ipc test: add workaround to block_reserved_weight exception test

libmultiprocess currently handles uncaught exceptions from IPC methods badly
when an `mp.Context` parameter is passed and the IPC call executes on an a
worker thread, with the uncaught exception leading to a std::terminate call.

bitcoin-core/libmultiprocess#218 was created to fix
this, but before that change is available, update an IPC test which can trigger
this behavior to handle it and recover when mp.Context parameters are added in
the an upcoming commit.

Having this workaround makes the test a little more complicated and less strict
but reduces dependencies between pending PRs so they don't need to be reviewed
or merged in a particular order.

Author: ryanofsky

test/functional/interface_ipc_mining.py

@@ -6,6 +6,7 @@
 import asyncio
 from contextlib import AsyncExitStack
 from io import BytesIO
+import re
 from test_framework.blocktools import NULL_OUTPOINT
 from test_framework.messages import (
     MAX_BLOCK_WEIGHT,
@@ -257,12 +258,21 @@ async def async_routine():
                 empty_block = await mining_get_block(empty_template, ctx)
                 assert_equal(len(empty_block.vtx), 1)
 
-                self.log.debug("Enforce minimum reserved weight for IPC clients too")
-                opts.blockReservedWeight = 0
-                try:
-                    await mining.createNewBlock(opts)
-                    raise AssertionError("createNewBlock unexpectedly succeeded")
-                except capnp.lib.capnp.KjException as e:
+            self.log.debug("Enforce minimum reserved weight for IPC clients too")
+            opts.blockReservedWeight = 0
+            try:
+                await mining.createNewBlock(opts)
+                raise AssertionError("createNewBlock unexpectedly succeeded")
+            except capnp.lib.capnp.KjException as e:
+                if e.type == "DISCONNECTED":
+                    # The remote exception isn't caught currently and leads to a
+                    # std::terminate call. Just detect and restart in this case.
+                    # This bug is fixed with
+                    # https://github.com/bitcoin-core/libmultiprocess/pull/218
+                    assert_equal(e.description, "Peer disconnected.")
+                    self.nodes[0].wait_until_stopped(expected_ret_code=(-11, -6, 1, 66), expected_stderr=re.compile(""))
+                    self.start_node(0)
+                else:
                     assert_equal(e.description, "remote exception: std::exception: block_reserved_weight (0) must be at least 2000 weight units")
                     assert_equal(e.type, "FAILED")