This is an implementation of the client side of TCP Fast Open (TFO)

[RFC7413]. It also includes a pre-shared key mode of operation in which
the server requires the client to be in possession of a shared secret in
order to successfully open TFO connections with that server.

The names of some existing fastopen sysctls have changed (e.g.,
net.inet.tcp.fastopen.enabled -> net.inet.tcp.fastopen.server_enable).

Reviewed by:	tuexen
MFC after:	1 month
Sponsored by:	Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D14047

newlib/libc/sys/rtems/include/netinet/tcp.h

@@ -101,8 +101,6 @@ struct tcphdr {
 #define	   TCPOLEN_SIGNATURE		18
 #define	TCPOPT_FAST_OPEN	34
 #define	   TCPOLEN_FAST_OPEN_EMPTY	2
-#define	   TCPOLEN_FAST_OPEN_MIN	6
-#define	   TCPOLEN_FAST_OPEN_MAX	18
 
 /* Miscellaneous constants */
 #define	MAX_SACK_BLKS	6	/* Max # SACK blocks stored at receiver side */
@@ -152,6 +150,10 @@ struct tcphdr {
 #define TCP_MAXHLEN	(0xf<<2)	/* max length of header in bytes */
 #define TCP_MAXOLEN	(TCP_MAXHLEN - sizeof(struct tcphdr))
 					/* max space left for options */
+
+#define TCP_FASTOPEN_MIN_COOKIE_LEN	4	/* Per RFC7413 */
+#define TCP_FASTOPEN_MAX_COOKIE_LEN	16	/* Per RFC7413 */
+#define TCP_FASTOPEN_PSK_LEN		16	/* Same as TCP_FASTOPEN_KEY_LEN */
 #endif /* __BSD_VISIBLE */
 
 /*
@@ -252,6 +254,16 @@ struct tcp_info {
 	/* Padding to grow without breaking ABI. */
 	u_int32_t	__tcpi_pad[26];		/* Padding. */
 };
+
+/*
+ * If this structure is provided when setting the TCP_FASTOPEN socket
+ * option, and the enable member is non-zero, a subsequent connect will use
+ * pre-shared key (PSK) mode using the provided key.
+ */
+struct tcp_fastopen {
+	int enable;
+	uint8_t psk[TCP_FASTOPEN_PSK_LEN];
+};
 #endif
 #define TCP_FUNCTION_NAME_LEN_MAX 32