From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	ip-172-31-65-14.ec2.internal
X-Spam-Level: 
X-Spam-Status: No, score=-0.9 required=3.0 tests=BAYES_00,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no
	version=3.4.6
Path: eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: magardner2010 <magardner2010@gmail.com>
Newsgroups: comp.lang.ada
Subject: gnat -xdr flag confusion.
Date: Tue, 4 Jul 2023 13:56:26 +0300
Organization: A noiseless patient Spider
Message-ID: <u80tsr$33eu$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Tue, 4 Jul 2023 10:56:27 -0000 (UTC)
Injection-Info: dont-email.me; posting-host="8b58e21d8aa207bd5829e6e61f9e0d23";
	logging-data="101854"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+tMcdlOxeSQZQE0dz1PxHRVSGGoROuGoc="
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.12.0
Cancel-Lock: sha1:tz+SJ4kSBFD7kINmNsRvFYUfZm0=
Content-Language: en-GB
Xref: news.eternal-september.org comp.lang.ada:65422
List-Id: <comp.lang.ada>

I'm still working on the p2p one-to-many data streaming protocol thing 
(at https://github.com/smeagolthellama/szakdolgozat-notes/tree/main/ada) 
and I'm trying to get it to communicate with a C thing via the xdr 
protocol. I'm trying to transfer a Child_Set, where
```
     type Child_Number is range 0 .. 2;
     subtype Child_Index is Child_Number range 1 .. Child_Number'Last;

     type Child_Set is array (Child_Index) of GNAT.Sockets.Sock_Addr_Type;
```
With the help of chatGPT, I wrote the following xdr spec file:
```
const CHILD_NUMBER = 2;

typedef unsigned int uint32;
typedef unsigned char uint8;

enum family_type {
   FAMILY_INET = 0,
   FAMILY_INET6 = 1,
   FAMILY_UNIX = 2,
   FAMILY_UNSPEC = 3
};

union inet_addr_type switch (family_type family) {
   case FAMILY_INET:
     opaque sin_v4[4];
   case FAMILY_INET6:
     opaque sin_v6[16];
   default:
     void;
};

struct address_and_port{
   inet_addr_type addr;
   unsigned int port;
};

union sock_addr_type switch (family_type family) {
   case FAMILY_UNIX:
     string name<>;
   case FAMILY_INET:
     address_and_port anp4;
   case FAMILY_INET6:
     address_and_port anp6;
   case FAMILY_UNSPEC:
     void;
};

struct child_set {
   sock_addr_type child_set_array[CHILD_NUMBER];
};
```
and using rpcgen, generated a C thing to encode/decode the messages the 
ada program is sending.

However, if the ada code encodes the object with 'write, then it creates 
something about 4 bytes too short, and if I use 'output, it is parsed as 
starting with family_type 256, which is not a member of the enum. Given 
that the gnat documentation for the -xdr flag is literally two lines, I 
don't really know where to look for more information on what I'm doing 
wrong. My current hypotheses include the C code having the family type 
recorded too many times (but I don't know how to check or fix that in 
the .x file) or the ada code not encoding the data according to the xdr 
standard correctly (but I am using the flag, and neither 'write or 
'output fixes it).