proof: fix panic for keys with all 0xff bytes

CHANGELOG.md

@@ -14,6 +14,10 @@ https://github.com/cosmos/iavl. This also affects the module import path, which
 
 - Proofs are now encoded using Protobuf instead of Amino. The binary encoding is identical.
 
+### Bug Fixes
+
+- \#288 Fix panics when generating proofs for keys that are all `0xFF`.
+
 ## 0.14.0 (July 2, 2020)
 
 **Important information:** the pruning functionality introduced with IAVL 0.13.0 via the options 

proof_iavl_test.go

@@ -35,8 +35,7 @@ func TestProofOp(t *testing.T) {
 		{0xaa, false, "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"},
 		{0xe4, true, "d4010ad1010a280808100a18012220e39776faa9ef2b83ae828860d24f807efab321d02b78081c0e68e1bf801b0e220a2808061006180122201d6b29f2c439fc9f15703eb7031e4a216002ea36ee9496583f97b20302b6a74e0a2808041004180122208bc4764843fdd745dc853fa62f2fac0001feae9e46136192f466c09773e2ed050a280802100218012a2077ad141b2010cf7107de941aac5b46f44fa4f41251076656a72308263a964fb91a270a01e412205e1effe9b7bab73dce628ccd9f0cbbb16c1e6efc6c4f311e59992a467bc119fd1801"},
 		{0xf7, true, "d4010ad1010a280808100a18012220e39776faa9ef2b83ae828860d24f807efab321d02b78081c0e68e1bf801b0e220a2808061006180122201d6b29f2c439fc9f15703eb7031e4a216002ea36ee9496583f97b20302b6a74e0a2808041004180122208bc4764843fdd745dc853fa62f2fac0001feae9e46136192f466c09773e2ed050a28080210021801222032af6e3eec2b63d5fe1bd992a89ef3467b3cee639c068cace942f01326098f171a270a01f7122050868f20258bbc9cce0da2719e8654c108733dd2f663b8737c574ec0ead93eb31801"},
-		{0xfe, false, "d4010ad1010a280808100a18012220e39776faa9ef2b83ae828860d24f807efab321d02b78081c0e68e1bf801b0e220a2808061006180122201d6b29f2c439fc9f15703eb7031e4a216002ea36ee9496583f97b20302b6a74e0a2808041004180122208bc4764843fdd745dc853fa62f2fac0001feae9e46136192f466c09773e2ed050a28080210021801222032af6e3eec2b63d5fe1bd992a89ef3467b3cee639c068cace942f01326098f171a270a01f7122050868f20258bbc9cce0da2719e8654c108733dd2f663b8737c574ec0ead93eb31801"},
-		//{0xff, false, ""}, // FIXME This panics, see https://github.com/cosmos/iavl/issues/286
+		{0xff, false, "d4010ad1010a280808100a18012220e39776faa9ef2b83ae828860d24f807efab321d02b78081c0e68e1bf801b0e220a2808061006180122201d6b29f2c439fc9f15703eb7031e4a216002ea36ee9496583f97b20302b6a74e0a2808041004180122208bc4764843fdd745dc853fa62f2fac0001feae9e46136192f466c09773e2ed050a28080210021801222032af6e3eec2b63d5fe1bd992a89ef3467b3cee639c068cace942f01326098f171a270a01f7122050868f20258bbc9cce0da2719e8654c108733dd2f663b8737c574ec0ead93eb31801"},
 	}
 
 	for _, tc := range testcases {

util.go

@@ -72,6 +72,9 @@ func cpIncr(bz []byte) (ret []byte) {
 		}
 		ret[i] = byte(0x00)
 		if i == 0 {
+			// here, the original bz is all 0xFF, so we keep the original and append 0x00
+			// instead of returning all 0x00
+			ret = cp(bz)
 			return append(ret, 0x00)
 		}
 	}