Add function to register wal hook

Author: gfanto

_example/wal_hook/main.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"database/sql"
+	"log"
+	"os"
+
+	"github.com/mattn/go-sqlite3"
+)
+
+func main() {
+	sql.Register("sqlite3_with_wal_hook_example",
+		&sqlite3.SQLiteDriver{
+			ConnectHook: func(conn *sqlite3.SQLiteConn) error {
+				conn.RegisterWalHook(func(dbName string, nPages int) int {
+					if nPages >= 1 {
+						if _, err := conn.Exec("PRAGMA wal_checkpoint(TRUNCATE);", nil); err != nil {
+							log.Fatal(err)
+						}
+					}
+					return sqlite3.SQLITE_OK
+				})
+				return nil
+			},
+		})
+	defer os.Remove("./foo.db")
+
+	db, err := sql.Open("sqlite3_with_wal_hook_example", "./foo.db?_journal=WAL")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer db.Close()
+
+	_, err = db.Exec("create table foo(id int, value text)")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	tx, err := db.Begin()
+	if err != nil {
+		log.Fatal(err)
+	}
+	stmt, err := tx.Prepare("insert into foo(id, value) values(?, ?)")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer stmt.Close()
+	for i := 0; i < 100; i++ {
+		if _, err := stmt.Exec(i, "value"); err != nil {
+			log.Fatal(err)
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		log.Fatal(err)
+	}
+
+	var busy, log_, checkpointed int
+	err = db.QueryRow("PRAGMA wal_checkpoint(PASSIVE);").Scan(&busy, &log_, &checkpointed)
+	if err != nil {
+		log.Fatal(err)
+	}
+	log.Printf("busy=%d log=%d checkpointed=%d\n", busy, log_, checkpointed) // busy=0 log=0 checkpointed=0
+}

callback.go

@@ -76,6 +76,12 @@ func updateHookTrampoline(handle unsafe.Pointer, op int, db *C.char, table *C.ch
 	callback(op, C.GoString(db), C.GoString(table), rowid)
 }
 
+//export walHookTrampoline
+func walHookTrampoline(hadlePtr unsafe.Pointer, _ *C.sqlite3, name *C.char, pages int) int {
+	callback := lookupHandle(hadlePtr).(func(string, int) int)
+	return callback(C.GoString(name), pages)
+}
+
 //export authorizerTrampoline
 func authorizerTrampoline(handle unsafe.Pointer, op int, arg1 *C.char, arg2 *C.char, arg3 *C.char) int {
 	callback := lookupHandle(handle).(func(int, string, string, string) int)

sqlite3.go

@@ -167,6 +167,7 @@ int compareTrampoline(void*, int, char*, int, char*);
 int commitHookTrampoline(void*);
 void rollbackHookTrampoline(void*);
 void updateHookTrampoline(void*, int, char*, char*, sqlite3_int64);
+int walHookTrampoline(void *, sqlite3*, const char*, int);
 
 int authorizerTrampoline(void*, int, char*, char*, char*, char*);
 
@@ -590,6 +591,27 @@ func (c *SQLiteConn) RegisterUpdateHook(callback func(int, string, string, int64
 	}
 }
 
+// RegisterWalHook sets the WAL hook for a connection.
+//
+// The callback is invoked after each commit in WAL mode. The parameters
+// are the connection, the database name ("main" or attached), and the
+// number of pages currently in the WAL.
+//
+// The callback should normally return SQLITE_OK (0). A non-zero return
+// propagates as an error on the committing statement, though the commit
+// itself still occurs.
+//
+// If there is an existing WAL hook for this connection, it will be
+// removed. If callback is nil the existing hook (if any) will be removed
+// without creating a new one.
+func (c *SQLiteConn) RegisterWalHook(callback func(dbName string, nPages int) int) {
+	if callback == nil {
+		C.sqlite3_wal_hook(c.db, nil, nil)
+	} else {
+		C.sqlite3_wal_hook(c.db, (*[0]byte)(C.walHookTrampoline), newHandle(c, callback))
+	}
+}
+
 // RegisterAuthorizer sets the authorizer for connection.
 //
 // The parameters to the callback are the operation (one of the constants

sqlite3_test.go

@@ -18,6 +18,7 @@ import (
 	"math/rand"
 	"net/url"
 	"os"
+	"path/filepath"
 	"reflect"
 	"regexp"
 	"runtime"
@@ -1786,6 +1787,46 @@ func TestUpdateAndTransactionHooks(t *testing.T) {
 	}
 }
 
+func TestWalHook(t *testing.T) {
+	var walHookCalled bool
+	sql.Register("sqlite3_WalHook", &SQLiteDriver{
+		ConnectHook: func(conn *SQLiteConn) error {
+			conn.RegisterWalHook(func(dbName string, nPages int) int {
+				walHookCalled = true
+				if dbName != "main" {
+					t.Errorf("Expected dbName to be 'main', got %q", dbName)
+				}
+				if nPages <= 0 {
+					t.Errorf("Expected nPages to be positive, got %d", nPages)
+				}
+				return SQLITE_OK
+			})
+			return nil
+		},
+	})
+
+	dbPath := filepath.Join(t.TempDir(), "test.db?cache=shared&_journal_mode=WAL")
+	db, err := sql.Open("sqlite3_WalHook", dbPath)
+	if err != nil {
+		t.Fatal("Failed to open database:", err)
+	}
+	defer db.Close()
+
+	_, err = db.Exec("CREATE TABLE foo (id integer primary key)")
+	if err != nil {
+		t.Fatal("Failed to create table:", err)
+	}
+
+	_, err = db.Exec("INSERT INTO foo VALUES (1)")
+	if err != nil {
+		t.Fatal("Failed to insert:", err)
+	}
+
+	if !walHookCalled {
+		t.Error("Expected wal hook to be called, but it wasn't")
+	}
+}
+
 func TestAuthorizer(t *testing.T) {
 	var authorizerReturn = 0