fix: add cross-impl shard test

Ref: ipfs/js-ipfs-unixfs#358

Author: rvagg

data/builder/dir_test.go

@@ -3,6 +3,7 @@ package builder
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"testing"
@@ -12,18 +13,15 @@ import (
 	dagpb "github.com/ipld/go-codec-dagpb"
 	"github.com/ipld/go-ipld-prime"
 	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
+	"github.com/multiformats/go-multihash"
 	"github.com/stretchr/testify/require"
 )
 
 func mkEntries(cnt int, ls *ipld.LinkSystem) ([]dagpb.PBLink, error) {
 	entries := make([]dagpb.PBLink, 0, cnt)
 	for i := 0; i < cnt; i++ {
 		r := bytes.NewBufferString(fmt.Sprintf("%d", i))
-		f, s, err := BuildUnixFSFile(r, "", ls)
-		if err != nil {
-			return nil, err
-		}
-		e, err := BuildUnixFSDirectoryEntry(fmt.Sprintf("file %d", i), int64(s), f)
+		e, err := mkEntry(r, fmt.Sprintf("file %d", i), ls)
 		if err != nil {
 			return nil, err
 		}
@@ -32,6 +30,48 @@ func mkEntries(cnt int, ls *ipld.LinkSystem) ([]dagpb.PBLink, error) {
 	return entries, nil
 }
 
+func mkEntry(r io.Reader, name string, ls *ipld.LinkSystem) (dagpb.PBLink, error) {
+	f, s, err := BuildUnixFSFile(r, "", ls)
+	if err != nil {
+		return nil, err
+	}
+	return BuildUnixFSDirectoryEntry(name, int64(s), f)
+}
+
+// Cross-impl reference test: directory of files with single character
+// names, starting from ' ' and ending with '~', but excluding the special
+// characters '/' and '.'. Each file should contain a single byte with the
+// same value as the character in its name. Files are added to a sharded
+// directory with a fanout of 16, using CIDv1 throughout, and should result
+// in the root CID of:
+//
+//	bafybeihnipspiyy3dctpcx7lv655qpiuy52d7b2fzs52dtrjqwmvbiux44
+func TestBuildUnixFSDirectoryShardAltFanout_Reference(t *testing.T) {
+	ls := cidlink.DefaultLinkSystem()
+	storage := cidlink.Memory{}
+	ls.StorageReadOpener = storage.OpenRead
+	ls.StorageWriteOpener = storage.OpenWrite
+	entries := make([]dagpb.PBLink, 0)
+	for ch := ' '; ch <= '~'; ch++ {
+		if ch == '/' || ch == '.' {
+			continue
+		}
+		s := string(ch)
+		r := bytes.NewBuffer([]byte(s))
+		e, err := mkEntry(r, s, &ls)
+		require.NoError(t, err)
+		entries = append(entries, e)
+	}
+	lnk, sz, err := BuildUnixFSShardedDirectory(16, multihash.MURMUR3X64_64, entries, &ls)
+	require.NoError(t, err)
+	var totStored int
+	for _, blk := range storage.Bag {
+		totStored += len(blk)
+	}
+	require.Equal(t, totStored, int(sz))
+	require.Equal(t, "bafybeihnipspiyy3dctpcx7lv655qpiuy52d7b2fzs52dtrjqwmvbiux44", lnk.String())
+}
+
 func TestBuildUnixFSDirectory(t *testing.T) {
 	ls := cidlink.DefaultLinkSystem()
 	storage := cidlink.Memory{}