isValidScheme

fn isValidScheme(scheme: []const u8) bool {
    if (scheme.len == 0) return false;
    if (!std.ascii.isAlphabetic(scheme[0])) return false;
    for (scheme[1..]) |byte| {
        switch (byte) {
            'A'...'Z', 'a'...'z', '0'...'9', '+', '-', '.' => continue,
            else => return false,
        }
    }
    return true;
}