Golang (8) - 码厩

#39 Golang `archive` 包

Golang GoStdLib 2021-03-01

标准库中的 archive 支持 tar，zip 两种打包格式。

https://en.wikipedia.org/wiki/Tar_(computing)

最常用的 tar 包：

func createTarArchive(sourceDir, targetFile string) error {
    file, err := os.Create(targetFile)
    if err != nil {
        return err
    }
    defer file.Close()

    tarWriter := tar.NewWriter(file)
    defer tarWriter.Close()

    return filepath.Walk(sourceDir, func(path string, info os.FileInfo, err error) error {
        if err != nil {
            return err
        }

        header, err := tar.FileInfoHeader(info, info.Name())
        if err != nil {
            return err
        }

        if err := tarWriter.WriteHeader(header); err != nil {
            return err
        }

        if !info.IsDir() {
            file, err := os.Open(path)
            if err != nil {
                return err
            }
            defer file.Close()

            _, err = io.Copy(tarWriter, file)
            if err != nil {
                return err
            }
        }

        return nil
    })
}

func extractTarArchive(sourceFile, targetDir string) error {
    file, err := os.Open(sourceFile)
    if err != nil {
        return err
    }
    defer file.Close()

    tarReader := tar.NewReader(file)
    for {
        header, err := tarReader.Next()
        if err == io.EOF {
            break
        }
        if err != nil {
            return err
        }
        targetPath := filepath.Join(targetDir, header.Name)
        if err := os.MkdirAll(filepath.Dir(targetPath), 0755); err != nil {
            return err
        }
        if header.Typeflag == tar.TypeReg {
            file, err := os.Create(targetPath)
            if err != nil {
                return err
            }
            defer file.Close()
            _, err = io.Copy(file, tarReader)
            if err != nil {
                return err
            }
        }
    }

    return nil
}

#38 Golang 数组 & 切片

Golang 2021-02-24

2020/12/15，Golang 数组操作
2020/02/24，Golang 数组 & 切片
数组: [Len]Type{Value...}
切片：[]Type{Value...}

数组声明时可以使用 ... 当作长度，表示自动判断。
数组声明时，可以只初始化其中的部分值。

a := [...]int{2: 1, 4: 2} // [5]int{0, 0, 1, 0, 4}

b := [5]int{1, 2, 3} // [5]int{1, 2, 3, 0, 0}

基本操作

a := [...]int{1, 2, 3}
var b []int

// 新增
b = append(b, 1)
// 删除元素
s = append(s[:index], s[index+1:]...)

// 遍历
for i := range a {
    fmt.Println(a[i])
}
for index, value := range a {
    fmt.Printf("%v: %v", index, value)
}
for _, value := range a {
    fmt.Printf("%v", value)
}
for i := 0; i < len(array); i++ {
    fmt.Printf("value: %d\n", array[i])
}

// 判断元素是否存在/获取元素序号
func Index(target int, array []int) int {
    for i, v := range array {
        if target == v {
            return i
        }
    }
    return -1
}

示例

package main

import (
    "fmt"
    "reflect"
)

func main() {
    a := [5]int{1, 3, 5, 7, 9}
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(a), a)
    // [5]int   [5]int{1, 3, 5, 7, 9}

    // array => slice
    b := a[:] // a[0:len(a)]
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(b), b)
    // []int    []int{1, 3, 5, 7, 9}

    // slice => array
    // c := ([5]int)(b) // cannot convert b (type []int) to type [5]int
    c := (*[5]int)(b) // 切片只能转换成数组指针
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(c), c)
    // *[5]int  &[5]int{1, 3, 5, 7, 9}

    // 用类型别名试试：
    type NumArr [5]int
    c2 := (*NumArr)(b)
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(c2), c2)
    // *main.NumArr &main.NumArr{1, 3, 5, 7, 9}

    // 只能遍历赋值
    d := [5]int{}
    for index, v := range b {
        d[index] = v
    }
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(d), d)

    // 通过 copy 的方法实现 slice2array
    e := [5]int{}
    copy(e[:], b) // return length of b
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(e), e)
}

去重

func Unique(arr []int) []int {
    arrLen := len(arr) - 1

    for arrLen > 0 {
        for i := arrLen - 1; i >= 0; i-- {
            if arr[arrLen] == arr[i] {
                arr = append(arr[:i], arr[i+1:]...)
                break
            }
        }
        arrLen--
    }

    return arr
}

func UniqueOptimized(arr []int) []int {
    uniqueArr := make([]int, 0, len(arr))
    uniqueMap := make(map[int]struct{})

    for _, num := range arr {
        if _, ok := uniqueMap[num]; !ok {
            uniqueArr = append(uniqueArr, num)
            uniqueMap[num] = struct{}{}
        }
    }

    return uniqueArr
}

// BenchmarkUniqueOriginal-20           135           8658964 ns/op               0 B/op          0 allocs/op
// BenchmarkUniqueOptimized-20         3501            347027 ns/op          285402 B/op        208 allocs/op

