Add ability to customize the io.Reader (#7)

go.mod

@@ -0,0 +1,8 @@
+module github.com/influxdata/tail
+
+go 1.13
+
+require (
+	gopkg.in/fsnotify.v1 v1.2.1
+	gopkg.in/tomb.v1 v1.0.0-20140529071818-c131134a1947
+)

go.sum

@@ -0,0 +1,6 @@
+github.com/influxdata/tail v1.0.0 h1:RGikfjB/b5C/YP3p47YD48eE0WSsJyAVbBHNpoTHdX0=
+github.com/influxdata/tail v1.0.0/go.mod h1:xTFF2SILpIYc5N+Srb0d5qpx7d+f733nBrbasb13DtQ=
+gopkg.in/fsnotify.v1 v1.2.1 h1:x2hwAFVlj5ptNfCIgr3KRZm9IQcKDCWJbQDO7QxUXOo=
+gopkg.in/fsnotify.v1 v1.2.1/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
+gopkg.in/tomb.v1 v1.0.0-20140529071818-c131134a1947 h1:aNEcl02ps/eZaBJi2LycKl0jPsUryySSSgrCxieZRYA=
+gopkg.in/tomb.v1 v1.0.0-20140529071818-c131134a1947/go.mod h1:dt/ZhP58zS4L8KSrWDmTeBkI65Dw0HsyUHuEVlX15mw=

tail.go

@@ -57,12 +57,13 @@ 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 // 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
+	OpenReaderFunc func(rd io.Reader) io.Reader
 
 	// Generic IO
 	Follow      bool // Continue looking for new lines (tail -f)
@@ -396,11 +397,16 @@ func (tail *Tail) waitForChanges() error {
 
 func (tail *Tail) openReader() {
 	tail.lk.Lock()
+	var rd io.Reader = tail.file
+	if tail.OpenReaderFunc != nil {
+		rd = tail.OpenReaderFunc(rd)
+	}
+
 	if tail.MaxLineSize > 0 {
 		// add 2 to account for newline characters
-		tail.reader = bufio.NewReaderSize(tail.file, tail.MaxLineSize+2)
+		tail.reader = bufio.NewReaderSize(rd, tail.MaxLineSize+2)
 	} else {
-		tail.reader = bufio.NewReader(tail.file)
+		tail.reader = bufio.NewReader(rd)
 	}
 	tail.lk.Unlock()
 }