database.py: add init error context

Author: aiooss-anssi

README.md

@@ -92,6 +92,17 @@ using:
 kill -USR2 $(pidof suricata)
 ```
 
+### How can I start the webapp in read-only mode?
+
+A SQLite database is generated in `webapp/database/database.db` on the first run
+of the uvicorn webapp.
+If you want to host a read-only Shovel instance (e.g. after the end of a CTF
+event for further analysis), you may run the webapp in immutable mode using the
+following environment variable:
+```
+DATABASE_URL=file:database/database.db?immutable=1
+```
+
 ## Licensing
 
 Copyright (C) 2023  ANSSI

webapp/database.py

@@ -114,7 +114,10 @@ async def connect(self):
         # WAL journal mode allows multiple concurrent readers
         await self.con.execute("PRAGMA journal_mode=wal")
         await self.con.execute("PRAGMA synchronous=normal")
-        await self.init_database_structure()
+        try:
+            await self.init_database_structure()
+        except aiosqlite.OperationalError as e:
+            raise RuntimeError(f"unable to create database '{self.database_uri}'") from e
 
     async def is_readonly(self) -> bool:
         assert self.con is not None, "database connection closed"