johnsonjh/gfpsgo

// Copyright 2021 Jeffrey H. Johnson <trnsz@pobox.com>
// Copyright 2018 psgo 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 host extracts data from the host, such as the system's boot time
// or the tick rate of the system clock.
package host

import (
    "bufio"
    "fmt"
    "os"
    "strconv"
    "strings"
)

// BootTime parses /proc/uptime returns the boot time in seconds since the
// Epoch, 1970-01-01 00:00:00 +0000 (UTC).
func BootTime() (int64, error) {
    if bootTime != nil {
        return *bootTime, nil
    }

    f, err := os.Open("/proc/stat")
    if err != nil {
        return 0, err
    }

    btimeStr := ""
    scanner := bufio.NewScanner(f)
    for scanner.Scan() {
        fields := strings.Fields(scanner.Text())
        if len(fields) < 2 {
            continue
        }
        if fields[0] == "btime" {
            btimeStr = fields[1]
        }
    }

    if btimeStr == "" {
        return 0, fmt.Errorf("couldn't extract boot time from /proc/stat")
    }

    btimeSec, err := strconv.ParseInt(btimeStr, 10, 64)
    if err != nil {
        return 0, fmt.Errorf(
            "error parsing boot time from /proc/stat: %w",
            err,
        )
    }
    bootTime = &btimeSec
    return btimeSec, nil
}