chore: add header error tests

Ref: ipld/js-car#28

the primary difference with js-car is that go-car requires a non-empty roots
array whereas js-car is fine with empty roots array, hence the test fixture
differences


This commit was moved from ipld/go-car@2876c18

ipld/car/.gitignore

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

ipld/car/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,

ipld/car/car_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/hex"
 	"io"
+	"strings"
 	"testing"
 
 	cid "github.com/ipfs/go-cid"
@@ -234,3 +235,80 @@ func TestEOFHandling(t *testing.T) {
 		}
 	})
 }
+
+func TestBadHeaders(t *testing.T) {
+	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)
+		}
+	})
+
+	t.Run("{version:2}", func(t *testing.T) {
+		err := makeCar(t, "0aa16776657273696f6e02")
+		if err.Error() != "invalid car version: 2" {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+
+	// an unfortunate error because we don't use a pointer
+	t.Run("{roots:[baeaaaa3bmjrq]}", func(t *testing.T) {
+		err := makeCar(t, "13a165726f6f747381d82a480001000003616263")
+		if err.Error() != "invalid car version: 0" {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+
+	t.Run("{version:\"1\",roots:[baeaaaa3bmjrq]}", func(t *testing.T) {
+		err := makeCar(t, "1da265726f6f747381d82a4800010000036162636776657273696f6e6131")
+		if !strings.HasPrefix(err.Error(), "invalid header: ") {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+
+	t.Run("{version:1}", func(t *testing.T) {
+		err := makeCar(t, "0aa16776657273696f6e01")
+		if err.Error() != "empty car, no roots" {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+
+	t.Run("{version:1,roots:{cid:baeaaaa3bmjrq}}", func(t *testing.T) {
+		err := makeCar(t, "20a265726f6f7473a163636964d82a4800010000036162636776657273696f6e01")
+		if !strings.HasPrefix(err.Error(), "invalid header: ") {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+
+	t.Run("{version:1,roots:[baeaaaa3bmjrq],blip:true}", func(t *testing.T) {
+		err := makeCar(t, "22a364626c6970f565726f6f747381d82a4800010000036162636776657273696f6e01")
+		if !strings.HasPrefix(err.Error(), "invalid header: ") {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+
+	t.Run("[1,[]]", func(t *testing.T) {
+		err := makeCar(t, "03820180")
+		if !strings.HasPrefix(err.Error(), "invalid header: ") {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+
+	// 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
+	t.Run("null", func(t *testing.T) {
+		err := makeCar(t, "01f6")
+		if !strings.HasPrefix(err.Error(), "invalid car version: 0") {
+			t.Fatalf("bad error: %v", err)
+		}
+	})
+}