Remove `index.Save` API

It's two lines of code extra and we already have read from and write to
APIs for index.

Remove `hydrate` cli since the assumptions it makes about appending
index are no longer true. header needs updating for example. Removing to
be re-added when needed as part of a propper CARv2 CLI.

v2/example_test.go

@@ -25,7 +25,12 @@ func ExampleWrapV1File() {
 	if err != nil {
 		panic(err)
 	}
-	defer cr.Close()
+	defer func() {
+		if err := cr.Close(); err != nil {
+			panic(err)
+		}
+	}()
+
 	roots, err := cr.Roots()
 	if err != nil {
 		panic(err)

v2/index/example_test.go

@@ -2,6 +2,7 @@ package index_test
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"reflect"
 
@@ -44,16 +45,20 @@ func ExampleReadFrom() {
 	// Frame with CID bafy2bzaced4ueelaegfs5fqu4tzsh6ywbbpfk3cxppupmxfdhbpbhzawfw5oy starts at offset 61 relative to CARv1 data payload.
 }
 
-// ExampleSave unmarshalls an index from an indexed CARv2 file, and stores it as a separate
+// ExampleWriteTo unmarshalls an index from an indexed CARv2 file, and stores it as a separate
 // file on disk.
-func ExampleSave() {
+func ExampleWriteTo() {
 	// Open the CARv2 file
 	src := "../testdata/sample-wrapped-v2.car"
 	cr, err := carv2.OpenReader(src)
 	if err != nil {
 		panic(err)
 	}
-	defer cr.Close()
+	defer func() {
+		if err := cr.Close(); err != nil {
+			panic(err)
+		}
+	}()
 
 	// Read and unmarshall index within CARv2 file.
 	idx, err := index.ReadFrom(cr.IndexReader())
@@ -63,17 +68,25 @@ func ExampleSave() {
 
 	// Store the index alone onto destination file.
 	dest := "../testdata/sample-index.carindex"
-	err = index.Save(idx, dest)
+	f, err := os.Create(dest)
+	if err != nil {
+		panic(err)
+	}
+	defer func() {
+		if err := f.Close(); err != nil {
+			panic(err)
+		}
+	}()
+	err = index.WriteTo(idx, f)
 	if err != nil {
 		panic(err)
 	}
 
-	// Open the destination file that contains the index only.
-	f, err := os.Open(dest)
+	// Seek to the beginning of tile to read it back.
+	_, err = f.Seek(0, io.SeekStart)
 	if err != nil {
 		panic(err)
 	}
-	defer f.Close()
 
 	// Read and unmarshall the destination file as a separate index instance.
 	reReadIdx, err := index.ReadFrom(f)

v2/index/index.go

@@ -4,7 +4,6 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
-	"os"
 
 	internalio "github.com/ipld/go-car/v2/internal/io"
 
@@ -52,16 +51,6 @@ func New(codec multicodec.Code) (Index, error) {
 	}
 }
 
-// Save writes a generated index into the given `path` replacing the file if it exists.
-func Save(idx Index, path string) error {
-	stream, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o640)
-	if err != nil {
-		return err
-	}
-	defer stream.Close()
-	return WriteTo(idx, stream)
-}
-
 // WriteTo writes the given idx into w.
 // The written bytes include the index encoding.
 // This can then be read back using index.ReadFrom

v2/index/index_test.go

@@ -128,33 +128,6 @@ func TestWriteTo(t *testing.T) {
 	require.Equal(t, wantIdx, gotIdx)
 }
 
-func TestSave(t *testing.T) {
-	// Read sample index on file
-	idxf, err := os.Open("../testdata/sample-index.carindex")
-	require.NoError(t, err)
-	t.Cleanup(func() { require.NoError(t, idxf.Close()) })
-
-	// Unmarshall to get expected index
-	wantIdx, err := ReadFrom(idxf)
-	require.NoError(t, err)
-
-	// Save the same index at destination
-	dest := filepath.Join(t.TempDir(), "index-write-to-test.carindex")
-	require.NoError(t, Save(wantIdx, dest))
-
-	// Open the saved file
-	destF, err := os.Open(dest)
-	require.NoError(t, err)
-	t.Cleanup(func() { require.NoError(t, destF.Close()) })
-
-	// Read the written index back
-	gotIdx, err := ReadFrom(destF)
-	require.NoError(t, err)
-
-	// Assert they are equal
-	require.Equal(t, wantIdx, gotIdx)
-}
-
 func TestMarshalledIndexStartsWithCodec(t *testing.T) {
 	// Read sample index on file
 	idxf, err := os.Open("../testdata/sample-index.carindex")

v2/internal/carbs/doc.go

-// Package carbs provides a read-only blockstore interface directly reading out of a car file.
-// TODO to be refactored
-package carbs

v2/internal/carbs/util/hydrate.go

-package main
-
-import (
-	"fmt"
-	"os"
-
-	carv2 "github.com/ipld/go-car/v2"
-
-	"github.com/ipld/go-car/v2/index"
-)
-
-func main() {
-	if len(os.Args) < 2 {
-		fmt.Printf("Usage: hydrate <file.car>\n")
-		return
-	}
-	db := os.Args[1]
-
-	idx, err := carv2.GenerateIndexFromFile(db)
-	if err != nil {
-		fmt.Printf("Error generating index: %v\n", err)
-		return
-	}
-
-	fmt.Printf("Saving...\n")
-
-	if err := index.Save(idx, db); err != nil {
-		fmt.Printf("Error saving : %v\n", err)
-	}
-}