[Doc] Add `recvfrom` and `sendto` to socket API.

doc/witx/typenames.witx

@@ -280,8 +280,12 @@
     $poll_fd_readwrite
     ;;; The right to invoke `sock_recv`.
     $sock_recv
+    ;;; The right to invoke `sock_recv_from`.
+    $sock_recv_from
     ;;; The right to invoke `sock_send`.
     $sock_send
+    ;;; The right to invoke `sock_send_to`.
+    $sock_send_to
     ;;; The right to invoke `sock_shutdown`.
     $sock_shutdown
   )

doc/witx/wasi_ephemeral_sock.witx

@@ -15,6 +15,8 @@
 
   ;;; Receive a message from a socket.
   ;;; Note: This is similar to `recv` in POSIX.
+  ;;; Note: This is identical to `recvfrom` with a null pointer passed as its
+  ;;; as its address in POSIX.
   (@interface func (export "recv")
     (param $fd $fd)
     ;;; The pointer to and length of the buffer for data received.
@@ -27,8 +29,26 @@
     (result $bufused $size)
   )
 
+  ;;; Receive a message from a socket.
+  ;;; Note: This is similar to `recvfrom` in POSIX.
+  (@interface func (export "recv_from")
+    (param $fd $fd)
+    ;;; The pointer to and length of the buffer for data received.
+    (param $buf (@witx pointer u8))
+    (param $buf_len $size)
+    ;;; The pointer to and length of the buffer for source address.
+    (param $addr_buf (@witx pointer u8))
+    (param $addr_buf_len $size)
+    ;;; Message flags.
+    (param $flags $riflags)
+    (result $error $errno)
+    ;;; Number of bytes used in the buffer.
+    (result $bufused $size)
+  )
+
   ;;; Send a message from a socket.
   ;;; Note: This is similar to `send` in POSIX.
+  ;;; Note: This may be used only when the socket is in a connected state.
   (@interface func (export "send")
     (param $fd $fd)
     ;;; The pointer to and length of the buffer for data.
@@ -41,6 +61,23 @@
     (result $bufused $size)
   )
 
+  ;;; Send a message from a socket.
+  ;;; Note: This is similar to `sendto` in POSIX.
+  (@interface func (export "send_to")
+    (param $fd $fd)
+    ;;; The pointer to and length of the buffer for data.
+    (param $buf (@witx pointer u8))
+    (param $buf_len $size)
+    ;;; The pointer to and length of the buffer for destination address.
+    (param $addr_buf (@witx pointer u8))
+    (param $addr_buf_len $size)
+    ;;; Message flags.
+    (param $_flags $siflags)
+    (result $error $errno)
+    ;;; Number of bytes transmitted.
+    (result $bufused $size)
+  )
+
   ;;; Shut down socket send and receive channels.
   ;;; Note: This is similar to `shutdown` in POSIX.
   (@interface func (export "shutdown")