可以看到，一个性能好一些（只用 4% 的时间），资源使用多一些。

使用反射

https://blog.csdn.net/youngwhz1/article/details/83026263

func SliceRemoveDuplicate(a interface{}) (ret []interface{}) {
    if reflect.TypeOf(a).Kind() != reflect.Slice {
        fmt.Printf("<SliceRemoveDuplicate> <a> is not slice but %T\n", a)
        return ret
    }
    va := reflect.ValueOf(a)
    for i := 0; i < va.Len(); i++ {
        if i > 0 && reflect.DeepEqual(va.Index(i-1).Interface(), va.Index(i).Interface()) {
            continue
        }
        ret = append(ret, va.Index(i).Interface())
    }
    return ret
}

func SliceInsert(s []interface{}, index int, value interface{}) []interface{} {
    rear := append([]interface{}{}, s[index:]...)
    return append(append(s[:index], value), rear...)
}

func SliceInsert2(s *[]interface{}, index int, value interface{}) {
    rear := append([]interface{}{}, (*s)[index:]...)
    *s = append(append((*s)[:index], value), rear...)
}

func SliceInsert3(s interface{}, index int, value interface{}) bool {
    if ps, ok := s.(*[]string); ok {
        if val, ok := value.(string); ok {
            rear := append([]string{}, (*ps)[index:]...)
            *ps = append(append((*ps)[:index], val), rear...)
            return true
        }
    } else if ps, ok := s.(*[]int); ok {
        if val, ok := value.(int); ok {
            rear := append([]int{}, (*ps)[index:]...)
            *ps = append(append((*ps)[:index], val), rear...)
        }
    } else if ps, ok := s.(*[]float64); ok {
        if val, ok := value.(float64); ok {
            rear := append([]float64{}, (*ps)[index:]...)
            *ps = append(append((*ps)[:index], val), rear...)
        }
    } else {
        fmt.Printf("<SliceInsert3> Unsupported type: %T\n", s)
    }
    return false
}

func SliceRemove(s []interface{}, index int) []interface{} {
    return append(s[:index], s[index+1:]...)
}

func SliceRemove2(s *[]interface{}, index int) {
    *s = append((*s)[:index], (*s)[index+1:]...)
}

func SliceRemove3(s interface{}, index int) bool {
    if ps, ok := s.(*[]string); ok {
        *ps = append((*ps)[:index], (*ps)[index+1:]...)
    } else if ps, ok := s.(*[]int); ok {
        *ps = append((*ps)[:index], (*ps)[index+1:]...)
    } else if ps, ok := s.(*[]float64); ok {
        *ps = append((*ps)[:index], (*ps)[index+1:]...)
    } else {
        fmt.Printf("<SliceRemove3> Unsupported type: %T\n", s)
        return false
    }
    return true
}

func SliceClear(s *[]interface{}) {
    *s = append([]interface{}{})
}

func SliceClear2(s *[]interface{}) {
    *s = (*s)[0:0]
}

func SliceClear3(s interface{}) bool {
    if ps, ok := s.(*[]string); ok {
        *ps = (*ps)[0:0]
        //*ps = append([]string{})
    } else if ps, ok := s.(*[]int); ok {
        *ps = (*ps)[0:0]
        //*ps = append([]int{})
    } else if ps, ok := s.(*[]float64); ok {
        *ps = (*ps)[0:0]
        //*ps = append([]float64{})
    } else {
        fmt.Printf("<SliceClear3> Unsupported type: %T\n", s)
        return false
    }
    return true
}

泛型实现

func Insert[S ~[]E, E any](s S, i int, v ...E) S {
    tot := len(s) + len(v)
    if tot <= cap(s) {
        s2 := s[:tot]
        copy(s2[i+len(v):], s[i:])
        copy(s2[i:], v)
        return s2
    }
    s2 := make(S, tot)
    copy(s2, s[:i])
    copy(s2[i:], v)
    copy(s2[i+len(v):], s[i:])
    return s2
}

内置方法 `make`

make(Type, Len, Cap) 可以用来为 slice, map, channel 三种类型初始化（类似：C 语言 (int *)malloc(5)）。

这里就看 Slice 的情况。

s1 := make([]int, 5)

s2 := make([]int, 5, 10)
// s2[8] = 1 // panic: runtime error: index out of range [8] with length 5
s2 = append(s2, 1)

