return write error when encoding header fields

encoder.go

@@ -51,9 +51,9 @@ func (e *Encoder) WriteField(f HeaderField) error {
 		e.writeLiteralFieldWithoutNameReference(f)
 	}
 
-	e.w.Write(e.buf)
+	_, err := e.w.Write(e.buf)
 	e.buf = e.buf[:0]
-	return nil
+	return err
 }
 
 // Close declares that the encoding is complete and resets the Encoder

encoder_test.go

@@ -2,21 +2,36 @@ package qpack
 
 import (
 	"bytes"
+	"io"
 
 	"golang.org/x/net/http2/hpack"
 
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
 )
 
+// errWriter wraps bytes.Buffer and optionally fails on every write
+// useful for testing misbehaving writers
+type errWriter struct {
+	bytes.Buffer
+	fail bool
+}
+
+func (ew *errWriter) Write(b []byte) (int, error) {
+	if ew.fail {
+		return 0, io.ErrClosedPipe
+	}
+	return ew.Buffer.Write(b)
+}
+
 var _ = Describe("Encoder", func() {
 	var (
 		encoder *Encoder
-		output  *bytes.Buffer
+		output  *errWriter
 	)
 
 	BeforeEach(func() {
-		output = &bytes.Buffer{}
+		output = &errWriter{}
 		encoder = NewEncoder(output)
 	})
 
@@ -82,6 +97,12 @@ var _ = Describe("Encoder", func() {
 		Expect(data).To(BeEmpty())
 	})
 
+	It("encodes fails to encode when writer errs", func() {
+		hf := HeaderField{Name: "foobar", Value: "lorem ipsum"}
+		output.fail = true
+		Expect(encoder.WriteField(hf)).To(MatchError("io: read/write on closed pipe"))
+	})
+
 	It("encodes multiple fields", func() {
 		hf1 := HeaderField{Name: "foobar", Value: "lorem ipsum"}
 		hf2 := HeaderField{Name: "raboof", Value: "dolor sit amet"}