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writer.go
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writer.go
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package pullprogress
import (
"encoding/json"
"io"
"strings"
"time"
)
const (
defaultCountTimeThreshhold = 10 * time.Second
defaultProgressTimeThreshhold = 45 * time.Second
defaultStableThreshhold = 3
)
// NewPullProgressWriter creates a writer that periodically reports
// on pull progress of an image. It only reports when the state of the
// different layers has changed and uses time threshholds to limit the
// rate of the reports.
func NewPullProgressWriter(reportFn func(*ProgressReport)) io.Writer {
pipeIn, pipeOut := io.Pipe()
progressWriter := &pullProgressWriter{
Writer: pipeOut,
decoder: json.NewDecoder(pipeIn),
layerStatus: map[string]Status{},
reportFn: reportFn,
countTimeThreshhold: defaultCountTimeThreshhold,
progressTimeThreshhold: defaultProgressTimeThreshhold,
stableThreshhold: defaultStableThreshhold,
}
go func() {
err := progressWriter.readProgress()
if err != nil {
pipeIn.CloseWithError(err)
}
}()
return progressWriter
}
// Status is a structure representation of a Docker pull progress line
type Status struct {
ID string `json:"id"`
Status string `json:"status"`
ProgressDetail Detail `json:"progressDetail"`
Progress string `json:"progress"`
}
// Detail is the progressDetail structure in a Docker pull progress line
type Detail struct {
Current int64 `json:"current"`
Total int64 `json:"total"`
}
// ProgressReport is a report of the progress of an image pull. It provides counts
// of layers in a given state. It also provides a percentage of downloaded data
// of those layers that are currently getting downloaded
type ProgressReport struct {
Waiting int
Downloading int
Extracting int
Complete int
DownloadPct float32
}
type statusType int
const (
statusWaiting statusType = iota
statusDownloading
statusExtracting
statusComplete
)
type pullProgressWriter struct {
io.Writer
decoder *json.Decoder
layerStatus map[string]Status
lastLayerCount int
stableLines int
stableThreshhold int
countTimeThreshhold time.Duration
progressTimeThreshhold time.Duration
lastReport *ProgressReport
lastReportTime time.Time
reportFn func(*ProgressReport)
}
func (w *pullProgressWriter) readProgress() error {
for {
status := &Status{}
err := w.decoder.Decode(status)
if err == io.EOF {
break
}
if err != nil {
return err
}
err = w.processStatus(status)
if err != nil {
return err
}
}
return nil
}
func (w *pullProgressWriter) isStableLayerCount() bool {
// If the number of layers has changed since last status, we're not stable
if w.lastLayerCount != len(w.layerStatus) {
w.lastLayerCount = len(w.layerStatus)
w.stableLines = 0
return false
}
// Only proceed after we've received status for the same number
// of layers at least 3 times. If not, they're still increasing
w.stableLines++
if w.stableLines < w.stableThreshhold {
// We're not stable enough yet
return false
}
return true
}
func (w *pullProgressWriter) processStatus(status *Status) error {
// determine if it's a status we want to process
if !isLayerStatus(status) {
return nil
}
w.layerStatus[status.ID] = *status
// if the number of layers has not stabilized yet, return and wait for more
// progress
if !w.isStableLayerCount() {
return nil
}
report := createProgressReport(w.layerStatus)
// check if the count of layers in each state has changed
if countsChanged(report, w.lastReport) {
// only report on changed counts if the change occurs after
// a predefined set of seconds (10 sec by default). This prevents
// multiple reports in rapid succession
if time.Since(w.lastReportTime) > w.countTimeThreshhold {
w.lastReport = report
w.lastReportTime = time.Now()
w.reportFn(report)
}
} else {
// If counts haven't changed, but enough time has passed (45 sec by default),
// at least report on download progress
if time.Since(w.lastReportTime) > w.progressTimeThreshhold {
w.lastReport = report
w.lastReportTime = time.Now()
w.reportFn(report)
}
}
return nil
}
func countsChanged(new, old *ProgressReport) bool {
if old == nil {
return true
}
return new.Waiting != old.Waiting ||
new.Downloading != old.Downloading ||
new.Extracting != old.Extracting ||
new.Complete != old.Complete
}
func layerStatusToPullStatus(str string) statusType {
switch str {
case "Downloading":
return statusDownloading
case "Extracting", "Verifying Checksum", "Download complete":
return statusExtracting
case "Pull complete", "Already exists":
return statusComplete
default: // "Pull fs layer" or "Waiting"
return statusWaiting
}
}
func isLayerStatus(status *Status) bool {
// ignore status lines with no layer id
if len(status.ID) == 0 {
return false
}
// ignore status lines with the initial named layer
if strings.HasPrefix(status.Status, "Pulling from") {
return false
}
return true
}
func createProgressReport(layerStatus map[string]Status) *ProgressReport {
report := &ProgressReport{}
var totalDownload, totalCurrent int64
for _, status := range layerStatus {
pullStatus := layerStatusToPullStatus(status.Status)
switch pullStatus {
case statusWaiting:
report.Waiting++
case statusDownloading:
report.Downloading++
totalDownload += status.ProgressDetail.Total
totalCurrent += status.ProgressDetail.Current
case statusExtracting:
report.Extracting++
case statusComplete:
report.Complete++
}
}
if totalDownload == 0 {
report.DownloadPct = 0
} else {
report.DownloadPct = float32(totalCurrent) / float32(totalDownload) * 100.0
}
return report
}