rlp: stricter rules for structs and pointers

The rules have changed as follows:

* When decoding into pointers, empty values no longer produce
  a nil pointer. This can be overriden for struct fields using the
  struct tag "nil".
* When decoding into structs, the input list must contain an element
  for each field.

1 files changed, 37 insertions, 14 deletions

diff --git a/rlp/typecache.go b/rlp/typecache.go
index 398f25d90..d512012e9 100644
--- a/rlp/typecache.go
+++ b/rlp/typecache.go
@@ -7,7 +7,7 @@ import (
 
 var (
 	typeCacheMutex sync.RWMutex
-	typeCache      = make(map[reflect.Type]*typeinfo)
+	typeCache      = make(map[typekey]*typeinfo)
 )
 
 type typeinfo struct {
@@ -15,13 +15,25 @@ type typeinfo struct {
 	writer
 }
 
+// represents struct tags
+type tags struct {
+	nilOK bool
+}
+
+type typekey struct {
+	reflect.Type
+	// the key must include the struct tags because they
+	// might generate a different decoder.
+	tags
+}
+
 type decoder func(*Stream, reflect.Value) error
 
 type writer func(reflect.Value, *encbuf) error
 
-func cachedTypeInfo(typ reflect.Type) (*typeinfo, error) {
+func cachedTypeInfo(typ reflect.Type, tags tags) (*typeinfo, error) {
 	typeCacheMutex.RLock()
-	info := typeCache[typ]
+	info := typeCache[typekey{typ, tags}]
 	typeCacheMutex.RUnlock()
 	if info != nil {
 		return info, nil
@@ -29,11 +41,12 @@ func cachedTypeInfo(typ reflect.Type) (*typeinfo, error) {
 	// not in the cache, need to generate info for this type.
 	typeCacheMutex.Lock()
 	defer typeCacheMutex.Unlock()
-	return cachedTypeInfo1(typ)
+	return cachedTypeInfo1(typ, tags)
 }
 
-func cachedTypeInfo1(typ reflect.Type) (*typeinfo, error) {
-	info := typeCache[typ]
+func cachedTypeInfo1(typ reflect.Type, tags tags) (*typeinfo, error) {
+	key := typekey{typ, tags}
+	info := typeCache[key]
 	if info != nil {
 		// another goroutine got the write lock first
 		return info, nil
@@ -41,21 +54,27 @@ func cachedTypeInfo1(typ reflect.Type) (*typeinfo, error) {
 	// put a dummmy value into the cache before generating.
 	// if the generator tries to lookup itself, it will get
 	// the dummy value and won't call itself recursively.
-	typeCache[typ] = new(typeinfo)
-	info, err := genTypeInfo(typ)
+	typeCache[key] = new(typeinfo)
+	info, err := genTypeInfo(typ, tags)
 	if err != nil {
 		// remove the dummy value if the generator fails
-		delete(typeCache, typ)
+		delete(typeCache, key)
 		return nil, err
 	}
-	*typeCache[typ] = *info
-	return typeCache[typ], err
+	*typeCache[key] = *info
+	return typeCache[key], err
+}
+
+type field struct {
+	index int
+	info  *typeinfo
 }
 
 func structFields(typ reflect.Type) (fields []field, err error) {
 	for i := 0; i < typ.NumField(); i++ {
 		if f := typ.Field(i); f.PkgPath == "" { // exported
-			info, err := cachedTypeInfo1(f.Type)
+			tags := parseStructTag(f.Tag.Get("rlp"))
+			info, err := cachedTypeInfo1(f.Type, tags)
 			if err != nil {
 				return nil, err
 			}
@@ -65,9 +84,13 @@ func structFields(typ reflect.Type) (fields []field, err error) {
 	return fields, nil
 }
 
-func genTypeInfo(typ reflect.Type) (info *typeinfo, err error) {
+func parseStructTag(tag string) tags {
+	return tags{nilOK: tag == "nil"}
+}
+
+func genTypeInfo(typ reflect.Type, tags tags) (info *typeinfo, err error) {
 	info = new(typeinfo)
-	if info.decoder, err = makeDecoder(typ); err != nil {
+	if info.decoder, err = makeDecoder(typ, tags); err != nil {
 		return nil, err
 	}
 	if info.writer, err = makeWriter(typ); err != nil {