fix: handle missing columns in older Signal DB schemas (#201)

Some older Signal Desktop databases (e.g. January 2024) are missing
  columns that the messages query hardcodes: timestamp, serverTimestamp,
  sourceServiceId, hasAttachments, readStatus, seenStatus, expireTimer.
Use PRAGMA table_info(messages) to detect available columns and fall
  back to NULL AS <colname> for any that are absent.
  Fixes #171

Co-authored-by: Claude Sonnet 4.6 <claude-sonnet-4-6@anthropic.com>

Author: fybx

sigexport/data.py

@@ -75,6 +75,13 @@ def fetch_data(
         if not chats or (result[4] in chats_list or result[5] in chats_list):
             convos[cid] = []
 
+    # Check which columns exist (older DB schemas may be missing some)
+    c.execute("PRAGMA table_info(messages)")
+    msg_cols = {row[1] for row in c.fetchall()}
+
+    def col(name: str) -> str:
+        return name if name in msg_cols else f"NULL AS {name}"
+
     # Add date range filtering to the query if provided
     where_clause = ""
 
@@ -98,14 +105,14 @@ def fetch_data(
         json,
         id,
         body,
-        sourceServiceId,
-        timestamp,
+        {col("sourceServiceId")},
+        {col("timestamp")},
         sent_at,
-        serverTimestamp,
-        hasAttachments,
-        readStatus,
-        seenStatus,
-        expireTimer
+        {col("serverTimestamp")},
+        {col("hasAttachments")},
+        {col("readStatus")},
+        {col("seenStatus")},
+        {col("expireTimer")}
     FROM messages
     {where_clause}
     ORDER BY sent_at