如果有预留空间，append 的时候可以不用重新分配内存并遍历赋值。
如果切片有扩容的需要，就最好采用 make 来初始化。

如果不指定容量，则切片的容量和长度将相等。

#37 Golang: 临时文件

Golang 2021-02-22

创建临时文件
使用编辑器编辑
获取内容
删除临时文件

package main

import (
    "bufio"
    "fmt"
    "io/ioutil"
    "log"
    "os"
    "os/exec"
)

func main() {
    // create a tmp file
    // ioutil.TempFile creates a temp file and opens the file for reading and writing
    // and returns the resulting *os.File (file descriptor).
    tmpFile, err := ioutil.TempFile(os.TempDir(), "todo-tmp-")
    if err != nil {
        log.Fatal("Cannot create temporary file", err)
    }
    // defer os.Remove(tmpFile.Name())
    defer tmpFile.Close()
    fmt.Println("Created File: " + tmpFile.Name())

    // choose editor by env var
    editor := os.Getenv("EDITOR")
    args := []string{}
    if editor == "" {
        editor = "vim"
        args = append(args, "--clean")
        fmt.Println("No EDITOR enviroment variable set, use " + editor)
    } else {
        fmt.Println("Using EDITOR enviroment variable: " + editor)
    }
    args = append(args, tmpFile.Name())
    fmt.Println("Opening file with " + editor + " with args: " + fmt.Sprint(args))

    // check the editor command is available
    // _, err = exec.LookPath(editor)
    // if err != nil {
    //  log.Fatal("Cannot find editor: " + editor)
    // }

    // call the editor
    cmd := exec.Command(editor, args...)
    cmd.Stdin = os.Stdin
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    err = cmd.Run()
    if err != nil {
        log.Fatal("Cannot run editor: " + editor)
    }

    // read the file
    // data, err := ioutil.ReadFile(tmpFile.Name())
    // if err != nil {
    //  log.Fatal("Cannot read file: " + tmpFile.Name())
    // }
    tmpFile.Seek(0, 0)
    s := bufio.NewScanner(tmpFile)
    for s.Scan() {
        fmt.Println("Content:\n\n" + s.Text())
    }
    if err = s.Err(); err != nil {
        log.Fatal("error reading temp file", err)
    }
}

#36 Golang `strings` 包

Golang GoStdLib 2021-02-21

func Clone(s string) string                 //
func Compare(a, b string) int               // 比较
func Contains(s, substr string) bool        // 包含子字符串
func ContainsAny(s, chars string) bool      // 包含任意Char
func ContainsRune(s string, r rune) bool    // 包含Rune
func Count(s, substr string) int            // 计数
func Cut(s, sep string) (before, after string, found bool)
func EqualFold(s, t string) bool                    //
func Fields(s string) []string                      // 切割
func FieldsFunc(s string, f func(rune) bool) []string
func HasPrefix(s, prefix string) bool               // 前缀判断 startswith
func HasSuffix(s, suffix string) bool               // 后缀判断 endswith
func Index(s, substr string) int                    // 查找
func IndexAny(s, chars string) int                  // 查找Any
func IndexByte(s string, c byte) int                // 查找Byte
func IndexFunc(s string, f func(rune) bool) int     // 查找Func
func IndexRune(s string, r rune) int                // 查找Rune
func Join(elems []string, sep string) string        // 连接
func LastIndex(s, substr string) int                // 右查找
func LastIndexAny(s, chars string) int              // 右查找Any
func LastIndexByte(s string, c byte) int            // 右查找Byte
func LastIndexFunc(s string, f func(rune) bool) int // 右查找Func
func Map(mapping func(rune) rune, s string) string  //
func Repeat(s string, count int) string             // 重复
func Replace(s, old, new string, n int) string      // 替换
func ReplaceAll(s, old, new string) string          // 替换 = Replace -1
func Split(s, sep string) []string                  // 切割
func SplitAfter(s, sep string) []string             //
func SplitAfterN(s, sep string, n int) []string     //
func SplitN(s, sep string, n int) []string          //
func Title(s string) string                         //
func ToLower(s string) string                       // 转小写
func ToLowerSpecial(c unicode.SpecialCase, s string) string
func ToTitle(s string) string                       // Title
func ToTitleSpecial(c unicode.SpecialCase, s string) string
func ToUpper(s string) string
func ToUpperSpecial(c unicode.SpecialCase, s string) string
func ToValidUTF8(s, replacement string) string
func Trim(s, cutset string) string
func TrimFunc(s string, f func(rune) bool) string
func TrimLeft(s, cutset string) string
func TrimLeftFunc(s string, f func(rune) bool) string
func TrimPrefix(s, prefix string) string
func TrimRight(s, cutset string) string
func TrimRightFunc(s string, f func(rune) bool) string
func TrimSpace(s string) string
func TrimSuffix(s, suffix string) string

