File: Add methods to read/write using buffers

libos/include/os/File.h

@@ -31,9 +31,12 @@ namespace os
         void set_close_on_exec();
 
         Result<void> write(StringView str);
+        Result<void> write(const Buffer& buf);
 
         Result<String> read_line();
 
+        Result<void> read(Buffer& buf, usize size);
+
         Result<int> getchar();
 
         File(Badge<File>);

libos/src/File.cpp

@@ -101,6 +101,13 @@ namespace os
         return {};
     }
 
+    Result<void> File::write(const Buffer& buf)
+    {
+        TRY(raw_write(buf.data(), buf.size()));
+
+        return {};
+    }
+
     Result<String> File::read_line()
     {
         Vector<char> data;
@@ -124,6 +131,17 @@ namespace os
         return String::from_cstring(data.data());
     }
 
+    Result<void> File::read(Buffer& buf, usize size)
+    {
+        u8* slice = TRY(buf.slice(0, size));
+
+        usize nread = TRY(raw_read(slice, size));
+
+        TRY(buf.try_resize(nread));
+
+        return {};
+    }
+
     Result<int> File::getchar()
     {
         char value;