Repository: fxamacker/cbor (go)

Issue:
bug: Decoder.Decode() should return io.UnexpectedEOF instead of io.EOF if CBOR data item is truncated
If CBOR data item is truncated at EOF, then Decoder.Decode() should return `io.UnexpectedEOF` instead of `io.EOF`.

Pull request description:
Make Decoder.Decode() return io.UnexpectedEOF instead of io.EOF if CBOR data item is truncated
If CBOR data item is truncated at EOF, then Decoder.Decode() should return io.UnexpectedEOF instead of io.EOF.

Closes #378

Patch:
diff --git a/decode.go b/decode.go
index c444451..0db569a 100644
--- a/decode.go
+++ b/decode.go
@@ -569,6 +569,10 @@ type decoder struct {
 	dm   *decMode
 }
 
+// value decodes CBOR data item into the value pointed to by v.
+// If CBOR data item is invalid, error is returned and offset isn't changed.
+// If CBOR data item is valid but fails to be decode into v for other reasons,
+// error is returned and offset is moved to the next CBOR data item.
 func (d *decoder) value(v interface{}) error {
 	// v can't be nil, non-pointer, or nil pointer value.
 	if v == nil {
diff --git a/stream.go b/stream.go
index 1d4ec70..dd5a377 100644
--- a/stream.go
+++ b/stream.go
@@ -16,6 +16,7 @@ type Decoder struct {
 	buf       []byte
 	off       int // next read offset in buf
 	bytesRead int
+	readError error
 }
 
 // NewDecoder returns a new decoder that reads and decodes from r using
@@ -31,22 +32,30 @@ func (dec *Decoder) Decode(v interface{}) error {
 			return err
 		}
 	}
-
-	dec.d.reset(dec.buf[dec.off:])
-	err := dec.d.value(v)
-	dec.off += dec.d.off
-	dec.bytesRead += dec.d.off
-	if err != nil {
+	for {
+		dec.d.reset(dec.buf[dec.off:])
+		err := dec.d.value(v)
+		// Increment dec.off even if err is not nil because
+		// dec.d.off points to the next CBOR data item if current
+		// CBOR data item is valid but failed to be decoded into v.
+		// This allows next CBOR data item to be decoded in next
+		// call to this function.
+		dec.off += dec.d.off
+		dec.bytesRead += dec.d.off
+		if err == nil {
+			return nil
+		}
 		if err != io.ErrUnexpectedEOF {
 			return err
 		}
 		// Need to read more data.
-		if n, e := dec.read(); n == 0 {
-			return e
+		if n, err := dec.read(); n == 0 {
+			if err == io.EOF {
+				err = io.ErrUnexpectedEOF
+			}
+			return err
 		}
-		return dec.Decode(v)
 	}
-	return nil
 }
 
 // NumBytesRead returns the number of bytes read.
@@ -55,6 +64,10 @@ func (dec *Decoder) NumBytesRead() int {
 }
 
 func (dec *Decoder) read() (int, error) {
+	if dec.readError != nil {
+		return 0, dec.readError
+	}
+
 	// Grow buf if needed.
 	const minRead = 512
 	if cap(dec.buf)-len(dec.buf)+dec.off < minRead {
@@ -71,6 +84,7 @@ func (dec *Decoder) read() (int, error) {
 	// Read from reader and reslice buf.
 	n, err := dec.r.Read(dec.buf[len(dec.buf):cap(dec.buf)])
 	dec.buf = dec.buf[0 : len(dec.buf)+n]
+	dec.readError = err
 	return n, err
 }
 


Test patch:
diff --git a/stream_test.go b/stream_test.go
index 8d4282e..7165039 100644
--- a/stream_test.go
+++ b/stream_test.go
@@ -5,6 +5,7 @@ package cbor
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"reflect"
@@ -40,14 +41,16 @@ func TestDecoder(t *testing.T) {
 			}
 		}
 	}
-	// no more data
-	var v interface{}
-	err := decoder.Decode(&v)
-	if v != nil {
-		t.Errorf("Decode() = %v (%T), want nil (no more data)", v, v)
-	}
-	if err != io.EOF {
-		t.Errorf("Decode() returned error %v, want io.EOF (no more data)", err)
+	for i := 0; i < 2; i++ {
+		// no more data
+		var v interface{}
+		err := decoder.Decode(&v)
+		if v != nil {
+			t.Errorf("Decode() = %v (%T), want nil (no more data)", v, v)
+		}
+		if err != io.EOF {
+			t.Errorf("Decode() returned error %v, want io.EOF (no more data)", err)
+		}
 	}
 }
 
