rlp: add Flat

This commit is contained in:
Felix Lange 2015-02-11 19:28:56 +01:00
parent ddccea75e8
commit b94f85de22
2 changed files with 58 additions and 0 deletions

View File

@ -32,6 +32,48 @@ type Encoder interface {
EncodeRLP(io.Writer) error
}
// Flat wraps a value (which must encode as a list) so
// it encodes as the list's elements.
//
// Example: suppose you have defined a type
//
// type foo struct { A, B uint }
//
// Under normal encoding rules,
//
// rlp.Encode(foo{1, 2}) --> 0xC20102
//
// This function can help you achieve the following encoding:
//
// rlp.Encode(rlp.Flat(foo{1, 2})) --> 0x0102
func Flat(val interface{}) Encoder {
return flatenc{val}
}
type flatenc struct{ val interface{} }
func (e flatenc) EncodeRLP(out io.Writer) error {
// record current output position
var (
eb = out.(*encbuf)
prevstrsize = len(eb.str)
prevnheads = len(eb.lheads)
)
if err := eb.encode(e.val); err != nil {
return err
}
// check that a new list header has appeared
if len(eb.lheads) == prevnheads || eb.lheads[prevnheads].offset == prevstrsize-1 {
return fmt.Errorf("rlp.Flat: %T did not encode as list", e.val)
}
// remove the new list header
newhead := eb.lheads[prevnheads]
copy(eb.lheads[prevnheads:], eb.lheads[prevnheads+1:])
eb.lheads = eb.lheads[:len(eb.lheads)-1]
eb.lhsize -= newhead.tagsize()
return nil
}
// Encode writes the RLP encoding of val to w. Note that Encode may
// perform many small writes in some cases. Consider making w
// buffered.
@ -123,6 +165,13 @@ func (head *listhead) encode(buf []byte) []byte {
}
}
func (head *listhead) tagsize() int {
if head.size < 56 {
return 1
}
return 1 + intsize(uint64(head.size))
}
func newencbuf() *encbuf {
return &encbuf{sizebuf: make([]byte, 9)}
}

View File

@ -177,6 +177,15 @@ var encTests = []encTest{
{val: &recstruct{5, nil}, output: "C205C0"},
{val: &recstruct{5, &recstruct{4, &recstruct{3, nil}}}, output: "C605C404C203C0"},
// flat
{val: Flat(uint(1)), error: "rlp.Flat: uint did not encode as list"},
{val: Flat(simplestruct{A: 3, B: "foo"}), output: "0383666F6F"},
{
// value generates more list headers after the Flat
val: []interface{}{"foo", []uint{1, 2}, Flat([]uint{3, 4}), []uint{5, 6}, "bar"},
output: "D083666F6FC201020304C2050683626172",
},
// nil
{val: (*uint)(nil), output: "80"},
{val: (*string)(nil), output: "80"},