type Builder
    func (b *Builder) Cap() int
    func (b *Builder) Grow(n int)
    func (b *Builder) Len() int
    func (b *Builder) Reset()
    func (b *Builder) String() string
    func (b *Builder) Write(p []byte) (int, error)
    func (b *Builder) WriteByte(c byte) error
    func (b *Builder) WriteRune(r rune) (int, error)
    func (b *Builder) WriteString(s string) (int, error)

type Reader
    func NewReader(s string) *Reader
    func (r *Reader) Len() int
    func (r *Reader) Read(b []byte) (n int, err error)
    func (r *Reader) ReadAt(b []byte, off int64) (n int, err error)
    func (r *Reader) ReadByte() (byte, error)
    func (r *Reader) ReadRune() (ch rune, size int, err error)
    func (r *Reader) Reset(s string)
    func (r *Reader) Seek(offset int64, whence int) (int64, error)
    func (r *Reader) Size() int64
    func (r *Reader) UnreadByte() error
    func (r *Reader) UnreadRune() error
    func (r *Reader) WriteTo(w io.Writer) (n int64, err error)

type Replacer
    func NewReplacer(oldnew ...string) *Replacer
    func (r *Replacer) Replace(s string) string
    func (r *Replacer) WriteString(w io.Writer, s string) (n int, err error)

Builder

Reader

Replacer

参考资料与拓展阅读

2020/12/08, Golang 字符串 string
https://pkg.go.dev/strings

#35 Golang `reflect` 包

Golang GoStdLib GoReflect 2021-02-17

2021/02/09, Golang 反射简单示例
2021/02/17, Golang reflect 包
2021/04/06, Go 反射

func Copy(dst, src Value) int
func DeepEqual(x, y any) bool
func Swapper(slice any) func(i, j int)
type ChanDir
    func (d ChanDir) String() string
type Kind
    func (k Kind) String() string
type MapIter
    func (iter *MapIter) Key() Value
    func (iter *MapIter) Next() bool
    func (iter *MapIter) Reset(v Value)
    func (iter *MapIter) Value() Value
type Method
    func (m Method) IsExported() bool
type SelectCase
type SelectDir
type SliceHeader
type StringHeader
type StructField
    func VisibleFields(t Type) []StructField
    func (f StructField) IsExported() bool
type StructTag
    func (tag StructTag) Get(key string) string
    func (tag StructTag) Lookup(key string) (value string, ok bool)

Type

func ArrayOf(length int, elem Type) Type
func ChanOf(dir ChanDir, t Type) Type
func FuncOf(in, out []Type, variadic bool) Type
func MapOf(key, elem Type) Type
func PointerTo(t Type) Type
func PtrTo(t Type) Type
func SliceOf(t Type) Type
func StructOf(fields []StructField) Type
func TypeOf(i any) Type

