encoder: Don't forget to handle/propagate error in Encode()

Previously errors from underlying .encode() were ignored completely and
not returned to callers.

encode.go

@@ -29,9 +29,12 @@ func NewEncoder(w io.Writer) *Encoder {
 // Encode writes the pickle encoding of v to w, the encoder's writer
 func (e *Encoder) Encode(v interface{}) error {
 	rv := reflectValueOf(v)
-	e.encode(rv)
-	e.w.Write([]byte{opStop})
-	return nil
+	err := e.encode(rv)
+	if err != nil {
+		return err
+	}
+	_, err = e.w.Write([]byte{opStop})
+	return err
 }
 
 func (e *Encoder) encode(rv reflect.Value) error {

encode_test.go

@@ -2,6 +2,7 @@ package ogórek
 
 import (
 	"bytes"
+	"io"
 	"reflect"
 	"testing"
 )
@@ -38,7 +39,10 @@ func TestEncode(t *testing.T) {
 	for _, tt := range tests {
 		p := &bytes.Buffer{}
 		e := NewEncoder(p)
-		e.Encode(tt.input)
+		err := e.Encode(tt.input)
+		if err != nil {
+			t.Errorf("%s: encode error: %v", tt.name, err)
+		}
 
 		d := NewDecoder(bytes.NewReader(p.Bytes()))
 		output, _ := d.Decode()
@@ -52,5 +56,35 @@ func TestEncode(t *testing.T) {
 			t.Errorf("%s: got\n%q\n expected\n%q", tt.name, output, want)
 		}
 
+		for l := int64(p.Len())-1; l >= 0; l-- {
+			p.Reset()
+			e := NewEncoder(LimitWriter(p, l))
+			err = e.Encode(tt.input)
+			if err != io.EOF {
+				t.Errorf("%s: encoder did not handle write error @%v: got %#v", tt.name, l, err)
+			}
+		}
+
+	}
+}
+
+// like io.LimitedReader but for writes
+// XXX it would be good to have it in stdlib
+type LimitedWriter struct {
+	W io.Writer
+	N int64
+}
+
+func (l *LimitedWriter) Write(p []byte) (n int, err error) {
+	if l.N <= 0 {
+		return 0, io.EOF
 	}
+	if int64(len(p)) > l.N {
+		p = p[0:l.N]
+	}
+	n, err = l.W.Write(p)
+	l.N -= int64(n)
+	return
 }
+
+func LimitWriter(w io.Writer, n int64) io.Writer { return &LimitedWriter{w, n} }