Fix #249.

Author: ncruces

config.go

@@ -350,6 +350,8 @@ func (c *Conn) HardHeapLimit(n int64) int64 {
 }
 
 // EnableChecksums enables checksums on a database.
+// If the database is in WAL mode,
+// you should shutdown and reopen all database connections before continuing.
 //
 // https://sqlite.org/cksumvfs.html
 func (c *Conn) EnableChecksums(schema string) error {

util/sql3util/sql3util.go

@@ -5,5 +5,5 @@ package sql3util
 //
 // https://sqlite.org/fileformat.html#pages
 func ValidPageSize(s int) bool {
-	return 512 <= s && s <= 65536 && s&(s-1) == 0
+	return s&(s-1) == 0 && 512 <= s && s <= 65536
 }

vfs/cksm.go

@@ -68,7 +68,7 @@ func (c cksmFile) ReadAt(p []byte, off int64) (n int, err error) {
 
 func (c cksmFile) WriteAt(p []byte, off int64) (n int, err error) {
 	// SQLite is writing the first page of a database file.
-	if c.isDB && off == 0 && len(p) >= 100 &&
+	if (!c.isDB || off == 0) && sql3util.ValidPageSize(len(p)) &&
 		bytes.HasPrefix(p, []byte("SQLite format 3\000")) {
 		c.init((*[100]byte)(p))
 	}