implement some of fd_prestat_get

lib/wasi/src/lib.rs

@@ -15,7 +15,7 @@ use std::ffi::c_void;
 
 pub use self::utils::is_wasi_module;
 
-use wasmer_runtime_core::{debug, func, import::ImportObject, imports};
+use wasmer_runtime_core::{func, import::ImportObject, imports};
 
 pub fn generate_import_object(args: Vec<Vec<u8>>, envs: Vec<Vec<u8>>) -> ImportObject {
     let state_gen = move || {

lib/wasi/src/state.rs

@@ -194,6 +194,21 @@ impl WasiFs {
             fs_rights_inheriting: fd.rights, // TODO(lachlan): Is this right?
         })
     }
+
+    pub fn prestat_fd(&self, fd: __wasi_fd_t) -> Result<__wasi_prestat_t, __wasi_errno_t> {
+        let fd = self.fd_map.get(&fd).ok_or(__WASI_EBADF)?;
+
+        let inode_val = &self.inodes[fd.inode];
+
+        if inode_val.is_preopened {
+            Ok(PrestatEnum::PreOpenDir {
+                pr_name_len: inode_val.name.len() as u32,
+            }
+            .get_untagged())
+        } else {
+            Err(__WASI_EBADF)
+        }
+    }
 }
 
 pub struct WasiState<'a> {

lib/wasi/src/syscalls/mod.rs

@@ -380,6 +380,14 @@ pub fn fd_pread(
     }
 }
 
+/// ### `fd_prestat_get()`
+/// Get metadata about a preopened file descriptor
+/// Input:
+/// - `__wasi_fd_t fd`
+///     The preopened file descriptor to query
+/// Output:
+/// - `__wasi_prestat *buf`
+///     Where the metadata will be written
 pub fn fd_prestat_get(
     ctx: &mut Ctx,
     fd: __wasi_fd_t,
@@ -388,13 +396,12 @@ pub fn fd_prestat_get(
     debug!("wasi::fd_prestat_get: fd={}", fd);
     let memory = ctx.memory(0);
 
-    if let Ok(prestat_ptr) = buf.deref(memory) {
-        // open fd
-        // write info to prestat_ptr
-        __WASI_ESUCCESS
-    } else {
-        __WASI_EFAULT
-    }
+    let prestat_ptr = wasi_try!(buf.deref(memory));
+
+    let state = get_wasi_state(ctx);
+    prestat_ptr.set(wasi_try!(state.fs.prestat_fd(fd)));
+
+    __WASI_ESUCCESS
 }
 
 pub fn fd_prestat_dir_name(

lib/wasi/src/syscalls/types.rs

@@ -191,6 +191,37 @@ pub struct __wasi_prestat_t {
     u: __wasi_prestat_u,
 }
 
+#[derive(Copy, Clone)]
+pub enum PrestatEnum {
+    PreOpenDir { pr_name_len: u32 },
+}
+
+impl __wasi_prestat_t {
+    pub fn get_tagged(&self) -> PrestatEnum {
+        match self.pr_type {
+            __WASI_PREOPENTYPE_DIR => PrestatEnum::PreOpenDir {
+                pr_name_len: unsafe { self.u.dir.pr_name_len },
+            },
+            _ => panic!("Invalid enum variant in __wasi_prestat_t: {}", self.pr_type),
+        }
+    }
+}
+
+impl PrestatEnum {
+    pub fn get_untagged(&self) -> __wasi_prestat_t {
+        match self {
+            PrestatEnum::PreOpenDir { pr_name_len } => __wasi_prestat_t {
+                pr_type: __WASI_PREOPENTYPE_DIR,
+                u: __wasi_prestat_u {
+                    dir: __wasi_prestat_u_dir_t {
+                        pr_name_len: *pr_name_len,
+                    },
+                },
+            },
+        }
+    }
+}
+
 unsafe impl ValueType for __wasi_prestat_t {}
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]