net: tcp: Add better type safety for connection handlers

This creates a `struct net_conn_handle` that's only used as an opaque
pointer.  The purpose is to avoid assigning a void* to a void** in
connection registering/unregistering functions, avoiding a
previously-caught bug by issuing an incompatible pointer types warning:

	warning: passing argument 7 of 'net_tcp_register' from
		incompatible pointer type [-Wincompatible-pointer-types]

Suggested by Andy Ross in 5beec6.  This particular commit didn't catch
any bugs, but the one caught in 5beec6 wouldn't exist if this were in
place at the time.

Change-Id: I5c13fb4c5826adce6397feb7b400d36e426c4a87
Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>

include/net/yaip/net_context.h

@@ -125,6 +125,8 @@ typedef void (*net_context_accept_cb_t)(struct net_context *new_context,
 
 struct net_tcp;
 
+struct net_conn_handle;
+
 /**
  * Note that we do not store the actual source IP address in the context
  * because the address is already be set in the network interface struct.
@@ -141,7 +143,7 @@ struct net_context {
 	struct sockaddr remote;
 
 	/** Connection handle */
-	void *conn_handler;
+	struct net_conn_handle *conn_handler;
 
 	/** Receive callback to be called when desired packet
 	 * has been received.

net/yaip/connection.c

@@ -347,7 +347,7 @@ static inline enum net_verdict cache_check(enum net_ip_protocol proto,
 #define cache_check(...) NET_CONTINUE
 #endif /* CONFIG_NET_CONN_CACHE */
 
-int net_conn_unregister(void *handle)
+int net_conn_unregister(struct net_conn_handle *handle)
 {
 	struct net_conn *conn = (struct net_conn *)handle;
 
@@ -427,7 +427,7 @@ int net_conn_register(enum net_ip_protocol proto,
 		      uint16_t local_port,
 		      net_conn_cb_t cb,
 		      void *user_data,
-		      void **handle)
+		      struct net_conn_handle **handle)
 {
 	int i;
 	uint8_t rank = 0;
@@ -556,7 +556,7 @@ int net_conn_register(enum net_ip_protocol proto,
 #endif /* NET_DEBUG */
 
 		if (handle) {
-			*handle = &conns[i];
+			*handle = (struct net_conn_handle *)&conns[i];
 		}
 
 		return 0;

net/yaip/connection.h

@@ -37,6 +37,8 @@ extern "C" {
 
 struct net_conn;
 
+struct net_conn_handle;
+
 /**
  * @brief Function that is called by connection subsystem when UDP/TCP
  * packet is received and which matches local and remote IP address
@@ -95,7 +97,7 @@ struct net_conn {
  * @param local_port Local port of the connection end point.
  * @param cb Callback to be called
  * @param user_data User data supplied by caller.
- * @param handle UDP handle that can be used when unregistering
+ * @param handle Connection handle that can be used when unregistering
  *
  * @return Return 0 if the registration succeed, <0 otherwise.
  */
@@ -106,7 +108,7 @@ int net_conn_register(enum net_ip_protocol proto,
 		      uint16_t local_port,
 		      net_conn_cb_t cb,
 		      void *user_data,
-		      void **handle);
+		      struct net_conn_handle **handle);
 
 /**
  * @brief Unregister connection handler.
@@ -115,7 +117,7 @@ int net_conn_register(enum net_ip_protocol proto,
  *
  * @return Return 0 if the unregistration succeed, <0 otherwise.
  */
-int net_conn_unregister(void *handle);
+int net_conn_unregister(struct net_conn_handle *handle);
 
 /**
  * @brief Called by net_core.c when a network packet is received.

net/yaip/tcp.h

@@ -162,7 +162,7 @@ static inline int net_tcp_register(const struct sockaddr *remote_addr,
 				   uint16_t local_port,
 				   net_conn_cb_t cb,
 				   void *user_data,
-				   void **handle)
+				   struct net_conn_handle **handle)
 {
 	return net_conn_register(IPPROTO_TCP, remote_addr, local_addr,
 				 remote_port, local_port, cb, user_data,
@@ -176,7 +176,7 @@ static inline int net_tcp_register(const struct sockaddr *remote_addr,
  *
  * @return Return 0 if the unregistration succeed, <0 otherwise.
  */
-static inline int net_tcp_unregister(void *handle)
+static inline int net_tcp_unregister(struct net_conn_handle *handle)
 {
 	return net_conn_unregister(handle);
 }

net/yaip/udp.h

@@ -91,7 +91,7 @@ static inline int net_udp_register(const struct sockaddr *remote_addr,
 				   uint16_t local_port,
 				   net_conn_cb_t cb,
 				   void *user_data,
-				   void **handle)
+				   struct net_conn_handle **handle)
 {
 	return net_conn_register(IPPROTO_UDP, remote_addr, local_addr,
 				 remote_port, local_port, cb, user_data,
@@ -105,7 +105,7 @@ static inline int net_udp_register(const struct sockaddr *remote_addr,
  *
  * @return Return 0 if the unregistration succeed, <0 otherwise.
  */
-static inline int net_udp_unregister(void *handle)
+static inline int net_udp_unregister(struct net_conn_handle *handle)
 {
 	return net_conn_unregister(handle);
 }

tests/net/tcp/src/main.c

@@ -222,7 +222,7 @@ struct ud {
 	uint16_t remote_port;
 	uint16_t local_port;
 	char *test;
-	void *handle;
+	struct net_conn_handle *handle;
 };
 
 static struct ud *returned_ud;
@@ -446,7 +446,7 @@ static void set_port(sa_family_t family, struct sockaddr *raddr,
 
 static bool test_register(void)
 {
-	void *handlers[CONFIG_NET_MAX_CONN];
+	struct net_conn_handle *handlers[CONFIG_NET_MAX_CONN];
 	struct net_if *iface = net_if_get_default();
 	struct net_if_addr *ifaddr;
 	struct ud *ud;

tests/net/udp/src/main.c

@@ -363,8 +363,8 @@ static void set_port(sa_family_t family, struct sockaddr *raddr,
 
 static bool run_tests(void)
 {
-	void *handlers[CONFIG_NET_MAX_CONN];
-	struct net_if *iface = net_if_get_default();;
+	struct net_conn_handle *handlers[CONFIG_NET_MAX_CONN];
+	struct net_if *iface = net_if_get_default();
 	struct net_if_addr *ifaddr;
 	struct ud *ud;
 	int ret, i = 0;