first commit

src/db/header_sync.rs

@@ -0,0 +1,51 @@
+//! Reject header batches whose IMAP reads overlap a completed cache removal.
+//!
+//! The generation is per user database, not per UID: a later sync may discover
+//! new destination UIDs or reuse UIDs after UIDVALIDITY changes. No tombstones
+//! or locks held over network calls are needed.
+
+use rusqlite::{Connection, OptionalExtension, Transaction, TransactionBehavior};
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub(crate) struct HeaderSync {
+    generation: u64,
+}
+
+impl HeaderSync {
+    /// Capture before reading IMAP state, and retain for the whole sync pass.
+    pub(crate) fn capture(conn: &Connection) -> Result<Self, String> {
+        let generation = conn
+            .query_row(
+                "SELECT value FROM user_meta WHERE key = 'header_sync_generation'",
+                [],
+                |row| row.get::<_, String>(0),
+            )
+            .optional()
+            .map_err(|e| e.to_string())?
+            .map(|value| value.parse::<u64>().map_err(|e| e.to_string()))
+            .transpose()?
+            .unwrap_or(0);
+        Ok(Self { generation })
+    }
+
+    /// Serialize the check and all header/index/status writes with removals.
+    pub(crate) fn begin_write(self, conn: &Connection) -> Result<Transaction<'_>, String> {
+        let transaction = Transaction::new_unchecked(conn, TransactionBehavior::Immediate)
+            .map_err(|e| e.to_string())?;
+        if Self::capture(conn)?.generation != self.generation {
+            return Err("Header sync superseded by cache removal; retry on next sync".into());
+        }
+        Ok(transaction)
+    }
+}
+
+/// Must run in the same write transaction as the removal or UIDVALIDITY reset.
+pub(crate) fn invalidate(conn: &Transaction<'_>) -> Result<(), String> {
+    conn.execute(
+        "INSERT INTO user_meta (key, value) VALUES ('header_sync_generation', '1')
+         ON CONFLICT(key) DO UPDATE SET value = CAST(value AS INTEGER) + 1",
+        [],
+    )
+    .map_err(|e| e.to_string())?;
+    Ok(())
+}