qpdf/libqpdf/QPDFPageObjectHelper.cc

#include <qpdf/QPDFPageObjectHelper.hh>

#include <qpdf/Pl_Buffer.hh>
#include <qpdf/Pl_Concatenate.hh>
#include <qpdf/QIntC.hh>
#include <qpdf/QPDF.hh>
#include <qpdf/QPDFAcroFormDocumentHelper.hh>
#include <qpdf/QPDFExc.hh>
#include <qpdf/QPDFMatrix.hh>
#include <qpdf/QTC.hh>
#include <qpdf/QUtil.hh>
#include <qpdf/ResourceFinder.hh>

namespace
{
    class ContentProvider: public QPDFObjectHandle::StreamDataProvider
    {
      public:
        ContentProvider(QPDFObjectHandle from_page) :
            from_page(from_page)
        {
        }
        ~ContentProvider() override = default;
        void provideStreamData(QPDFObjGen const&, Pipeline* pipeline) override;

      private:
        QPDFObjectHandle from_page;
    };
} // namespace

void
ContentProvider::provideStreamData(QPDFObjGen const&, Pipeline* p)
{
    Pl_Concatenate concat("concatenate", p);
    std::string description = "contents from page object " + from_page.getObjGen().unparse(' ');
    std::string all_description;
    from_page.getKey("/Contents").pipeContentStreams(&concat, description, all_description);
    concat.manualFinish();
}

namespace
{
    class InlineImageTracker: public QPDFObjectHandle::TokenFilter
    {
      public:
        InlineImageTracker(QPDF*, size_t min_size, QPDFObjectHandle resources);
        ~InlineImageTracker() override = default;
        void handleToken(QPDFTokenizer::Token const&) override;
        QPDFObjectHandle convertIIDict(QPDFObjectHandle odict);

        QPDF* qpdf;
        size_t min_size;
        QPDFObjectHandle resources;
        std::string dict_str;
        std::string bi_str;
        int min_suffix{1};
        bool any_images{false};
        enum { st_top, st_bi } state{st_top};
    };
} // namespace

InlineImageTracker::InlineImageTracker(QPDF* qpdf, size_t min_size, QPDFObjectHandle resources) :
    qpdf(qpdf),
    min_size(min_size),
    resources(resources)
{
}

QPDFObjectHandle
InlineImageTracker::convertIIDict(QPDFObjectHandle odict)
{
    QPDFObjectHandle dict = QPDFObjectHandle::newDictionary();
    dict.replaceKey("/Type", QPDFObjectHandle::newName("/XObject"));
    dict.replaceKey("/Subtype", QPDFObjectHandle::newName("/Image"));
    std::set<std::string> keys = odict.getKeys();
    for (auto key: keys) {
        QPDFObjectHandle value = odict.getKey(key);
        if (key == "/BPC") {
            key = "/BitsPerComponent";
        } else if (key == "/CS") {
            key = "/ColorSpace";
        } else if (key == "/D") {
            key = "/Decode";
        } else if (key == "/DP") {
            key = "/DecodeParms";
        } else if (key == "/F") {
            key = "/Filter";
        } else if (key == "/H") {
            key = "/Height";
        } else if (key == "/IM") {
            key = "/ImageMask";
        } else if (key == "/I") {
            key = "/Interpolate";
        } else if (key == "/W") {
            key = "/Width";
        }

