Re: [PATCH v1 3/9] qapi: golang: Generate qapi's struct types in Go

[Daniel P . Berrangé]

On Fri, Sep 29, 2023 at 03:29:34PM +0200, Victor Toso wrote:
> Hi,
> 
> On Thu, Sep 28, 2023 at 03:06:23PM +0100, Daniel P. Berrangé wrote:
> > On Wed, Sep 27, 2023 at 01:25:38PM +0200, Victor Toso wrote:
> > > This patch handles QAPI struct types and generates the equivalent
> > > types in Go. The following patch adds extra logic when a member of the
> > > struct has a Type that can take JSON Null value (e.g: StrOrNull in
> > > QEMU)
> > > 
> > > The highlights of this implementation are:
> > > 
> > > 1. Generating an Go struct that requires a @base type, the @base type
> > >    fields are copied over to the Go struct. The advantage of this
> > >    approach is to not have embed structs in any of the QAPI types.
> > >    Note that embedding a @base type is recursive, that is, if the
> > >    @base type has a @base, all of those fields will be copied over.
> > > 
> > > 2. About the Go struct's fields:
> > > 
> > >    i) They can be either by Value or Reference.
> > > 
> > >   ii) Every field that is marked as optional in the QAPI specification
> > >       are translated to Reference fields in its Go structure. This
> > >       design decision is the most straightforward way to check if a
> > >       given field was set or not. Exception only for types that can
> > >       take JSON Null value.
> > > 
> > >  iii) Mandatory fields are always by Value with the exception of QAPI
> > >       arrays, which are handled by Reference (to a block of memory) by
> > >       Go.
> > > 
> > >   iv) All the fields are named with Uppercase due Golang's export
> > >       convention.
> > > 
> > >    v) In order to avoid any kind of issues when encoding or decoding,
> > >       to or from JSON, we mark all fields with its @name and, when it is
> > >       optional, member, with @omitempty
> > > 
> > > Example:
> > > 
> > > qapi:
> > >  | { 'struct': 'BlockdevCreateOptionsFile',
> > >  |   'data': { 'filename': 'str',
> > >  |             'size': 'size',
> > >  |             '*preallocation': 'PreallocMode',
> > >  |             '*nocow': 'bool',
> > >  |             '*extent-size-hint': 'size'} }
> > > 
> > > go:
> > > | type BlockdevCreateOptionsFile struct {
> > > |     Filename       string        `json:"filename"`
> > > |     Size           uint64        `json:"size"`
> > > |     Preallocation  *PreallocMode `json:"preallocation,omitempty"`
> > > |     Nocow          *bool         `json:"nocow,omitempty"`
> > > |     ExtentSizeHint *uint64       `json:"extent-size-hint,omitempty"`
> > > | }
> > 
> > Note, 'omitempty' shouldn't be used on pointer fields, only
> > scalar fields. The pointer fields are always omitted when nil.
> 
> 'omitempty' should be used with pointer fields unless you want to
> Marshal JSON Null, which is not the expected output.

Oh doh, did't notice that.


With regards,
Daniel
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