如何在应用程序中丢弃在导入的第三方程序包中定义的标志

Question

Consider, my application uses a third party library. I want my application to accept only the flags defined in my application and not the flags defined in imported packages.

package main

import (
    "flag"
    "fmt"
    log "github.com/golang/glog"
)

var myFlag int

func init() {
    flag.IntVar(&myFlag, "my_flag", 0, "need only my flags")
    confDir := "/Users/foo/test/logs" //assume this is read from configuration file
    flag.Set("log_dir", confDir)
    flag.Parse()
}

func main() {
    flag.Parse()
    log.Errorln("flag", myFlag)
    log.V(0).Infoln("flag", myFlag)
    fmt.Println("test", myFlag)
}

In above code sample, log package has many flags. After compiling when I execute following command, all flags including "my_flag" and flags from log package are displayed. But, I want to set the values for log package flags from my code with values obtained from configuration file.

  -alsologtostderr
        log to standard error as well as files
  -log_backtrace_at value
        when logging hits line file:N, emit a stack trace
  -log_dir string
        If non-empty, write log files in this directory
  -logtostderr
        log to standard error instead of files
  -my_flag int
        need only my flags
  -stderrthreshold value
        logs at or above this threshold go to stderr
  -v value
        log level for V logs
  -vmodule value
        comma-separated list of pattern=N settings for file-filtered logging

How to restrict my application executable from accepting other flags?

Answer 1

If you want to discard the flags of other packages, then you can use a new flagset instead of the default one.

package main

import (
    "flag"
    "fmt"
    "os"
)

var myFlag int

func main() {
    f := flag.NewFlagSet(os.Args[0], flag.ExitOnError)
    f.IntVar(&myFlag, "my_flag", 0, "need only my flags")
    confDir := "/Users/foo/test/logs" //assume this is read from configuration file
    f.Set("log_dir", confDir)
    f.Parse(os.Args[1:])
    fmt.Println("test", myFlag)
}