On Jun 10, 2016, at 4:09 PM, Guy Harris <[email protected]> wrote:
> The spec should discuss that more, including emphasizing that a reader must
> pay attention to the block total length when processing options - or deciding
> whether there are any options to process. I'll look at doing that.
OK, the spec now says
All the block bodies MAY embed optional fields. Optional fields can be
used to insert some information that may be useful when reading data, but that
is not really needed for packet processing. Therefore, each tool can either
read the content of the optional fields (if any), or skip some of them or even
all at once.
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 3.1) can be used to determine how many bytes of optional
fields, if any, are present in the block. That value can be used to determine
whether the block has optional fields (if it is zero, there are no optional
fields), to check, when processing optional fields, whether any optional fields
remain, and to skip all the optional fields.
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