net: add sndbuf socket option

Introduce set/get SO_SNDBUF option using the setsockopt
function. In addition, for TCP, check the sndbuf value
before queuing data.

Signed-off-by: Mohan Kumar Kumar <mohankm@fb.com>

include/zephyr/net/net_context.h

@@ -315,6 +315,9 @@ __net_socket struct net_context {
 #endif
 #if defined(CONFIG_NET_CONTEXT_RCVBUF)
 		uint16_t rcvbuf;
+#endif
+#if defined(CONFIG_NET_CONTEXT_SNDBUF)
+		uint16_t sndbuf;
 #endif
 	} options;
 
@@ -1064,6 +1067,7 @@ enum net_context_option {
 	NET_OPT_RCVTIMEO        = 4,
 	NET_OPT_SNDTIMEO        = 5,
 	NET_OPT_RCVBUF		= 6,
+	NET_OPT_SNDBUF		= 7,
 };
 
 /**

subsys/net/ip/Kconfig

@@ -594,6 +594,13 @@ config NET_CONTEXT_RCVBUF
 	  The default value is set by CONFIG_NET_TCP_MAX_RECV_WINDOW_SIZE. For
 	  TCP sockets, the rcvbuf will determine the receive window size.
 
+config NET_CONTEXT_SNDBUF
+	bool "Add SNDBUF support to net_context"
+	help
+	  It is possible to define the maximum socket send buffer per socket.
+	  For TCP sockets, the sndbuf will determine the total size of queued
+	  data in the TCP layer.
+
 config NET_TEST
 	bool "Network Testing"
 	help

subsys/net/ip/net_context.c

@@ -1260,6 +1260,21 @@ static int get_context_rcvbuf(struct net_context *context,
 #endif
 }
 
+static int get_context_sndbuf(struct net_context *context,
+				void *value, size_t *len)
+{
+#if defined(CONFIG_NET_CONTEXT_SNDBUF)
+	*((int *)value) = context->options.sndbuf;
+
+	if (len) {
+		*len = sizeof(int);
+	}
+	return 0;
+#else
+	return -ENOTSUP;
+#endif
+}
+
 /* If buf is not NULL, then use it. Otherwise read the data to be written
  * to net_pkt from msghdr.
  */
@@ -2251,6 +2266,27 @@ static int set_context_rcvbuf(struct net_context *context,
 #endif
 }
 
+static int set_context_sndbuf(struct net_context *context,
+				const void *value, size_t len)
+{
+#if defined(CONFIG_NET_CONTEXT_SNDBUF)
+	int sndbuf_value = *((int *)value);
+
+	if (len != sizeof(int)) {
+		return -EINVAL;
+	}
+
+	if ((sndbuf_value < 0) || (sndbuf_value > UINT16_MAX)) {
+		return -EINVAL;
+	}
+
+	context->options.sndbuf = (uint16_t) sndbuf_value;
+	return 0;
+#else
+	return -ENOTSUP;
+#endif
+}
+
 int net_context_set_option(struct net_context *context,
 			   enum net_context_option option,
 			   const void *value, size_t len)
@@ -2284,6 +2320,9 @@ int net_context_set_option(struct net_context *context,
 	case NET_OPT_RCVBUF:
 		ret = set_context_rcvbuf(context, value, len);
 		break;
+	case NET_OPT_SNDBUF:
+		ret = set_context_sndbuf(context, value, len);
+		break;
 	}
 
 	k_mutex_unlock(&context->lock);
@@ -2324,6 +2363,9 @@ int net_context_get_option(struct net_context *context,
 	case NET_OPT_RCVBUF:
 		ret = get_context_rcvbuf(context, value, len);
 		break;
+	case NET_OPT_SNDBUF:
+		ret = get_context_sndbuf(context, value, len);
+		break;
 	}
 
 	k_mutex_unlock(&context->lock);

subsys/net/ip/tcp.c

@@ -1782,6 +1782,9 @@ static void tcp_in(struct tcp *conn, struct net_pkt *pkt)
 
 	if (th) {
 		size_t max_win;
+		int sndbuf;
+		size_t sndbuf_len;
+
 
 		conn->send_win = ntohs(th_win(th));
 
@@ -1798,6 +1801,17 @@ static void tcp_in(struct tcp *conn, struct net_pkt *pkt)
 				   CONFIG_NET_BUF_DATA_SIZE) / 3;
 		}
 
+		if (IS_ENABLED(CONFIG_NET_CONTEXT_SNDBUF) &&
+			conn->state != TCP_SYN_SENT &&
+			net_context_get_option(conn->context,
+					       NET_OPT_SNDBUF,
+					       &sndbuf,
+					       &sndbuf_len) == 0) {
+			if (sndbuf > 0) {
+				max_win = sndbuf;
+			}
+		}
+
 		max_win = MAX(max_win, NET_IPV6_MTU);
 		if ((size_t)conn->send_win > max_win) {
 			NET_DBG("Lowering send window from %zd to %zd",

subsys/net/lib/sockets/sockets.c

@@ -1763,6 +1763,20 @@ int zsock_getsockopt_ctx(struct net_context *ctx, int level, int optname,
 				return 0;
 			}
 			break;
+
+		case SO_SNDBUF:
+			if (IS_ENABLED(CONFIG_NET_CONTEXT_SNDBUF)) {
+				ret = net_context_get_option(ctx,
+							     NET_OPT_SNDBUF,
+							     optval, optlen);
+				if (ret < 0) {
+					errno = -ret;
+					return -1;
+				}
+
+				return 0;
+			}
+			break;
 		}
 	}
 
@@ -1830,6 +1844,21 @@ int zsock_setsockopt_ctx(struct net_context *ctx, int level, int optname,
 
 			break;
 
+		case SO_SNDBUF:
+			if (IS_ENABLED(CONFIG_NET_CONTEXT_SNDBUF)) {
+				ret = net_context_set_option(ctx,
+							     NET_OPT_SNDBUF,
+							     optval, optlen);
+				if (ret < 0) {
+					errno = -ret;
+					return -1;
+				}
+
+				return 0;
+			}
+
+			break;
+
 		case SO_REUSEADDR:
 			/* Ignore for now. Provided to let port
 			 * existing apps.