Provide callback progress hooks for long copies.

Signed-off-by: Erik Hollensbe <github@hollensbe.org>

copy/copy.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"io/ioutil"
 	"reflect"
+	"time"
 
 	pb "gopkg.in/cheggaaa/pb.v1"
 
@@ -46,6 +47,8 @@ type imageCopier struct {
 	diffIDsAreNeeded  bool
 	canModifyManifest bool
 	reportWriter      io.Writer
+	progressInterval  time.Duration
+	progress          chan types.ProgressProperties
 }
 
 // newDigestingReader returns an io.Reader implementation with contents of source, which will eventually return a non-EOF error
@@ -93,14 +96,22 @@ type Options struct {
 	ReportWriter     io.Writer
 	SourceCtx        *types.SystemContext
 	DestinationCtx   *types.SystemContext
+	ProgressInterval time.Duration                 // time to wait between reports to signal the progress channel
+	Progress         chan types.ProgressProperties // Reported to when ProgressInterval has arrived for a single artifact+offset.
 }
 
 // Image copies image from srcRef to destRef, using policyContext to validate source image admissibility.
 func Image(policyContext *signature.PolicyContext, destRef, srcRef types.ImageReference, options *Options) error {
+	if options == nil {
+		options = &Options{}
+	}
+
 	reportWriter := ioutil.Discard
-	if options != nil && options.ReportWriter != nil {
+
+	if options.ReportWriter != nil {
 		reportWriter = options.ReportWriter
 	}
+
 	writeReport := func(f string, a ...interface{}) {
 		fmt.Fprintf(reportWriter, f, a...)
 	}
@@ -139,7 +150,7 @@ func Image(policyContext *signature.PolicyContext, destRef, srcRef types.ImageRe
 	}
 
 	var sigs [][]byte
-	if options != nil && options.RemoveSignatures {
+	if options.RemoveSignatures {
 		sigs = [][]byte{}
 	} else {
 		writeReport("Getting image source signatures\n")
@@ -174,6 +185,8 @@ func Image(policyContext *signature.PolicyContext, destRef, srcRef types.ImageRe
 		diffIDsAreNeeded:  src.UpdatedImageNeedsLayerDiffIDs(manifestUpdates),
 		canModifyManifest: canModifyManifest,
 		reportWriter:      reportWriter,
+		progressInterval:  options.ProgressInterval,
+		progress:          options.Progress,
 	}
 
 	if err := ic.copyLayers(); err != nil {
@@ -200,7 +213,7 @@ func Image(policyContext *signature.PolicyContext, destRef, srcRef types.ImageRe
 		return err
 	}
 
-	if options != nil && options.SignBy != "" {
+	if options.SignBy != "" {
 		mech, err := signature.NewGPGSigningMechanism()
 		if err != nil {
 			return errors.Wrap(err, "Error initializing GPG")
@@ -490,6 +503,17 @@ func (ic *imageCopier) copyBlobFromStream(srcStream io.Reader, srcInfo types.Blo
 		inputInfo.Size = -1
 	}
 
+	// === Report progress using the ic.progress channel, if required.
+	if ic.progress != nil && ic.progressInterval > 0 {
+		destStream = &progressReader{
+			source:   destStream,
+			channel:  ic.progress,
+			interval: ic.progressInterval,
+			artifact: srcInfo,
+			lastTime: time.Now(),
+		}
+	}
+
 	// === Finally, send the layer stream to dest.
 	uploadedInfo, err := ic.dest.PutBlob(destStream, inputInfo)
 	if err != nil {

copy/progress_reader.go

@@ -0,0 +1,28 @@
+package copy
+
+import (
+	"io"
+	"time"
+
+	"github.com/containers/image/types"
+)
+
+// progressReader is a reader that reports its progress on an interval.
+type progressReader struct {
+	source   io.Reader
+	channel  chan types.ProgressProperties
+	interval time.Duration
+	artifact types.BlobInfo
+	lastTime time.Time
+	offset   uint64
+}
+
+func (r *progressReader) Read(p []byte) (int, error) {
+	n, err := r.source.Read(p)
+	r.offset += uint64(n)
+	if time.Since(r.lastTime) > r.interval {
+		r.channel <- types.ProgressProperties{Artifact: r.artifact, Offset: r.offset}
+		r.lastTime = time.Now()
+	}
+	return n, err
+}

types/types.go

@@ -294,6 +294,13 @@ type SystemContext struct {
 	DockerDisableV1Ping bool
 }
 
+// ProgressProperties is used to pass information from the copy code to a monitor which
+// can use the real-time information to produce output or react to changes.
+type ProgressProperties struct {
+	Artifact BlobInfo
+	Offset   uint64
+}
+
 var (
 	// ErrBlobNotFound can be returned by an ImageDestination's HasBlob() method
 	ErrBlobNotFound = errors.New("no such blob present")