[pcap-ng-format] opt_endofopt unnecessary?

[Guy Harris]

Section 2.5 "Options" of the pcap-NG spec says:

> Skipping all the optional fields at once is straightforward because most of the blocks are made of a first part with fixed format, and a second optional part. Therefore, the Block Length field (present in the General Block Structure, see Section 2.1) can be used to skip everything till the next block.

This also means that the Block Length field can be used to determine the number of bytes of options in the block.  That also means that the Block Length field can be used to determine when you're at the end of the block when scanning options, so there doesn't need to be an opt_endofopt option at the end of the list of options to mark the end.

Furthermore, any robust pcap-NG reading code has to stop processing options when it runs out of bytes in the block, regardless of whether there's an opt_endofopt option, so that option doesn't simplify the option parsing code.

The spec doesn't explicitly say opt_endofopt is required, it just says "It delimits the end of the optional fields."

My inclination would be to deprecate it, so that a reader:

	must not assume it's present (which is the case anyway, even if it gives an error if it's not present, as a reader has to handle malformed files without crashing or doing anything else wrong by reading past the end of the block);

	must not return an error if it's absent;

	must stop parsing options if it's present (in case some app writes one out and then has other junk past it in the block).