Function msg_lsp_buffer 

pub fn msg_lsp_buffer(
    lsp_id: u16,
    flags: u8,
    path: &str,
    text: &[u8],
) -> Vec<u8> 

Build a C2S_LSP_BUFFER: text is the full buffer content, LZ4-compressed on the wire. A LSP_BUFFER_RELEASE must carry empty text.