Header error tests

.gitignore

@@ -0,0 +1,3 @@
+car/car
+main
+coverage.txt

car.go

@@ -77,7 +77,7 @@ func ReadHeader(br *bufio.Reader) (*CarHeader, error) {
 
 	var ch CarHeader
 	if err := cbor.DecodeInto(hb, &ch); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("invalid header: %v", err)
 	}
 
 	return &ch, nil
@@ -130,14 +130,14 @@ func NewCarReader(r io.Reader) (*CarReader, error) {
 		return nil, err
 	}
 
-	if len(ch.Roots) == 0 {
-		return nil, fmt.Errorf("empty car")
-	}
-
 	if ch.Version != 1 {
 		return nil, fmt.Errorf("invalid car version: %d", ch.Version)
 	}
 
+	if len(ch.Roots) == 0 {
+		return nil, fmt.Errorf("empty car, no roots")
+	}
+
 	return &CarReader{
 		br:     br,
 		Header: ch,

car_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/hex"
 	"io"
+	"strings"
 	"testing"
 
 	cid "github.com/ipfs/go-cid"
@@ -234,3 +235,91 @@ func TestEOFHandling(t *testing.T) {
 		}
 	})
 }
+
+func TestBadHeaders(t *testing.T) {
+	testCases := []struct {
+		name   string
+		hex    string
+		errStr string // either the whole error string
+		errPfx string // or just the prefix
+	}{
+		{
+			"{version:2}",
+			"0aa16776657273696f6e02",
+			"invalid car version: 2",
+			"",
+		},
+		{
+			// an unfortunate error because we don't use a pointer
+			"{roots:[baeaaaa3bmjrq]}",
+			"13a165726f6f747381d82a480001000003616263",
+			"invalid car version: 0",
+			"",
+		}, {
+			"{version:\"1\",roots:[baeaaaa3bmjrq]}",
+			"1da265726f6f747381d82a4800010000036162636776657273696f6e6131",
+			"", "invalid header: ",
+		}, {
+			"{version:1}",
+			"0aa16776657273696f6e01",
+			"empty car, no roots",
+			"",
+		}, {
+			"{version:1,roots:{cid:baeaaaa3bmjrq}}",
+			"20a265726f6f7473a163636964d82a4800010000036162636776657273696f6e01",
+			"",
+			"invalid header: ",
+		}, {
+			"{version:1,roots:[baeaaaa3bmjrq],blip:true}",
+			"22a364626c6970f565726f6f747381d82a4800010000036162636776657273696f6e01",
+			"",
+			"invalid header: ",
+		}, {
+			"[1,[]]",
+			"03820180",
+			"",
+			"invalid header: ",
+		}, {
+			// this is an unfortunate error, it'd be nice to catch it better but it's
+			// very unlikely we'd ever see this in practice
+			"null",
+			"01f6",
+			"",
+			"invalid car version: 0",
+		},
+	}
+
+	makeCar := func(t *testing.T, byts string) error {
+		fixture, err := hex.DecodeString(byts)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = NewCarReader(bytes.NewReader(fixture))
+		return err
+	}
+
+	t.Run("Sanity check {version:1,roots:[baeaaaa3bmjrq]}", func(t *testing.T) {
+		err := makeCar(t, "1ca265726f6f747381d82a4800010000036162636776657273696f6e01")
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := makeCar(t, tc.hex)
+			if err == nil {
+				t.Fatal("expected error from bad header, didn't get one")
+			}
+			if tc.errStr != "" {
+				if err.Error() != tc.errStr {
+					t.Fatalf("bad error: %v", err)
+				}
+			} else {
+				if !strings.HasPrefix(err.Error(), tc.errPfx) {
+					t.Fatalf("bad error: %v", err)
+				}
+			}
+		})
+	}
+}