Provide access to sqlite3_trace_v2().

sqlite3.go

@@ -9,6 +9,7 @@ package sqlite3
 #cgo CFLAGS: -std=gnu99
 #cgo CFLAGS: -DSQLITE_ENABLE_RTREE -DSQLITE_THREADSAFE
 #cgo CFLAGS: -DSQLITE_ENABLE_FTS3 -DSQLITE_ENABLE_FTS3_PARENTHESIS -DSQLITE_ENABLE_FTS4_UNICODE61
+#cgo CFLAGS: -DSQLITE_TRACE_SIZE_LIMIT=15
 #ifndef USE_LIBSQLITE3
 #include <sqlite3-binding.h>
 #else
@@ -99,6 +100,8 @@ int _sqlite3_create_function(
 void callbackTrampoline(sqlite3_context*, int, sqlite3_value**);
 void stepTrampoline(sqlite3_context*, int, sqlite3_value**);
 void doneTrampoline(sqlite3_context*);
+
+void traceCallbackTrampoline(unsigned traceEventCode, void *ctx, void *p, void *x);
 */
 import "C"
 import (
@@ -513,6 +516,55 @@ func (c *SQLiteConn) RegisterAggregator(name string, impl interface{}, pure bool
 	return nil
 }
 
+// SetTrace installs or removes the trace callback for the given database connection.
+// It's not named 'RegisterTrace' because only one callback can be kept and called.
+// Calling SetTrace a second time on same database connection
+// overrides (cancels) any prior callback and all its settings:
+// event mask, etc.
+func (c *SQLiteConn) SetTrace(requested *TraceConfig) error {
+	connHandle := uintptr(unsafe.Pointer(c.db))
+
+	_, _ = popTraceMapping(connHandle)
+
+	if requested == nil {
+		// The traceMap entry was deleted already by popTraceMapping():
+		// can disable all events now, no need to watch for TraceClose.
+		err := c.setSQLiteTrace(0)
+		return err
+	}
+
+	reqCopy := *requested
+
+	// Disable potentially expensive operations
+	// if their result will not be used. We are doing this
+	// just in case the caller provided nonsensical input.
+	if reqCopy.EventMask&TraceStmt == 0 {
+		reqCopy.WantExpandedSQL = false
+	}
+
+	addTraceMapping(connHandle, reqCopy)
+
+	// The callback trampoline function does cleanup on Close event,
+	// regardless of the presence or absence of the user callback.
+	// Therefore it needs the Close event to be selected:
+	actualEventMask := reqCopy.EventMask | TraceClose
+	err := c.setSQLiteTrace(actualEventMask)
+	return err
+}
+
+func (c *SQLiteConn) setSQLiteTrace(sqliteEventMask uint) error {
+	rv := C.sqlite3_trace_v2(c.db,
+		C.uint(sqliteEventMask),
+		(*[0]byte)(unsafe.Pointer(C.traceCallbackTrampoline)),
+		unsafe.Pointer(c.db)) // Fourth arg is same as first: we are
+	// passing the database connection handle as callback context.
+
+	if rv != C.SQLITE_OK {
+		return c.lastError()
+	}
+	return nil
+}
+
 // AutoCommit return which currently auto commit or not.
 func (c *SQLiteConn) AutoCommit() bool {
 	return int(C.sqlite3_get_autocommit(c.db)) != 0