Reorder push command operations

Narrow down the window of opportunity for race conditions

Reference issue: #18
The idea was presented in this PR: #19

Author: hypnoglow

cmd/helms3/push.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"time"
 
 	"github.com/pkg/errors"
 	"k8s.io/helm/pkg/chartutil"
@@ -16,7 +17,15 @@ import (
 	"github.com/hypnoglow/helm-s3/pkg/index"
 )
 
+const (
+	pushCommandDefaultTimeout = time.Second * 15
+)
+
 func runPush(chartPath string, repoName string) error {
+	// Just one big timeout for the whole operation.
+	ctx, cancel := context.WithTimeout(context.Background(), pushCommandDefaultTimeout)
+	defer cancel()
+
 	fpath, err := filepath.Abs(chartPath)
 	if err != nil {
 		return errors.WithMessage(err, "get chart abs path")
@@ -36,7 +45,8 @@ func runPush(chartPath string, repoName string) error {
 
 	storage := awss3.NewStorage(awsConfig)
 
-	// Load chart and calculate required params like hash.
+	// Load chart, calculate required params like hash,
+	// and upload the chart right away.
 
 	chart, err := chartutil.LoadFile(fname)
 	if err != nil {
@@ -48,15 +58,26 @@ func runPush(chartPath string, repoName string) error {
 		return err
 	}
 
+	fchart, err := os.Open(fname)
+	if err != nil {
+		return errors.Wrap(err, "open chart file")
+	}
+
+	if _, err := storage.Upload(ctx, repoEntry.URL+"/"+fname, fchart); err != nil {
+		return errors.WithMessage(err, "upload chart to s3")
+	}
+
+	// Next, update the repository index.
+	// The gap between index fetching and uploading should be as small as
+	// possible to make the best effort to avoid race conditions.
+	// See https://github.com/hypnoglow/helm-s3/issues/18 for more info.
+
 	hash, err := provenance.DigestFile(fname)
 	if err != nil {
 		return errors.WithMessage(err, "get chart digest")
 	}
 
-	// Fetch current index.
-
-	ctx, cancel := context.WithTimeout(context.Background(), defaultTimeout)
-	defer cancel()
+	// Fetch current index, update it and upload it back.
 
 	b, err := storage.FetchRaw(ctx, repoEntry.URL+"/index.yaml")
 	if err != nil {
@@ -68,28 +89,14 @@ func runPush(chartPath string, repoName string) error {
 		return errors.WithMessage(err, "load index from downloaded file")
 	}
 
-	// Update index.
-
 	idx.Add(chart.GetMetadata(), fname, repoEntry.URL, hash)
 	idx.SortEntries()
 
-	// Finally, upload both chart file and index.
-
-	fchart, err := os.Open(fname)
-	if err != nil {
-		return errors.Wrap(err, "open chart file")
-	}
 	idxReader, err := idx.Reader()
 	if err != nil {
 		return errors.WithMessage(err, "get index reader")
 	}
 
-	ctx, cancel = context.WithTimeout(context.Background(), defaultTimeout*2)
-	defer cancel()
-
-	if _, err := storage.Upload(ctx, repoEntry.URL+"/"+fname, fchart); err != nil {
-		return errors.WithMessage(err, "upload chart to s3")
-	}
 	if _, err := storage.Upload(ctx, repoEntry.URL+"/index.yaml", idxReader); err != nil {
 		return errors.WithMessage(err, "upload index to s3")
 	}