Doc cleanup and extension (#22)

* update and complete documentation
* small linter fixes

Author: nxadm

CHANGES.md

@@ -1,3 +1,7 @@
+# Version v1.4.7
+* Documentation update and cleanup release.
+* Small linter cleanups.
+
 # Version v1.4.6
 
 * Document the usage of Cleanup when re-reading a file (thanks to @lesovsky) for issue #18.

README.md

@@ -1,33 +1,44 @@
 ![ci](https://github.com/nxadm/tail/workflows/ci/badge.svg)[![Go Reference](https://pkg.go.dev/badge/github.com/nxadm/tail.svg)](https://pkg.go.dev/github.com/nxadm/tail)
 
-This project is an active, drop-in replacement for the
-[abandoned](https://en.wikipedia.org/wiki/HPE_Helion) Go tail library at
-[hpcloud](https://github.com/hpcloud/tail). This fork adds support for go
-modules, updates the dependencies, adds features and fixes bugs. Go 1.9 is the
-oldest compiler release supported.
+# tail functionality in Go
 
-# Go package for tail-ing files
+nxadm/tail provides a Go library that emulates the features of the BSD `tail`
+program. The library comes with full support for truncation/move detection as
+it is designed to work with log rotation tools. The library works on all
+operating systems supported by Go, including POSIX systems like Linux and
+*BSD, and MS Windows. Go 1.9 is the oldest compiler release supported.
 
-A Go package striving to emulate the features of the BSD `tail` program.
+A simple example:
 
 ```Go
-t, err := tail.TailFile("/var/log/nginx.log", tail.Config{Follow: true})
+// Create a tail
+t, err := tail.TailFile(
+	"/var/log/nginx.log", tail.Config{Follow: true, ReOpen: true})
 if err != nil {
     panic(err)
 }
 
+// Print the text of each received line
 for line := range t.Lines {
     fmt.Println(line.Text)
 }
 ```
 
-See [API documentation](http://godoc.org/github.com/nxadm/tail).
-
-## Log rotation
-
-Tail comes with full support for truncation/move detection as it is
-designed to work with log rotation tools.
+See [API documentation](https://pkg.go.dev/github.com/nxadm/tail).
 
 ## Installing
 
     go get github.com/nxadm/tail/...
+
+## History
+
+This project is an active, drop-in replacement for the
+[abandoned](https://en.wikipedia.org/wiki/HPE_Helion) Go tail library at
+[hpcloud](https://github.com/hpcloud/tail). Next to
+[addressing open issues/PRs of the original project](https://github.com/nxadm/tail/issues/6),
+nxadm/tail continues the development by keeping up to date with the Go toolchain
+(e.g. go modules) and dependencies, completing the documentation, adding features
+and fixing bugs.
+
+## Examples
+Examples, e.g. used to debug an issue, are kept in the [examples directory](/examples).

cmd/gotail/gotail.go

@@ -1,3 +1,4 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // Copyright (c) 2015 HPE Software Inc. All rights reserved.
 // Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
 
@@ -36,15 +37,15 @@ func main() {
 	}
 
 	if n != 0 {
-		config.Location = &tail.SeekInfo{-n, io.SeekEnd}
+		config.Location = &tail.SeekInfo{Offset: -n, Whence: io.SeekEnd}
 	}
 
 	done := make(chan bool)
 	for _, filename := range flag.Args() {
 		go tailFile(filename, config, done)
 	}
 
-	for _, _ = range flag.Args() {
+	for range flag.Args() {
 		<-done
 	}
 }

examples/01-tailAndPrint/main.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"fmt"
+
 	"github.com/nxadm/tail"
 )
 

examples/02-closeAndReopen/main.go

@@ -5,8 +5,9 @@ package main
 
 import (
 	"fmt"
-	"github.com/nxadm/tail"
 	"time"
+
+	"github.com/nxadm/tail"
 )
 
 var logFile = "/var/log/syslog"
@@ -35,7 +36,6 @@ func main() {
 	// As the documentation states: "This function is meant to be invoked from a process's exit handler".
 	//t.Cleanup()
 
-
 	// Reopen the file and print it
 	t, err = tail.TailFile(logFile, tail.Config{Follow: true})
 	if err != nil {
@@ -46,6 +46,4 @@ func main() {
 	for line := range t.Lines {
 		fmt.Println(line.Text)
 	}
-
-
 }

tail.go

@@ -1,6 +1,12 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // Copyright (c) 2015 HPE Software Inc. All rights reserved.
 // Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
 
