I would use header for this:
(def chunk
(header :int-be
#(ordered-map
:type (b/repeated :byte :length 4)
:data (b/repeated :byte :length %)
:crc (b/repeated :byte :length 4))
#(count (:data %))))
The resulting data structure would not contain the field length in this
case. Length only gets used to configure the inner codec for the body (the
map with :type, :data and :crc). You can read this codec as: "Read a
big-endian integer, then use this value to construct a new codec to read
the body. When writing, count the :data field, write the length using :type and
then write the body".
Steffen
2014-02-03 Stathis Sideris <[email protected]>:
> Hello,
>
> Is it possible to use 'repeated with a dynamic size if the length-defining
> prefix does not directly precede the content? For example, see PNG chunks:
>
>
> http://en.wikipedia.org/wiki/Portable_Network_Graphics#.22Chunks.22_within_the_file
>
> The codec would be:
>
> (def chunk
> (b/ordered-map
> :length :int-be
> :type (b/repeated :byte :length 4)
> :data (b/repeated :byte :length ???)
> :crc (b/repeated :byte :length 4)))
>
> What do I put in the place of "???"
>
> Thanks,
>
> Stathis
>
>
> On Friday, 31 January 2014 08:12:23 UTC, Steffen Dienst wrote:
>>
>> Thanks, I fixed the documentation issues. Feel free to share your id3
>> tags parser, if you like :) You can see that mine is still stuck at the
>> very beginning..
>>
>>
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