mining: enforce minimum reserved weight for IPC

Sjors · Sjors · commit d443301666ba · 2026-01-09T09:03:19.000+07:00
Previously a lower value was silently clamped to MINIMUM_BLOCK_RESERVED_WEIGHT.
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
@@ -67,6 +67,7 @@
 #include <any>
 #include <memory>
 #include <optional>
+#include <stdexcept>
 #include <utility>
 
 #include <boost/signals2/signal.hpp>
@@ -963,6 +964,16 @@ class MinerImpl : public Mining
 
     std::unique_ptr<BlockTemplate> createNewBlock(const BlockCreateOptions& options) override
     {
+        // Reject too-small values instead of clamping so callers don't silently
+        // end up mining with different options than requested. This matches the
+        // behavior of the `-blockreservedweight` startup option, which rejects
+        // values below MINIMUM_BLOCK_RESERVED_WEIGHT.
+        if (options.block_reserved_weight && options.block_reserved_weight < MINIMUM_BLOCK_RESERVED_WEIGHT) {
+            throw std::runtime_error(strprintf("block_reserved_weight (%zu) must be at least %u weight units",
+                                               *options.block_reserved_weight,
+                                               MINIMUM_BLOCK_RESERVED_WEIGHT));
+        }
+
         // Ensure m_tip_block is set so consumers of BlockTemplate can rely on that.
         if (!waitTipChanged(uint256::ZERO, MillisecondsDouble::max())) return {};
 
diff --git a/src/node/types.h b/src/node/types.h
@@ -41,7 +41,8 @@ struct BlockCreateOptions {
     bool use_mempool{true};
     /**
      * The default reserved weight for the fixed-size block header,
-     * transaction count and coinbase transaction.
+     * transaction count and coinbase transaction. Minimum: 2000 weight units
+     * (MINIMUM_BLOCK_RESERVED_WEIGHT).
      *
      * Cap'n Proto IPC clients do not currently have a way of leaving this field
      * unset and will always provide a value.
diff --git a/test/functional/interface_ipc.py b/test/functional/interface_ipc.py
@@ -272,6 +272,16 @@ async def wait_for_block():
                 assert empty_template is not None
                 block = await self.parse_and_deserialize_block(empty_template, ctx)
                 assert_equal(len(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:
+                    assert_equal(e.description, "remote exception: std::exception: block_reserved_weight (0) must be at least 2000 weight units")
+                    assert_equal(e.type, "FAILED")
+
                 # Restore opts
                 opts.blockReservedWeight = 4000
 
