Hi All,
Tying to use binpac to create a new protocol analyzer I run into a small issue relative to byte alignment. I am thinking this must be a known aspect however I didn’t find much documentation about it.
Padding in binpac works well inside the packet. However, sometime the packet ends with a structure that requires padding but the packet doesn’t carry the extra bytes for the padding. As a result binpac fires an exception and the parsing is terminated before extracting the data.
Here is a sample code:
type ByteArray = record{
len : uint32;
data: uint8[len];
pad : padding align 4;
};
When the last 6 bytes of a packet that ends with the above record is: 00 00 00 02 AA BB (with: len=00 00 00 02; data ={AA, BB}) binpac throws:
0.000000 binpac exception: binpac exception: out_of_bound: ByteArray: 8 > 6
Removing the padding entry from the code above results in a correct execution, however the padding is needed for the case when ByteArray is strictly inside the packet.
The solution I am thinking is way too complex (pass some arguments that will help decide if the padding is needed), but I was wondering if there is a much more elegant approach.
Another option will be to change the binpac compiler code (pac_record.cc) in method: void RecordPaddingField::GenFieldEnd(Output* out_cc, Env* env, const DataPtr& field_begin) but I am thinking this case should be covered in a different way.
Any suggestions would be greatly appreciated.
Thank you,
Laurentiu Cucos
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