codec: return io.ErrUnexpectedEOF (not io.EOF) when incomplete data read

Fixes #398

codec/codec_test.go

@@ -4276,10 +4276,11 @@ func doTestJsonInvalidUnicode(t *testing.T, h Handle) {
 	for k, v := range m {
 		// call testUnmarshal directly, so we can check for EOF
 		// testUnmarshalErr(&s, []byte(k), jh, t, "-")
+		// t.Logf("%s >> %s", k, v)
 		var s string
 		err = testUnmarshal(&s, []byte(k), jh)
 		if err != nil {
-			if err == io.EOF {
+			if err == io.EOF || err == io.ErrUnexpectedEOF {
 				continue
 			}
 			t.Logf("%s: unmarshal failed: %v", "-", err)

codec/helper.go

@@ -110,8 +110,7 @@ package codec
 //
 // ------------------------------------------
 // Bounds Checking
-//    - Allow bytesDecReader to incur "bounds check error", and
-//      recover that as an io.EOF.
+//    - Allow bytesDecReader to incur "bounds check error", and recover that as an io error.
 //      This allows the bounds check branch to always be taken by the branch predictor,
 //      giving better performance (in theory), while ensuring that the code is shorter.
 //
@@ -2473,7 +2472,7 @@ func panicValToErr(h errDecorator, v interface{}, err *error) {
 	case runtime.Error:
 		d, dok := h.(*Decoder)
 		if dok && d.bytes && isSliceBoundsError(xerr.Error()) {
-			*err = io.EOF
+			*err = io.ErrUnexpectedEOF
 		} else {
 			h.wrapErr(xerr, err)
 		}

codec/msgpack.go

@@ -1174,7 +1174,7 @@ func (c *msgpackSpecRpcCodec) ReadRequestBody(body interface{}) error {
 
 func (c *msgpackSpecRpcCodec) parseCustomHeader(expectTypeByte byte, msgid *uint64, methodOrError *string) (err error) {
 	if cls := c.cls.load(); cls.closed {
-		return io.EOF
+		return io.ErrUnexpectedEOF
 	}
 
 	// We read the response header by hand

codec/reader.go

@@ -350,9 +350,9 @@ func (z *ioDecReader) unreadn1() {
 
 // bytesDecReader is a decReader that reads off a byte slice with zero copying
 //
-// Note: we do not try to convert index'ing out of bounds to an io.EOF.
+// Note: we do not try to convert index'ing out of bounds to an io error.
 // instead, we let it bubble up to the exported Encode/Decode method
-// and recover it as an io.EOF.
+// and recover it as an io error.
 //
 // Every function here MUST defensively check bounds either explicitly
 // or via a bounds check.