Merge pull request #10033 from SomberNight/202507_interface_fast_forward

interface: parallel header-chunks download

electrum/interface.py

@@ -832,32 +832,72 @@ class Interface(Logger):
         headers = list(util.chunks(bfh(res['hex']), size=HEADER_SIZE))
         return headers
 
-    async def request_chunk(
+    async def request_chunk_below_max_checkpoint(
         self,
-        height: int,
         *,
-        tip: Optional[int] = None,
-        can_return_early: bool = False,
-    ) -> Optional[Tuple[bool, int]]:
+        height: int,
+    ) -> None:
         if not is_non_negative_integer(height):
             raise Exception(f"{repr(height)} is not a block height")
+        assert height <= constants.net.max_checkpoint(), f"{height=} must be <= cp={constants.net.max_checkpoint()}"
         index = height // CHUNK_SIZE
-        if can_return_early and index in self._requested_chunks:
+        if index in self._requested_chunks:
             return None
-        #self.logger.debug(f"requesting chunk from height {height}")
-        size = CHUNK_SIZE
-        if tip is not None:
-            size = min(size, tip - index * CHUNK_SIZE + 1)
-            size = max(size, 0)
+        self.logger.debug(f"requesting chunk from height {height}")
         try:
             self._requested_chunks.add(index)
-            headers = await self.get_block_headers(start_height=index * CHUNK_SIZE, count=size)
+            headers = await self.get_block_headers(start_height=index * CHUNK_SIZE, count=CHUNK_SIZE)
         finally:
             self._requested_chunks.discard(index)
         conn = self.blockchain.connect_chunk(index, data=b"".join(headers))
         if not conn:
-            return conn, 0
-        return conn, len(headers)
+            raise RequestCorrupted(f"chunk ({index=}, for {height=}) does not connect to blockchain")
+        return None
+
+    async def _fast_forward_chain(
+        self,
+        *,
+        height: int,  # usually local chain tip + 1
+        tip: int,  # server tip. we should not request past this.
+    ) -> int:
+        """Request some headers starting at `height` to grow the blockchain of this interface.
+        Returns number of headers we managed to connect, starting at `height`.
+        """
+        if not is_non_negative_integer(height):
+            raise Exception(f"{repr(height)} is not a block height")
+        if not is_non_negative_integer(tip):
+            raise Exception(f"{repr(tip)} is not a block height")
+        if not (height > constants.net.max_checkpoint()
+                or height == 0 == constants.net.max_checkpoint()):
+            raise Exception(f"{height=} must be > cp={constants.net.max_checkpoint()}")
+        assert height <= tip, f"{height=} must be <= {tip=}"
+        # Request a few chunks of headers concurrently.
+        # tradeoffs:
+        # - more chunks: higher memory requirements
+        # - more chunks: higher concurrency => syncing needs fewer network round-trips
+        # - if a chunk does not connect, bandwidth for all later chunks is wasted
+        async with OldTaskGroup() as group:
+            tasks = []  # type: List[Tuple[int, asyncio.Task[Sequence[bytes]]]]
+            index0 = height // CHUNK_SIZE
+            for chunk_cnt in range(10):
+                index = index0 + chunk_cnt
+                start_height = index * CHUNK_SIZE
+                if start_height > tip:
+                    break
+                end_height = min(start_height + CHUNK_SIZE - 1, tip)
+                size = end_height - start_height + 1
+                tasks.append((index, await group.spawn(self.get_block_headers(start_height=start_height, count=size))))
+        # try to connect chunks
+        num_headers = 0
+        for index, task in tasks:
+            headers = task.result()
+            conn = self.blockchain.connect_chunk(index, data=b"".join(headers))
+            if not conn:
+                break
+            num_headers += len(headers)
+        # We started at a chunk boundary, instead of requested `height`. Need to correct for that.
+        offset = height - index0 * CHUNK_SIZE
+        return max(0, num_headers - offset)
 
     def is_main_server(self) -> bool:
         return (self.network.interface == self or
@@ -1021,9 +1061,9 @@ class Interface(Logger):
                 # We are far from the tip.
                 # It is more efficient to process headers in large batches (CPU/disk_usage/logging).
                 # (but this wastes a little bandwidth, if we are not on a chunk boundary)
-                # TODO we should request (some) chunks concurrently. would help when we are many chunks behind
-                could_connect, num_headers = await self.request_chunk(height, tip=next_height)
-                if not could_connect:
+                num_headers = await self._fast_forward_chain(
+                    height=height, tip=next_height)
+                if num_headers == 0:
                     if height <= constants.net.max_checkpoint():
                         raise GracefulDisconnect('server chain conflicts with checkpoints or genesis')
                     last, height = await self.step(height)
@@ -1031,7 +1071,7 @@ class Interface(Logger):
                 # report progress to gui/etc
                 util.trigger_callback('blockchain_updated')
                 util.trigger_callback('network_updated')
-                height = (height // CHUNK_SIZE * CHUNK_SIZE) + num_headers
+                height += num_headers
                 assert height <= next_height+1, (height, self.tip)
                 last = ChainResolutionMode.CATCHUP
             else:

electrum/lnverifier.py

@@ -102,7 +102,7 @@ class LNChannelVerifier(NetworkJobOnDefaultServer):
             header = blockchain.read_header(block_height)
             if header is None:
                 if block_height <= constants.net.max_checkpoint():
-                    await self.taskgroup.spawn(self.interface.request_chunk(block_height, can_return_early=True))
+                    await self.taskgroup.spawn(self.interface.request_chunk_below_max_checkpoint(height=block_height))
                 continue
             self.started_verifying_channel.add(short_channel_id)
             await self.taskgroup.spawn(self.verify_channel(block_height, short_channel_id))

electrum/network.py

@@ -1311,19 +1311,6 @@ class Network(Logger, NetworkRetryManager[ServerAddr]):
         # otherwise:
         return _("Unknown error")
 
-    @best_effort_reliable
-    @catch_server_exceptions
-    async def request_chunk(
-        self,
-        height: int,
-        *,
-        tip: Optional[int] = None,
-        can_return_early: bool = False,
-    ) -> Optional[Tuple[bool, int]]:
-        if self.interface is None:  # handled by best_effort_reliable
-            raise RequestTimedOut()
-        return await self.interface.request_chunk(height, tip=tip, can_return_early=can_return_early)
-
     @best_effort_reliable
     @catch_server_exceptions
     async def get_transaction(self, tx_hash: str, *, timeout=None) -> str:

electrum/verifier.py

@@ -88,7 +88,7 @@ class SPV(NetworkJobOnDefaultServer):
             if header is None:
                 if tx_height <= constants.net.max_checkpoint():
                     # FIXME these requests are not counted (self._requests_sent += 1)
-                    await self.taskgroup.spawn(self.interface.request_chunk(tx_height, can_return_early=True))
+                    await self.taskgroup.spawn(self.interface.request_chunk_below_max_checkpoint(height=tx_height))
                 continue
             # request now
             self.logger.info(f'requested merkle {tx_hash}')