kei2100 / follow

An io.Reader that keeps track of the file rotations (behaves like `tail -F`)

follow

A file Reader that behaves like tail -F

func ExampleReader() {
	dir, _ := os.MkdirTemp("", "ExampleReader")
	logpath := filepath.Join(dir, "test.log")
	logfile, _ := os.Create(logpath)
	// Create follow.Reader.
	// follow.Reader is a file Reader that behaves like `tail -F`
	opts := []follow.OptionFunc{
		follow.WithPositionFile(posfile.InMemory(nil, 0)),
		follow.WithRotatedFilePathPatterns([]string{filepath.Join(dir, "test.log.*")}),
		follow.WithDetectRotateDelay(0),
		follow.WithWatchRotateInterval(100 * time.Millisecond),
	}
	reader, _ := follow.Open(logpath, opts...)
	defer reader.Close()
	// Reads log files while tracking their rotation
	go func() {
		for {
			b, _ := io.ReadAll(reader)
			if len(b) > 0 {
				fmt.Print(string(b))
			}
			time.Sleep(100 * time.Millisecond)
		}
	}()
	// Write to logfile
	fmt.Fprintln(logfile, "1")
	fmt.Fprintln(logfile, "2")
	// Rotate logfile
	logfile.Close()
	os.Rename(logpath, logpath+".1")
	logfile, _ = os.Create(logpath)
	// Write to new logfile
	fmt.Fprintln(logfile, "3")
	fmt.Fprintln(logfile, "4")
	logfile.Close()
	time.Sleep(time.Second)

	// Output:
	// 1
	// 2
	// 3
	// 4
}

follow's Issues

Support Go 1.17 go:build lines

https://tip.golang.org/doc/go1.17

//go:build lines

The go command now understands //go:build lines and prefers them over // +build lines. The new syntax uses boolean expressions, just like Go, and should be less error-prone. As of this release, the new syntax is fully supported, and all Go files should be updated to have both forms with the same meaning. To aid in migration, gofmt now automatically synchronizes the two forms. For more details on the syntax and migration plan, see https://golang.org/design/draft-gobuild.

Upgrade golang stack to 1.16.0 in appveyor.yml

refs

• https://www.appveyor.com/docs/windows-images-software/#golang
• 1f60e7b