Re: Understanding D specs

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hi Pete,

> 0044.00  ** Connection Description Info structure
> 0045.00 D p_CnnDscInfo    S               *   inz(*NULL)
> 0046.00 D dsCnnDscInfo    DS                  based(p_CnnDscInfo)
> 0046.01 D  dsLenCnnInfo                 10I 0
> 0046.02 D  dsCnnIntrAdd                 20A
> 0046.03 D  dsCnnPwdVal                   1A
> 0046.04 D  dsCnnWrkTyp                  12A
> 0050.01 D  dsCnnSSLCnn                   1A

Heh... it always brings a smile to my face when I see my code resurface!
and this is undoubtedly my code, with one difference...

In my copy of this data structure, I don't have dsCnnSSLCnn.  Did you add
that?


> Offset
> Dec Hex  Type     Field
> 0   0    INT(4)       Length of connection description information
> 4   4    CHAR(20) Client internet address
> 24 18    CHAR(1)  Client password validated
> 25 19    CHAR(12) Workstation type
> 39 27    CHAR(1)  Secure socket layer connection
> 40 28    CHAR(20) Server (local) internet address
> 60 3C    CHAR(1)  Client authentication level
> 61 3D    CHAR(3)  Reserved
> 64 40    INT(4)   Client certificate valid rc
> 68 44    INT(4)   Offset to client certificate
> 72 48    INT(4)   Client certificate length

When you don't specify from & to positions in a data structure, and you
don't specify overlay, the compiler simply puts the fields one after the
other, so that they occupy contiguous bytes in the structure.

If you know the size of each variable in the data structure, you can
calculate the from/to positions, like this:

     D dsCnnDscInfo    DS                  based(p_CnnDscInfo)
     D  dsLenCnnInfo                 10I 0

A "10I 0" field is 4 bytes long.  Since it's at the start of the data
structure, it'll take up positions 1-4.

     D  dsCnnIntrAdd                 20A

This field goes immediately after the last one.  Since the last one ended
in position 4, this one starts in position 5.   Since it's 20 bytes long,
it occupies positions 5-24

     D  dsCnnPwdVal                   1A

again, right after...  positions 25-25.

     D  dsCnnWrkTyp                  12A

positions 26-37

     D  dsCnnSSLCnn                   1A

position 38 -- which is a problem because, according to the stuff you
posted from the manual, it should start in position 40.  Note that all of
the others start in the correct position, but this one does not.

There must be an undocumented 2-byte "reserved" field that's between
dsCnnWrkTyp and dsCnnSSLCnn.  ILE RPG has a neat feature that you can use
to add spaces into a data structure -- you can define a field with no name
just to take up space.

I'd define the complete data structure as follows (untested):

      D dsCnnDscInfo    DS                  based(p_CnnDscInfo)
      D  dsCnnLen                     10I 0
      D  dsCnnAddr                    20A
      D  dsCnnPWvalid                  1A
      D  dsCnnWStype                  12A
      D                                2A
      D  dsCnnSSLCnn                   1A
      D  dsCnnSrvrIP                  20A
      D  dsCnnCliAuth                  1A
      D                                3A
      D  dsCnnCrtRC                   10I 0
      D  dsCnnCrtOff                  10I 0
      D  dsCnnCrtLen                  10I 0

Actually, if I had this project to do over, I'd switch it to use qualified
data structures, but I wrote it before the QUALIFIED keyword was added to
the language.

> Just need a bit of direction so I know where to look for the SSL connection
> flag.

Hopefully I've answered that question.

A note of caution about telnet exit programs:

When defining a program like this, please be very careful about who
has access to change it.   When you set the "peAllowSignOn" parameter to
'1' (or *ON) the system will allow people to auto-sign on.  EVEN IF THEY
HAVE THE WRONG PASSWORD.

Only set peAutoSignOn = '1' if the dsCnnPWvalid field tells you that the
password is valid.

and then, make sure that the compiled *PGM object is locked down.
Otherwise, a programmer could change peAllowSignOn to *ON, recompile it,
log on as QSECOFR, and change it back...

If you make it so that only people with *ALLOBJ can recompile this
program, you shouldn't have any problems.