Add sock_accept() to snapshot1 (WebAssembly#458)

This function allows a server to accept incoming connections. A few
notes are in order.

Although there are legitimate questions about the capabilities model in
numerous networking APIs, this particular API is both immensely useful
and not a violation of the capabilities model. There is still no way to
create an arbitrary socket. The only thing that WASM can do is accept
incoming connections on a predefined listening socket.

Signed-off-by: Nathaniel McCallum <[email protected]>

phases/snapshot/docs.md

@@ -450,6 +450,11 @@ The right to invoke [`sock_shutdown`](#sock_shutdown).
 
 Bit: 28
 
+- <a href="#rights.sock_accept" name="rights.sock_accept"></a> `sock_accept`: `bool`
+The right to invoke [`sock_accept`](#sock_accept).
+
+Bit: 29
+
 ## <a href="#fd" name="fd"></a> `fd`: `Handle`
 A file descriptor handle.
 
@@ -2011,7 +2016,7 @@ The path at which to create the directory.
 
 #### <a href="#path_filestat_get" name="path_filestat_get"></a> `path_filestat_get(fd: fd, flags: lookupflags, path: string) -> Result<filestat, errno>`
 Return the attributes of a file or directory.
-Note: This is similar to `fstatat` in POSIX.
+Note: This is similar to `stat` in POSIX.
 
 ##### Params
 - <a href="#path_filestat_get.fd" name="path_filestat_get.fd"></a> `fd`: [`fd`](#fd)
@@ -2414,6 +2419,33 @@ The buffer to fill with random data.
 - <a href="#random_get.error.err" name="random_get.error.err"></a> `err`: [`errno`](#errno)
 
 
+---
+
+#### <a href="#sock_accept" name="sock_accept"></a> `sock_accept(fd: fd, flags: fdflags) -> Result<fd, errno>`
+Accept a new incoming connection.
+Note: This is similar to `accept` in POSIX.
+
+##### Params
+- <a href="#sock_accept.fd" name="sock_accept.fd"></a> `fd`: [`fd`](#fd)
+The listening socket.
+
+- <a href="#sock_accept.flags" name="sock_accept.flags"></a> `flags`: [`fdflags`](#fdflags)
+The desired values of the file descriptor flags.
+
+##### Results
+- <a href="#sock_accept.error" name="sock_accept.error"></a> `error`: `Result<fd, errno>`
+New socket connection
+
+###### Variant Layout
+- size: 8
+- align: 4
+- tag_size: 4
+###### Variant cases
+- <a href="#sock_accept.error.ok" name="sock_accept.error.ok"></a> `ok`: [`fd`](#fd)
+
+- <a href="#sock_accept.error.err" name="sock_accept.error.err"></a> `err`: [`errno`](#errno)
+
+
 ---
 
 #### <a href="#sock_recv" name="sock_recv"></a> `sock_recv(fd: fd, ri_data: iovec_array, ri_flags: riflags) -> Result<(size, roflags), errno>`

phases/snapshot/witx/typenames.witx

@@ -270,6 +270,8 @@
     $poll_fd_readwrite
     ;;; The right to invoke `sock_shutdown`.
     $sock_shutdown
+    ;;; The right to invoke `sock_accept`.
+    $sock_accept
   )
 )
 

phases/snapshot/witx/wasi_snapshot_preview1.witx

@@ -473,6 +473,17 @@
     (result $error (expected (error $errno)))
   )
 
+  ;;; Accept a new incoming connection.
+  ;;; Note: This is similar to `accept` in POSIX.
+  (@interface func (export "sock_accept")
+    ;;; The listening socket.
+    (param $fd $fd)
+    ;;; The desired values of the file descriptor flags.
+    (param $flags $fdflags)
+    ;;; New socket connection
+    (result $error (expected $fd (error $errno)))
+  )
+
   ;;; Receive a message from a socket.
   ;;; Note: This is similar to `recv` in POSIX, though it also supports reading
   ;;; the data into multiple buffers in the manner of `readv`.