all: add TxnState

Part of a debugging attempt.

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

Author: crawshaw

cgosqlite/cgosqlite.go

@@ -131,6 +131,15 @@ func (db *DB) Checkpoint(dbName string, mode sqliteh.Checkpoint) (int, int, erro
 	return int(nLog), int(nCkpt), errCode(res)
 }
 
+func (db *DB) TxnState(schema string) sqliteh.TxnState {
+	var cSchema *C.char
+	if schema != "" {
+		cSchema = C.CString(schema)
+		defer C.free(unsafe.Pointer(cSchema))
+	}
+	return sqliteh.TxnState(C.sqlite3_txn_state(db.db, cSchema))
+}
+
 func (db *DB) Prepare(query string, prepFlags sqliteh.PrepareFlags) (stmt sqliteh.Stmt, remainingQuery string, err error) {
 	csql := C.CString(query)
 	defer C.free(unsafe.Pointer(csql))

sqlite.go

@@ -717,6 +717,18 @@ func BusyTimeout(sqlconn SQLConn, d time.Duration) error {
 	})
 }
 
+// TxnState calls sqlite3_txn_state on the underlying connection.
+func TxnState(sqlconn SQLConn, schema string) (state sqliteh.TxnState, err error) {
+	return state, sqlconn.Raw(func(driverConn interface{}) error {
+		c, ok := driverConn.(*conn)
+		if !ok {
+			return fmt.Errorf("sqlite.BusyTimeout: sql.Conn is not the sqlite driver: %T", driverConn)
+		}
+		state = c.db.TxnState(schema)
+		return nil
+	})
+}
+
 // Checkpoint calls sqlite3_wal_checkpoint_v2 on the underlying connection.
 func Checkpoint(sqlconn SQLConn, dbName string, mode sqliteh.Checkpoint) (numFrames, numFramesCheckpointed int, err error) {
 	err = sqlconn.Raw(func(driverConn interface{}) error {

sqlite_test.go

@@ -567,6 +567,44 @@ func TestTrace(t *testing.T) {
 	expectEv(ctx, "INSERT INTO t2 (c) VALUES (1)", "UNIQUE constraint failed")
 }
 
+func TestTxnState(t *testing.T) {
+	dbFile := t.TempDir() + "/test.db"
+	db, err := sql.Open("sqlite3", "file:"+dbFile)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := db.Exec("PRAGMA journal_mode=WAL"); err != nil {
+		t.Fatal(err)
+	}
+
+	ctx := context.Background()
+	sqlConn, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if state, err := TxnState(sqlConn, ""); err != nil {
+		t.Fatal(err)
+	} else if state != sqliteh.SQLITE_TXN_NONE {
+		t.Errorf("state=%v, want SQLITE_TXN_NONE", state)
+	}
+	if err := ExecScript(sqlConn, "BEGIN; CREATE TABLE t (c);"); err != nil {
+		t.Fatal(err)
+	}
+	if state, err := TxnState(sqlConn, ""); err != nil {
+		t.Fatal(err)
+	} else if state != sqliteh.SQLITE_TXN_WRITE {
+		t.Errorf("state=%v, want SQLITE_TXN_WRITE", state)
+	}
+	if err := ExecScript(sqlConn, "COMMIT; BEGIN; SELECT * FROM (t);"); err != nil {
+		t.Fatal(err)
+	}
+	if state, err := TxnState(sqlConn, ""); err != nil {
+		t.Fatal(err)
+	} else if state != sqliteh.SQLITE_TXN_READ {
+		t.Errorf("state=%v, want SQLITE_TXN_READ", state)
+	}
+}
+
 func BenchmarkPersist(b *testing.B) {
 	ctx := context.Background()
 	db := openTestDB(b)

sqliteh/sqliteh.go

@@ -47,6 +47,8 @@ type DB interface {
 	BusyTimeout(time.Duration)
 	// Checkpoint is sqlite3_wal_checkpoint_v2.
 	Checkpoint(db string, mode Checkpoint) (numFrames, numFramesCheckpointed int, err error)
+	// TxnState is sqlite3_txn_state.
+	TxnState(schema string) TxnState
 }
 
 // Stmt is an sqlite3_stmt* database connection object.
@@ -354,6 +356,32 @@ func (mode Checkpoint) String() string {
 	}
 }
 
+// TxnState is a transaction state.
+// It is used by sqlite3_txn_state.
+//
+// https://sqlite.org/c3ref/txn_state.html
+type TxnState int
+
+const (
+	SQLITE_TXN_NONE  TxnState = 0
+	SQLITE_TXN_READ  TxnState = 1
+	SQLITE_TXN_WRITE TxnState = 2
+)
+
+func (state TxnState) String() string {
+	switch state {
+	default:
+		var buf [20]byte
+		return "SQLITE_TXN_UNKNOWN(" + string(itoa(buf[:], int64(state))) + ")"
+	case SQLITE_TXN_NONE:
+		return "SQLITE_TXN_NONE"
+	case SQLITE_TXN_READ:
+		return "SQLITE_TXN_READ"
+	case SQLITE_TXN_WRITE:
+		return "SQLITE_TXN_WRITE"
+	}
+}
+
 // ErrCode is an SQLite error code as a Go error.
 // It must not be one of the status codes SQLITE_OK, SQLITE_ROW, or SQLITE_DONE.
 type ErrCode Code