Draft a prototype stdio design for wasip3.

wit-0.3.0-draft/stdio.wit

@@ -1,17 +1,74 @@
 @since(version = 0.3.0)
 interface stdin {
-  @since(version = 0.3.0)
-  get-stdin: func() -> stream<u8>;
+    use stdio.{error};
+
+    /// Reads data from a “standard input”.
+    ///
+    /// This function reads at most `amount` bytes from a
+    /// “standard input” source.
+    @since(version = 0.3.0)
+    read: func(amount: u32) -> result<list<u8>, error>;
 }
 
 @since(version = 0.3.0)
 interface stdout {
-  @since(version = 0.3.0)
-  set-stdout: func(data: stream<u8>);
+    use stdio.{error};
+
+    /// Writes data to a “standard output”.
+    ///
+    /// This function writes the bytes of `data` to a “standard output”
+    /// destination.
+    ///
+    /// The data may be either text or binary; if it is text, it is recommended
+    /// to be encoded as UTF-8, to allow terminal implementations on non-UTF-8
+    /// host environments to transcode it into their native text encoding.
+    @since(version = 0.3.0)
+    write: func(data: list<u8>) -> result<_, error>;
 }
 
 @since(version = 0.3.0)
 interface stderr {
-  @since(version = 0.3.0)
-  set-stderr: func(data: stream<u8>);
+    use stdio.{error};
+
+    /// Writes data to a “standard error”.
+    ///
+    /// This function writes the bytes of `data` to a “standard error”
+    /// destination.
+    ///
+    /// As with `stdout.write`, the data may be tierh text or binary, and
+    /// if it is text, it is recommended to be encoded as UTF-8.
+    @since(version = 0.3.0)
+    write: func(data: list<u8>) -> result<_, error>;
+}
+
+/// Types common to the stdio interfaces.
+@since(version = 0.3.0)
+interface stdio {
+    /// An error code for stdio functions.
+    @since(version = 0.3.0)
+    enum error {
+        /// An I/O error occurred and the operation not completed successfully.
+        ///
+        /// After a `read` or `write` function has returned `io`, it thereafter
+        /// always returns `io`.
+        io,
+
+        /// The other end was dropped and so this end must now be dropped.
+        ///
+        /// For `read`, this means the end of the stream has been reached.
+        ///
+        /// For `write`, this means that the consumer has no need for further
+        /// data from this stream. This doesn't signify an error; it just
+        /// instructs the producer to stop sending data.
+        ///
+        /// After a `read` or `write` function has returned `dropped`, it
+        /// thereafter always returns `dropped`.
+        dropped,
+    }
 }
+
+// FIXME: Provide a way to keep reading after a `dropped`, for the `tail -f` idiom?
+
+// FIXME: Should write return the number of bytes written?
+
+// FIXME: How can we avoid the whole situation that caused wasip2 to have `check-write`?