From cc162a8ef32c3e2bc9cf765a3862e417ad8221f4 Mon Sep 17 00:00:00 2001
From: James Tucker <james@tailscale.com>
Date: Tue, 6 Jan 2026 17:04:32 -0800
Subject: [PATCH] cgsqlite,.: fix regression with empty strings

A final step refactor in 81bdfd09bc8b066266d470291f00ec589f1c2403
introduced a bug where empty strings became NULL in some code paths.

This fixes the regression and introduces a test to prevent reoccurrence.

Updates tailscale/corp#9199
---
 cgosqlite/cgosqlite.go |  6 +++--
 sqlite_test.go         | 57 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/cgosqlite/cgosqlite.go b/cgosqlite/cgosqlite.go
index e68c4bb..eff9a12 100644
--- a/cgosqlite/cgosqlite.go
+++ b/cgosqlite/cgosqlite.go
@@ -57,7 +57,9 @@ import (
 	"github.com/tailscale/sqlite/sqliteh"
 )
 
-var emptyStrPtr = (*C.char)(unsafe.Pointer(unsafe.StringData("")))
+// emptyChar is the empty string constant used when binding empty strings to
+// avoid the need to allocate new storage in each invocation.
+var emptyChar [1]C.char
 
 func init() {
 	C.sqlite3_initialize()
@@ -298,7 +300,7 @@ func (stmt *Stmt) BindNull(col int) error {
 
 func (stmt *Stmt) BindText64(col int, val string) error {
 	if len(val) == 0 {
-		return errCode(C.sqlite3_bind_text64(stmt.stmt, C.int(col), emptyStrPtr, 0, C.SQLITE_STATIC, C.SQLITE_UTF8))
+		return errCode(C.sqlite3_bind_text64(stmt.stmt, C.int(col), &emptyChar[0], 0, C.SQLITE_STATIC, C.SQLITE_UTF8))
 	}
 	v := C.CString(val) // freed by sqlite
 	return errCode(C.sqlite3_bind_text64(stmt.stmt, C.int(col), v, C.sqlite3_uint64(len(val)), (*[0]byte)(C.free), C.SQLITE_UTF8))
diff --git a/sqlite_test.go b/sqlite_test.go
index a9f85d5..de6fab9 100644
--- a/sqlite_test.go
+++ b/sqlite_test.go
@@ -335,6 +335,63 @@ func TestEmptyString(t *testing.T) {
 	}
 }
 
+// TestEmptyStringNotNull verifies that binding an empty string results in an
+// empty string value, not NULL. This is a regression test for a bug where
+// unsafe.StringData("") could return nil, causing sqlite3_bind_text64 to
+// receive a NULL pointer and treat the value as NULL instead of "".
+func TestEmptyStringNotNull(t *testing.T) {
+	db := openTestDB(t)
+	ctx := context.Background()
+
+	exec(t, db, "CREATE TABLE t (id INTEGER PRIMARY KEY, val TEXT)")
+	exec(t, db, "INSERT INTO t (id, val) VALUES (?, ?)", 1, "")
+	exec(t, db, "INSERT INTO t (id, val) VALUES (?, ?)", 2, nil)
+	exec(t, db, "INSERT INTO t (id, val) VALUES (?, ?)", 3, "ok")
+
+	var val sql.NullString
+	if err := db.QueryRowContext(ctx, "SELECT val FROM t WHERE id = 1").Scan(&val); err != nil {
+		t.Fatal(err)
+	}
+	if !val.Valid {
+		t.Fatal("empty string was stored as NULL")
+	}
+	if val.String != "" {
+		t.Fatalf("val=%q, want empty string", val.String)
+	}
+
+	if err := db.QueryRowContext(ctx, "SELECT val FROM t WHERE id = 2").Scan(&val); err != nil {
+		t.Fatal(err)
+	}
+	if val.Valid {
+		t.Fatalf("NULL was stored as %q", val.String)
+	}
+
+	var countEmpty, countNull int
+	if err := db.QueryRowContext(ctx, "SELECT count(*) FROM t WHERE val = ''").Scan(&countEmpty); err != nil {
+		t.Fatal(err)
+	}
+	if countEmpty != 1 {
+		t.Fatalf("countEmpty=%d, want 1", countEmpty)
+	}
+	if err := db.QueryRowContext(ctx, "SELECT count(*) FROM t WHERE val IS NULL").Scan(&countNull); err != nil {
+		t.Fatal(err)
+	}
+	if countNull != 1 {
+		t.Fatalf("countNull=%d, want 1", countNull)
+	}
+
+	var length sql.NullInt64
+	if err := db.QueryRowContext(ctx, "SELECT length(val) FROM t WHERE id = 1").Scan(&length); err != nil {
+		t.Fatal(err)
+	}
+	if !length.Valid {
+		t.Fatal("length of empty string returned NULL")
+	}
+	if length.Int64 != 0 {
+		t.Fatalf("length=%d, want 0", length.Int64)
+	}
+}
+
 func TestExecScript(t *testing.T) {
 	db := openTestDB(t)
 	conn, err := db.Conn(context.Background())