use std.os.sendfile with zig std.http.server

std.http.server.sendfile.zig

fn sendfile(res: *std.http.Server.Response, filename: []const u8) !void {
    var file = std.fs.cwd().openFile(filename, .{}) catch {
        // TODO - Add any extra 404 handling code here
        res.status = .not_found;
        try res.do();
        return;
    };

    defer file.close();
    const file_len = try file.getEndPos();

    res.transfer_encoding = .{ .content_length = file_len };
    try res.do();

    const zero_iovec = &[0]std.os.iovec_const{};   
    var send_total: usize = 0;

    while (true) {
        const send_len = try std.os.sendfile(
            res.connection.conn.stream.handle, 
            file.handle, 
            send_total, 
            file_len, 
            zero_iovec, zero_iovec, 0);

        if (send_len == 0)
            break;

        send_total += send_len;
    }
}

// Example Usage from a handler function
fn handler(res: *Server.Response) !void {
    while (true) { 
        defer res.reset();
        try res.wait();
        switch (res.request.method) {
            .GET => {
                // TODO - sanity check that they are asking for a file here
                // TODO - validate the file / 404 check / check if its a file or dir or whatever ...
                try sendfile(res, res.request.target[1..]);
            },
            else => {
                // do the thing
            },
        }
        if (res.connection.conn.closing) break;
    }
}