output/null: Add the null output device

This commit adds the null output device; to use, set the filetype
to "nullsink" for each output that should discard and never persist
logs/alerts/etc.

This is implemented as an "internal eve output plugin" just like the
syslog eve output type.

src/Makefile.am

@@ -386,6 +386,7 @@ noinst_HEADERS = \
 	log-tlslog.h \
 	log-tlsstore.h \
 	output-eve-stream.h \
+	output-eve-null.h \
 	output-filedata.h \
 	output-file.h \
 	output-filestore.h \
@@ -1039,6 +1040,7 @@ libsuricata_c_a_SOURCES = \
 	output-json-tftp.c \
 	output-json-tls.c \
 	output-eve-syslog.c \
+	output-eve-null.c \
 	output-lua.c \
 	output-packet.c \
 	output-stats.c \

src/output-eve-null.c

@@ -0,0 +1,85 @@
+/* Copyright (C) 2023 Open Information Security Foundation
+ *
+ * You can copy, redistribute or modify this Program under the terms of
+ * the GNU General Public License version 2 as published by the Free
+ * Software Foundation.
+ *
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * version 2 along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+/**
+ * \file
+ *
+ * \author Jeff Lucovsky <jlucovsky@oisf.net>
+ *
+ * File-like output for logging: null/discard device
+ */
+
+#include "suricata-common.h" /* errno.h, string.h, etc. */
+
+#include "output.h" /* DEFAULT_LOG_* */
+#include "output-eve-null.h"
+
+#ifdef OS_WIN32
+void NullLogInitialize(void)
+{
+}
+#else /* !OS_WIN32 */
+
+#define OUTPUT_NAME "nullsink"
+
+static int NullLogInit(ConfNode *conf, bool threaded, void **init_data)
+{
+    *init_data = NULL;
+    return 0;
+}
+
+static int NullLogWrite(const char *buffer, int buffer_len, void *init_data, void *thread_data)
+{
+    return 0;
+}
+
+static int NullLogThreadInit(void *init_data, int thread_id, void **thread_data)
+{
+    *thread_data = NULL;
+    return 0;
+}
+
+static int NullLogThreadDeInit(void *init_data, void *thread_data)
+{
+    return 0;
+}
+
+static void NullLogDeInit(void *init_data)
+{
+}
+
+void NullLogInitialize(void)
+{
+    SCLogDebug("Registering the %s logger", OUTPUT_NAME);
+
+    SCEveFileType *file_type = SCCalloc(1, sizeof(SCEveFileType));
+
+    if (file_type == NULL) {
+        FatalError("Unable to allocate memory for eve file type %s", OUTPUT_NAME);
+    }
+
+    file_type->name = OUTPUT_NAME;
+    file_type->Init = NullLogInit;
+    file_type->Deinit = NullLogDeInit;
+    file_type->Write = NullLogWrite;
+    file_type->ThreadInit = NullLogThreadInit;
+    file_type->ThreadDeinit = NullLogThreadDeInit;
+    if (!SCRegisterEveFileType(file_type)) {
+        FatalError("Failed to register EVE file type: %s", OUTPUT_NAME);
+    }
+}
+#endif /* !OS_WIN32 */

src/output-eve-null.h

@@ -0,0 +1,25 @@
+/* Copyright (C) 2023 Open Information Security Foundation
+ *
+ * You can copy, redistribute or modify this Program under the terms of
+ * the GNU General Public License version 2 as published by the Free
+ * Software Foundation.
+ *
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * version 2 along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+/**
+ * \file
+ *
+ * \author Jeff Lucovsky <jlucovsky@oisf.net>
+ *
+ * File-like output for logging: null/discard device
+ */
+void NullLogInitialize(void);

src/output-json.c

@@ -47,7 +47,10 @@
 #include "app-layer-parser.h"
 #include "util-classification-config.h"
 #include "util-syslog.h"
+
+/* Internal output plugins */
 #include "output-eve-syslog.h"
+#include "output-eve-null.h"
 
 #include "output.h"
 #include "output-json.h"
@@ -98,6 +101,7 @@ void OutputJsonRegister (void)
     // Register output file types that use the new eve filetype registration
     // API.
     SyslogInitialize();
+    NullLogInitialize();
 }
 
 json_t *SCJsonString(const char *val)