AWS: what is the difference between Response.Acknowledge and Response.Build ?

[Natasha Kerensikova <lithiumcat@instinctive.eu>]

Hello,

I have little question about these functions in AWS.Response:

   function Build
     (Content_Type  : String;
      Message_Body  : String;
      Status_Code   : Messages.Status_Code      := Messages.S200;
      Cache_Control : Messages.Cache_Option     := Messages.Unspecified;
      Encoding      : Messages.Content_Encoding := Messages.Identity)
      return Data
   with Post => not Is_Empty (Build'Result);
   --  Return a message whose body is passed into Message_Body. The
   --  Content_Type parameter is the MIME type for the message
   --  body. Status_Code is the response status (see Messages.Status_Code
   --  definition).


   function Acknowledge
     (Status_Code  : Messages.Status_Code;
      Message_Body : String := "";
      Content_Type : String := MIME.Text_HTML) return Data
   --  Returns a message to the Web browser. This routine must be used to
   --  send back an error message to the Web browser. For example if a
   --  requested resource cannot be served a message with status code S404
   --  must be sent.

What is exactly the difference between `Build (Type_Str, Body_Str, S404);`
and `Acknowledge (S404, Body_Str, Type_Str);` ?

Peeking into the implementation, it seems there is currently no
difference between them, however the quoted comments imply a semantic
difference. I guess that means that it means that an implementation
difference might emerge in the future.

The problem with comments is that they can be a bit more ambiguous than
Ada code.

Is "must" as strong as when it is used in RFCs? Or is more like a piece
of advice?

What is an "error message"? Does it include 3xx HTTP codes?

Or am I wrong interpreting the comments, with Acknowldge and Build
equivalent when a response body is present, while Acknowldge is able to
build header-only responses?


Thanks in advance for your insights,
Natasha