From b94f85de22cd53b87872543c959064cd2043c40d Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Wed, 11 Feb 2015 19:28:56 +0100
Subject: rlp: add Flat
---
rlp/encode.go | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
rlp/encode_test.go | 9 +++++++++
2 files changed, 58 insertions(+)
diff --git a/rlp/encode.go b/rlp/encode.go
index d80b66315..6ae4a123a 100644
--- a/rlp/encode.go
+++ b/rlp/encode.go
@@ -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)}
}
diff --git a/rlp/encode_test.go b/rlp/encode_test.go
index 18b843737..9b3085658 100644
--- a/rlp/encode_test.go
+++ b/rlp/encode_test.go
@@ -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"},
--
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