOURNAL_NATIVE_PROTOCOL/.

lib/base/CMakeLists.txt

@@ -6,6 +6,7 @@ mkclass_target(configuration.ti configuration-ti.cpp configuration-ti.hpp)
 mkclass_target(datetime.ti datetime-ti.cpp datetime-ti.hpp)
 mkclass_target(filelogger.ti filelogger-ti.cpp filelogger-ti.hpp)
 mkclass_target(function.ti function-ti.cpp function-ti.hpp)
+mkclass_target(journaldlogger.ti journaldlogger-ti.cpp journaldlogger-ti.hpp)
 mkclass_target(logger.ti logger-ti.cpp logger-ti.hpp)
 mkclass_target(perfdatavalue.ti perfdatavalue-ti.cpp perfdatavalue-ti.hpp)
 mkclass_target(streamlogger.ti streamlogger-ti.cpp streamlogger-ti.hpp)
@@ -36,6 +37,7 @@ set(base_SOURCES
   function.cpp function.hpp function-ti.hpp function-script.cpp functionwrapper.hpp
   initialize.cpp initialize.hpp
   io-engine.cpp io-engine.hpp
+  journaldlogger.cpp journaldlogger.hpp journaldlogger-ti.hpp
   json.cpp json.hpp json-script.cpp
   lazy-init.hpp
   library.cpp library.hpp
@@ -123,6 +125,7 @@ if(HAVE_SYSTEMD)
     NAMES systemd/sd-daemon.h
     HINTS ${SYSTEMD_ROOT_DIR})
   include_directories(${SYSTEMD_INCLUDE_DIR})
+  add_definitions(-DSD_JOURNAL_SUPPRESS_LOCATION)
 endif()
 
 add_library(base OBJECT ${base_SOURCES})

lib/base/journaldlogger.cpp

@@ -0,0 +1,87 @@
+/* Icinga 2 | (c) 2021 Icinga GmbH | GPLv2+ */
+
+#include "base/i2-base.hpp"
+#if !defined(_WIN32) && defined(HAVE_SYSTEMD)
+#include "base/journaldlogger.hpp"
+#include "base/journaldlogger-ti.cpp"
+#include "base/configtype.hpp"
+#include "base/statsfunction.hpp"
+#include "base/sysloglogger.hpp"
+#include <systemd/sd-journal.h>
+
+using namespace icinga;
+
+REGISTER_TYPE(JournaldLogger);
+
+REGISTER_STATSFUNCTION(JournaldLogger, &JournaldLogger::StatsFunc);
+
+void JournaldLogger::StatsFunc(const Dictionary::Ptr& status, const Array::Ptr&)
+{
+	DictionaryData nodes;
+
+	for (const JournaldLogger::Ptr& journaldlogger : ConfigType::GetObjectsByType<JournaldLogger>()) {
+		nodes.emplace_back(journaldlogger->GetName(), 1); //add more stats
+	}
+
+	status->Set("journaldlogger", new Dictionary(std::move(nodes)));
+}
+
+void JournaldLogger::OnConfigLoaded()
+{
+	ObjectImpl<JournaldLogger>::OnConfigLoaded();
+	m_ConfiguredJournalFields.clear();
+	m_ConfiguredJournalFields.push_back(
+		String("SYSLOG_FACILITY=") + Value(SyslogHelper::FacilityToNumber(GetFacility())));
+	const String identifier = GetIdentifier();
+	if (!identifier.IsEmpty()) {
+		m_ConfiguredJournalFields.push_back(String("SYSLOG_IDENTIFIER=" + identifier));
+	}
+}
+
+void JournaldLogger::ValidateFacility(const Lazy<String>& lvalue, const ValidationUtils& utils)
+{
+	ObjectImpl<JournaldLogger>::ValidateFacility(lvalue, utils);
+	if (!SyslogHelper::ValidateFacility(lvalue()))
+		BOOST_THROW_EXCEPTION(ValidationError(this, { "facility" }, "Invalid facility specified."));
+}
+
+/**
+ * Processes a log entry and outputs it to journald.
+ *
+ * @param entry The log entry.
+ */
+void JournaldLogger::ProcessLogEntry(const LogEntry& entry)
+{
+	const std::vector<String> sdFields {
+		String("MESSAGE=") + entry.Message.GetData(),
+		String("PRIORITY=") + Value(SyslogHelper::SeverityToNumber(entry.Severity)),
+		String("ICINGA2_FACILITY=") + entry.Facility,
+	};
+	SystemdJournalSend(sdFields);
+}
+
+void JournaldLogger::Flush()
+{
+	/* Nothing to do here. */
+}
+
+void JournaldLogger::SystemdJournalSend(const std::vector<String>& varJournalFields) const
+{
+	struct iovec iovec[m_ConfiguredJournalFields.size() + varJournalFields.size()];
+	int iovecCount = 0;
+
+	for (const String& journalField: m_ConfiguredJournalFields) {
+		iovec[iovecCount] = IovecFromString(journalField);
+		iovecCount++;
+	}
+	for (const String& journalField: varJournalFields) {
+		iovec[iovecCount] = IovecFromString(journalField);
+		iovecCount++;
+	}
+	sd_journal_sendv(iovec, iovecCount);
+}
+
+struct iovec JournaldLogger::IovecFromString(const String& s) {
+	return { const_cast<char *>(s.CStr()), s.GetLength() };
+}
+#endif /* !_WIN32 && HAVE_SYSTEMD */

lib/base/journaldlogger.hpp

@@ -0,0 +1,44 @@
+/* Icinga 2 | (c) 2021 Icinga GmbH | GPLv2+ */
+
+#ifndef JOURNALDLOGGER_H
+#define JOURNALDLOGGER_H
+
+#include "base/i2-base.hpp"
+#if !defined(_WIN32) && defined(HAVE_SYSTEMD)
+#include "base/journaldlogger-ti.hpp"
+#include <sys/uio.h>
+
+namespace icinga
+{
+
+/**
+ * A logger that logs to systemd journald.
+ *
+ * @ingroup base
+ */
+class JournaldLogger final : public ObjectImpl<JournaldLogger>
+{
+public:
+	DECLARE_OBJECT(JournaldLogger);
+	DECLARE_OBJECTNAME(JournaldLogger);
+
+	static void StaticInitialize();
+	static void StatsFunc(const Dictionary::Ptr& status, const Array::Ptr& perfdata);
+
+	void OnConfigLoaded() override;
+	void ValidateFacility(const Lazy<String>& lvalue, const ValidationUtils& utils) override;
+
+protected:
+	void SystemdJournalSend(const std::vector<String>& varJournalFields) const;
+	static struct iovec IovecFromString(const String& s);
+
+	std::vector<String> m_ConfiguredJournalFields;
+
+	void ProcessLogEntry(const LogEntry& entry) override;
+	void Flush() override;
+};
+
+}
+#endif /* !_WIN32 && HAVE_SYSTEMD */
+
+#endif /* JOURNALDLOGGER_H */

lib/base/journaldlogger.ti

@@ -0,0 +1,21 @@
+/* Icinga 2 | (c) 2021 Icinga GmbH | GPLv2+ */
+
+#include "base/logger.hpp"
+
+library base;
+
+namespace icinga
+{
+
+class JournaldLogger : Logger
+{
+	activation_priority -100;
+
+	[config] String facility {
+		default {{{ return "LOG_USER"; }}}
+	};
+
+	[config] String identifier;
+};
+
+}