        if (key == "/ColorSpace") {
            if (value.isName()) {
                std::string name = value.getName();
                if (name == "/G") {
                    name = "/DeviceGray";
                } else if (name == "/RGB") {
                    name = "/DeviceRGB";
                } else if (name == "/CMYK") {
                    name = "/DeviceCMYK";
                } else if (name == "/I") {
                    name = "/Indexed";
                } else {
                    // This is a key in the page's /Resources -> /ColorSpace dictionary. We need to
                    // look it up and use its value as the color space for the image.
                    QPDFObjectHandle colorspace = resources.getKey("/ColorSpace");
                    if (colorspace.isDictionary() && colorspace.hasKey(name)) {
                        QTC::TC("qpdf", "QPDFPageObjectHelper colorspace lookup");
                        value = colorspace.getKey(name);
                    } else {
                        resources.warnIfPossible("unable to resolve colorspace " + name);
                    }
                    name.clear();
                }
                if (!name.empty()) {
                    value = QPDFObjectHandle::newName(name);
                }
            }
        } else if (key == "/Filter") {
            std::vector<QPDFObjectHandle> filters;
            if (value.isName()) {
                filters.push_back(value);
            } else if (value.isArray()) {
                filters = value.getArrayAsVector();
            }
            for (auto& iter: filters) {
                std::string name;
                if (iter.isName()) {
                    name = iter.getName();
                }
                if (name == "/AHx") {
                    name = "/ASCIIHexDecode";
                } else if (name == "/A85") {
                    name = "/ASCII85Decode";
                } else if (name == "/LZW") {
                    name = "/LZWDecode";
                } else if (name == "/Fl") {
                    name = "/FlateDecode";
                } else if (name == "/RL") {
                    name = "/RunLengthDecode";
                } else if (name == "/CCF") {
                    name = "/CCITTFaxDecode";
                } else if (name == "/DCT") {
                    name = "/DCTDecode";
                } else {
                    name.clear();
                }
                if (!name.empty()) {
                    iter = QPDFObjectHandle::newName(name);
                }
            }
            if (value.isName() && (filters.size() == 1)) {
                value = filters.at(0);
            } else if (value.isArray()) {
                value = QPDFObjectHandle::newArray(filters);
            }
        }
        dict.replaceKey(key, value);
    }
    return dict;
}

void
InlineImageTracker::handleToken(QPDFTokenizer::Token const& token)
{
    if (state == st_bi) {
        if (token.getType() == QPDFTokenizer::tt_inline_image) {
            std::string image_data(token.getValue());
            size_t len = image_data.length();
            if (len >= this->min_size) {
                QTC::TC("qpdf", "QPDFPageObjectHelper externalize inline image");
                QPDFObjectHandle dict = convertIIDict(QPDFObjectHandle::parse(dict_str));
                dict.replaceKey("/Length", QPDFObjectHandle::newInteger(QIntC::to_longlong(len)));
                std::string name = resources.getUniqueResourceName("/IIm", this->min_suffix);
                QPDFObjectHandle image = QPDFObjectHandle::newStream(
                    this->qpdf, std::make_shared<Buffer>(std::move(image_data)));
                image.replaceDict(dict);
                resources.getKey("/XObject").replaceKey(name, image);
                write(name);
                write(" Do\n");
                any_images = true;
            } else {
                QTC::TC("qpdf", "QPDFPageObjectHelper keep inline image");
                write(bi_str);
                writeToken(token);
                state = st_top;
            }
        } else if (token.isWord("ID")) {
            bi_str += token.getValue();
            dict_str += " >>";
        } else if (token.isWord("EI")) {
            state = st_top;
        } else {
            bi_str += token.getRawValue();
            dict_str += token.getRawValue();
        }
    } else if (token.isWord("BI")) {
        bi_str = token.getValue();
        dict_str = "<< ";
        state = st_bi;
    } else {
        writeToken(token);
    }
}

QPDFPageObjectHelper::QPDFPageObjectHelper(QPDFObjectHandle oh) :
    QPDFObjectHelper(oh)
{
}

QPDFObjectHandle
QPDFPageObjectHelper::getAttribute(std::string const& name, bool copy_if_shared)
{
    return getAttribute(name, copy_if_shared, nullptr, false);
}

QPDFObjectHandle
QPDFPageObjectHelper::getAttribute(
    std::string const& name,
    bool copy_if_shared,
    std::function<QPDFObjectHandle()> get_fallback,
    bool copy_if_fallback)
{
    const bool is_form_xobject = this->oh.isFormXObject();
    bool inherited = false;
    auto dict = is_form_xobject ? oh.getDict() : oh;
    auto result = dict.getKey(name);