Value

func Append(s Value, x ...Value) Value
func AppendSlice(s, t Value) Value
func Indirect(v Value) Value
func MakeChan(typ Type, buffer int) Value
func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value
func MakeMap(typ Type) Value
func MakeMapWithSize(typ Type, n int) Value
func MakeSlice(typ Type, len, cap int) Value
func New(typ Type) Value
func NewAt(typ Type, p unsafe.Pointer) Value
func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool)
func ValueOf(i any) Value
func Zero(typ Type) Value
func (v Value) Addr() Value
func (v Value) Bool() bool
func (v Value) Bytes() []byte
func (v Value) Call(in []Value) []Value
func (v Value) CallSlice(in []Value) []Value
func (v Value) CanAddr() bool
func (v Value) CanComplex() bool
func (v Value) CanConvert(t Type) bool
func (v Value) CanFloat() bool
func (v Value) CanInt() bool
func (v Value) CanInterface() bool
func (v Value) CanSet() bool
func (v Value) CanUint() bool
func (v Value) Cap() int
func (v Value) Close()
func (v Value) Comparable() bool
func (v Value) Complex() complex128
func (v Value) Convert(t Type) Value
func (v Value) Elem() Value
func (v Value) Equal(u Value) bool
func (v Value) Field(i int) Value
func (v Value) FieldByIndex(index []int) Value
func (v Value) FieldByIndexErr(index []int) (Value, error)
func (v Value) FieldByName(name string) Value
func (v Value) FieldByNameFunc(match func(string) bool) Value
func (v Value) Float() float64
func (v Value) Grow(n int)
func (v Value) Index(i int) Value
func (v Value) Int() int64
func (v Value) Interface() (i any)
func (v Value) InterfaceData() [2]uintptrDEPRECATED
func (v Value) IsNil() bool
func (v Value) IsValid() bool
func (v Value) IsZero() bool
func (v Value) Kind() Kind
func (v Value) Len() int
func (v Value) MapIndex(key Value) Value
func (v Value) MapKeys() []Value
func (v Value) MapRange() *MapIter
func (v Value) Method(i int) Value
func (v Value) MethodByName(name string) Value
func (v Value) NumField() int
func (v Value) NumMethod() int
func (v Value) OverflowComplex(x complex128) bool
func (v Value) OverflowFloat(x float64) bool
func (v Value) OverflowInt(x int64) bool
func (v Value) OverflowUint(x uint64) bool
func (v Value) Pointer() uintptr
func (v Value) Recv() (x Value, ok bool)
func (v Value) Send(x Value)
func (v Value) Set(x Value)
func (v Value) SetBool(x bool)
func (v Value) SetBytes(x []byte)
func (v Value) SetCap(n int)
func (v Value) SetComplex(x complex128)
func (v Value) SetFloat(x float64)
func (v Value) SetInt(x int64)
func (v Value) SetIterKey(iter *MapIter)
func (v Value) SetIterValue(iter *MapIter)
func (v Value) SetLen(n int)
func (v Value) SetMapIndex(key, elem Value)
func (v Value) SetPointer(x unsafe.Pointer)
func (v Value) SetString(x string)
func (v Value) SetUint(x uint64)
func (v Value) SetZero()
func (v Value) Slice(i, j int) Value
func (v Value) Slice3(i, j, k int) Value
func (v Value) String() string
func (v Value) TryRecv() (x Value, ok bool)
func (v Value) TrySend(x Value) bool
func (v Value) Type() Type
func (v Value) Uint() uint64
func (v Value) UnsafeAddr() uintptr
func (v Value) UnsafePointer() unsafe.Pointer

#34 Golang: 目录与文件操作汇总

Golang 2021-02-16

Golang os 包中有很多文件系统相关的操作。

创建文件

// *os.File
file, err = os.Create("abc.txt")
if err != nil {
    log.Fatal(err)
}
defer file.Close()

删除文件

os.Remove()

读写文件

// ioutil
func ReadFile(filename string) ([]byte, error)
func WriteFile(filename string, data []byte, perm os.FileMode) error

// os
func Open(name string) (*File, error)
func OpenFile(name string, flag int, perm FileMode) (*File, error)

func ReadFileToString(filename string) ([]string, error) {
    file, err := os.Open(filename)
    if err != nil {
        return nil, err
    }
    defer file.Close()

    scanner := bufio.NewScanner(file)

    var data []string

    for scanner.Scan() {
        line := scanner.Text()
        data = append(data, line)
    }
    if err = scanner.Err(); err != nil {
        return nil, err
    }

    return data, nil
}

// 写

// 如果文件大于指定大小，则截断到指定大小
// 如果文件小于指定大小，则填充到指定大小
file, err := os.Truncate("abc.txt", 1024)
if err != nil {
    log.Fatal(err)
}

裁剪文件（Truncate）

file, err := os.OpenFile("abc.txt", os.O_RDWR, 0644)
if err != nil {
    log.Fatal(err)
}
defer file.Close()

err := file.Truncate(1024)
if err != nil {
    log.Fatal(err)
}

// os.Truncate(path string, size int64) error
err := os.Truncate("abc.txt", 1024)
if err != nil {
    fmt.Println("截断文件失败:", err)
}

创建目录（mkdir）

err := os.Mkdir(dirName, 0755) // 不能创建已经存在的目录
// err := os.MkdirAll(dirPath, 0755) // mkdir -p
if err != nil {
    fmt.Println("创建目录失败:", err)
    return
}

删除目录（rm）

err := os.Remove(dirName) // 不能删除非空目录
// err := os.RemoveAll(dirName) // rm -rf
if err != nil {
    fmt.Println("删除目录失败:", err)
    return
}

查看目录（List/Walk）

dirEntries, err := os.ReadDir(dirPath)
if err != nil {
    return err
}
for _, entry := range dirEntries {
    entryPath := filepath.Join(dirPath, entry.Name())
    if entry.IsDir() {
        fmt.Println("目录:", entryPath)
    } else {
        fmt.Println("文件:", entryPath)
    }
}

package main

import (
    "fmt"
    "os"
    "path/filepath"
)

func visit(path string, info os.FileInfo, err error) error {
    if err != nil {
        fmt.Println("访问目录失败:", err)
        return nil
    }
    if info.IsDir() {
        fmt.Println("目录:", path)
    } else {
        fmt.Println("文件:", path)
    }
    return nil
}

func main() {
    dirPath := "/path/to/directory"
    err := filepath.Walk(dirPath, visit)
    if err != nil {
        fmt.Println("遍历目录失败:", err)
        return
    }
}

