implement wasi::readlink

lib/runtime-core/src/memory/ptr.rs

@@ -126,6 +126,15 @@ impl<T: Copy + ValueType> WasmPtr<T, Array> {
             [index as usize..slice_full_len];
         Some(cell_ptrs)
     }
+
+    pub fn get_utf8_string<'a>(self, memory: &'a Memory, str_len: u32) -> Option<&'a str> {
+        if self.offset as usize + str_len as usize > memory.size().bytes().0 {
+            return None;
+        }
+        let ptr = unsafe { memory.view::<u8>().as_ptr().add(self.offset as usize) as *const u8 };
+        let slice: &[u8] = unsafe { std::slice::from_raw_parts(ptr, str_len as usize) };
+        std::str::from_utf8(slice).ok()
+    }
 }
 
 unsafe impl<T: Copy, Ty> WasmExternType for WasmPtr<T, Ty> {

lib/wasi/src/ptr.rs

@@ -75,4 +75,9 @@ impl<T: Copy + ValueType> WasmPtr<T, ptr::Array> {
     ) -> Result<&'a [Cell<T>], __wasi_errno_t> {
         self.0.deref(memory, index, length).ok_or(__WASI_EFAULT)
     }
+
+    #[inline(always)]
+    pub fn get_utf8_string<'a>(self, memory: &'a Memory, str_len: u32) -> Option<&'a str> {
+        self.0.get_utf8_string(memory, str_len)
+    }
 }

lib/wasi/src/syscalls/mod.rs

@@ -1608,7 +1608,29 @@ pub fn path_readlink(
     buf_used: WasmPtr<u32>,
 ) -> __wasi_errno_t {
     debug!("wasi::path_readlink");
-    unimplemented!("wasi::path_readlink")
+    let state = get_wasi_state(ctx);
+    let memory = ctx.memory(0);
+
+    let base_dir = wasi_try!(state.fs.fd_map.get(&dir_fd).ok_or(__WASI_EBADF));
+    let path_str = wasi_try!(path.get_utf8_string(memory, path_len).ok_or(__WASI_EINVAL));
+    let result = wasi_try!(std::fs::read_link(path_str).ok().ok_or(__WASI_EIO));
+    let result_path_as_str = result.to_string_lossy();
+    let bytes = result_path_as_str.bytes();
+    if bytes.len() < buf_len as usize {
+        return __WASI_EOVERFLOW;
+    }
+
+    let out = wasi_try!(buf.deref(memory, 0, buf_len));
+    let mut bytes_written = 0;
+    for b in bytes {
+        out[bytes_written].set(b);
+        bytes_written += 1;
+    }
+
+    let bytes_out = wasi_try!(buf_used.deref(memory));
+    bytes_out.set(bytes_written as u32);
+
+    __WASI_ESUCCESS
 }
 
 pub fn path_remove_directory(