src, doc, test: allow generating patchset

Author: louwers

doc/api/sqlite.md

@@ -207,6 +207,13 @@ database2.applyChangeset(changeset);  // Will now contain the same data as datab
 Retrieves a changeset containing all changes since the changeset was created. Can be called multiple times.
 An exception is thrown if the database is not open. This method is a wrapper around [`sqlite3session_changeset()`][].
 
+### `session.patchset()`
+
+* Returns: {Uint8Array} Binary patchset that can be applied to other databases.
+
+Similar to the method above, but generates a more compact patchset. See [Changesets and Patchsets][] in the documentation of SQLite.
+An exception is thrown if the database is not open. This method is a wrapper around [`sqlite3session_patchset()`][].
+
 ## Class: `StatementSync`
 
 <!-- YAML
@@ -380,7 +387,9 @@ exception.
 [`sqlite3session_attach()`]: https://www.sqlite.org/session/sqlite3session_attach.html
 [`sqlite3session_create()`]: https://www.sqlite.org/session/sqlite3session_create.html
 [`sqlite3session_changeset()`]: https://www.sqlite.org/session/sqlite3session_changeset.html
+[`sqlite3session_patchset()`]: https://www.sqlite.org/session/sqlite3session_patchset.html
 [`sqlite3changeset_apply()`]: https://www.sqlite.org/session/sqlite3changeset_apply.html
+[Changesets and Patchsets]: https://www.sqlite.org/sessionintro.html#changesets_and_patchsets
 [connection]: https://www.sqlite.org/c3ref/sqlite3.html
 [data types]: https://www.sqlite.org/datatype3.html
 [in memory]: https://www.sqlite.org/inmemorydb.html

src/node_sqlite.cc

@@ -886,14 +886,22 @@ Local<FunctionTemplate> Session::GetConstructorTemplate(
     tmpl->SetClassName(FIXED_ONE_BYTE_STRING(env->isolate(), "Session"));
     tmpl->InstanceTemplate()->SetInternalFieldCount(
         Session::kInternalFieldCount);
-    SetProtoMethod(isolate, tmpl, "changeset", Session::Changeset);
+    SetProtoMethod(isolate,
+                   tmpl,
+                   "changeset",
+                   Session::Changeset<sqlite3session_changeset>);
+    SetProtoMethod(isolate,
+                   tmpl,
+                   "patchset",
+                   Session::Changeset<sqlite3session_patchset>);
     env->set_sqlite_session_constructor_template(tmpl);
   }
   return tmpl;
 }
 
 void Session::MemoryInfo(MemoryTracker* tracker) const {}
 
+template<Sqlite3ChangesetGenFunc sqliteChangesetFunc>
 void Session::Changeset(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Session* session;
   ASSIGN_OR_RETURN_UNWRAP(&session, args.This());
@@ -903,7 +911,7 @@ void Session::Changeset(const v8::FunctionCallbackInfo<v8::Value>& args) {
 
   int nChangeset;
   void* pChangeset;
-  int r = sqlite3session_changeset(session->session_, &nChangeset, &pChangeset);
+  int r = sqliteChangesetFunc(session->session_, &nChangeset, &pChangeset);
   CHECK_ERROR_OR_THROW(env->isolate(), db, r, SQLITE_OK, void());
 
   auto freeChangeset = OnScopeLeave([&] {

src/node_sqlite.h

@@ -84,13 +84,16 @@ class StatementSync : public BaseObject {
   v8::Local<v8::Value> ColumnNameToValue(const int column);
 };
 
+using Sqlite3ChangesetGenFunc = int (*)(sqlite3_session*, int*, void**);
+
 class Session : public BaseObject {
  public:
   Session(Environment* env,
           v8::Local<v8::Object> object,
           BaseObjectWeakPtr<DatabaseSync> database,
           sqlite3_session* session);
   ~Session() override;
+  template<Sqlite3ChangesetGenFunc sqliteChangesetFunc>
   static void Changeset(const v8::FunctionCallbackInfo<v8::Value>& args);
   void MemoryInfo(MemoryTracker* tracker) const override;
   static v8::Local<v8::FunctionTemplate> GetConstructorTemplate(

test/parallel/test-sqlite.js

@@ -997,15 +997,29 @@ suite('session extension', () => {
     t.assert.strictEqual(sessionTest.changeset().length, 0);
   });
 
-  test("wrong argument name of other database", (t) => {
+  test('wrong argument name of other database', (t) => {
     const database = new DatabaseSync(':memory:');
     t.assert.throws(() => {
-      const session = database.createSession({
+      database.createSession({
         db: 123
       });
     }, {
       name: 'TypeError',
       message: 'The "options.db" argument must be a string.'
     });
-  })
+  });
+
+  test('generate patchset', (t) => {
+    const database = new DatabaseSync(':memory:');
+    database.exec('CREATE TABLE data(key INTEGER PRIMARY KEY, value TEXT)');
+
+    database.exec("INSERT INTO data VALUES ('1', 'Lorem ipsum dolor sit amet, consectetur adipiscing elit.')");
+
+    const session = database.createSession();
+    database.exec("UPDATE data SET value = 'hi' WHERE key = 1");
+
+    t.assert.ok(
+      session.patchset().length < session.changeset().length,
+      'expected patchset to be smaller than changeset');
+  });
 });