Re: string manipulation

[Guy Harris <guy () alum mit edu>]

On Jan 25, 2010, at 1:37 PM, Brian Oleksa wrote:

> Does each packet have to have it's own hf_value..??

Each *packet* doesn't have to have its own hf_ value.

Each *field in the protocol* *is* supposed to have its own hf_ value.

> Or could I just use 
> something like that following for all strings (hf_helen_text)..??
>
>        { &hf_helen_text,
>            { "Text", "helen.text", FT_STRING, BASE_NONE, NULL, 0x0,
>                "Text", HFILL}}

You could, but that would be wrong.

It would mean that either

        1) all text fields would look like

                Text: {string value}

or

        2) you'd have to use proto_tree_add_string_format() and do extra work for no benefit.

It would also mean that if somebody wanted to find packets where a *particular* string, such as the flow name, had a 
particular value, they couldn't just do

        helen.flowname == "test"

> I am also fixing all the places where I used "hf_helen_length".
> What is wrong with using hf_helen_length (as this could be very generic)..??

What's wrong with it is that it's *too* generic. :-)  See above.

> For example... would you create a hf_value such as (hf_helen_nos) for 
> the following example..??
>
>                    // Number of Satellites:
>                        guint8 nos;
>                        nos = tvb_get_guint8(tvb,offset);
>                        proto_tree_add_uint_format(helen_sub_tree, 
> hf_helen_length, tvb, offset, 1, 0,
>                                "Number of Satellites: %d", nos);

I would most definitely do so!  That's how Wireshark dissectors are supposed to work.

> What would this hf_item look like..?? Would it look something like this..??
>
>        { &hf_helen_nos,
>            { "nos", "helen.len", FT_UINT8, BASE_DEC, NULL, 0x0,
>                "nos", HFILL}},

No, it would look like

      { &hf_helen_nos,
           { "Number of Satellites", "helen.nos", FT_UINT8, BASE_DEC, NULL, 0x0,
               "Number of satellites", HFILL}},

although the second "Number of satellites" could give more detail - it's used in tooltips as a description of the field.
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