Internal: split chain service (#487)

Problem: the chain service is in charge of providing all chain-related
functionalities, namely: verify signature and read/write on chain. It
turns out that most use cases of the chain service only care about
signature verification, meaning that the dependencies required for the
chain service are not necessary most of the time. As we plan on adding
more dependencies for chain readers, the chain service is getting too
complex for its own good.

Solution: split the chain service into a signature verifier class and a
chain connector class. This way, the signature verifier can be
instantiated without dependencies in all the places where it is required
and the chain connector can get a bit more complex without impacting the
rest.

Other changes:
* Removed the conditional import of chain connectors as they must all be
  installed on each node.

src/aleph/api_entrypoint.py

@@ -6,7 +6,7 @@
 from configmanager import Config
 
 import aleph.config
-from aleph.chains.chain_service import ChainService
+from aleph.chains.signature_verifier import SignatureVerifier
 from aleph.db.connection import make_engine, make_session_factory
 from aleph.services.cache.node_cache import NodeCache
 from aleph.services.ipfs import IpfsService
@@ -25,7 +25,7 @@
     APP_STATE_STORAGE_SERVICE,
     APP_STATE_MQ_CHANNEL,
     APP_STATE_MQ_WS_CHANNEL,
-    APP_STATE_CHAIN_SERVICE,
+    APP_STATE_SIGNATURE_VERIFIER,
 )
 
 
@@ -53,9 +53,7 @@ async def configure_aiohttp_app(
             ipfs_service=ipfs_service,
             node_cache=node_cache,
         )
-        chain_service = ChainService(
-            storage_service=storage_service, session_factory=session_factory
-        )
+        signature_verifier = SignatureVerifier()
 
         app = create_aiohttp_app()
 
@@ -74,7 +72,7 @@ async def configure_aiohttp_app(
         app[APP_STATE_NODE_CACHE] = node_cache
         app[APP_STATE_STORAGE_SERVICE] = storage_service
         app[APP_STATE_SESSION_FACTORY] = session_factory
-        app[APP_STATE_CHAIN_SERVICE] = chain_service
+        app[APP_STATE_SIGNATURE_VERIFIER] = signature_verifier
 
     return app
 
@@ -95,5 +93,4 @@ async def create_app() -> web.Application:
 
 
 if __name__ == "__main__":
-    import asyncio
     web.run_app(create_app(), host="127.0.0.1", port=8000)

src/aleph/chains/abc.py

@@ -0,0 +1,24 @@
+import abc
+
+from configmanager import Config
+
+from aleph.schemas.pending_messages import BasePendingMessage
+from aleph.types.chain_sync import ChainEventType
+
+
+class Verifier(abc.ABC):
+    @abc.abstractmethod
+    async def verify_signature(self, message: BasePendingMessage) -> bool:
+        ...
+
+
+class ChainReader(abc.ABC):
+    @abc.abstractmethod
+    async def fetcher(self, config: Config):
+        ...
+
+
+class ChainWriter(ChainReader):
+    @abc.abstractmethod
+    async def packer(self, config: Config):
+        ...

src/aleph/chains/avalanche.py

@@ -8,7 +8,7 @@
 
 from aleph.chains.common import get_verification_buffer
 from aleph.schemas.pending_messages import BasePendingMessage
-from .connector import Verifier
+from .abc import Verifier
 
 LOGGER = logging.getLogger("chains.avalanche")
 CHAIN_NAME = "AVAX"

src/aleph/chains/bsc.py

@@ -2,7 +2,7 @@
 from configmanager import Config
 
 from aleph.chains.chaindata import ChainDataService
-from aleph.chains.connector import ChainReader
+from aleph.chains.abc import ChainReader
 from aleph.chains.indexer_reader import AlephIndexerReader
 from aleph.types.chain_sync import ChainEventType
 from aleph.types.db_session import DbSessionFactory