Add CLI progress bars to the packer tool

Since packing can be quite slow, it is nice to display progress to the
caller. We use the excellent github.com/vbauerster/mpb library to do so,
and add a bit of colour with github.com/logrusru/aurora.

Finally, augment the inspector and packer with a summary printer that
displays the overall file size/count, and compression ratio for each
compression type.

cmd/htpacker/packer/packer.go

@@ -45,6 +45,24 @@ type FileToPack struct {
 	DisableBrotli bool `yaml:"disable_brotli"`
 }
 
+// Progress is a callback object which reports packing progress.
+type Progress interface {
+	// Count reports the number of items that have begun processing.
+	Count(n int)
+
+	// Begin denotes the processing of an input file.
+	Begin(filename, compression string)
+
+	// End denotes the completion of input file processing.
+	End(filename, compression string)
+}
+
+type ignoreProgress int
+
+func (ignoreProgress) Count(_ int)       {}
+func (ignoreProgress) Begin(_, _ string) {}
+func (ignoreProgress) End(_, _ string)   {}
+
 const (
 	// minCompressionSaving means we'll only use the compressed version of
 	// the file if it's at least this many bytes smaller than the original.
@@ -68,8 +86,18 @@ const (
 	sendfileLimit = 0x7FFFF000
 )
 
-// Pack a file.
+// Pack a file. Use Pack2 for progress reporting.
 func Pack(filesToPack FilesToPack, outputFilename string) error {
+	return Pack2(filesToPack, outputFilename, nil)
+}
+
+// Pack2 will pack a file, with progress reporting. The progress interface may
+// be nil.
+func Pack2(filesToPack FilesToPack, outputFilename string, progress Progress) error {
+	if progress == nil {
+		progress = ignoreProgress(0)
+	}
+
 	finalFname, w, err := writefile.New(outputFilename)
 	if err != nil {
 		return err
@@ -79,7 +107,8 @@ func Pack(filesToPack FilesToPack, outputFilename string) error {
 	// we use this little structure to serialise file writes below, and
 	// it has a couple of convenience methods for common operations
 	packer := packer{
-		w: w,
+		w:        w,
+		progress: progress,
 	}
 
 	// write initial header (will rewrite offset/length when known)
@@ -124,6 +153,7 @@ func Pack(filesToPack FilesToPack, outputFilename string) error {
 		Files: make(map[string]*packed.File),
 	}
 
+	var count int
 PackingLoop:
 	for path, fileToPack := range filesToPack {
 		select {
@@ -132,6 +162,8 @@ PackingLoop:
 			break PackingLoop
 		default:
 			packer.packFile(path, fileToPack)
+			count++
+			progress.Count(count)
 		}
 	}
 
@@ -199,12 +231,13 @@ func compressionWorthwhile(data []byte, compressed os.FileInfo) bool {
 // of compression. Unexported methods assume they are called in a context where
 // the lock is not needed or already taken; exported methods take the lock.
 type packer struct {
-	w       *os.File
-	lock    sync.Mutex
-	cpus    chan struct{}
-	errors  chan error
-	aborted chan struct{}
-	dir     *packed.Directory
+	w        *os.File
+	lock     sync.Mutex
+	cpus     chan struct{}
+	errors   chan error
+	aborted  chan struct{}
+	dir      *packed.Directory
+	progress Progress
 }
 
 // pad will move the file write pointer to the next padding boundary. It is not
@@ -312,11 +345,15 @@ func (p *packer) packFile(path string, fileToPack FileToPack) {
 	// list of operations on this input file that we'll carry out asynchronously
 	ops := []func() error{
 		func() error {
+			p.progress.Begin(fileToPack.Filename, "uncompressed")
+			defer p.progress.End(fileToPack.Filename, "uncompressed")
 			return p.Uncompressed(fileToPack.Filename, info)
 		},
 	}
 	if !fileToPack.DisableCompression && !fileToPack.DisableGzip {
 		ops = append(ops, func() error {
+			p.progress.Begin(fileToPack.Filename, "gzip")
+			defer p.progress.End(fileToPack.Filename, "gzip")
 			if err := p.Gzip(data, info); err != nil {
 				return fmt.Errorf("gzip compression of %s "+
 					"failed: %v", fileToPack.Filename, err)
@@ -326,6 +363,8 @@ func (p *packer) packFile(path string, fileToPack FileToPack) {
 	}
 	if !fileToPack.DisableCompression && !fileToPack.DisableBrotli {
 		ops = append(ops, func() error {
+			p.progress.Begin(fileToPack.Filename, "brotli")
+			defer p.progress.End(fileToPack.Filename, "brotli")
 			if err := p.Brotli(data, info); err != nil {
 				return fmt.Errorf("brotli compression of %s "+
 					"failed: %v", fileToPack.Filename, err)