WiFiClient::remoteIP and remoteIP6 IPv6 support

For RemoteIP and AF_INET6 socket i added support ip6 to ip4 mapping,
so .remoteIP will return IPv4 address on dual stack socket, if available.

Scenarios tested:
WiFiTelnetToSerial, wifiMulti.IPv6(true), connect both from IPv4 and IPv6
WiFiTelnetToSerial, wifiMulti.IPv6(true); but set to listen on IPv4 only.
WiFiTelnetToSerial, IPv6 disabled, with or without bind to specific IP4.
AsyncUDPServer, without IPv6 support.

Signed-off-by: Denys Fedoryshchenko <[email protected]>

Author: nuclearcat

libraries/WiFi/src/WiFiClient.cpp

@@ -23,6 +23,11 @@
 #include <lwip/netdb.h>
 #include <errno.h>
 
+#define IN6_IS_ADDR_V4MAPPED(a) \
+        ((((__const uint32_t *) (a))[0] == 0) \
+         && (((__const uint32_t *) (a))[1] == 0) \
+         && (((__const uint32_t *) (a))[2] == htonl (0xffff)))
+
 #define WIFI_CLIENT_DEF_CONN_TIMEOUT_MS  (3000)
 #define WIFI_CLIENT_MAX_WRITE_RETRY      (10)
 #define WIFI_CLIENT_SELECT_TIMEOUT_US    (1000000)
@@ -562,8 +567,24 @@ IPAddress WiFiClient::remoteIP(int fd) const
     struct sockaddr_storage addr;
     socklen_t len = sizeof addr;
     getpeername(fd, (struct sockaddr*)&addr, &len);
-    struct sockaddr_in *s = (struct sockaddr_in *)&addr;
-    return IPAddress((uint32_t)(s->sin_addr.s_addr));
+
+    // IPv4 socket, old way
+    if (((struct sockaddr*)&addr)->sa_family == AF_INET) {
+        struct sockaddr_in *s = (struct sockaddr_in *)&addr;
+        return IPAddress((uint32_t)(s->sin_addr.s_addr));
+    }
+
+    // IPv6, but it might be IPv4 mapped address
+    if (((struct sockaddr*)&addr)->sa_family == AF_INET6) {
+        struct sockaddr_in6 *saddr6 = (struct sockaddr_in6 *)&addr;
+        if (IN6_IS_ADDR_V4MAPPED(saddr6->sin6_addr.un.u32_addr)) {
+            return IPAddress(IPv4, (uint8_t*)saddr6->sin6_addr.s6_addr+12);
+        } else {
+            return IPAddress(IPv6, (uint8_t*)(saddr6->sin6_addr.s6_addr));
+        }
+    }
+    log_e("WiFiClient::remoteIP Not AF_INET or AF_INET6?");
+    return (IPAddress(0,0,0,0));
 }
 
 uint16_t WiFiClient::remotePort(int fd) const