From ce388d3783dfa8d43c0119d10a422fe47cf36cee Mon Sep 17 00:00:00 2001
From: Daira Hopwood <daira@jacaranda.org>
Date: Mon, 30 Aug 2021 19:49:45 +0100
Subject: [PATCH] Further simplify parsing. This also ensures that the encoding
 ends with a receiver value, not a type or length.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
---
 unified_address.py | 49 ++++++++++++++++++++--------------------------
 1 file changed, 21 insertions(+), 28 deletions(-)

diff --git a/unified_address.py b/unified_address.py
index a1dec6a..f1cfcf4 100644
--- a/unified_address.py
+++ b/unified_address.py
@@ -54,39 +54,32 @@ def decode_unified(addr_str):
     assert suffix == padding(hrp)
     rest = decoded[:-16]
 
-    s = 0
     result = {}
     while len(rest) > 0:
-        if s == 0:
-            (receiver_type, rest) = parse_compact_size(rest)
-            s = 1
-        elif s == 1:
-            (receiver_len, rest) = parse_compact_size(rest)
-            expected_len = {0: 20, 1: 20, 2: 43, 3: 43}.get(receiver_type)
-            if expected_len is not None:
-                assert receiver_len == expected_len, "incorrect receiver length"
-            s = 2
-        elif s == 2:
-            assert len(rest) >= receiver_len
-            (receiver, rest) = (rest[:receiver_len], rest[receiver_len:])
+        (receiver_type, rest) = parse_compact_size(rest)
+        (receiver_len, rest) = parse_compact_size(rest)
 
-            if receiver_type == 0 or receiver_type == 1:
-                assert not ('transparent' in result), "duplicate transparent receiver detected"
-                assert len(receiver) == 20
-                result['transparent'] = receiver
-                s = 0
+        expected_len = {0: 20, 1: 20, 2: 43, 3: 43}.get(receiver_type)
+        if expected_len is not None:
+            assert receiver_len == expected_len, "incorrect receiver length"
 
-            elif receiver_type == 2:
-                assert not ('sapling' in result), "duplicate sapling receiver detected"
-                assert len(receiver) == 43
-                result['sapling'] = receiver
-                s = 0
+        assert len(rest) >= receiver_len
+        (receiver, rest) = (rest[:receiver_len], rest[receiver_len:])
 
-            elif receiver_type == 3:
-                assert not ('orchard' in result), "duplicate orchard receiver detected"
-                assert len(receiver) == 43
-                result['orchard'] = receiver
-                s = 0
+        if receiver_type == 0 or receiver_type == 1:
+            assert not ('transparent' in result), "duplicate transparent receiver detected"
+            assert len(receiver) == 20
+            result['transparent'] = receiver
+
+        elif receiver_type == 2:
+            assert not ('sapling' in result), "duplicate sapling receiver detected"
+            assert len(receiver) == 43
+            result['sapling'] = receiver
+
+        elif receiver_type == 3:
+            assert not ('orchard' in result), "duplicate orchard receiver detected"
+            assert len(receiver) == 43
+            result['orchard'] = receiver
 
     return result