review feedback: follow the spec and pad shares when generating the s…

…hare commitment instead of not allowing chains

update failing test to new expected result now that the square size is 128 instead of 64

x/lazyledgerapp/types/payformessage.go

@@ -206,7 +206,10 @@ func (msg *SignedTransactionDataPayForMessage) GetSigners() []sdk.AccAddress {
 // https://github.com/lazyledger/lazyledger-specs/blob/master/rationale/message_block_layout.md#non-interactive-default-rules
 func CreateCommit(k uint64, namespace, message []byte) ([]byte, error) {
 	// break message into shares
-	shares := ChunkMessage(message)
+	shares := chunkMessage(message)
+
+	// add padding if necessary
+	shares = addSharePadding(shares)
 
 	// organize shares for merkle mountain range
 	heights := PowerOf2MountainRange(uint64(len(shares)), k)
@@ -234,8 +237,8 @@ func CreateCommit(k uint64, namespace, message []byte) ([]byte, error) {
 	return merkle.HashFromByteSlices(subTreeRoots), nil
 }
 
-// ChunkMessage breaks the message into 256 byte pieces
-func ChunkMessage(message []byte) [][]byte {
+// chunkMessage breaks the message into 256 byte pieces
+func chunkMessage(message []byte) [][]byte {
 	var shares [][]byte
 	for i := 0; i < len(message); i += ShareSize {
 		end := i + ShareSize
@@ -247,6 +250,22 @@ func ChunkMessage(message []byte) [][]byte {
 	return shares
 }
 
+// addSharePadding will add padding to the last share if necessary
+func addSharePadding(shares [][]byte) [][]byte {
+	if len(shares) == 0 {
+		return shares
+	}
+
+	// add padding to the last share if necessary
+	if len(shares[len(shares)-1]) != ShareSize {
+		padded := make([]byte, ShareSize)
+		copy(padded, shares[len(shares)-1])
+		shares[len(shares)-1] = padded
+	}
+
+	return shares
+}
+
 // PowerOf2MountainRange returns the heights of the subtrees for binary merkle
 // mountian range
 func PowerOf2MountainRange(l, k uint64) []uint64 {

x/lazyledgerapp/types/payformessage_test.go

@@ -111,12 +111,39 @@ func TestGetCommitmentSignBytes(t *testing.T) {
 					TipRateMax:  1000,
 				},
 			},
-			expected: []byte(`{"fee":{"base_rate_max":"10000","tip_rate_max":"1000"},"message_namespace_id":"AQIDBAECAwQ=","message_share_commitment":"kLkMnfL0wruFOdgRJ4KnyjJBLJWlKxbEyks8SI0cfZs=","message_size":"4","nonce":"1"}`),
+			expected: []byte(`{"fee":{"base_rate_max":"10000","tip_rate_max":"1000"},"message_namespace_id":"AQIDBAECAwQ=","message_share_commitment":"byozRVIrw5NF/rU1PPyq6BAo3g2ny3uLTiOFedtgSwo=","message_size":"4","nonce":"1"}`),
 		},
 	}
 	for _, tt := range tests {
-		res, err := tt.msg.GetCommitmentSignBytes(64)
+		res, err := tt.msg.GetCommitmentSignBytes(SquareSize)
 		assert.NoError(t, err)
 		assert.Equal(t, tt.expected, res)
 	}
 }
+
+func TestShareChunkingAndPadding(t *testing.T) {
+	type test struct {
+		input  []byte
+		expect [][]byte
+	}
+	tests := []test{
+		{
+			input:  []byte{1},
+			expect: [][]byte{append([]byte{1}, bytes.Repeat([]byte{0}, ShareSize-1)...)},
+		},
+		{
+			input:  bytes.Repeat([]byte{1}, ShareSize),
+			expect: [][]byte{bytes.Repeat([]byte{1}, ShareSize)},
+		},
+	}
+	for _, tt := range tests {
+		shares := chunkMessage(tt.input)
+		shares = addSharePadding(shares)
+		for _, share := range shares {
+			if len(share) != ShareSize {
+				t.Errorf("invalid share length: got %d wanted core.ShareSize (%d)", len(share), ShareSize)
+			}
+		}
+		assert.Equal(t, tt.expect, shares)
+	}
+}