From 90f3c150846673942f2a154c7c5adf9c4e4fbf80 Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benpicco@googlemail.com>
Date: Thu, 29 Oct 2020 18:37:05 +0100
Subject: [PATCH] socket_zep: send dummy HELLO packet on connect

---
 cpu/native/include/socket_zep.h    | 33 ++++++++++++++++++++++++++++++
 cpu/native/socket_zep/socket_zep.c | 23 ++++++++++++++++++++-
 makefiles/pseudomodules.inc.mk     |  1 +
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/cpu/native/include/socket_zep.h b/cpu/native/include/socket_zep.h
index 01bbad616c..7529e7d8ef 100644
--- a/cpu/native/include/socket_zep.h
+++ b/cpu/native/include/socket_zep.h
@@ -13,6 +13,39 @@
  *
  * @see @ref net_zep for protocol definitions
  *
+ * This ZEP implementation can send a dummy HELLO packet on startup.
+ * This is used to make dispatchers aware of the node.
+ * To enable this behavior, add
+ *
+ * ```
+ * USEMODULE += socket_zep_hello
+ * ```
+ *
+ * to your Makefile.
+ *
+ * A ZEP dispatcher can just drop those packets (ZEP type 0xFF) if it
+ * chooses to parse the ZEP header.
+ *
+ * The header of the HELLO packet will look like this:
+ *
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |         Preamble (EX)         |  Version (2)  |  Type  (255)  |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |                                                               |
+ *     +                                                               +
+ *     |                                                               |
+ *     +                         Reserved (0)                         +
+ *     |                                                               |
+ *     +                                                               +
+ *     |                                                               |
+ *     +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |               |      'H'      |      'E'      |      'L'      |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |      'L'      |      'O'      |       0       |       0       |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |       0       |       0       |       0       |       0       |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
  * @{
  *
  * @file
diff --git a/cpu/native/socket_zep/socket_zep.c b/cpu/native/socket_zep/socket_zep.c
index 487a145393..f88b2c3608 100644
--- a/cpu/native/socket_zep/socket_zep.c
+++ b/cpu/native/socket_zep/socket_zep.c
@@ -40,6 +40,9 @@
  * (https://pubs.opengroup.org/onlinepubs/9699919799.2016edition/basedefs/time.h.html) */
 #define TV_USEC_PER_SEC         (1000000L)
 
+/* dummy packet to register with ZEP dispatcher */
+#define SOCKET_ZEP_V2_TYPE_HELLO   (255)
+
 static size_t _zep_hdr_fill_v2_data(socket_zep_t *dev, zep_v2_data_hdr_t *hdr,
                                     size_t payload_len)
 {
@@ -390,6 +393,21 @@ static int _connect_remote(socket_zep_t *dev, const socket_zep_params_t *params)
     return res;
 }
 
+static void _send_zep_hello(socket_zep_t *dev)
+{
+    if (IS_USED(MODULE_SOCKET_ZEP_HELLO)) {
+        /* dummy packet */
+        zep_v2_data_hdr_t hdr = {
+            .hdr.preamble = "EX",
+            .hdr.version  = 2,
+            .type = SOCKET_ZEP_V2_TYPE_HELLO,
+            .resv = "HELLO",
+        };
+
+        real_write(dev->sock_fd, &hdr, sizeof(hdr));
+    }
+}
+
 void socket_zep_setup(socket_zep_t *dev, const socket_zep_params_t *params)
 {
     int res;
@@ -408,7 +426,10 @@ void socket_zep_setup(socket_zep_t *dev, const socket_zep_params_t *params)
         dev->sock_fd = res;
     }
 
-    _connect_remote(dev, params);
+    if (_connect_remote(dev, params) == 0) {
+        /* send dummy data to connect to dispatcher */
+        _send_zep_hello(dev);
+    }
 
     /* generate hardware address from local address */
     uint8_t ss_array[sizeof(struct sockaddr_storage)] = { 0 };
diff --git a/makefiles/pseudomodules.inc.mk b/makefiles/pseudomodules.inc.mk
index 388dcf4dc4..4e29d69dc9 100644
--- a/makefiles/pseudomodules.inc.mk
+++ b/makefiles/pseudomodules.inc.mk
@@ -116,6 +116,7 @@ PSEUDOMODULES += sock_dtls
 PSEUDOMODULES += sock_ip
 PSEUDOMODULES += sock_tcp
 PSEUDOMODULES += sock_udp
+PSEUDOMODULES += socket_zep_hello
 PSEUDOMODULES += soft_uart_modecfg
 PSEUDOMODULES += stdin
 PSEUDOMODULES += stdio_cdc_acm