rippled/src/libxrpl/json/Writer.cpp

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2012, 2013 Ripple Labs Inc.

    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.

    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================

#include <xrpl/basics/ToString.h>
#include <xrpl/json/Output.h>
#include <xrpl/json/Writer.h>

#include <cstddef>
#include <map>
#include <memory>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

namespace Json {

namespace {

std::map<char, char const*> jsonSpecialCharacterEscape = {
    {'"', "\\\""},
    {'\\', "\\\\"},
    {'/', "\\/"},
    {'\b', "\\b"},
    {'\f', "\\f"},
    {'\n', "\\n"},
    {'\r', "\\r"},
    {'\t', "\\t"}};

static size_t const jsonEscapeLength = 2;

// All other JSON punctuation.
char const closeBrace = '}';
char const closeBracket = ']';
char const colon = ':';
char const comma = ',';
char const openBrace = '{';
char const openBracket = '[';
char const quote = '"';

static auto const integralFloatsBecomeInts = false;

size_t
lengthWithoutTrailingZeros(std::string const& s)
{
    auto dotPos = s.find('.');
    if (dotPos == std::string::npos)
        return s.size();

    auto lastNonZero = s.find_last_not_of('0');
    auto hasDecimals = dotPos != lastNonZero;

    if (hasDecimals)
        return lastNonZero + 1;

    if (integralFloatsBecomeInts || lastNonZero + 2 > s.size())
        return lastNonZero;

    return lastNonZero + 2;
}

}  // namespace

class Writer::Impl
{
public:
    explicit Impl(Output const& output) : output_(output)
    {
    }
    ~Impl() = default;

    Impl(Impl&&) = delete;
    Impl&
    operator=(Impl&&) = delete;

    bool
    empty() const
    {
        return stack_.empty();
    }

    void
    start(CollectionType ct)
    {
        char ch = (ct == array) ? openBracket : openBrace;
        output({&ch, 1});
        stack_.push(Collection());
        stack_.top().type = ct;
    }

    void
    output(boost::beast::string_view const& bytes)
    {
        markStarted();
        output_(bytes);
    }

    void
    stringOutput(boost::beast::string_view const& bytes)
    {
        markStarted();
        std::size_t position = 0, writtenUntil = 0;

        output_({&quote, 1});
        auto data = bytes.data();
        for (; position < bytes.size(); ++position)
        {
            auto i = jsonSpecialCharacterEscape.find(data[position]);
            if (i != jsonSpecialCharacterEscape.end())
            {
                if (writtenUntil < position)
                {
                    output_({data + writtenUntil, position - writtenUntil});
                }
                output_({i->second, jsonEscapeLength});
                writtenUntil = position + 1;
            };
        }
        if (writtenUntil < position)
            output_({data + writtenUntil, position - writtenUntil});
        output_({&quote, 1});
    }

    void
    markStarted()
    {
        check(!isFinished(), "isFinished() in output.");
        isStarted_ = true;
    }

    void
    nextCollectionEntry(CollectionType type, std::string const& message)
    {
        check(!empty(), "empty () in " + message);

        auto t = stack_.top().type;
        if (t != type)
        {
            check(
                false,
                "Not an " +
                    ((type == array ? "array: " : "object: ") + message));
        }
        if (stack_.top().isFirst)
            stack_.top().isFirst = false;
        else
            output_({&comma, 1});
    }

    void
    writeObjectTag(std::string const& tag)
    {
#ifndef NDEBUG
        // Make sure we haven't already seen this tag.
        auto& tags = stack_.top().tags;
        check(tags.find(tag) == tags.end(), "Already seen tag " + tag);
        tags.insert(tag);
#endif

        stringOutput(tag);
        output_({&colon, 1});
    }

    bool
    isFinished() const
    {
        return isStarted_ && empty();
    }

    void
    finish()
    {
        check(!empty(), "Empty stack in finish()");

        auto isArray = stack_.top().type == array;
        auto ch = isArray ? closeBracket : closeBrace;
        output_({&ch, 1});
        stack_.pop();
    }

    void
    finishAll()
    {
        if (isStarted_)
        {
            while (!isFinished())
                finish();
        }
    }

    Output const&
    getOutput() const
    {
        return output_;
    }

private:
    // JSON collections are either arrrays, or objects.
    struct Collection
    {
        explicit Collection() = default;

        /** What type of collection are we in? */
        Writer::CollectionType type;

        /** Is this the first entry in a collection?
         *  If false, we have to emit a , before we write the next entry. */
        bool isFirst = true;

#ifndef NDEBUG
        /** What tags have we already seen in this collection? */
        std::set<std::string> tags;
#endif
    };

    using Stack = std::stack<Collection, std::vector<Collection>>;

    Output output_;
    Stack stack_;

    bool isStarted_ = false;
};

Writer::Writer(Output const& output) : impl_(std::make_unique<Impl>(output))
{
}

Writer::~Writer()
{
    if (impl_)
        impl_->finishAll();
}

Writer::Writer(Writer&& w) noexcept
{
    impl_ = std::move(w.impl_);
}

Writer&
Writer::operator=(Writer&& w) noexcept
{
    impl_ = std::move(w.impl_);
    return *this;
}

void
Writer::output(char const* s)
{
    impl_->stringOutput(s);
}

void
Writer::output(std::string const& s)
{
    impl_->stringOutput(s);
}

void
Writer::output(Json::Value const& value)
{
    impl_->markStarted();
    outputJson(value, impl_->getOutput());
}

void
Writer::output(float f)
{
    auto s = ripple::to_string(f);
    impl_->output({s.data(), lengthWithoutTrailingZeros(s)});
}

void
Writer::output(double f)
{
    auto s = ripple::to_string(f);
    impl_->output({s.data(), lengthWithoutTrailingZeros(s)});
}

void
Writer::output(std::nullptr_t)
{
    impl_->output("null");
}

void
Writer::output(bool b)
{
    impl_->output(b ? "true" : "false");
}

void
Writer::implOutput(std::string const& s)
{
    impl_->output(s);
}

void
Writer::finishAll()
{
    if (impl_)
        impl_->finishAll();
}

void
Writer::rawAppend()
{
    impl_->nextCollectionEntry(array, "append");
}

void
Writer::rawSet(std::string const& tag)
{
    check(!tag.empty(), "Tag can't be empty");

    impl_->nextCollectionEntry(object, "set");
    impl_->writeObjectTag(tag);
}

void
Writer::startRoot(CollectionType type)
{
    impl_->start(type);
}

void
Writer::startAppend(CollectionType type)
{
    impl_->nextCollectionEntry(array, "startAppend");
    impl_->start(type);
}

void
Writer::startSet(CollectionType type, std::string const& key)
{
    impl_->nextCollectionEntry(object, "startSet");
    impl_->writeObjectTag(key);
    impl_->start(type);
}

void
Writer::finish()
{
    if (impl_)
        impl_->finish();
}

}  // namespace Json