探讨如何在Golang应用程序中实现热部署

package main

import (
    "fmt"
    "os"
    "os/signal"
    "reflect"
    "sync"
    "syscall"
    "time"
)

func main() {
    done := make(chan bool)
    wg := sync.WaitGroup{}

    wg.Add(1)
    go Monitor(done, &wg)

    for n := 0; n < 100; n++ {
        fmt.Println(n)
        time.Sleep(1 * time.Second)
    }

    done <- true
    wg.Wait()
}

func Monitor(done chan bool, wg *sync.WaitGroup) {
    defer wg.Done()

    c := make(chan os.Signal, 1)
    signal.Notify(c, syscall.SIGHUP)

    for {
        select {
        case <-done:
            return
        case <-c:
            fmt.Println("Reloading...")
            Reload()
            fmt.Println("Reloaded!")
        }
    }
}

func Reload() {
    fmt.Println("Before reload")

    f, err := os.Open("test.go")
    if err != nil {
        fmt.Println(err)
        return
    }

    buf := make([]byte, 1024)
    incompleteLine := ""
    for {
        n, _ := f.Read(buf)
        if n == 0 {
            break
        }
        incompleteLine, _ = checkLines(buf[:n], incompleteLine)
    }

    fmt.Println("Loading new code")
    code := fmt.Sprintf(`package main

import (
    "fmt"
)

func run() {
    fmt.Println("New code is running")
}
`)
    Set("run", code)
}

func checkLines(buf []byte, incompleteLine string) (string, error) {
    line := incompleteLine + string(buf)

    complete := true
    for j := 0; j < len(line); j++ {
        if line[j] == '\n' {
            //run complete line...
            fmt.Println(line[:j])
            complete = false
        }
    }
    if complete {
        return "", nil
    }
    return line, nil
}

func Set(funcName string, code string) {
    codeVal := reflect.ValueOf(&code).Elem()
    ptrToCode := codeVal.Addr().Interface().(*string)

    // use function name as package name
    fn := funcName + ": "

    b := []byte(*ptrToCode)
    _, err := Compile(fn, b)
    if err != nil {
        fmt.Println(err)
    }

    // create a new function value of the same type as Run
    v := reflect.MakeFunc(reflect.TypeOf(Run), Compile(fn, b))

    // copy it in
    f := reflect.ValueOf(Run).Elem()
    f.Set(v)
}

func Compile(fn string, src []byte) (func(), error) {
    // no optimization means no inlining, etc, which means func values are inherently invalid
    f, err := CompileWithOpt(fn, src, 0)
    if err != nil {
        return nil, err
    }
    return f, nil
}

func CompileWithOpt(fn string, src []byte, opt int) (func(), error) {
    // we'll prepend some code to show the function name on panics
    src = append([]byte("func "+fn+"() {\n"), src...)
    src = append(src, '\n', '}')

    parsed, err := parser.ParseFile(token.NewFileSet(), "", src, parser.AllErrors)

    if err != nil {
        return nil, err
    }

    conf := types.Config{}
    info := &types.Info{}

    pkgs, err := conf.Check("", token.NewFileSet(), []*ast.File{parsed}, info)
    if err != nil {
        return nil, err
    }
    pkg := pkgs

    for _, n := range parsed.Decls {
        fn, ok := n.(*ast.FuncDecl)
        if !ok {
            continue
        }
        if fn.Name.Name != "run" {
            continue
        }
        var buf bytes.Buffer
        if err := printer.Fprint(&buf, token.NewFileSet(), fn); err != nil {
            return nil, err
        }

        fmt.Println("Compile", buf.String())
    }

    code := string(src)
    fn := func() {
        fmt.Println("Before run")

        err = eval(code, pkg, info)
        if err != nil {
            fmt.Println(err)
            return
        }

        fmt.Println("After run")
    }
    return fn, nil
}

func eval(code string, pkg *types.Package, info *types.Info) error {
    fset := token.NewFileSet()
    file, err := parser.ParseFile(fset, "", code, 0)
    if err != nil {
        fmt.Println(err)
        return err
    }

    conf := types.Config{
        Importer: importer.From("gc", nil, types.GcImport),
    }
    checker := types.NewChecker(&conf, fset, pkg, info)

    if _, err := checker.Files([]*ast.File{file}); err != nil {
        fmt.Println(err)
        return err
    }

    // compile/run, like in the previous example
    var buf bytes.Buffer
    if err := printer.Fprint(&buf, fset, file); err != nil {
        return err
    }

    fmt.Println(buf.String())

    return nil
}

func Run() {
    fmt.Println("Current code is running")
}