decoder: add template/example

Add fictional example / template for a packet decoder. It's not invoked
anywhere.

src/Makefile.am

@@ -60,6 +60,7 @@ decode-teredo.c decode-teredo.h \
 decode-udp.c decode-udp.h \
 decode-vlan.c decode-vlan.h \
 decode-mpls.c decode-mpls.h \
+decode-template.c decode-template.h \
 defrag-config.c defrag-config.h \
 defrag.c defrag.h \
 defrag-hash.c defrag-hash.h \

src/decode-template.c

@@ -0,0 +1,97 @@
+/* Copyright (C) 2015 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.
+ */
+
+/**
+ * \ingroup decode
+ *
+ * @{
+ */
+
+
+/**
+ * \file
+ *
+ * \author XXX Your Name <your@email.com>
+ *
+ * Decodes XXX describe the protocol
+ */
+
+#include "suricata-common.h"
+#include "suricata.h"
+#include "decode.h"
+#include "decode-events.h"
+#include "decode-template.h"
+
+#include "util-unittest.h"
+#include "util-debug.h"
+
+/**
+ * \brief Function to decode XXX packets
+ * \param tv thread vars
+ * \param dtv decoder thread vars
+ * \param p packet
+ * \param pkt raw packet data
+ * \param len length in bytes of pkt array
+ * \retval TM_ECODE_OK or TM_ECODE_FAILED on serious error
+ */
+
+int DecodeTEMPLATE(ThreadVars *tv, DecodeThreadVars *dtv, Packet *p,
+                   const uint8_t *pkt, uint16_t len, PacketQueue *pq)
+{
+    /* TODO add counter for your type of packet to DecodeThreadVars,
+     * and register it in DecodeRegisterPerfCounters */
+    //StatsIncr(tv, dtv->counter_template);
+
+    /* Validation: make sure that the input data is big enough to hold
+     *             the header */
+    if (len < sizeof(TemplateHdr)) {
+        /* in case of errors, we set events. Events are defined in
+         * decode-events.h, and are then exposed to the detection
+         * engine through detect-engine-events.h */
+        //ENGINE_SET_EVENT(p,TEMPLATE_HEADER_TOO_SMALL);
+        return TM_ECODE_FAILED;
+    }
+
+    /* Now we can access the header */
+    const TemplateHdr *hdr = (const TemplateHdr *)pkt;
+
+    /* lets assume we have UDP encapsulated */
+    if (hdr->proto == 17) {
+        /* we need to pass on the pkt and it's length minus the current
+         * header */
+        size_t hdr_len = sizeof(TemplateHdr);
+
+        /* in this example it's clear that hdr_len can't be bigger than
+         * 'len', but in more complex cases checking that we can't underflow
+         * len is very important
+        if (hdr_len < len) {
+         */
+
+        /* invoke the next decoder on the remainder of the data */
+        return DecodeUDP(tv, dtv, p, (uint8_t *)pkt + hdr_len, len - hdr_len, pq);
+        //}
+    } else {
+        //ENGINE_SET_EVENT(p,TEMPLATE_UNSUPPORTED_PROTOCOL);
+        return TM_ECODE_FAILED;
+    }
+
+    return TM_ECODE_OK;
+}
+
+/**
+ * @}
+ */

src/decode-template.h

@@ -0,0 +1,37 @@
+/* Copyright (C) 2015 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 XXX
+ *
+ */
+
+#ifndef __DECODE_TEMPLATE_H__
+#define __DECODE_TEMPLATE_H__
+
+#include "decode.h"
+#include "threadvars.h"
+
+typedef struct TemplateHdr_ {
+    uint8_t proto;
+    uint8_t pad0;
+    uint16_t pad1;
+} __attribute__((__packed__)) TemplateHdr;
+
+#endif /* __DECODE_TEMPLATE_H__ */