+//nxadm/tail provides a Go library that emulates the features of the BSD `tail`
+//program. The library comes with full support for truncation/move detection as
+//it is designed to work with log rotation tools. The library works on all
+//operating systems supported by Go, including POSIX systems like Linux and
+//*BSD, and MS Windows. Go 1.9 is the oldest compiler release supported.
 package tail
 
 import (
@@ -22,26 +28,31 @@ import (
 )
 
 var (
+	// ErrStop is returned when the tail of a file has been marked to be stopped.
 	ErrStop = errors.New("tail should now stop")
 )
 
 type Line struct {
-	Text     string
-	Num      int
-	SeekInfo SeekInfo
-	Time     time.Time
-	Err      error // Error from tail
+	Text     string    // The contents of the file
+	Num      int       // The line number
+	SeekInfo SeekInfo  // SeekInfo
+	Time     time.Time // Present time
+	Err      error     // Error from tail
 }
 
-// NewLine returns a Line with present time.
+// Deprecated: this function is no longer used internally and it has little of no
+// use in the API. As such, it will be removed from the API in a future major
+// release.
+//
+// NewLine returns a * pointer to a Line struct.
 func NewLine(text string, lineNum int) *Line {
 	return &Line{text, lineNum, SeekInfo{}, time.Now(), nil}
 }
 
-// SeekInfo represents arguments to `io.Seek`
+// SeekInfo represents arguments to io.Seek. See: https://golang.org/pkg/io/#SectionReader.Seek
 type SeekInfo struct {
 	Offset int64
-	Whence int // io.Seek*
+	Whence int
 }
 
 type logger interface {
@@ -59,26 +70,28 @@ type logger interface {
 // Config is used to specify how a file must be tailed.
 type Config struct {
 	// File-specifc
-	Location    *SeekInfo // Seek to this location before tailing
-	ReOpen      bool      // Reopen recreated files (tail -F)
-	MustExist   bool      // Fail early if the file does not exist
-	Poll        bool      // Poll for file changes instead of using inotify
-	Pipe        bool      // Is a named pipe (mkfifo)
-	RateLimiter *ratelimiter.LeakyBucket
+	Location  *SeekInfo // Tail from this location. If nil, start at the beginning of the file
+	ReOpen    bool      // Reopen recreated files (tail -F)
+	MustExist bool      // Fail early if the file does not exist
+	Poll      bool      // Poll for file changes instead of using the default inotify
+	Pipe      bool      // The file is a named pipe (mkfifo)
 
 	// Generic IO
 	Follow      bool // Continue looking for new lines (tail -f)
 	MaxLineSize int  // If non-zero, split longer lines into multiple lines
 
-	// Logger, when nil, is set to tail.DefaultLogger
-	// To disable logging: set field to tail.DiscardingLogger
+	// Optionally, use a ratelimiter (e.g. created by the ratelimiter/NewLeakyBucket function)
+	RateLimiter *ratelimiter.LeakyBucket
+
+	// Optionally use a Logger. When nil, the Logger is set to tail.DefaultLogger.
+	// To disable logging, set it to tail.DiscardingLogger
 	Logger logger
 }
 
 type Tail struct {
-	Filename string
-	Lines    chan *Line
-	Config
+	Filename string     // The filename
+	Lines    chan *Line // A consumable channel of *Line
+	Config              // Tail.Configuration
 
 	file    *os.File
 	reader  *bufio.Reader
@@ -93,16 +106,17 @@ type Tail struct {
 }
 
 var (
-	// DefaultLogger is used when Config.Logger == nil
+	// DefaultLogger logs to os.Stderr and it is used when Config.Logger == nil
 	DefaultLogger = log.New(os.Stderr, "", log.LstdFlags)
 	// DiscardingLogger can be used to disable logging output
 	DiscardingLogger = log.New(ioutil.Discard, "", 0)
 )
 
-// TailFile begins tailing the file. Output stream is made available
-// via the `Tail.Lines` channel. To handle errors during tailing,
-// invoke the `Wait` or `Err` method after finishing reading from the
-// `Lines` channel.
+// TailFile begins tailing the file. And returns a pointer to a Tail struct
+// and an error. An output stream is made available via the Tail.Lines
+// channel (e.g. to be looped and printed). To handle errors during tailing,
+// after finishing reading from the Lines channel, invoke the `Wait` or `Err`
+// method on the returned *Tail.
 func TailFile(filename string, config Config) (*Tail, error) {
 	if config.ReOpen && !config.Follow {
 		util.Fatal("cannot set ReOpen without Follow.")
@@ -138,10 +152,9 @@ func TailFile(filename string, config Config) (*Tail, error) {
 	return t, nil
 }
 
