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, 253 insertions, 0 deletions

diff --git a/tools/source/misc/json_writer.cxx b/tools/source/misc/json_writer.cxx
new file mode 100644
index 000000000000..a233381038c4
--- /dev/null
+++ b/tools/source/misc/json_writer.cxx
@@ -0,0 +1,253 @@
+/* -*- 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/.
+ */
+
+#include <tools/json_writer.hxx>
+#include <stdio.h>
+#include <cstring>
+
+namespace tools
+{
+/** These buffers are short-lived, so rather waste some space and avoid the cost of
+ * repeated calls into the allocator */
+constexpr int DEFAULT_BUFFER_SIZE = 2048;
+
+JsonWriter::JsonWriter()
+    : mSpaceAllocated(DEFAULT_BUFFER_SIZE)
+    , maBuffer(new char[mSpaceAllocated])
+    , mStartNodeCount(0)
+    , mPos(maBuffer.get())
+{
+    *mPos = '{';
+    ++mPos;
+    *mPos = ' ';
+    ++mPos;
+}
+
+JsonWriter::~JsonWriter() { assert(!maBuffer && "forgot to extract data?"); }
+
+ScopedJsonWriterNode JsonWriter::startNode(const char* pNodeName)
+{
+    auto len = strlen(pNodeName);
+    ensureSpace(len + 4);
+    *mPos = '"';
+    ++mPos;
+    memcpy(mPos, pNodeName, len);
+    mPos += len;
+    strncpy(mPos, "\": { ", 5);
+    mPos += 5;
+    mStartNodeCount++;
+    mbFirstFieldInNode = true;
+    return ScopedJsonWriterNode(*this);
+}
+
+void JsonWriter::endNode()
+{
+    assert(mStartNodeCount && "mismatched StartNode/EndNode somewhere");
+    --mStartNodeCount;
+    ensureSpace(1);
+    *mPos = '}';
+    ++mPos;
+}
+
+void JsonWriter::put(const char* pPropName, const OUString& rPropVal)
+{
+    addCommaBeforeField();
+
+    auto nPropNameLength = strlen(pPropName);
+    auto nWorstCasePropValLength = rPropVal.getLength() * 2;
+    ensureSpace(nPropNameLength + nWorstCasePropValLength + 6);
+    *mPos = '"';
+    ++mPos;
+    memcpy(mPos, pPropName, nPropNameLength);
+    mPos += nPropNameLength;
+    strncpy(mPos, "\": \"", 4);
+    mPos += 4;
+
+    // Convert from UTF-16 to UTF-8 and perform escaping
+    for (int i = 0; i < rPropVal.getLength(); ++i)
+    {
+        sal_Unicode ch = rPropVal[i];
+        if (ch == '\\')
+        {
+            *mPos = static_cast<char>(ch);
+            ++mPos;
+            *mPos = static_cast<char>(ch);
+            ++mPos;
+        }
+        else if (ch == '"')
+        {
+            *mPos = '\\';
+            ++mPos;
+            *mPos = static_cast<char>(ch);
+            ++mPos;
+        }
+        else if (ch <= 0x7F)
+        {
+            *mPos = static_cast<char>(ch);
+            ++mPos;
+        }
+        else if (ch <= 0x7FF)
+        {
+            *mPos = 0xC0 | (ch >> 6); /* 110xxxxx */
+            ++mPos;
+            *mPos = 0x80 | (ch & 0x3F); /* 10xxxxxx */
+            ++mPos;
+        }
+        else
+        {
+            *mPos = 0xE0 | (ch >> 12); /* 1110xxxx */
+            ++mPos;
+            *mPos = 0x80 | ((ch >> 6) & 0x3F); /* 10xxxxxx */
+            ++mPos;
+            *mPos = 0x80 | (ch & 0x3F); /* 10xxxxxx */
+            ++mPos;
+        }
+    }
+
+    *mPos = '"';
+    ++mPos;
+}
+
+void JsonWriter::put(const char* pPropName, const OString& rPropVal)
+{
+    addCommaBeforeField();
+
+    auto nPropNameLength = strlen(pPropName);
+    auto nWorstCasePropValLength = rPropVal.getLength();
+    ensureSpace(nPropNameLength + nWorstCasePropValLength + 6);
+    *mPos = '"';
+    ++mPos;
+    memcpy(mPos, pPropName, nPropNameLength);
+    mPos += nPropNameLength;
+    strncpy(mPos, "\": \"", 4);
+    mPos += 4;
+
+    // copy and perform escaping
+    for (int i = 0; i < rPropVal.getLength(); ++i)
+    {
+        char ch = rPropVal[i];
+        if (ch == '\\')
+        {
+            *mPos = ch;
+            ++mPos;
+            *mPos = ch;
+            ++mPos;
+        }
+        else if (ch == '"')
+        {
+            *mPos = '\\';
+            ++mPos;
+            *mPos = ch;
+            ++mPos;
+        }
+        else
+        {
+            *mPos = ch;
+            ++mPos;
+        }
+    }
+
+    *mPos = '"';
+    ++mPos;
+}
+
+void JsonWriter::put(const char* pPropName, const char* pPropVal)
+{
+    addCommaBeforeField();
+
+    auto nPropNameLength = strlen(pPropName);
+    auto nPropValLength = strlen(pPropVal);
+    auto nWorstCasePropValLength = nPropValLength * 2;
+    ensureSpace(nPropNameLength + nWorstCasePropValLength + 6);
+    *mPos = '"';
+    ++mPos;
+    memcpy(mPos, pPropName, nPropNameLength);
+    mPos += nPropNameLength;
+    strncpy(mPos, "\": \"", 4);
+    mPos += 4;
+
+    // copy and perform escaping
+    for (;;)
+    {
+        char ch = *pPropVal;
+        if (!ch)
+            break;
+        ++pPropVal;
+        if (ch == '\\')
+        {
+            *mPos = ch;
+            ++mPos;
+            *mPos = ch;
+            ++mPos;
+        }
+        else if (ch == '"')
+        {
+            *mPos = '\\';
+            ++mPos;
+            *mPos = ch;
+            ++mPos;
+        }
+        else
+        {
+            *mPos = ch;
+            ++mPos;
+        }
+    }
+
+    *mPos = '"';
+    ++mPos;
+}
+
+void JsonWriter::put(const char* pPropName, int nPropVal)
+{
+    addCommaBeforeField();
+
+    auto nPropNameLength = strlen(pPropName);
+    auto nWorstCasePropValLength = 32;
+    ensureSpace(nPropNameLength + nWorstCasePropValLength + 6);
+    *mPos = '"';
+    ++mPos;
+    memcpy(mPos, pPropName, nPropNameLength);
+    mPos += nPropNameLength;
+    strncpy(mPos, "\": ", 3);
+    mPos += 3;
+
+    mPos += sprintf(mPos, "%d", nPropVal);
+}
+
+void JsonWriter::addCommaBeforeField()
+{
+    if (mbFirstFieldInNode)
+        mbFirstFieldInNode = false;
+    else
+    {
+        *mPos = ',';
+        ++mPos;
+        *mPos = ' ';
+        ++mPos;
+    }
+}
+
+/** Hands ownership of the the underlying storage buffer to the caller,
+  * after this no more document modifications may be written. */
+char* JsonWriter::extractData()
+{
+    assert(mStartNodeCount == 0 && "did not close all nodes");
+    assert(maBuffer && "data already extracted");
+    // add closing brace
+    *mPos = '}';
+    ++mPos;
+    // null-terminate
+    *mPos = 0;
+    mPos = nullptr;
+    return maBuffer.release();
+}
+
+} // namespace tools
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */