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Tue, 5 Jul 2022 16:47:29 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.72]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6218A1415108; Tue, 5 Jul 2022 16:47:28 +0000 (UTC) Date: Tue, 5 Jul 2022 17:47:25 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Andrea Bolognani Cc: Victor Toso , qemu-devel@nongnu.org, Eric Blake , Markus Armbruster , John Snow Subject: Re: [RFC PATCH v2 5/8] qapi: golang: Generate qapi's event types in Go Message-ID: References: <20220617121932.249381-1-victortoso@redhat.com> <20220617121932.249381-6-victortoso@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.6 (2022-06-05) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.7 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jul 05, 2022 at 08:45:54AM -0700, Andrea Bolognani wrote: > On Fri, Jun 17, 2022 at 02:19:29PM +0200, Victor Toso wrote: > > This patch handles QAPI event types and generates data structures in > > Go that handles it. > > > > We also define a Event interface and two helper functions MarshalEvent > > and UnmarshalEvent. > > > > At the moment of this writing, this patch generates 51 structures (50 > > events) > > > > Example: > > > > qapi: > > | { 'event': 'MEMORY_DEVICE_SIZE_CHANGE', > > | 'data': { '*id': 'str', 'size': 'size', 'qom-path' : 'str'} } > > > > go: > > | type MemoryDeviceSizeChangeEvent struct { > > | EventTimestamp Timestamp `json:"-"` > > | Id *string `json:"id,omitempty"` > > | Size uint64 `json:"size"` > > | QomPath string `json:"qom-path"` > > | } > > > > usage: > > | input := `{"event":"MEMORY_DEVICE_SIZE_CHANGE",` + > > | `"timestamp":{"seconds":1588168529,"microseconds":201316},` + > > | `"data":{"id":"vm0","size":1073741824,"qom-path":"/machine/unattached/device[2]"}}` > > | e, err := UnmarshalEvent([]byte(input) > > | if err != nil { > > | panic(err) > > | } > > | if e.GetName() == `MEMORY_DEVICE_SIZE_CHANGE` { > > | m := e.(*MemoryDeviceSizeChangeEvent) > > | // m.QomPath == "/machine/unattached/device[2]" > > | } > > func (s *AcpiDeviceOstEvent) GetTimestamp() Timestamp { > > return s.EventTimestamp > > } > > Does this even need a getter? The struct member is public, and Go > code seems to favor direct member access. It satisfies the 'Event' interface, so you can fetch timestamp without needing to know the specific event struct you're dealing with. > > > type Timestamp struct { > > Seconds int64 `json:"seconds"` > > Microseconds int64 `json:"microseconds"` > > } > > > > type Event interface { > > GetName() string > > GetTimestamp() Timestamp > > } > > > > func UnmarshalEvent(data []byte) (Event, error) { > > base := struct { > > Name string `json:"event"` > > EventTimestamp Timestamp `json:"timestamp"` > > }{} > > if err := json.Unmarshal(data, &base); err != nil { > > return nil, errors.New(fmt.Sprintf("Failed to decode event: %s", string(data))) > > } > > > > switch base.Name { > > > > case "ACPI_DEVICE_OST": > > event := struct { > > Data AcpiDeviceOstEvent `json:"data"` > > }{} > > > > if err := json.Unmarshal(data, &event); err != nil { > > return nil, errors.New(fmt.Sprintf("Failed to unmarshal: %s", string(data))) > > } > > event.Data.EventTimestamp = base.EventTimestamp > > return &event.Data, nil > > > > // more cases here > > } > > return nil, errors.New("Failed to recognize event") > > } > > While I understand the need to have some way to figure out exactly > what type of event we're looking at before being able to unmarshal > the JSON data, I don't like how we force users to go through a > non-standard API for it. > > Here's how I think we should do it: > > func GetEventType(data []byte) (Event, error) { > type event struct { > Name string `json:"event"` > } > > tmp := event{} > if err := json.Unmarshal(data, &tmp); err != nil { > return nil, errors.New(fmt.Sprintf("Failed to decode event: > %s", string(data))) > } > > switch tmp.Name { > case "ACPI_DEVICE_OST": > return &AcpiDeviceOstEvent{}, nil > > // more cases here > } > > return nil, errors.New("Failed to recognize event") > } > > func (s *AcpiDeviceOstEvent) UnmarshalJSON(data []byte) error { > type eventData struct { > Info ACPIOSTInfo `json:"info"` > } > type event struct { > Name string `json:"event"` > EventTimestamp Timestamp `json:"timestamp"` > Data eventData `json:"data"` > } > > tmp := event{} > err := json.Unmarshal(data, &tmp) > if err != nil { > return err > } > if tmp.Name != "ACPI_DEVICE_OST" { > return errors.New("name") > } > > s.EventTimestamp = tmp.EventTimestamp > s.Info = tmp.Data.Info > return nil > } > > This way, client code can look like > > in := `{"event":"ACPI_DEVICE_OST","timestamp":{"seconds":1265044230,"microseconds":450486},"data":{"info":{"device":"d1","slot":"0","slot-type":"DIMM","source":1,"status":0}}}` > > e, err := qapi.GetEventType([]byte(in)) > if err != nil { > panic(err) > } > // e is of type AcpiDeviceOstEvent > > err = json.Unmarshal([]byte(in), &e) > if err != nil { > panic(err) > } > > where only the first part (figuring out the type of the event) needs > custom APIs, and the remaining code looks just like your average JSON > handling. I don't think this kind of detail really needs to be exposed to clients. Also parsing the same json doc twice just feels wrong. I think using the dummy union structs is the right approach, but I'd just call it 'EventFromJSON' rather than 'UnmarshalJSON' to make it clear this is different from a normal 'UnmarshalJSON' method. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|