    if (!is_form_xobject && result.isNull() &&
        (name == "/MediaBox" || name == "/CropBox" || name == "/Resources" || name == "/Rotate")) {
        QPDFObjectHandle node = dict;
        QPDFObjGen::set seen{};
        while (seen.add(node) && node.hasKey("/Parent")) {
            node = node.getKey("/Parent");
            result = node.getKey(name);
            if (!result.isNull()) {
                QTC::TC("qpdf", "QPDFPageObjectHelper non-trivial inheritance");
                inherited = true;
                break;
            }
        }
    }
    if (copy_if_shared && (inherited || result.isIndirect())) {
        QTC::TC("qpdf", "QPDFPageObjectHelper copy shared attribute", is_form_xobject ? 0 : 1);
        result = dict.replaceKeyAndGetNew(name, result.shallowCopy());
    }
    if (result.isNull() && get_fallback) {
        result = get_fallback();
        if (copy_if_fallback && !result.isNull()) {
            QTC::TC("qpdf", "QPDFPageObjectHelper copied fallback");
            result = dict.replaceKeyAndGetNew(name, result.shallowCopy());
        } else {
            QTC::TC("qpdf", "QPDFPageObjectHelper used fallback without copying");
        }
    }
    return result;
}

QPDFObjectHandle
QPDFPageObjectHelper::getMediaBox(bool copy_if_shared)
{
    return getAttribute("/MediaBox", copy_if_shared);
}

QPDFObjectHandle
QPDFPageObjectHelper::getCropBox(bool copy_if_shared, bool copy_if_fallback)
{
    return getAttribute(
        "/CropBox",
        copy_if_shared,
        [this, copy_if_shared]() { return this->getMediaBox(copy_if_shared); },
        copy_if_fallback);
}

QPDFObjectHandle
QPDFPageObjectHelper::getTrimBox(bool copy_if_shared, bool copy_if_fallback)
{
    return getAttribute(
        "/TrimBox",
        copy_if_shared,
        [this, copy_if_shared, copy_if_fallback]() {
            return this->getCropBox(copy_if_shared, copy_if_fallback);
        },
        copy_if_fallback);
}

QPDFObjectHandle
QPDFPageObjectHelper::getArtBox(bool copy_if_shared, bool copy_if_fallback)
{
    return getAttribute(
        "/ArtBox",
        copy_if_shared,
        [this, copy_if_shared, copy_if_fallback]() {
            return this->getCropBox(copy_if_shared, copy_if_fallback);
        },
        copy_if_fallback);
}

QPDFObjectHandle
QPDFPageObjectHelper::getBleedBox(bool copy_if_shared, bool copy_if_fallback)
{
    return getAttribute(
        "/BleedBox",
        copy_if_shared,
        [this, copy_if_shared, copy_if_fallback]() {
            return this->getCropBox(copy_if_shared, copy_if_fallback);
        },
        copy_if_fallback);
}

void
QPDFPageObjectHelper::forEachXObject(
    bool recursive,
    std::function<void(QPDFObjectHandle& obj, QPDFObjectHandle& xobj_dict, std::string const& key)>
        action,
    std::function<bool(QPDFObjectHandle)> selector)
{
    QTC::TC(
        "qpdf",
        "QPDFPageObjectHelper::forEachXObject",
        recursive ? (this->oh.isFormXObject() ? 0 : 1) : (this->oh.isFormXObject() ? 2 : 3));
    QPDFObjGen::set seen;
    std::list<QPDFPageObjectHelper> queue;
    queue.push_back(*this);
    while (!queue.empty()) {
        auto& ph = queue.front();
        if (seen.add(ph)) {
            auto xobj_dict = ph.getAttribute("/Resources", false).getKeyIfDict("/XObject");
            if (xobj_dict.isDictionary()) {
                for (auto const& key: xobj_dict.getKeys()) {
                    QPDFObjectHandle obj = xobj_dict.getKey(key);
                    if ((!selector) || selector(obj)) {
                        action(obj, xobj_dict, key);
                    }
                    if (recursive && obj.isFormXObject()) {
                        queue.emplace_back(obj);
                    }
                }
            }
        }
        queue.pop_front();
    }
}

void
QPDFPageObjectHelper::forEachImage(
    bool recursive,
    std::function<void(QPDFObjectHandle& obj, QPDFObjectHandle& xobj_dict, std::string const& key)>
        action)
{
    forEachXObject(recursive, action, [](QPDFObjectHandle obj) { return obj.isImage(); });
}