查看文件信息（Stat）

fp.Stat()  // 句柄上执行 Stat 方法

fi, err = os.Stat(filepath)
// type FileInfo interface {
//  Name() string       // base name of the file
//  Size() int64        // length in bytes for regular files; system-dependent for others
//  Mode() FileMode     // file mode bits
//  ModTime() time.Time // modification time
//  IsDir() bool        // abbreviation for Mode().IsDir()
//  Sys() any           // underlying data source (can return nil)
// }

// FileMode -> fs.FileMode -> type FileMode uint32
// func (m FileMode) IsDir() bool
// func (m FileMode) IsRegular() bool
// func (m FileMode) Perm() FileMode
// func (m FileMode) String() string
// func (m FileMode) Type() FileMode
// const (
//  // The single letters are the abbreviations
//  // used by the String method's formatting.
//  ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
//  ModeAppend                                     // a: append-only
//  ModeExclusive                                  // l: exclusive use
//  ModeTemporary                                  // T: temporary file; Plan 9 only
//  ModeSymlink                                    // L: symbolic link
//  ModeDevice                                     // D: device file
//  ModeNamedPipe                                  // p: named pipe (FIFO)
//  ModeSocket                                     // S: Unix domain socket
//  ModeSetuid                                     // u: setuid
//  ModeSetgid                                     // g: setgid
//  ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
//  ModeSticky                                     // t: sticky
//  ModeIrregular                                  // ?: non-regular file; nothing else is known about this file

//  // Mask for the type bits. For regular files, none will be set.
//  ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular

//  ModePerm FileMode = 0777 // Unix permission bits
// )

// is exists
func IsNotExist(err error) bool
// 注意：这个方法只有在出现异常，并且异常是路径已存在导致的，才会返回 True
func IsExist(err error) bool

// is dir
if fi.IsDir() {
    ...
}

// is file
if fi.Mode().IsRegular() {
    ...
}

// readable

// writable

// executable

移动文件

os.Rename(src, dst)

复制文件

sourceFile, err := os.Open(sourceFilePath)
if err != nil {
    return err
}
defer sourceFile.Close()
destinationFile, err := os.Create(destinationFilePath)
if err != nil {
    return err
}
defer destinationFile.Close()
_, err = io.Copy(destinationFile, sourceFile)

创建链接

os.Link()
os.Symlink()

临时目录和临时文件

tempFile, err := os.CreateTemp("", "tmp*.txt")  // *os.File
tempFilePath := tempFile.Name()

tempDir, err := os.MkdirTemp("", "tmp") // string

权限

fp.Chmod()
fp.Chown()  // os.Getuid(), os.Getgid()

#33 Golang `io` 包

Golang GoStdLib 2021-02-14

io, io/fs, io/util, os

find /usr/share/go-1.17/src/io/ -type f | grep -Fv _test.go
/usr/share/go-1.17/src/io/ioutil/testdata/hello
/usr/share/go-1.17/src/io/ioutil/tempfile.go
/usr/share/go-1.17/src/io/ioutil/ioutil.go
/usr/share/go-1.17/src/io/pipe.go
/usr/share/go-1.17/src/io/fs/fs.go
/usr/share/go-1.17/src/io/fs/readfile.go
/usr/share/go-1.17/src/io/fs/readdir.go
/usr/share/go-1.17/src/io/fs/sub.go
/usr/share/go-1.17/src/io/fs/stat.go
/usr/share/go-1.17/src/io/fs/walk.go
/usr/share/go-1.17/src/io/fs/glob.go
/usr/share/go-1.17/src/io/io.go
/usr/share/go-1.17/src/io/multi.go

方法

https://pkg.go.dev/io

`io/fs` 包

func Glob(fsys FS, pattern string) (matches []string, err error)
func ReadFile(fsys FS, name string) ([]byte, error)
func ValidPath(name string) bool
func WalkDir(fsys FS, root string, fn WalkDirFunc) error

`io/util` 包 (原 `ioutil`)

1.6 以及之后新版本，iouitl 包依然保留，但是只是对 io 包的封装。

Package ioutil implements some I/O utility functions.
As of Go 1.16, the same functionality is now provided by package io or package os, and those implementations should be preferred in new code. See the specific function documentation for details.

