libsql-sqlite3: Add libsql_wal_disable_checkpoint() API

SQLite unconditionally checkpoints when the last connection is closed to
a database. Let's add a libSQL extension API to give callers control
over that.

Author: penberg

libsql-sqlite3/src/main.c

@@ -2425,6 +2425,30 @@ void *libsql_close_hook(
   return pRet;
 }
 
+/*
+** Disable WAL checkpointing.
+**
+** Note: This function disables WAL checkpointing entirely, including when
+** the last database connection is closed. This is different from
+** sqlite3_wal_autocheckpoint() which only disables automatic checkpoints
+** for the current connection, but still allows checkpointing when the
+** connection is closed.
+**/
+int libsql_wal_disable_checkpoint(sqlite3 *db) {
+#ifndef SQLITE_OMIT_WAL
+#ifdef SQLITE_ENABLE_API_ARMOR
+  if( !sqlite3SafetyCheckOk(db) ){
+    return SQLITE_MISUSE_BKPT;
+  }
+#endif
+  sqlite3_mutex_enter(db->mutex);
+  db->walCheckPointDisabled = 1;
+  db->xWalCallback = 0;
+  sqlite3_mutex_leave(db->mutex);
+#endif
+  return SQLITE_OK;
+}
+
 /*
 ** Register a function to be invoked prior to each autovacuum that
 ** determines the number of pages to vacuum.
@@ -2522,6 +2546,7 @@ void *sqlite3_wal_hook(
 #endif
   sqlite3_mutex_enter(db->mutex);
   pRet = db->pWalArg;
+  db->walCheckPointDisabled = 0;
   db->xWalCallback = xCallback;
   db->pWalArg = pArg;
   sqlite3_mutex_leave(db->mutex);

libsql-sqlite3/src/sqlite.h.in

@@ -10549,6 +10549,21 @@ int sqlite3_preupdate_blobwrite(sqlite3 *);
 */
 void *libsql_close_hook(sqlite3 *db, void (*xClose)(void *pCtx, sqlite3 *db), void *arg);
 
+/*
+** CAPI3REF: Disable WAL checkpointing
+** METHOD: sqlite3
+**
+** ^The [libsql_wal_disable_checkpoint(D)] interface disables automatic
+** checkpointing of the WAL file for [database connection] D.
+**
+** Note: This function disables WAL checkpointing entirely, including when
+** the last database connection is closed. This is different from
+** sqlite3_wal_autocheckpoint() which only disables automatic checkpoints
+** for the current connection, but still allows checkpointing when the
+** connection is closed.
+*/
+int libsql_wal_disable_checkpoint(sqlite3 *db);
+
 /*
 ** CAPI3REF: Low-level system error code
 ** METHOD: sqlite3

libsql-sqlite3/src/sqliteInt.h

@@ -1755,6 +1755,7 @@ struct sqlite3 {
   PreUpdate *pPreUpdate;        /* Context for active pre-update callback */
 #endif /* SQLITE_ENABLE_PREUPDATE_HOOK */
 #ifndef SQLITE_OMIT_WAL
+  int walCheckPointDisabled;
   int (*xWalCallback)(void *, sqlite3 *, const char *, int);
   void *pWalArg;
 #endif

libsql-sqlite3/src/wal.c

@@ -2256,9 +2256,14 @@ static int sqlite3WalClose(
       if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
         pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
       }
-      rc = sqlite3WalCheckpoint(pWal, db,
-          SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0, NULL, NULL
-      );
+      /* Don't checkpoint on close if automatic WAL checkpointing is disabled. */
+      if( !db->walCheckPointDisabled ){
+        rc = sqlite3WalCheckpoint(pWal, db,
+            SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0, NULL, NULL
+        );
+      } else {
+        rc = SQLITE_ERROR;
+      }
       if( rc==SQLITE_OK ){
         int bPersist = -1;
         sqlite3OsFileControlHint(