core.sqlite: add helper SqliteTool to get table schemas

my/core/sqlite.py

@@ -134,3 +134,46 @@ def select(cols: tuple[str, str, str, str, str, str, str, str], rest: str, *, db
 def select(cols, rest, *, db):
     # db arg is last cause that results in nicer code formatting..
     return db.execute('SELECT ' + ','.join(cols) + ' ' + rest)
+
+
+class SqliteTool:
+    def __init__(self, connection: sqlite3.Connection) -> None:
+        self.connection = connection
+
+    def _get_sqlite_master(self) -> dict[str, str]:
+        res = {}
+        for c in self.connection.execute('SELECT name, type FROM sqlite_master'):
+            [name, type_] = c
+            assert type_ in {'table', 'index', 'view', 'trigger'}, (name, type_)  # just in case
+            res[name] = type_
+        return res
+
+    def get_table_names(self) -> list[str]:
+        master = self._get_sqlite_master()
+        res = []
+        for name, type_ in master.items():
+            if type_ != 'table':
+                continue
+            res.append(name)
+        return res
+
+    def get_table_schema(self, name: str) -> dict[str, str]:
+        """
+        Returns map from column name to column type
+
+        NOTE: Sometimes this doesn't work if the db has some extensions (e.g. happens for facebook apps)
+              In this case you might still be able to use get_table_names
+        """
+        schema: dict[str, str] = {}
+        for row in self.connection.execute(f'PRAGMA table_info(`{name}`)'):
+            col   = row[1]
+            type_ = row[2]
+            # hmm, somewhere between 3.34.1 and 3.37.2, sqlite started normalising type names to uppercase
+            # let's do this just in case since python < 3.10 are using the old version
+            # e.g. it could have returned 'blob' and that would confuse blob check (see _check_allowed_blobs)
+            type_ = type_.upper()
+            schema[col] = type_
+        return schema
+
+    def get_table_schemas(self) -> dict[str, dict[str, str]]:
+        return {name: self.get_table_schema(name) for name in self.get_table_names()}

my/fbmessenger/android.py

@@ -15,7 +15,7 @@ from my.core import LazyLogger, Paths, Res, datetime_aware, get_files, make_conf
 from my.core.common import unique_everseen
 from my.core.compat import assert_never
 from my.core.error import echain
-from my.core.sqlite import sqlite_connection
+from my.core.sqlite import sqlite_connection, SqliteTool
 
 from my.config import fbmessenger as user_config  # isort: skip
 
@@ -86,8 +86,8 @@ def _entities() -> Iterator[Res[Entity]]:
     for idx, path in enumerate(paths):
         logger.info(f'processing [{idx:>{width}}/{total:>{width}}] {path}')
         with sqlite_connection(path, immutable=True, row_factory='row') as db:
+            use_msys = "logging_events_v2" in SqliteTool(db).get_table_names()
             try:
-                use_msys = len(list(db.execute('SELECT * FROM sqlite_master WHERE name = "logging_events_v2"'))) > 0
                 if use_msys:
                     yield from _process_db_msys(db)
                 else: