feat: add option to create blockstore that writes a plain CARv1

v2/blockstore/readwrite.go

@@ -40,6 +40,18 @@ type ReadWrite struct {
 	opts carv2.Options
 }
 
+// WriteAsCarV1 is a write option which makes a CAR blockstore write the output
+// as a CARv1 only, with no CARv2 header or index. Indexing is used internally
+// during write but is discarded upon finalization.
+//
+// Note that this option only affects the blockstore, and is ignored by the root
+// go-car/v2 package.
+func WriteAsCarV1(asCarV1 bool) carv2.Option {
+	return func(o *carv2.Options) {
+		o.WriteAsCarV1 = asCarV1
+	}
+}
+
 // AllowDuplicatePuts is a write option which makes a CAR blockstore not
 // deduplicate blocks in Put and PutMany. The default is to deduplicate,
 // which matches the current semantics of go-ipfs-blockstore v1.
@@ -122,33 +134,39 @@ func OpenReadWrite(path string, roots []cid.Cid, opts ...carv2.Option) (*ReadWri
 		rwbs.header = rwbs.header.WithIndexPadding(p)
 	}
 
-	rwbs.dataWriter = internalio.NewOffsetWriter(rwbs.f, int64(rwbs.header.DataOffset))
-	v1r := internalio.NewOffsetReadSeeker(rwbs.f, int64(rwbs.header.DataOffset))
+	offset := int64(rwbs.header.DataOffset)
+	if rwbs.opts.WriteAsCarV1 {
+		offset = 0
+	}
+	rwbs.dataWriter = internalio.NewOffsetWriter(rwbs.f, offset)
+	v1r := internalio.NewOffsetReadSeeker(rwbs.f, offset)
 	rwbs.ronly.backing = v1r
 	rwbs.ronly.idx = rwbs.idx
 	rwbs.ronly.carv2Closer = rwbs.f
 
 	if resume {
-		if err = rwbs.resumeWithRoots(roots); err != nil {
+		if err = rwbs.resumeWithRoots(!rwbs.opts.WriteAsCarV1, roots); err != nil {
 			return nil, err
 		}
 	} else {
-		if err = rwbs.initWithRoots(roots); err != nil {
+		if err = rwbs.initWithRoots(!rwbs.opts.WriteAsCarV1, roots); err != nil {
 			return nil, err
 		}
 	}
 
 	return rwbs, nil
 }
 
-func (b *ReadWrite) initWithRoots(roots []cid.Cid) error {
-	if _, err := b.f.WriteAt(carv2.Pragma, 0); err != nil {
-		return err
+func (b *ReadWrite) initWithRoots(v2 bool, roots []cid.Cid) error {
+	if v2 {
+		if _, err := b.f.WriteAt(carv2.Pragma, 0); err != nil {
+			return err
+		}
 	}
 	return carv1.WriteHeader(&carv1.CarHeader{Roots: roots, Version: 1}, b.dataWriter)
 }
 
-func (b *ReadWrite) resumeWithRoots(roots []cid.Cid) error {
+func (b *ReadWrite) resumeWithRoots(v2 bool, roots []cid.Cid) error {
 	// On resumption it is expected that the CARv2 Pragma, and the CARv1 header is successfully written.
 	// Otherwise we cannot resume from the file.
 	// Read pragma to assert if b.f is indeed a CARv2.
@@ -158,36 +176,39 @@ func (b *ReadWrite) resumeWithRoots(roots []cid.Cid) error {
 		// Or the write must have failed before pragma was written.
 		return err
 	}
-	if version != 2 {
-		// The file is not a CARv2 and we cannot resume from it.
+	if !((version == 1 && !v2) || (version == 2 && v2)) {
+		// The file is not the expected version and we cannot resume from it.
 		return fmt.Errorf("cannot resume on CAR file with version %v", version)
 	}
 
-	// Check if file was finalized by trying to read the CARv2 header.
-	// We check because if finalized the CARv1 reader behaviour needs to be adjusted since
-	// EOF will not signify end of CARv1 payload. i.e. index is most likely present.
 	var headerInFile carv2.Header
-	_, err = headerInFile.ReadFrom(internalio.NewOffsetReadSeeker(b.f, carv2.PragmaSize))
-
-	// If reading CARv2 header succeeded, and CARv1 offset in header is not zero then the file is
-	// most-likely finalized. Check padding and truncate the file to remove index.
-	// Otherwise, carry on reading the v1 payload at offset determined from b.header.
-	if err == nil && headerInFile.DataOffset != 0 {
-		if headerInFile.DataOffset != b.header.DataOffset {
-			// Assert that the padding on file matches the given WithDataPadding option.
-			wantPadding := headerInFile.DataOffset - carv2.PragmaSize - carv2.HeaderSize
-			gotPadding := b.header.DataOffset - carv2.PragmaSize - carv2.HeaderSize
-			return fmt.Errorf(
-				"cannot resume from file with mismatched CARv1 offset; "+
-					"`WithDataPadding` option must match the padding on file. "+
-					"Expected padding value of %v but got %v", wantPadding, gotPadding,
-			)
-		} else if headerInFile.DataSize == 0 {
-			// If CARv1 size is zero, since CARv1 offset wasn't, then the CARv2 header was
-			// most-likely partially written. Since we write the header last in Finalize then the
-			// file most-likely contains the index and we cannot know where it starts, therefore
-			// can't resume.
-			return errors.New("corrupt CARv2 header; cannot resume from file")
+
+	if v2 {
+		// Check if file was finalized by trying to read the CARv2 header.
+		// We check because if finalized the CARv1 reader behaviour needs to be adjusted since
+		// EOF will not signify end of CARv1 payload. i.e. index is most likely present.
+		_, err = headerInFile.ReadFrom(internalio.NewOffsetReadSeeker(b.f, carv2.PragmaSize))
+
+		// If reading CARv2 header succeeded, and CARv1 offset in header is not zero then the file is
+		// most-likely finalized. Check padding and truncate the file to remove index.
+		// Otherwise, carry on reading the v1 payload at offset determined from b.header.
+		if err == nil && headerInFile.DataOffset != 0 {
+			if headerInFile.DataOffset != b.header.DataOffset {
+				// Assert that the padding on file matches the given WithDataPadding option.
+				wantPadding := headerInFile.DataOffset - carv2.PragmaSize - carv2.HeaderSize
+				gotPadding := b.header.DataOffset - carv2.PragmaSize - carv2.HeaderSize
+				return fmt.Errorf(
+					"cannot resume from file with mismatched CARv1 offset; "+
+						"`WithDataPadding` option must match the padding on file. "+
+						"Expected padding value of %v but got %v", wantPadding, gotPadding,
+				)
+			} else if headerInFile.DataSize == 0 {
+				// If CARv1 size is zero, since CARv1 offset wasn't, then the CARv2 header was
+				// most-likely partially written. Since we write the header last in Finalize then the
+				// file most-likely contains the index and we cannot know where it starts, therefore
+				// can't resume.
+				return errors.New("corrupt CARv2 header; cannot resume from file")
+			}
 		}
 	}
 
@@ -213,10 +234,13 @@ func (b *ReadWrite) resumeWithRoots(roots []cid.Cid) error {
 			return err
 		}
 	}
-	// Now that CARv2 header is present on file, clear it to avoid incorrect size and offset in
-	// header in case blocksotre is closed without finalization and is resumed from.
-	if err := b.unfinalize(); err != nil {
-		return fmt.Errorf("could not un-finalize: %w", err)
+
+	if v2 {
+		// Now that CARv2 header is present on file, clear it to avoid incorrect size and offset in
+		// header in case blocksotre is closed without finalization and is resumed from.
+		if err := b.unfinalize(); err != nil {
+			return fmt.Errorf("could not un-finalize: %w", err)
+		}
 	}
 
 	// TODO See how we can reduce duplicate code here.
@@ -354,6 +378,11 @@ func (b *ReadWrite) Discard() {
 // for more efficient subsequent read.
 // After this call, the blockstore can no longer be used.
 func (b *ReadWrite) Finalize() error {
+	if b.opts.WriteAsCarV1 {
+		b.Discard()
+		return nil
+	}
+
 	b.ronly.mu.Lock()
 	defer b.ronly.mu.Unlock()
 

v2/blockstore/readwrite_test.go

@@ -47,81 +47,120 @@ func TestReadWriteGetReturnsBlockstoreNotFoundWhenCidDoesNotExist(t *testing.T)
 	require.Nil(t, gotBlock)
 }
 
-func TestBlockstore(t *testing.T) {
-	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
-	defer cancel()
+func TestBlockstoreX(t *testing.T) {
+	originalCARv1Path := "../testdata/sample-v1.car"
+	originalCARv1ComparePath := "../testdata/sample-v1-noidentity.car"
+	originalCARv1ComparePathStat, err := os.Stat(originalCARv1ComparePath)
+	require.NoError(t, err)
+
+	variants := []struct {
+		name                  string
+		options               []carv2.Option
+		expectedV1StartOffset int64
+	}{
+		// no options, expect a standard CARv2 with the noidentity inner CARv1
+		{"noopt carv2", []carv2.Option{}, int64(carv2.PragmaSize + carv2.HeaderSize)},
+		// option to only write as a CARv1, expect the noidentity inner CARv1
+		{"carv1", []carv2.Option{blockstore.WriteAsCarV1(true)}, int64(0)},
+	}
 
-	f, err := os.Open("../testdata/sample-v1.car")
-	require.NoError(t, err)
-	t.Cleanup(func() { assert.NoError(t, f.Close()) })
-	r, err := carv1.NewCarReader(f)
-	require.NoError(t, err)
+	for _, variant := range variants {
+		t.Run(variant.name, func(t *testing.T) {
+			ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+			defer cancel()
 
-	path := filepath.Join(t.TempDir(), "readwrite.car")
-	ingester, err := blockstore.OpenReadWrite(path, r.Header.Roots)
-	require.NoError(t, err)
-	t.Cleanup(func() { ingester.Finalize() })
+			f, err := os.Open(originalCARv1Path)
+			require.NoError(t, err)
+			t.Cleanup(func() { assert.NoError(t, f.Close()) })
+			r, err := carv1.NewCarReader(f)
+			require.NoError(t, err)
 
-	cids := make([]cid.Cid, 0)
-	var idCidCount int
-	for {
-		b, err := r.Next()
-		if err == io.EOF {
-			break
-		}
-		require.NoError(t, err)
+			path := filepath.Join(t.TempDir(), "readwrite.car")
+			ingester, err := blockstore.OpenReadWrite(path, r.Header.Roots, variant.options...)
+			require.NoError(t, err)
+			t.Cleanup(func() { ingester.Finalize() })
+
+			cids := make([]cid.Cid, 0)
+			var idCidCount int
+			for {
+				b, err := r.Next()
+				if err == io.EOF {
+					break
+				}
+				require.NoError(t, err)
 
-		err = ingester.Put(ctx, b)
-		require.NoError(t, err)
-		cids = append(cids, b.Cid())
+				err = ingester.Put(ctx, b)
+				require.NoError(t, err)
+				cids = append(cids, b.Cid())
 
-		// try reading a random one:
-		candidate := cids[rng.Intn(len(cids))]
-		if has, err := ingester.Has(ctx, candidate); !has || err != nil {
-			t.Fatalf("expected to find %s but didn't: %s", candidate, err)
-		}
+				// try reading a random one:
+				candidate := cids[rng.Intn(len(cids))]
+				if has, err := ingester.Has(ctx, candidate); !has || err != nil {
+					t.Fatalf("expected to find %s but didn't: %s", candidate, err)
+				}
 
-		dmh, err := multihash.Decode(b.Cid().Hash())
-		require.NoError(t, err)
-		if dmh.Code == multihash.IDENTITY {
-			idCidCount++
-		}
-	}
+				dmh, err := multihash.Decode(b.Cid().Hash())
+				require.NoError(t, err)
+				if dmh.Code == multihash.IDENTITY {
+					idCidCount++
+				}
+			}
 
-	for _, c := range cids {
-		b, err := ingester.Get(ctx, c)
-		require.NoError(t, err)
-		if !b.Cid().Equals(c) {
-			t.Fatal("wrong item returned")
-		}
-	}
+			for _, c := range cids {
+				b, err := ingester.Get(ctx, c)
+				require.NoError(t, err)
+				if !b.Cid().Equals(c) {
+					t.Fatal("wrong item returned")
+				}
+			}
 
-	err = ingester.Finalize()
-	require.NoError(t, err)
-	robs, err := blockstore.OpenReadOnly(path)
-	require.NoError(t, err)
-	t.Cleanup(func() { assert.NoError(t, robs.Close()) })
+			err = ingester.Finalize()
+			require.NoError(t, err)
+			robs, err := blockstore.OpenReadOnly(path)
+			require.NoError(t, err)
+			t.Cleanup(func() { assert.NoError(t, robs.Close()) })
 
-	allKeysCh, err := robs.AllKeysChan(ctx)
-	require.NoError(t, err)
-	numKeysCh := 0
-	for c := range allKeysCh {
-		b, err := robs.Get(ctx, c)
-		require.NoError(t, err)
-		if !b.Cid().Equals(c) {
-			t.Fatal("wrong item returned")
-		}
-		numKeysCh++
-	}
-	expectedCidCount := len(cids) - idCidCount
-	require.Equal(t, expectedCidCount, numKeysCh, "AllKeysChan returned an unexpected amount of keys; expected %v but got %v", expectedCidCount, numKeysCh)
+			allKeysCh, err := robs.AllKeysChan(ctx)
+			require.NoError(t, err)
+			numKeysCh := 0
+			for c := range allKeysCh {
+				b, err := robs.Get(ctx, c)
+				require.NoError(t, err)
+				if !b.Cid().Equals(c) {
+					t.Fatal("wrong item returned")
+				}
+				numKeysCh++
+			}
+			expectedCidCount := len(cids) - idCidCount
+			require.Equal(t, expectedCidCount, numKeysCh, "AllKeysChan returned an unexpected amount of keys; expected %v but got %v", expectedCidCount, numKeysCh)
 
-	for _, c := range cids {
-		b, err := robs.Get(ctx, c)
-		require.NoError(t, err)
-		if !b.Cid().Equals(c) {
-			t.Fatal("wrong item returned")
-		}
+			for _, c := range cids {
+				b, err := robs.Get(ctx, c)
+				require.NoError(t, err)
+				if !b.Cid().Equals(c) {
+					t.Fatal("wrong item returned")
+				}
+			}
+
+			wrote, err := os.Open(path)
+			require.NoError(t, err)
+			_, err = wrote.Seek(variant.expectedV1StartOffset, io.SeekStart)
+			require.NoError(t, err)
+			hasher := sha512.New()
+			gotWritten, err := io.Copy(hasher, io.LimitReader(wrote, originalCARv1ComparePathStat.Size()))
+			require.NoError(t, err)
+			gotSum := hasher.Sum(nil)
+
+			hasher.Reset()
+			originalCarV1, err := os.Open(originalCARv1ComparePath)
+			require.NoError(t, err)
+			wantWritten, err := io.Copy(hasher, originalCarV1)
+			require.NoError(t, err)
+			wantSum := hasher.Sum(nil)
+
+			require.Equal(t, wantWritten, gotWritten)
+			require.Equal(t, wantSum, gotSum)
+		})
 	}
 }
 

v2/options.go

@@ -39,6 +39,7 @@ type Options struct {
 	BlockstoreAllowDuplicatePuts bool
 	BlockstoreUseWholeCIDs       bool
 	MaxTraversalLinks            uint64
+	WriteAsCarV1                 bool
 }
 
 // ApplyOptions applies given opts and returns the resulting Options.