fix newline handling

2 files changed, 56 insertions, 5 deletions

diff --git a/skate/map.go b/skate/map.go
index 9d3c98d..094d3e2 100644
--- a/skate/map.go
+++ b/skate/map.go
@@ -40,14 +40,25 @@ type PartialDoc struct {
 // doc). We want fields, but we do not want to bake in TSV into each function.
 type Mapper func([]byte) ([][]byte, error)
 
-// AsTSV serializes the result of a field mapper as TSV. This is a slim adapter,
-// e.g. to parallel.Processor, which expects this function signature.
+// AsTSV serializes the result of a field mapper as TSV. This is a slim
+// adapter, e.g. to parallel.Processor, which expects this function signature.
+// If the last byte of the last field is not a newline, it will be appended.
 func (f Mapper) AsTSV(p []byte) ([]byte, error) {
-	fields, err := f(p)
-	if err != nil {
+	var (
+		fields [][]byte
+		err    error
+	)
+	if fields, err = f(p); err != nil {
 		return nil, err
 	}
-	return bytes.Join(fields, bTab), nil
+	if len(fields) == 0 {
+		return nil, nil
+	}
+	b := bytes.Join(fields, bTab)
+	if len(b) > 0 && !bytes.HasSuffix(b, bNewline) {
+		b = append(b, bNewline...)
+	}
+	return b, nil
 }
 
 // WithPrefix adds a given prefix to the first element.
diff --git a/skate/map_test.go b/skate/map_test.go
index a439d33..a81cb3d 100644
--- a/skate/map_test.go
+++ b/skate/map_test.go
@@ -149,6 +149,46 @@ func TestMapperTitleSandcrawler(t *testing.T) {
 	}
 }
 
+func TestAsTSV(t *testing.T) {
+	var cases = []struct {
+		f    Mapper
+		err  error
+		want string
+	}{
+		{
+			f: Mapper(func(_ []byte) ([][]byte, error) {
+				return [][]byte{
+					[]byte("a"),
+					[]byte("b"),
+					[]byte("c"),
+				}, nil
+			}),
+			err:  nil,
+			want: "a\tb\tc\n",
+		},
+		{
+			f: Mapper(func(_ []byte) ([][]byte, error) {
+				return [][]byte{
+					[]byte("a"),
+					[]byte("b"),
+					[]byte("c\n"),
+				}, nil
+			}),
+			err:  nil,
+			want: "a\tb\tc\n",
+		},
+	}
+	for _, c := range cases {
+		got, err := c.f.AsTSV([]byte{})
+		if err != c.err {
+			t.Fatalf("got %v, want nil", got)
+		}
+		if string(got) != c.want {
+			t.Fatalf("got %v, want %v", string(got), c.want)
+		}
+	}
+}
+
 func prettySlice(p [][]byte) (result []string) {
 	result = make([]string, len(p))
 	for i, v := range p {