Re: Looking for pure C function APIs for server extension: language handler and SPI

From: pgsql-general-owner(at)postgresql(dot)org [mailto:pgsql-general-owner(at)postgresql(dot)org] On Behalf Of John McKown
Sent: Wednesday, 2 March 2016 1:03 PM
To: david(at)andl(dot)org
Cc: pgsql-general-owner+M220260=david=andl(dot)org(at)postgresql(dot)org; Postgres General <pgsql-general(at)postgresql(dot)org>
Subject: Re: [GENERAL] Looking for pure C function APIs for server extension: language handler and SPI

On Mon, Feb 29, 2016 at 5:55 PM, <david(at)andl(dot)org <mailto:david(at)andl(dot)org> > wrote:

What I need (to find or create) is a ‘pure’ C language API to support a Postgres server extension. By ‘pure’ I mean one that has no knowledge of Postgres internals and that could be called by a generic interface provided by some other tool that can support C language APIs.

​Well, since nobody else has replied yet, have you read: http://www.postgresql.org/docs/9.5/interactive/libpq.html

Thanks for noticing! Yes, but this is a server extension and libpq is client side. I want to use the generic language call handler and SPI query interface on the server, not client side.

libpq is the C callable API which communicates with the PostgreSQL server. There is a "shared object" and a normal library which can be "statically linked". But that's really all that _I_ know about it.

[dmb>]

​

The reason is that I’m looking to integrate a new language (Andl) into Postgres. To do that I need to find or create a ‘pure’ C-language API to interface with:

1. The generic language call interface (pl_language_handler), which must handle conversion of Incoming language call parameters and outgoing language call return value.

1. The backend query execution interface (SPI), which must handle conversion of outgoing query parameters and incoming query result values.

There are 5 generic data types: boolean, binary (blob), number (decimal/real/integer), text (string/varchar), time (date/datetime). Each data type needs to be converted between the Postgres internal data types (Datum) and some intermediate data type that can be passed through a pure C API. In my case that will be C# (MS or Mono), but others might want to use Java or whatever.

These conversion tasks are identical to those needed to implement an ODBC/JDBC or similar interface, but one bound directly to the server and not going through a client (socket) connection. I have already done this successfully with Sqlite, which already provides a pure C server API and excellent documentation to go with it, so I know what it might look like.

FYI apart from these two APIs (and their 4x5 conversions), the only other thing needed is some SQL code generation and I expect to have a working language of considerable power.

Any help, suggestions, pointers much appreciated.

Regards

David M Bennett FACS

_____

Andl - A New Database Language - andl.org <http://andl.org>

--

The man has the intellect of a lobotomized turtle.

Maranatha! <><
John McKown