Re: hf_http_response_code in packet-http.c

["Sultan, Hassan via Wireshark-dev" <wireshark-dev () wireshark org>]

> -----Original Message-----
> From: Pascal Quantin [mailto:pascal.quantin () gmail com]
> Sent: Thursday, July 13, 2017 10:39 AM
> To: Developer support list for Wireshark <wireshark-dev () wireshark org>
> Cc: Sultan, Hassan <sultah () amazon com>
> Subject: Re: [Wireshark-dev] hf_http_response_code in packet-http.c
>
> Hi Hassan,
>
>
> 2017-07-13 19:25 GMT+02:00 Sultan, Hassan via Wireshark-dev <wireshark-
> dev () wireshark org <mailto:wireshark-dev () wireshark org> >:
>
>
>
>
>       > -----Original Message-----
>       > From: Wireshark-dev [mailto:wireshark-dev-bounces () wireshark org
> <mailto:wireshark-dev-bounces () wireshark org> ] On Behalf
>       > Of Erik de Jong
>       > Sent: Wednesday, July 12, 2017 10:12 PM
>       > To: Developer support list for Wireshark <wireshark-
> dev () wireshark org <mailto:wireshark-dev () wireshark org> >
>       > Subject: Re: [Wireshark-dev] hf_http_response_code in packet-http.c
>       >
>       >
>       >
>       > On Thu, Jul 13, 2017 at 1:12 AM, Sultan, Hassan via Wireshark-dev
> <wireshark-
>       > dev () wireshark org <mailto:dev () wireshark org>  <mailto:wireshark-
> dev () wireshark org <mailto:wireshark-dev () wireshark org> > > wrote:
>       >
>       >
>       >       Hi,
>       >
>       >
>       >
>       >       I am starting to learn the Wireshark code base, and one thing
> puzzles
>       > me…
>       >
>       >
>       >
>       >       Why is hf_http_response_code defined as a FT_UINT16 with
> BASE_DEC
>       > rather than an FT_STRING ?
>       >
>       >
>       >
>       >       It’s a text field… not an integer.
>       >
>       >
>       > Presenting it as a number allows for filtering like:
>       > http.response.code > 200
>       >
>       > Which would not be possible when presented as a string.
>
>       Thanks for the info, but in that case would it not be more appropriate to
> have the normal field as an FT_STRING and add a generated field as FT_UINT16
> ? My understanding of generated fields is that this is their purpose : represent
> data that doesn't exactly correspond to the packet data.
>       We could still keep the field named as is today (hence ensuring all
> existing filters still work), but simply make it a generated field, and add an
> FT_STRING to represent the actual data as it is in the packet.
>
>       Thoughts ?
>
>
>
>
> Does having the field as it is designed today generating you any issue? For fields
> having numerical values only, it makes much more sense to have the digits
> directly instead of the string and that's already what we are doing in numerous
> places. And personally I do not see any valid reason to change that. Your
> suggestion implies that many fields would start to be duplicated without any
> added value.

My reason is that anyone wanting to build automation based on Wireshark's parsing will not be able to rely on 
Wireshark's reporting of field type & format to interpret the packet data.
The automation would walk through parsed fields and be told that the http response code is a 3-bytes UINT16 with value 
say 200, so bytes 00 00 c8, which is wrong. Right now the way these fields are setup works for human interpretation, by 
people looking at the rendered value on a screen, but it is far from ideal for automation. One could argue it's the 
main purpose of Wireshark, but I think it needlessly prevent a whole class of use-cases from being achieved with 
Wireshark's technology.

Thanks,

Hassan
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