server header validation, handle ping message

include/protocol.h

@@ -10,9 +10,11 @@
 #define OWD_DATA_LEN(HDR) (offsetof(__typeof__(HDR), _data_end))
 
 enum owd_msg_type {
-  OWD_MSG_ERR,
-  OWD_MSG_SYNC_REQUEST,
-  OWD_MSG_SYNC_RESPONSE,
+  OWD_MSG_ERR           = 0,
+  OWD_MSG_PING          = 1,
+  OWD_MSG_PONG          = 2,
+  OWD_MSG_SYNC_REQUEST  = 3,
+  OWD_MSG_SYNC_RESPONSE = 4,
 };
 
 enum owd_error_code {
@@ -30,6 +32,7 @@ struct owdhdr {
   uint8_t version;
   uint8_t msg_type;
   uint16_t length;
+  uint32_t tid;
 };
 
 struct owd_msg_err {
@@ -44,9 +47,25 @@ struct owd_msg_sync_response {
   OWD_DECL_DATA_END;
 };
 
-static inline void owd_hdr_populate(struct owdhdr *hdr, uint8_t msg_type, uint16_t length) {
+static inline void owd_hdr_populate(
+  struct owdhdr *hdr,
+  uint8_t msg_type,
+  uint16_t length,
+  uint32_t tid)
+{
   hdr->magic = htonl(OWD_MAGIC);
   hdr->version = OWD_VERSION;
   hdr->msg_type = msg_type;
   hdr->length = htons(length);
+  hdr->tid = htonl(tid);
+}
+
+static inline int owd_hdr_validate(struct owdhdr *hdr, ssize_t len) {
+  if (len < sizeof(struct owdhdr))
+    return 1;
+  if (hdr->magic != ntohl(OWD_MAGIC))
+    return 1;
+  if (hdr->version != OWD_VERSION)
+    return 1;
+  return 0;
 }