Cache CIDv1.buffer after first access

cid/cid.py

@@ -277,6 +277,7 @@ class CIDv1(BaseCID):
 
     def __init__(self, codec: str, multihash: str | bytes) -> None:
         super().__init__(1, codec, multihash)
+        self._buffer: bytes | None = None
 
     @property
     def buffer(self) -> bytes:
@@ -286,7 +287,11 @@ def buffer(self) -> bytes:
         :return: raw representation of the CID
         :rtype: bytes
         """
-        return b"".join([bytes([self.version]), multicodec.add_prefix(self.codec, self.multihash)])
+        if self._buffer is None:
+            self._buffer = b"".join(
+                [bytes([self.version]), multicodec.add_prefix(self.codec, self.multihash)]
+            )
+        return self._buffer
 
     def encode(self, encoding: str | None = "base32") -> bytes:
         """

newsfragments/70.performance.rst

@@ -0,0 +1 @@
+Cache ``CIDv1.buffer`` after the first access so repeated serialization does not recompute the byte representation.

tests/test_cid.py

@@ -80,6 +80,10 @@ def test_buffer(self, cid):
         assert buffer[0] == 1
         assert buffer[1:] == multicodec.add_prefix(self.TEST_CODEC, cid.multihash)
 
+    def test_buffer_cached(self, cid):
+        """.buffer: same bytes object is returned on repeated access"""
+        assert cid.buffer is cid.buffer
+
     def test_encode_default(self, cid):
         """#encode defaults to base32 encoding"""
         assert cid.encode() == b"bafybeifzjut3te2nhyekklss27nh3k72ysco7y32koao5eei66wof36n5e"