void
QPDFPageObjectHelper::forEachFormXObject(
    bool recursive,
    std::function<void(QPDFObjectHandle& obj, QPDFObjectHandle& xobj_dict, std::string const& key)>
        action)
{
    forEachXObject(recursive, action, [](QPDFObjectHandle obj) { return obj.isFormXObject(); });
}

std::map<std::string, QPDFObjectHandle>
QPDFPageObjectHelper::getPageImages()
{
    return getImages();
}

std::map<std::string, QPDFObjectHandle>
QPDFPageObjectHelper::getImages()
{
    std::map<std::string, QPDFObjectHandle> result;
    forEachImage(
        false, [&result](QPDFObjectHandle& obj, QPDFObjectHandle&, std::string const& key) {
            result[key] = obj;
        });
    return result;
}

std::map<std::string, QPDFObjectHandle>
QPDFPageObjectHelper::getFormXObjects()
{
    std::map<std::string, QPDFObjectHandle> result;
    forEachFormXObject(
        false, [&result](QPDFObjectHandle& obj, QPDFObjectHandle&, std::string const& key) {
            result[key] = obj;
        });
    return result;
}

void
QPDFPageObjectHelper::externalizeInlineImages(size_t min_size, bool shallow)
{
    if (shallow) {
        QPDFObjectHandle resources = getAttribute("/Resources", true);
        // Calling mergeResources also ensures that /XObject becomes direct and is not shared with
        // other pages.
        resources.mergeResources("<< /XObject << >> >>"_qpdf);
        InlineImageTracker iit(this->oh.getOwningQPDF(), min_size, resources);
        Pl_Buffer b("new page content");
        bool filtered = false;
        try {
            filterContents(&iit, &b);
            filtered = true;
        } catch (std::exception& e) {
            this->oh.warnIfPossible(
                std::string("Unable to filter content stream: ") + e.what() +
                "; not attempting to externalize inline images"
                " from this stream");
        }
        if (filtered && iit.any_images) {
            if (this->oh.isFormXObject()) {
                this->oh.replaceStreamData(
                    b.getBufferSharedPointer(),
                    QPDFObjectHandle::newNull(),
                    QPDFObjectHandle::newNull());
            } else {
                this->oh.replaceKey(
                    "/Contents",
                    QPDFObjectHandle::newStream(&this->oh.getQPDF(), b.getBufferSharedPointer()));
            }
        }
    } else {
        externalizeInlineImages(min_size, true);
        forEachFormXObject(
            true, [min_size](QPDFObjectHandle& obj, QPDFObjectHandle&, std::string const&) {
                QPDFPageObjectHelper(obj).externalizeInlineImages(min_size, true);
            });
    }
}

std::vector<QPDFAnnotationObjectHelper>
QPDFPageObjectHelper::getAnnotations(std::string const& only_subtype)
{
    std::vector<QPDFAnnotationObjectHelper> result;
    QPDFObjectHandle annots = this->oh.getKey("/Annots");
    if (annots.isArray()) {
        int nannots = annots.getArrayNItems();
        for (int i = 0; i < nannots; ++i) {
            QPDFObjectHandle annot = annots.getArrayItem(i);
            if (annot.isDictionaryOfType("", only_subtype)) {
                result.emplace_back(annot);
            }
        }
    }
    return result;
}

std::vector<QPDFObjectHandle>
QPDFPageObjectHelper::getPageContents()
{
    return this->oh.getPageContents();
}

void
QPDFPageObjectHelper::addPageContents(QPDFObjectHandle contents, bool first)
{
    this->oh.addPageContents(contents, first);
}

void
QPDFPageObjectHelper::rotatePage(int angle, bool relative)
{
    this->oh.rotatePage(angle, relative);
}

void
QPDFPageObjectHelper::coalesceContentStreams()
{
    this->oh.coalesceContentStreams();
}

void
QPDFPageObjectHelper::parsePageContents(QPDFObjectHandle::ParserCallbacks* callbacks)
{
    parseContents(callbacks);
}

void
QPDFPageObjectHelper::parseContents(QPDFObjectHandle::ParserCallbacks* callbacks)
{
    if (this->oh.isFormXObject()) {
        this->oh.parseAsContents(callbacks);
    } else {
        this->oh.parsePageContents(callbacks);
    }
}

