Make sure (immutable) test vectors are run with the segment size that was used

to generate them.

integration/test_vectors.py

@@ -36,7 +36,8 @@ async def test_capability(reactor, request, alice, case, expected):
     computed value.
     """
     # rewrite alice's config to match params and convergence
-    await reconfigure(reactor, request, alice, (1, case.params.required, case.params.total), case.convergence)
+    await reconfigure(
+        reactor, request, alice, (1, case.params.required, case.params.total), case.convergence, case.segment_size)
 
     # upload data in the correct format
     actual = upload(alice, case.fmt, case.data)

integration/util.py

@@ -46,6 +46,7 @@ from allmydata.util.configutil import (
     write_config,
 )
 from allmydata import client
+from allmydata.interfaces import DEFAULT_MAX_SEGMENT_SIZE
 
 import pytest_twisted
 
@@ -729,7 +730,10 @@ def upload(alice: TahoeProcess, fmt: CHK | SSK, data: bytes) -> str:
             return cli(*argv).decode("utf-8").strip()
 
 
-async def reconfigure(reactor, request, node: TahoeProcess, params: tuple[int, int, int], convergence: None | bytes) -> None:
+async def reconfigure(reactor, request, node: TahoeProcess,
+                      params: tuple[int, int, int],
+                      convergence: None | bytes,
+                      max_segment_size: None | int = None) -> None:
     """
     Reconfigure a Tahoe-LAFS node with different ZFEC parameters and
     convergence secret.
@@ -769,6 +773,16 @@ async def reconfigure(reactor, request, node: TahoeProcess, params: tuple[int, i
             changed = True
             config.write_private_config("convergence", base32.b2a(convergence))
 
+    if max_segment_size is not None:
+        cur_segment_size = int(config.get_config("client", "shares._max_immutable_segment_size_for_testing", DEFAULT_MAX_SEGMENT_SIZE))
+        if cur_segment_size != max_segment_size:
+            changed = True
+            config.set_config(
+                "client",
+                "shares._max_immutable_segment_size_for_testing",
+                str(max_segment_size)
+            )
+
     if changed:
         # restart the node
         print(f"Restarting {node.node_dir} for ZFEC reconfiguration")

src/allmydata/client.py

@@ -88,6 +88,7 @@ _client_config = configutil.ValidConfiguration(
             "shares.happy",
             "shares.needed",
             "shares.total",
+            "shares._max_immutable_segment_size_for_testing",
             "storage.plugins",
         ),
         "storage": (
@@ -896,6 +897,13 @@ class _Client(node.Node, pollmixin.PollMixin):
         DEP["k"] = int(self.config.get_config("client", "shares.needed", DEP["k"]))
         DEP["n"] = int(self.config.get_config("client", "shares.total", DEP["n"]))
         DEP["happy"] = int(self.config.get_config("client", "shares.happy", DEP["happy"]))
+        # At the moment this is only used for testing, thus the janky config
+        # attribute name.
+        DEP["max_segment_size"] = int(self.config.get_config(
+            "client",
+            "shares._max_immutable_segment_size_for_testing",
+            DEP["max_segment_size"])
+        )
 
         # for the CLI to authenticate to local JSON endpoints
         self._create_auth_token()