@@ -94,14 +97,98 @@ func TestDecoderUnmarshalTypeError(t *testing.T) {
 			}
 		}
 	}
-	// no more data
-	var v interface{}
-	err := decoder.Decode(&v)
-	if v != nil {
-		t.Errorf("Decode() = %v (%T), want nil (no more data)", v, v)
+	for i := 0; i < 2; i++ {
+		// no more data
+		var v interface{}
+		err := decoder.Decode(&v)
+		if v != nil {
+			t.Errorf("Decode() = %v (%T), want nil (no more data)", v, v)
+		}
+		if err != io.EOF {
+			t.Errorf("Decode() returned error %v, want io.EOF (no more data)", err)
+		}
+	}
+}
+
+func TestDecoderUnexpectedEOFError(t *testing.T) {
+	var buf bytes.Buffer
+	for _, tc := range unmarshalTests {
+		buf.Write(tc.cborData)
+	}
+	buf.Truncate(buf.Len() - 1)
+
+	decoder := NewDecoder(&buf)
+	bytesRead := 0
+	for i := 0; i < len(unmarshalTests)-1; i++ {
+		tc := unmarshalTests[i]
+		var v interface{}
+		if err := decoder.Decode(&v); err != nil {
+			t.Fatalf("Decode() returned error %v", err)
+		}
+		if tm, ok := tc.emptyInterfaceValue.(time.Time); ok {
+			if vt, ok := v.(time.Time); !ok || !tm.Equal(vt) {
+				t.Errorf("Decode() = %v (%T), want %v (%T)", v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+			}
+		} else if !reflect.DeepEqual(v, tc.emptyInterfaceValue) {
+			t.Errorf("Decode() = %v (%T), want %v (%T)", v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+		}
+		bytesRead += len(tc.cborData)
+		if decoder.NumBytesRead() != bytesRead {
+			t.Errorf("NumBytesRead() = %v, want %v", decoder.NumBytesRead(), bytesRead)
+		}
+	}
+	for i := 0; i < 2; i++ {
+		// truncated data
+		var v interface{}
+		err := decoder.Decode(&v)
+		if v != nil {
+			t.Errorf("Decode() = %v (%T), want nil (no more data)", v, v)
+		}
+		if err != io.ErrUnexpectedEOF {
+			t.Errorf("Decode() returned error %v, want io.UnexpectedEOF (truncated data)", err)
+		}
+	}
+}
+
+func TestDecoderReadError(t *testing.T) {
+	var buf bytes.Buffer
+	for _, tc := range unmarshalTests {
+		buf.Write(tc.cborData)
+	}
+	buf.Truncate(buf.Len() - 1)
+
+	readerErr := errors.New("reader error")
+
+	decoder := NewDecoder(NewErrorReader(buf.Bytes(), readerErr))
+	bytesRead := 0
+	for i := 0; i < len(unmarshalTests)-1; i++ {
+		tc := unmarshalTests[i]
+		var v interface{}
+		if err := decoder.Decode(&v); err != nil {
+			t.Fatalf("Decode() returned error %v", err)
+		}
+		if tm, ok := tc.emptyInterfaceValue.(time.Time); ok {
+			if vt, ok := v.(time.Time); !ok || !tm.Equal(vt) {
+				t.Errorf("Decode() = %v (%T), want %v (%T)", v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+			}
+		} else if !reflect.DeepEqual(v, tc.emptyInterfaceValue) {
+			t.Errorf("Decode() = %v (%T), want %v (%T)", v, v, tc.emptyInterfaceValue, tc.emptyInterfaceValue)
+		}
+		bytesRead += len(tc.cborData)
+		if decoder.NumBytesRead() != bytesRead {
+			t.Errorf("NumBytesRead() = %v, want %v", decoder.NumBytesRead(), bytesRead)
+		}
 	}
-	if err != io.EOF {
-		t.Errorf("Decode() returned error %v, want io.EOF (no more data)", err)
+	for i := 0; i < 2; i++ {
+		// truncated data because Reader returned error
+		var v interface{}
+		err := decoder.Decode(&v)
+		if v != nil {
+			t.Errorf("Decode() = %v (%T), want nil (no more data)", v, v)
+		}
+		if err != readerErr {
+			t.Errorf("Decode() returned error %v, want reader error", err)
+		}
 	}
 }
 
@@ -438,3 +525,25 @@ func TestNilRawMessageUnmarshalCBORError(t *testing.T) {
 		t.Errorf("UnmarshalCBOR() returned error %q, want %q", err.Error(), wantErrorMsg)
 	}
 }
+
+type ErrorReader struct {
+	data []byte
+	off  int
+	err  error
+}
+
+func NewErrorReader(data []byte, err error) *ErrorReader {
+	return &ErrorReader{data: data, err: err}
+}
+
+func (r *ErrorReader) Read(b []byte) (int, error) {
+	var n int
+	if r.off < len(r.data) {
+		n = copy(b, r.data[r.off:])
+		r.off += n
+	}
+	if n < len(b) {
+		return n, r.err
+	}
+	return n, nil
+}