void
QPDFPageObjectHelper::filterPageContents(QPDFObjectHandle::TokenFilter* filter, Pipeline* next)
{
    return filterContents(filter, next);
}

void
QPDFPageObjectHelper::filterContents(QPDFObjectHandle::TokenFilter* filter, Pipeline* next)
{
    if (this->oh.isFormXObject()) {
        this->oh.filterAsContents(filter, next);
    } else {
        this->oh.filterPageContents(filter, next);
    }
}

void
QPDFPageObjectHelper::pipePageContents(Pipeline* p)
{
    pipeContents(p);
}

void
QPDFPageObjectHelper::pipeContents(Pipeline* p)
{
    if (this->oh.isFormXObject()) {
        this->oh.pipeStreamData(p, 0, qpdf_dl_specialized);
    } else {
        this->oh.pipePageContents(p);
    }
}

void
QPDFPageObjectHelper::addContentTokenFilter(
    std::shared_ptr<QPDFObjectHandle::TokenFilter> token_filter)
{
    if (this->oh.isFormXObject()) {
        this->oh.addTokenFilter(token_filter);
    } else {
        this->oh.addContentTokenFilter(token_filter);
    }
}

bool
QPDFPageObjectHelper::removeUnreferencedResourcesHelper(
    QPDFPageObjectHelper ph, std::set<std::string>& unresolved)
{
    bool is_page = (!ph.oh.isFormXObject());
    if (!is_page) {
        QTC::TC("qpdf", "QPDFPageObjectHelper filter form xobject");
    }

    ResourceFinder rf;
    try {
        auto q = ph.oh.getOwningQPDF();
        size_t before_nw = (q ? q->numWarnings() : 0);
        ph.parseContents(&rf);
        size_t after_nw = (q ? q->numWarnings() : 0);
        if (after_nw > before_nw) {
            ph.oh.warnIfPossible("Bad token found while scanning content stream; "
                                 "not attempting to remove unreferenced objects from"
                                 " this object");
            return false;
        }
    } catch (std::exception& e) {
        QTC::TC("qpdf", "QPDFPageObjectHelper bad token finding names");
        ph.oh.warnIfPossible(
            std::string("Unable to parse content stream: ") + e.what() +
            "; not attempting to remove unreferenced objects"
            " from this object");
        return false;
    }

    // We will walk through /Font and /XObject dictionaries, removing any resources that are not
    // referenced. We must make copies of resource dictionaries down into the dictionaries are
    // mutating to prevent mutating one dictionary from having the side effect of mutating the one
    // it was copied from.
    QPDFObjectHandle resources = ph.getAttribute("/Resources", true);
    std::vector<QPDFObjectHandle> rdicts;
    std::set<std::string> known_names;
    std::vector<std::string> to_filter = {"/Font", "/XObject"};
    if (resources.isDictionary()) {
        for (auto const& iter: to_filter) {
            QPDFObjectHandle dict = resources.getKey(iter);
            if (dict.isDictionary()) {
                dict = resources.replaceKeyAndGetNew(iter, dict.shallowCopy());
                rdicts.push_back(dict);
                auto keys = dict.getKeys();
                known_names.insert(keys.begin(), keys.end());
            }
        }
    }

    std::set<std::string> local_unresolved;
    auto names_by_rtype = rf.getNamesByResourceType();
    for (auto const& i1: to_filter) {
        for (auto const& n_iter: names_by_rtype[i1]) {
            std::string const& name = n_iter.first;
            if (!known_names.count(name)) {
                unresolved.insert(name);
                local_unresolved.insert(name);
            }
        }
    }
    // Older versions of the PDF spec allowed form XObjects to omit their resources dictionaries, in
    // which case names were resolved from the containing page. This behavior seems to be widely
    // supported by viewers. If a form XObjects has a resources dictionary and has some unresolved
    // names, some viewers fail to resolve them, and others allow them to be inherited from the page
    // or from another form XObjects that contains them. Since this behavior is inconsistent across
    // viewers, we consider an unresolved name when a resources dictionary is present to be reason
    // not to remove unreferenced resources. An unresolved name in the absence of a resource
    // dictionary is not considered a problem. For form XObjects, we just accumulate a list of
    // unresolved names, and for page objects, we avoid removing any such names found in nested form
    // XObjects.

