new json writer for LOK

we shave about 3 memory copies off in the process, and
make the class play nicely with our string types.

Change-Id: I1f614fb35b1de499ac99e3b33ac638ad81054bed
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/96393
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

1 files changed, 86 insertions, 0 deletions

diff --git a/include/tools/json_writer.hxx b/include/tools/json_writer.hxx
new file mode 100644
index 000000000000..e811bb90e277
--- /dev/null
+++ b/include/tools/json_writer.hxx
@@ -0,0 +1,86 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+#pragma once
+
+#include <tools/toolsdllapi.h>
+#include <rtl/ustring.hxx>
+#include <memory>
+
+/** Simple JSON encoder designed specifically for LibreOfficeKit purposes.
+ *
+ * (1) Minimal allocations/re-allocations/copying
+ * (2) Small/simple JSON documents
+ * (3) ascii property names
+ */
+namespace tools
+{
+class ScopedJsonWriterNode;
+
+class TOOLS_DLLPUBLIC JsonWriter
+{
+    friend class ScopedJsonWriterNode;
+
+    int mSpaceAllocated;
+    std::unique_ptr<char[]> maBuffer;
+    int mStartNodeCount;
+    char* mPos;
+    bool mbFirstFieldInNode;
+
+public:
+    JsonWriter();
+    ~JsonWriter();
+
+    [[nodiscard]] ScopedJsonWriterNode startNode(const char*);
+
+    void put(const char* pPropName, const OUString& rPropValue);
+    void put(const char* pPropName, const OString& rPropValue);
+    void put(const char* pPropName, const char* pPropVal);
+    void put(const char*, int);
+
+    /** Hands ownership of the the underlying storage buffer to the caller,
+     * after this no more document modifications may be written. */
+    char* extractData();
+
+private:
+    void endNode();
+    void addCommaBeforeField();
+
+    inline void ensureSpace(int noMoreBytesRequired)
+    {
+        int currentUsed = mPos - maBuffer.get();
+        if (currentUsed + noMoreBytesRequired >= mSpaceAllocated)
+        {
+            auto newSize = std::max(mSpaceAllocated * 2, (currentUsed + noMoreBytesRequired) * 2);
+            auto pNew = new char[newSize];
+            memcpy(pNew, maBuffer.get(), currentUsed);
+            maBuffer.reset(pNew);
+            mPos = maBuffer.get();
+        }
+    }
+};
+
+/**
+ * Auto-closes the node.
+ */
+class ScopedJsonWriterNode
+{
+    friend class JsonWriter;
+
+    JsonWriter& mrWriter;
+
+    ScopedJsonWriterNode(JsonWriter& rWriter)
+        : mrWriter(rWriter)
+    {
+    }
+
+public:
+    ~ScopedJsonWriterNode() { mrWriter.endNode(); }
+};
+};
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */