make runtime compatible with wasm

runtime/internal/lib/io/fs/fs.go

@@ -0,0 +1,42 @@
+package fs
+
+import (
+	"io"
+	"io/fs"
+)
+
+func ReadFile(fsys fs.FS, name string) ([]byte, error) {
+	if fsys, ok := fsys.(fs.ReadFileFS); ok {
+		return fsys.ReadFile(name)
+	}
+
+	file, err := fsys.Open(name)
+	if err != nil {
+		return nil, err
+	}
+
+	var size int
+	if info, err := file.Stat(); err == nil {
+		size64 := info.Size()
+		if int64(int(size64)) == size64 {
+			size = int(size64)
+		}
+	}
+
+	data := make([]byte, 0, size+1)
+	for {
+		if len(data) >= cap(data) {
+			d := append(data[:cap(data)], 0)
+			data = d[:len(data)]
+		}
+		n, err := file.Read(data[len(data):cap(data)])
+		data = data[:len(data)+n]
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+			}
+			file.Close()
+			return data, err
+		}
+	}
+}