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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Reading a C record from socket - chicken / egg problem - now
 complete
Date: 23 Nov 2002 17:31:21 +0000
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wojtek@power.com.pl (Wojtek Narczynski) writes:

> I want to read a record like this:
> 
>    typedef struct {
>       unsigned char version;
>       unsigned char type;
>       unsigned char requestIdB1;
>       unsigned char requestIdB0;
>       unsigned char contentLengthB1;
>       unsigned char contentLengthB0;
>       unsigned char paddingLength;
>       unsigned char reserved;
>       unsigned char contentData[contentLength];
>       unsigned char paddingData[paddingLength];
>    } FCGI_Record;
> 
> from socket. The 'type' field indicates different record type, so I
> could declare different record types in Ada, but when I know 'type'
> the record is already in memory. How should I approach this: 1. use
> Unchecked_Conversion to convert to appropriate type? 2. Copy data into
> a new record of appropriate type? 3. Just live with the structure C
> imposes?

Declare a structure corresponding to the fields version .. reserved
inclusive (use Interfaces.C.unsigned_char). and read it from the socket.

Calculate the actual contentLength and paddingLength.

Use a declare block:

  declare
    type content is array (1 .. contentLength) of Interfaces.C.unsigned_char;
    type padding is array (1 .. paddingLength) of Interfaces.C.unsigned_char;
    type remainder is record
      c : content;
      p : padding;
    end record;
    r : remainder;
  begin
    -- read r from the socket and process it
  end;

I know this means doing 2 reads but that's the minimum.