test: introduce VARINT (de)serialization routines

test/functional/test_framework/messages.py

@@ -120,6 +120,26 @@ def deser_compact_size(f):
     return nit
 
 
+def ser_varint(l):
+    r = b""
+    while True:
+        r = bytes([(l & 0x7f) | (0x80 if len(r) > 0 else 0x00)]) + r
+        if l <= 0x7f:
+            return r
+        l = (l >> 7) - 1
+
+
+def deser_varint(f):
+    n = 0
+    while True:
+        dat = f.read(1)[0]
+        n = (n << 7) | (dat & 0x7f)
+        if (dat & 0x80) > 0:
+            n += 1
+        else:
+            return n
+
+
 def deser_string(f):
     nit = deser_compact_size(f)
     return f.read(nit)
@@ -1913,3 +1933,20 @@ class TestFrameworkScript(unittest.TestCase):
         check_addrv2("2bqghnldu6mcug4pikzprwhtjjnsyederctvci6klcwzepnjd46ikjyd.onion", CAddress.NET_TORV3)
         check_addrv2("255fhcp6ajvftnyo7bwz3an3t4a4brhopm3bamyh2iu5r3gnr2rq.b32.i2p", CAddress.NET_I2P)
         check_addrv2("fc32:17ea:e415:c3bf:9808:149d:b5a2:c9aa", CAddress.NET_CJDNS)
+
+    def test_varint_encode_decode(self):
+        def check_varint(num, expected_encoding_hex):
+            expected_encoding = bytes.fromhex(expected_encoding_hex)
+            self.assertEqual(ser_varint(num), expected_encoding)
+            self.assertEqual(deser_varint(BytesIO(expected_encoding)), num)
+
+        # test cases from serialize_tests.cpp:varint_bitpatterns
+        check_varint(0, "00")
+        check_varint(0x7f, "7f")
+        check_varint(0x80, "8000")
+        check_varint(0x1234, "a334")
+        check_varint(0xffff, "82fe7f")
+        check_varint(0x123456, "c7e756")
+        check_varint(0x80123456, "86ffc7e756")
+        check_varint(0xffffffff, "8efefefe7f")
+        check_varint(0xffffffffffffffff, "80fefefefefefefefe7f")