implement datasync

lib/wasi/src/state.rs

@@ -7,6 +7,7 @@ use generational_arena::{Arena, Index as Inode};
 use hashbrown::hash_map::{Entry, HashMap};
 use std::{
     cell::{Cell, RefCell},
+    io::{self, Write},
     ops::{Index, IndexMut},
     path::PathBuf,
     rc::Rc,
@@ -212,6 +213,31 @@ impl WasiFs {
             Err(__WASI_EBADF)
         }
     }
+
+    pub fn flush(&mut self, fd: __wasi_fd_t) -> Result<(), __wasi_errno_t> {
+        match fd {
+            0 => (),
+            1 => io::stdout().flush().map_err(|_| __WASI_EIO)?,
+            2 => io::stderr().flush().map_err(|_| __WASI_EIO)?,
+            _ => {
+                let fd = self.fd_map.get(&fd).ok_or(__WASI_EBADF)?;
+                if fd.rights & __WASI_RIGHT_FD_DATASYNC == 0 {
+                    return Err(__WASI_EACCES);
+                }
+
+                let inode = &mut self.inodes[fd.inode];
+
+                match &mut inode.kind {
+                    Kind::File { handle } => handle.flush().map_err(|_| __WASI_EIO)?,
+                    // TODO: verify this behavior
+                    Kind::Dir { .. } => return Err(__WASI_EISDIR),
+                    Kind::Symlink { .. } => unimplemented!(),
+                    Kind::Buffer { .. } => (),
+                }
+            }
+        }
+        Ok(())
+    }
 }
 
 pub struct WasiState<'a> {

lib/wasi/src/syscalls/mod.rs

@@ -256,7 +256,13 @@ pub fn fd_close(ctx: &mut Ctx, fd: __wasi_fd_t) -> __wasi_errno_t {
 ///     The file descriptor to sync
 pub fn fd_datasync(ctx: &mut Ctx, fd: __wasi_fd_t) -> __wasi_errno_t {
     debug!("wasi::fd_datasync");
-    unimplemented!()
+    let state = get_wasi_state(ctx);
+
+    if let Err(e) = state.fs.flush(fd) {
+        e
+    } else {
+        __WASI_ESUCCESS
+    }
 }
 
 /// ### `fd_fdstat_get()`