trace_decode.go

/*
	Copyright NetFoundry Inc.

	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

	https://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 channel

import (
	"encoding/json"
	"fmt"
	"reflect"
	"sort"
)

// TraceMessageDecoder decodes a Message into a JSON byte representation for tracing.
type TraceMessageDecoder interface {
	Decode(msg *Message) ([]byte, bool)
}

// TraceMessageDecode is a map of trace metadata fields, serializable to JSON.
type TraceMessageDecode map[string]interface{}

// DecoderFieldName is the JSON key for the decoder name in trace output.
const DecoderFieldName = "__decoder__"

// MessageFieldName is the JSON key for the message type name in trace output.
const MessageFieldName = "__message__"

// NewTraceMessageDecode creates a TraceMessageDecode with the decoder and message type pre-populated.
func NewTraceMessageDecode(decoder, message string) TraceMessageDecode {
	meta := make(map[string]interface{})
	meta[DecoderFieldName] = decoder
	meta[MessageFieldName] = message
	return meta
}

// MarshalTraceMessageDecode serializes the trace metadata to JSON.
func (d TraceMessageDecode) MarshalTraceMessageDecode() ([]byte, error) {
	data, err := json.Marshal(d)
	if err != nil {
		return nil, err
	}
	return data, nil
}

// MarshalResult serializes the trace metadata to JSON, returning (nil, true) on error.
func (d TraceMessageDecode) MarshalResult() ([]byte, bool) {
	data, err := json.Marshal(d)
	if err != nil {
		return nil, true
	}
	return data, true
}

func decodeTraceAndFormat(decode []byte) string {
	if len(decode) > 0 {
		meta := make(map[string]interface{})
		err := json.Unmarshal(decode, &meta)
		if err != nil {
			panic(err)
		}

		out := fmt.Sprintf("%-24s", fmt.Sprintf("%-8s %s", meta[DecoderFieldName], meta[MessageFieldName]))

		if len(meta) > 2 {
			keys := make([]string, 0)
			for k := range meta {
				if k != DecoderFieldName && k != MessageFieldName {
					keys = append(keys, k)
				}
			}
			sort.Strings(keys)

			out += " {"
			for i := 0; i < len(keys); i++ {
				k := keys[i]
				if i > 0 {
					out += " "
				}
				out += k
				out += "=["
				v := meta[k]
				switch v := v.(type) {
				case string:
					out += v
				case float64:
					out += fmt.Sprintf("%0.0f", v)
				case bool:
					out += fmt.Sprintf("%t", v)
				default:
					out += fmt.Sprintf("<%s>", reflect.TypeOf(v))
				}
				out += "]"
			}
			out += "}"
		}

		return out
	} else {
		return ""
	}
}