func NopCloser(r io.Reader) io.ReadCloser
func ReadAll(r io.Reader) ([]byte, error)
func ReadDir(dirname string) ([]fs.FileInfo, error)
func ReadFile(filename string) ([]byte, error)
func TempDir(dir, pattern string) (name string, err error)
func TempFile(dir, pattern string) (f *os.File, err error)
func WriteFile(filename string, data []byte, perm fs.FileMode) error

// grep -REv "^//" /usr/share/go-1.17/src/io/ioutil/tempfile.go
package ioutil

import (
        "os"
)

func TempFile(dir, pattern string) (f *os.File, err error) {
        return os.CreateTemp(dir, pattern)
}

func TempDir(dir, pattern string) (name string, err error) {
        return os.MkdirTemp(dir, pattern)
}

// grep -REv "^//" /usr/share/go-1.17/src/io/ioutil/ioutil.go
package ioutil

import (
        "io"
        "io/fs"
        "os"
        "sort"
)

func ReadAll(r io.Reader) ([]byte, error) {
        return io.ReadAll(r)
}

func ReadFile(filename string) ([]byte, error) {
        return os.ReadFile(filename)
}

func WriteFile(filename string, data []byte, perm fs.FileMode) error {
        return os.WriteFile(filename, data, perm)
}

func ReadDir(dirname string) ([]fs.FileInfo, error) {
        f, err := os.Open(dirname)
        if err != nil {
                return nil, err
        }
        list, err := f.Readdir(-1)
        f.Close()
        if err != nil {
                return nil, err
        }
        sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() })
        return list, nil
}

func NopCloser(r io.Reader) io.ReadCloser {
        return io.NopCloser(r)
}

var Discard io.Writer = io.Discard

引申

io 包是基础，提供了 Reader 和 Writer 接口。其他包则是实现这两个接口。

`string` 包：字符串 IO

相当于 Python io.StringIO

string.Reader

`bytes` 包：字节 IO

通过 []byte 模拟 io，相当于 Python io.BytesIO

bytes.Buffer (Reader + Writer)
bytes.Reader

`buffio` 包：缓冲 IO

就是加入了一个缓冲的功能，提升 IO 效率，减少直接系统调用。
也方便实现一些网络协议中的分包，比如 SMTP 协议中按换行切割。

bufio.Reader
bufio.Writer

package main

import (
    "bufio"
    "fmt"
    "os"
)

func main() {
    file, err := os.Open("test.txt")
    if err != nil {
        fmt.Println("无法打开文件:", err)
        return
    }
    defer file.Close()

    reader := bufio.NewReader(file)
    for {
        line, err := reader.ReadString('\n')
        if err != nil {
            // 文件结束或发生错误
            break
        }
        fmt.Print(line)
    }
}

`os` 包：系统 IO

os.File 文件类型

func Open(name string) (*File, error)
func OpenFile(name string, flag int, perm FileMode) (*File, error)

var Stdin = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
var Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
var Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")

`net` 包：网络 IO

网络编程的部分，这里就不继续展开了。

net.Conn 网络连接

func Pipe() (Conn, Conn)

func Dial(network, address string) (Conn, error)
func DialTimeout(network, address string, timeout time.Duration) (Conn, error)
func FileConn(f *os.File) (c Conn, err error)

func (d *Dialer) Dial(network, address string) (Conn, error)
func (d *Dialer) DialContext(ctx context.Context, network, address string) (Conn, error)

func FilePacketConn(f *os.File) (c PacketConn, err error)
func ListenPacket(network, address string) (PacketConn, error)

func DialIP(network string, laddr, raddr *IPAddr) (*IPConn, error)
func ListenIP(network string, laddr *IPAddr) (*IPConn, error)

func DialTCP(network string, laddr, raddr *TCPAddr) (*TCPConn, error)
func (l *TCPListener) Accept() (Conn, error)
func (l *TCPListener) AcceptTCP() (*TCPConn, error)

func DialUDP(network string, laddr, raddr *UDPAddr) (*UDPConn, error)
func ListenMulticastUDP(network string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, error)
func ListenUDP(network string, laddr *UDPAddr) (*UDPConn, error)

func DialUnix(network string, laddr, raddr *UnixAddr) (*UnixConn, error)
func ListenUnixgram(network string, laddr *UnixAddr) (*UnixConn, error)
func (l *UnixListener) Accept() (Conn, error)
func (l *UnixListener) AcceptUnix() (*UnixConn, error)

