model/annotation.go

// Copyright 2022 The OpenZipkin Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package model

import (
	"encoding/json"
	"errors"
	"time"
)

// ErrValidTimestampRequired error
var ErrValidTimestampRequired = errors.New("valid annotation timestamp required")

// Annotation associates an event that explains latency with a timestamp.
type Annotation struct {
	Timestamp time.Time
	Value     string
}

// MarshalJSON implements custom JSON encoding
func (a *Annotation) MarshalJSON() ([]byte, error) {
	return json.Marshal(&struct {
		Timestamp int64  `json:"timestamp"`
		Value     string `json:"value"`
	}{
		Timestamp: a.Timestamp.Round(time.Microsecond).UnixNano() / 1e3,
		Value:     a.Value,
	})
}

// UnmarshalJSON implements custom JSON decoding
func (a *Annotation) UnmarshalJSON(b []byte) error {
	type Alias Annotation
	annotation := &struct {
		TimeStamp uint64 `json:"timestamp"`
		*Alias
	}{
		Alias: (*Alias)(a),
	}
	if err := json.Unmarshal(b, &annotation); err != nil {
		return err
	}
	if annotation.TimeStamp < 1 {
		return ErrValidTimestampRequired
	}
	a.Timestamp = time.Unix(0, int64(annotation.TimeStamp)*1e3)
	return nil
}