subchunks

[Andre]

I'm a little confused on the format of subchunks. Could someone clear
this part of please.

The document states,
That is, for SUB-DATA, in the case of a COUNT value of 0, only an
ADDCHUNKNUM will be present following the COUNT, to indicate the add
chunk that contained the host key. In the case of COUNT >= 1, there
will be 1 or more [ADDCHUNKNUM PREFIX] pairs.

For the data below,

s:5282:4:26
54 94 1B FD 01 00 02 6F 3A 6B 14 54 ED 37 7F 37 6D 01 00 02 59 F9 14
7A 9F 41

hostkey = 54 94 1B FD
count = 01
ADDCHUNKNUM = 00 02 6F 3A
PREFIX = 6B 14 54 ED
ADDCHUNKNUM = 37 7F 37 6D
PREFIX = 01 00 02 59
ADDCHUNKNUM = F9 14 7A 9F
PREFIX = 41

hostkey = 4 bytes, count = 1 byte, ADDCHUNKNUM = 4 bytes, PREFIX = 4
bytes.

I'm a little confused because the last prefix is only 1 byte, am I
making a mistake somewhere?

Thanks in advance.

[Mark Maunder]

Hi Andre,

It looks like this sub-data actually contains two hostkeys. So you'd break it up like this:

Hostkey: 54 94 1B FD 

Count: 01 

Addchunknum: 00 02 6F 3A 

Prefix: 6B 14 54 ED 

Hostkey: 37 7F 37 6D 

Count: 01 

Addchunknum: 00 02 59 F9 

Prefix: 14 7A 9F 41

Notice the "count" is 1, not two, so you only parse the first addchunk/prefix combination, then assume there's another hostkey/count/data section because the length specified was 26 bytes in the "s:5282:4:26" header. 

In the docs you'll see the RBNF looks like this:

SUB-DATA    = (HOSTKEY COUNT (ADDCHUNKNUM | (ADDCHUNKNUM PREFIX)+))+

Notice the plus sign right at the end which indicates they can stuff multiple hostkey/count/data entries into a single sub-data section. 

Kind regards,

Mark.

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Mark Maunder <mmau...@gmail.com>
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[Andre]

Thank you Mark, that makes sense.

> Mark Maunder <mmaun...@gmail.com>
> France: (+33) 068-700-8029