#32 Golang SHA 函数

Golang 哈希 2021-02-12

哈希算法（hash）是一种将任意长度数据映射成固定长度数据的方法。有时也叫摘要算法。

有非常多不同的哈希算法，其中最常见的是 md5 和 sha （sha1/sha256/sha512）两种。Golang md5 在 2021/01/14, Go MD5 中已经写过了。这里就记录一下 Golang sha 的使用方法。

// crypto.sha1
func New() hash.Hash
func Sum(data []byte) [Size]byte {
    if boringEnabled {
        return boringSHA1(data)
    }
    var d digest
    d.Reset()
    d.Write(data)
    return d.checkSum()
}
func (d *digest) MarshalBinary() ([]byte, error)
func (d *digest) UnmarshalBinary(b []byte) error
func (d *digest) Reset()
func (d *digest) Size() int
func (d *digest) BlockSize() int
func (d *digest) Write(p []byte) (nn int, err error)
func (d *digest) Sum(in []byte) []byte
func (d *digest) checkSum() [Size]byte
func (d *digest) ConstantTimeSum(in []byte) []byte
func (d *digest) constSum() [Size]byte

// crypto.sha256
func New() hash.Hash
func New224() hash.Hash // sha224
func Sum224(data []byte) [Size224]byte
func Sum256(data []byte) [Size]byte

// crypto.sha512
func New() hash.Hash
func New384() hash.Hash
func New512_224() hash.Hash
func New512_256() hash.Hash
func Sum384(data []byte) [Size384]byte
func Sum512(data []byte) [Size]byte
func Sum512_224(data []byte) [Size224]byte
func Sum512_256(data []byte) [Size256]byte

用法都一样：

h := sha1.New()  // hash.Hash
io.WriteString(h, "His money is twice tainted:")
io.WriteString(h, " 'taint yours and 'taint mine.")
fmt.Printf("% x", h.Sum(nil))

h := sha1.New()
if _, err := io.Copy(h, f); err != nil {
    log.Fatal(err)
}
fmt.Printf("% x", h.Sum(nil))

`hash.Hash` 接口

type Hash interface {
    io.Writer
    Sum(b []byte) []byte
    Reset()
    Size() int
    BlockSize() int
}

函数

sha1.New() -> hash.Hash
sha1.Sum(data []byte) -> [Size]byte
sha256.New() -> hash.Hash
sha256.Sum256(data []byte) -> [Size]byte
sha256.New224() -> hash.Hash
sha256.Sum224(data []byte) -> [Size224]byte
sha512.New() -> hash.Hash
sha512.Sum512(data []byte) -> [Size]byte
sha512.New384() -> hash.Hash
sha512.Sum384(data []byte) -> [Size384]byte
sha512.New512_224() -> hash.Hash
sha512.Sum512_224(data []byte) -> [Size224]byte
sha512.New512_256() -> hash.Hash
sha512.Sum512_256(data []byte) -> [Size256]byte

package main

import (
    "crypto/md5"
    "crypto/sha1"
    "crypto/sha256"
    "crypto/sha512"
    "fmt"
    "hash/fnv"
    "io"
    "log"
    "os"
)

func main() {
    filepath := "go.mod"
    f, err := os.Open(filepath)
    if err != nil {
        log.Fatal(err)
    }
    defer f.Close()

    fi, err := f.Stat()
    fmt.Printf("%#v err:%#v\n", fi, err)
    data := make([]byte, fi.Size())
    n, err := f.Read(data)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%d, %#v, err:%#v\n", n, data, err)

    {
        hash := fnv.New32a()
        hash.Write(data)
        result := hash.Sum32()
        fmt.Printf("FNV-1a 32-bit hash: %d\n\n", result)
    }

    {
        fmt.Printf("MD5    : %x\n", md5.Sum(data))
        fmt.Printf("Sha1   : %x\n", sha1.Sum(data))
        fmt.Printf("Sha256 : %x\n", sha256.Sum256(data))
        fmt.Printf("Sha512 : %x\n", sha512.Sum512(data))
    }

    {
        f.Seek(0, 0)
        hasher := md5.New()
        _, err = io.Copy(hasher, f)
        if err != nil {
            log.Fatal(err)
        }
        sum := hasher.Sum(nil)
        fmt.Printf("MD5 2  : %x\n", sum)
    }
}

#31 Golang 基础

Golang 2021-02-09

工作这么多年之后，学习一门新的语言，对于语法方面的东西应该是只用看看就行了（重点在其生态的学习）。
所以，这只是对 Go 语法做一个简单的梳理。

#30 从自学 Go 语言说起 [编辑中]

Golang 2021-02-09

上一篇文章说的比较杂，这一片专门来谈一谈学习 Go 语言的一些感受吧。

#39 Golang archive 包