[Libguestfs] [PATCH nbdkit UNFINISHED] Add the ability to write plugins in golang.

[Richard W.M. Jones]

On Wed, Apr 15, 2020 at 05:27:07PM +0100, Daniel P. Berrangé wrote:
> On Fri, Apr 10, 2020 at 02:51:52PM +0100, Richard W.M. Jones wrote:
> > Similar to C, OCaml and Rust, this is not a plugin per se.  Instead
> > it's more of a method and set of tests around writing plugins in
> > golang.  They are standalone programs that compile into shared objects
> > that nbdkit can then load (so there is no "go plugin" between nbdkit
> > and the user plugin, unlike in scripting languages like Perl).
> 
> Why did you choose this approach ?

Do you mean the design of constructing the .so file directly using
--buildmode=c-shared?  I wasn't aware there was any other way to do
it.  Should we use some kind of module loading instead?

> Looking at the code below there's the general boilerplate that
> will be approx the same for all plugins with cut+paste tedium
> across projects, and then there's the "interesting" code in
> test.go
> 
> The methods in test.go though look quite unappealing from a
> Go programmer's POV, as the API contracts are full of CGo
> types and unsafe pointers.
>
> To make something that is attractive for Go programmers, I
> think it needs to hide all the low level CGo stuff entirely.
> 
> Implementing a nbdkit plugin should require nothing more
> that providing pure Go code that satisfies  a well defined
> Go "interface" type definition. There should not be any
> copy+paste of example boilerplate, nor any use of CGo.

I don't disagree, I just have no idea how to achieve this.

> As an illustration, consider an interface and basic infrastructure:
[...]

I'll have a go at changing it like this, but I don't see how this
changes any of the fundamental problems, but maybe I will understand
more once I've done that.

Rich.

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