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// Copyright 2019 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 procfs

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"strconv"
	"strings"

	"github.com/prometheus/procfs/internal/util"
)

// For the proc file format details,
// See:
// * Linux 2.6.23 https://elixir.bootlin.com/linux/v2.6.23/source/net/core/dev.c#L2343
// * Linux 4.17 https://elixir.bootlin.com/linux/v4.17/source/net/core/net-procfs.c#L162
// and https://elixir.bootlin.com/linux/v4.17/source/include/linux/netdevice.h#L2810.

// SoftnetStat contains a single row of data from /proc/net/softnet_stat
type SoftnetStat struct {
	// Number of processed packets
	Processed uint32
	// Number of dropped packets
	Dropped uint32
	// Number of times processing packets ran out of quota
	TimeSqueezed uint32
}

var softNetProcFile = "net/softnet_stat"

// NetSoftnetStat reads data from /proc/net/softnet_stat.
func (fs FS) NetSoftnetStat() ([]SoftnetStat, error) {
	b, err := util.ReadFileNoStat(fs.proc.Path(softNetProcFile))
	if err != nil {
		return nil, err
	}

	entries, err := parseSoftnet(bytes.NewReader(b))
	if err != nil {
		return nil, fmt.Errorf("failed to parse /proc/net/softnet_stat: %w", err)
	}

	return entries, nil
}

func parseSoftnet(r io.Reader) ([]SoftnetStat, error) {
	const minColumns = 9

	s := bufio.NewScanner(r)

	var stats []SoftnetStat
	for s.Scan() {
		columns := strings.Fields(s.Text())
		width := len(columns)

		if width < minColumns {
			return nil, fmt.Errorf("%d columns were detected, but at least %d were expected", width, minColumns)
		}

		// We only parse the first three columns at the moment.
		us, err := parseHexUint32s(columns[0:3])
		if err != nil {
			return nil, err
		}

		stats = append(stats, SoftnetStat{
			Processed:    us[0],
			Dropped:      us[1],
			TimeSqueezed: us[2],
		})
	}

	return stats, nil
}

func parseHexUint32s(ss []string) ([]uint32, error) {
	us := make([]uint32, 0, len(ss))
	for _, s := range ss {
		u, err := strconv.ParseUint(s, 16, 32)
		if err != nil {
			return nil, err
		}

		us = append(us, uint32(u))
	}

	return us, nil
}