go's io

大端序就是把数据高字节存贮到内存低地址中，小端序反之。

package main

import (
    "bufio"
    "encoding/binary"
    "fmt"
    "io"
    "math/rand"
    "os"
)

func main() {
    //TestIo()
    largeIo()

}

func largeIo()  {
    const filename = "large.in"
    const n = 100000000 // 8*100*1000*100 = 800M
    file, err := os.Create(filename)
    if err != nil {
        panic(err)
    }
    defer file.Close()
    p := randomSource(n)
    //io buffer 加快文件读写
    writer := bufio.NewWriter(file)
    writerSink(writer,p)
    writer.Flush() // flush掉 io buffer 中的数据
    //读
    file, err = os.Open(filename)
    if err != nil{
        panic(err)
    }
    defer file.Close()
    p = readerSource(bufio.NewReader(file))
    count := 0
    for v := range p{
        fmt.Println(v)
        count++
        if count >= 10{
            break
        }
    }

}
//文件读写测试
func TestIo() {
    //写
    file, err := os.Create("small.in") //二进制数据
    if err != nil {
        panic(err) //遇到错误，暂时不处理
    }
    defer file.Close()    //运行结束后，自动关闭文件
    p := randomSource(50) // smaill.in 的大小为 8*50,400字节
    writerSink(file, p)
    //读
    file, err = os.Open("small.in")
    if err != nil {
        panic(err)
    }
    defer file.Close()
    p = readerSource(file)
    for v := range p {
        fmt.Println(v)
    }
}

func readerSource(reader io.Reader) <-chan int {
    out := make(chan int)
    go func() {
        buffer := make([]byte, 8) //int: 64bit -> 8byte
        for {
            n, err := reader.Read(buffer)
            if n > 0 {
                v := int(binary.BigEndian.Uint64(buffer)) // Uint64 -> int
                out <- v
            }
            if err != nil {
                break
            }
        }
        close(out)
    }()
    return out
}

func writerSink(writer io.Writer, in <-chan int) {
    for v := range in {
        buffer := make([]byte, 8)
        binary.BigEndian.PutUint64(buffer, uint64(v))
        writer.Write(buffer)
    }
}
func randomSource(count int) <-chan int {
    out := make(chan int)
    go func() {
        for i := 0; i < count; i++ {
            out <- rand.Int()
        }
        close(out)
    }()
    return out
}