estargz: Build: replace golang.org/x/sync with WaitGroup.Go (go1.25)

It was only using minimal functionality of the errgroup (and didn't
use, e.g. `errgroup.WithContext`). Rewrite it with a sync.WaitGroup
from stdlib.

Also update to go1.25 and use WaitGroup.Go

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

estargz/build.go

@@ -40,7 +40,6 @@ import (
 	"github.com/containerd/stargz-snapshotter/estargz/errorutil"
 	"github.com/klauspost/compress/zstd"
 	digest "github.com/opencontainers/go-digest"
-	"golang.org/x/sync/errgroup"
 )
 
 type GzipHelperFunc func(io.Reader) (io.ReadCloser, error)
@@ -235,14 +234,16 @@ func Build(tarBlob *io.SectionReader, opt ...Option) (_ *Blob, rErr error) {
 	}
 	writers := make([]*Writer, len(tarParts))
 	payloads := make([]*os.File, len(tarParts))
-	var eg errgroup.Group
+	var wg sync.WaitGroup
+	errCh := make(chan error, len(tarParts)) // buffered to avoid goroutine leaks
 	for i, parts := range tarParts {
 		i, parts := i, parts
 		// builds verifiable stargz sub-blobs
-		eg.Go(func() error {
+		wg.Go(func() {
 			esgzFile, err := layerFiles.TempFile("", "esgzdata")
 			if err != nil {
-				return err
+				errCh <- err
+				return
 			}
 			sw := NewWriterWithCompressor(esgzFile, opts.compression)
 			sw.ChunkSize = opts.chunkSize
@@ -254,16 +255,20 @@ func Build(tarBlob *io.SectionReader, opt ...Option) (_ *Blob, rErr error) {
 				sw.needsOpenGzEntries[f] = struct{}{}
 			}
 			if err := sw.AppendTar(readerFromEntries(parts...)); err != nil {
-				return err
+				errCh <- err
+				return
 			}
 			writers[i] = sw
 			payloads[i] = esgzFile
-			return nil
 		})
 	}
-	if err := eg.Wait(); err != nil {
-		rErr = err
-		return nil, err
+	wg.Wait()
+	close(errCh)
+
+	for err := range errCh {
+		if err != nil {
+			return nil, err
+		}
 	}
 	tocAndFooter, tocDgst, err := closeWithCombine(writers...)
 	if err != nil {

estargz/go.mod

@@ -1,10 +1,9 @@
 module github.com/containerd/stargz-snapshotter/estargz
 
-go 1.24.0
+go 1.25.0
 
 require (
 	github.com/klauspost/compress v1.18.3
 	github.com/opencontainers/go-digest v1.0.0
 	github.com/vbatts/tar-split v0.12.2
-	golang.org/x/sync v0.19.0
 )

estargz/go.sum

@@ -4,5 +4,3 @@ github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8
 github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=
 github.com/vbatts/tar-split v0.12.2 h1:w/Y6tjxpeiFMR47yzZPlPj/FcPLpXbTUi/9H7d3CPa4=
 github.com/vbatts/tar-split v0.12.2/go.mod h1:eF6B6i6ftWQcDqEn3/iGFRFRo8cBIMSJVOpnNdfTMFA=
-golang.org/x/sync v0.19.0 h1:vV+1eWNmZ5geRlYjzm2adRgW2/mcpevXNg50YZtPCE4=
-golang.org/x/sync v0.19.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=