prometheus/util/jsonutil/marshal.go

// Copyright 2022 The Prometheus 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 jsonutil

import (
	"math"
	"strconv"

	jsoniter "github.com/json-iterator/go"
)

// MarshalTimestamp marshals a point timestamp using the passed jsoniter stream.
func MarshalTimestamp(t int64, stream *jsoniter.Stream) {
	// Write out the timestamp as a float divided by 1000.
	// This is ~3x faster than converting to a float.
	if t < 0 {
		stream.WriteRaw(`-`)
		t = -t
	}
	stream.WriteInt64(t / 1000)
	fraction := t % 1000
	if fraction != 0 {
		stream.WriteRaw(`.`)
		if fraction < 100 {
			stream.WriteRaw(`0`)
		}
		if fraction < 10 {
			stream.WriteRaw(`0`)
		}
		stream.WriteInt64(fraction)
	}
}

// MarshalValue marshals a point value using the passed jsoniter stream.
func MarshalValue(v float64, stream *jsoniter.Stream) {
	stream.WriteRaw(`"`)
	// Taken from https://github.com/json-iterator/go/blob/master/stream_float.go#L71 as a workaround
	// to https://github.com/json-iterator/go/issues/365 (jsoniter, to follow json standard, doesn't allow inf/nan).
	buf := stream.Buffer()
	abs := math.Abs(v)
	fmt := byte('f')
	// Note: Must use float32 comparisons for underlying float32 value to get precise cutoffs right.
	if abs != 0 {
		if abs < 1e-6 || abs >= 1e21 {
			fmt = 'e'
		}
	}
	buf = strconv.AppendFloat(buf, v, fmt, -1, 64)
	stream.SetBuffer(buf)
	stream.WriteRaw(`"`)
}