-// Tell returns the file's current position, like stdio's ftell().
-// But this value is not very accurate.
-// One line from the chan(tail.Lines) may have been read,
-// so it may have lost one line.
+// Tell returns the file's current position, like stdio's ftell() and an error.
+// Beware that this value may not be completely accurate because one line from
+// the chan(tail.Lines) may have been read already.
 func (tail *Tail) Tell() (offset int64, err error) {
 	if tail.file == nil {
 		return
@@ -167,7 +180,8 @@ func (tail *Tail) Stop() error {
 	return tail.Wait()
 }
 
-// StopAtEOF stops tailing as soon as the end of the file is reached.
+// StopAtEOF stops tailing as soon as the end of the file is reached. The function
+// returns an error,
 func (tail *Tail) StopAtEOF() error {
 	tail.Kill(errStopAtEOF)
 	return tail.Wait()

tail_posix.go

@@ -1,3 +1,4 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // +build !windows
 
 package tail
@@ -6,6 +7,11 @@ import (
 	"os"
 )
 
+// Deprecated: this function is only useful internally and, as such,
+// it will be removed from the API in a future major release.
+//
+// OpenFile proxies a os.Open call for a file so it can be correctly tailed
+// on POSIX and non-POSIX OSes like MS Windows.
 func OpenFile(name string) (file *os.File, err error) {
 	return os.Open(name)
 }

tail_test.go

@@ -1,3 +1,4 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // Copyright (c) 2015 HPE Software Inc. All rights reserved.
 // Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
 
@@ -7,6 +8,7 @@
 package tail
 
 import (
+	"fmt"
 	_ "fmt"
 	"io"
 	"io/ioutil"
@@ -27,6 +29,59 @@ func init() {
 	}
 }
 
+func TestTailFile(t *testing.T) {
+	t.SkipNow()
+}
+
+func ExampleTailFile_1() {
+	// Keep tracking a file even when recreated.
+	// Write a test file (ignoring error checking)
+
+	// /var/log/messages is typically continuously written and rotated daily.
+	testFileName := "/var/log/messages"
+	// ReOpen when truncated, wait for new input when EOL is reached
+	tailedFile, err := TailFile(testFileName, Config{ReOpen: true, Follow: true})
+	if err != nil {
+		panic(err)
+	}
+
+	for line := range tailedFile.Lines {
+		fmt.Println(line.Text)
+	}
+	// Prints all the lines in the logfile and keeps printing new input
+}
+
+func ExampleTailFile_2() {
+	// Tail a file until the EOF and exit.
+
+	// Write a test file (ignoring error checking)
+	testFileName := ".test/TailFail.txt"
+	file, err := os.Create(testFileName)
+	if err != nil {
+		panic(err)
+	}
+	_, err = file.WriteString("a\nb\nc\n")
+	if err != nil {
+		panic(err)
+	}
+	file.Close()
+	defer os.Remove(testFileName)
+
+	// Just tail a file using the defaults.
+	tailedFile, err := TailFile(testFileName, Config{})
+	if err != nil {
+		panic(err)
+	}
+
+	for line := range tailedFile.Lines {
+		fmt.Println(line.Text)
+	}
+	// Output:
+	//a
+	//b
+	//c
+}
+
 func TestMain(m *testing.M) {
 	// Use a smaller poll duration for faster test runs. Keep it below
 	// 100ms (which value is used as common delays for tests)

tail_windows.go

@@ -1,12 +1,19 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // +build windows
 
 package tail
 
 import (
-	"github.com/nxadm/tail/winfile"
 	"os"
+
+	"github.com/nxadm/tail/winfile"
 )
 
+// Deprecated: this function is only useful internally and, as such,
+// it will be removed from the API in a future major release.
+//
+// OpenFile proxies a os.Open call for a file so it can be correctly tailed
+// on POSIX and non-POSIX OSes like MS Windows.
 func OpenFile(name string) (file *os.File, err error) {
 	return winfile.OpenFile(name, os.O_RDONLY, 0)
 }

util/util.go

@@ -1,3 +1,4 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // Copyright (c) 2015 HPE Software Inc. All rights reserved.
 // Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
 

watch/filechanges.go

@@ -1,3 +1,4 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 package watch
 
 type FileChanges struct {

watch/inotify.go

@@ -1,3 +1,4 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // Copyright (c) 2015 HPE Software Inc. All rights reserved.
 // Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
 

watch/inotify_tracker.go

@@ -1,3 +1,4 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
 // Copyright (c) 2015 HPE Software Inc. All rights reserved.
 // Copyright (c) 2013 ActiveState Software Inc. All rights reserved.