Use defer and remove ReaderWithEOFContext

cbor_cid.go

@@ -13,7 +13,6 @@ func (c CborCid) MarshalCBOR(w io.Writer) error {
 }
 
 func (c *CborCid) UnmarshalCBOR(r io.Reader) error {
-	r = NewReaderWithEOFContext(r)
 	oc, err := ReadCid(r)
 	if err != nil {
 		return err

gen.go

@@ -1032,17 +1032,24 @@ func emitCborUnmarshalSliceField(w io.Writer, f Field) error {
 
 func emitCborUnmarshalStructTuple(w io.Writer, gti *GenTypeInfo) error {
 	err := doTemplate(w, gti, `
-func (t *{{ .Name}}) UnmarshalCBOR(r io.Reader) error {
-	r = cbg.NewReaderWithEOFContext(r)
+func (t *{{ .Name}}) UnmarshalCBOR(r io.Reader) (err error) {
 	*t = {{.Name}}{}
 
 	br := cbg.GetPeeker(r)
 	scratch := make([]byte, 8)
 
+	hasReadOnce := false
+	defer func() {
+		if err == io.EOF && hasReadOnce {
+			err = io.ErrUnexpectedEOF
+		}
+	}()
 	maj, extra, err := {{ ReadHeader "br" }}
 	if err != nil {
 		return err
 	}
+	hasReadOnce = true
+
 	if maj != cbg.MajArray {
 		return fmt.Errorf("cbor input should be of type array")
 	}
@@ -1191,17 +1198,24 @@ func emitCborMarshalStructMap(w io.Writer, gti *GenTypeInfo) error {
 
 func emitCborUnmarshalStructMap(w io.Writer, gti *GenTypeInfo) error {
 	err := doTemplate(w, gti, `
-func (t *{{ .Name}}) UnmarshalCBOR(r io.Reader) error {
-	r = cbg.NewReaderWithEOFContext(r)
+func (t *{{ .Name}}) UnmarshalCBOR(r io.Reader) (err error) {
 	*t = {{.Name}}{}
 
 	br := cbg.GetPeeker(r)
 	scratch := make([]byte, 8)
 
+	hasReadOnce := false
+	defer func() {
+		if err == io.EOF && hasReadOnce {
+			err = io.ErrUnexpectedEOF
+		}
+	}()
 	maj, extra, err := {{ ReadHeader "br" }}
 	if err != nil {
 		return err
 	}
+	hasReadOnce = true
+
 	if maj != cbg.MajMap {
 		return fmt.Errorf("cbor input should be of type map")
 	}

peeker.go

@@ -12,11 +12,6 @@ type BytePeeker interface {
 }
 
 func GetPeeker(r io.Reader) BytePeeker {
-	if r, ok := r.(*ReaderWithEOFContext); ok {
-		if r, ok := r.R.(BytePeeker); ok {
-			return r
-		}
-	}
 	if r, ok := r.(BytePeeker); ok {
 		return r
 	}