Improve EOF handling

car/main.go

@@ -26,7 +26,7 @@ var headerCmd = cli.Command{
 		}
 		defer fi.Close()
 
-		ch, err := car.ReadHeader(bufio.NewReader(fi))
+		ch, _, err := car.ReadHeader(bufio.NewReader(fi))
 		if err != nil {
 			return err
 		}

car_test.go

@@ -3,6 +3,8 @@ package car
 import (
 	"bytes"
 	"context"
+	"encoding/hex"
+	"io"
 	"testing"
 
 	cid "github.com/ipfs/go-cid"
@@ -160,3 +162,66 @@ func TestRoundtripSelective(t *testing.T) {
 		require.False(t, has)
 	}
 }
+
+func TestEOFHandling(t *testing.T) {
+	// fixture is a clean single-block, single-root CAR
+	fixture, err := hex.DecodeString("3aa265726f6f747381d82a58250001711220151fe9e73c6267a7060c6f6c4cca943c236f4b196723489608edb42a8b8fa80b6776657273696f6e012c01711220151fe9e73c6267a7060c6f6c4cca943c236f4b196723489608edb42a8b8fa80ba165646f646779f5")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	load := func(t *testing.T, byts []byte) *CarReader {
+		cr, err := NewCarReader(bytes.NewReader(byts))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		blk, err := cr.Next()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if blk.Cid().String() != "bafyreiavd7u6opdcm6tqmddpnrgmvfb4enxuwglhenejmchnwqvixd5ibm" {
+			t.Fatal("unexpected CID")
+		}
+
+		return cr
+	}
+
+	t.Run("CleanEOF", func(t *testing.T) {
+		cr := load(t, fixture)
+
+		blk, err := cr.Next()
+		if err != io.EOF {
+			t.Fatal("Didn't get expected EOF")
+		}
+		if blk != nil {
+			t.Fatal("EOF returned expected block")
+		}
+	})
+
+	t.Run("BadVarint", func(t *testing.T) {
+		fixtureBadVarint := append(fixture, 160)
+		cr := load(t, fixtureBadVarint)
+
+		blk, err := cr.Next()
+		if err != io.ErrUnexpectedEOF {
+			t.Fatal("Didn't get unexpected EOF")
+		}
+		if blk != nil {
+			t.Fatal("EOF returned unexpected block")
+		}
+	})
+
+	t.Run("TruncatedBlock", func(t *testing.T) {
+		fixtureTruncatedBlock := append(fixture, 100, 0, 0)
+		cr := load(t, fixtureTruncatedBlock)
+
+		blk, err := cr.Next()
+		if err != io.ErrUnexpectedEOF {
+			t.Fatal("Didn't get unexpected EOF")
+		}
+		if blk != nil {
+			t.Fatal("EOF returned unexpected block")
+		}
+	})
+}

util/util.go

@@ -100,8 +100,15 @@ func LdSize(d ...[]byte) uint64 {
 }
 
 func LdRead(r *bufio.Reader) ([]byte, error) {
+	if _, err := r.Peek(1); err != nil { // no more blocks, likely clean io.EOF
+		return nil, err
+	}
+
 	l, err := binary.ReadUvarint(r)
 	if err != nil {
+		if err == io.EOF {
+			return nil, io.ErrUnexpectedEOF // don't silently pretend this is a clean EOF
+		}
 		return nil, err
 	}