    if ((!local_unresolved.empty()) && resources.isDictionary()) {
        // It's not worth issuing a warning for this case. From qpdf 10.3, we are hopefully only
        // looking at names that are referencing fonts and XObjects, but until we're certain that we
        // know the meaning of every name in a content stream, we don't want to give warnings that
        // might be false positives. Also, this can happen in legitimate cases with older PDFs, and
        // there's nothing to be done about it, so there's no good reason to issue a warning. The
        // only sad thing is that it was a false positive that alerted me to a logic error in the
        // code, and any future such errors would now be hidden.
        QTC::TC("qpdf", "QPDFPageObjectHelper unresolved names");
        return false;
    }

    for (auto& dict: rdicts) {
        for (auto const& key: dict.getKeys()) {
            if (is_page && unresolved.count(key)) {
                // This name is referenced by some nested form xobject, so don't remove it.
                QTC::TC("qpdf", "QPDFPageObjectHelper resolving unresolved");
            } else if (!rf.getNames().count(key)) {
                dict.removeKey(key);
            }
        }
    }
    return true;
}

void
QPDFPageObjectHelper::removeUnreferencedResources()
{
    // Accumulate a list of unresolved names across all nested form XObjects.
    std::set<std::string> unresolved;
    bool any_failures = false;
    forEachFormXObject(
        true,
        [&any_failures, &unresolved](QPDFObjectHandle& obj, QPDFObjectHandle&, std::string const&) {
            if (!removeUnreferencedResourcesHelper(QPDFPageObjectHelper(obj), unresolved)) {
                any_failures = true;
            }
        });
    if (this->oh.isFormXObject() || (!any_failures)) {
        removeUnreferencedResourcesHelper(*this, unresolved);
    }
}

QPDFPageObjectHelper
QPDFPageObjectHelper::shallowCopyPage()
{
    QPDF& qpdf =
        this->oh.getQPDF("QPDFPageObjectHelper::shallowCopyPage called with a direct object");
    QPDFObjectHandle new_page = this->oh.shallowCopy();
    return {qpdf.makeIndirectObject(new_page)};
}

QPDFObjectHandle::Matrix
QPDFPageObjectHelper::getMatrixForTransformations(bool invert)
{
    QPDFObjectHandle::Matrix matrix(1, 0, 0, 1, 0, 0);
    QPDFObjectHandle bbox = getTrimBox(false);
    if (!bbox.isRectangle()) {
        return matrix;
    }
    QPDFObjectHandle rotate_obj = getAttribute("/Rotate", false);
    QPDFObjectHandle scale_obj = getAttribute("/UserUnit", false);
    if (!(rotate_obj.isNull() && scale_obj.isNull())) {
        QPDFObjectHandle::Rectangle rect = bbox.getArrayAsRectangle();
        double width = rect.urx - rect.llx;
        double height = rect.ury - rect.lly;
        double scale = (scale_obj.isNumber() ? scale_obj.getNumericValue() : 1.0);
        int rotate = (rotate_obj.isInteger() ? rotate_obj.getIntValueAsInt() : 0);
        if (invert) {
            if (scale == 0.0) {
                return matrix;
            }
            scale = 1.0 / scale;
            rotate = 360 - rotate;
        }

        // Ignore invalid rotation angle
        switch (rotate) {
        case 90:
            matrix = QPDFObjectHandle::Matrix(0, -scale, scale, 0, 0, width * scale);
            break;
        case 180:
            matrix = QPDFObjectHandle::Matrix(-scale, 0, 0, -scale, width * scale, height * scale);
            break;
        case 270:
            matrix = QPDFObjectHandle::Matrix(0, scale, -scale, 0, height * scale, 0);
            break;
        default:
            matrix = QPDFObjectHandle::Matrix(scale, 0, 0, scale, 0, 0);
            break;
        }
    }
    return matrix;
}

QPDFObjectHandle
QPDFPageObjectHelper::getFormXObjectForPage(bool handle_transformations)
{
    auto result =
        this->oh.getQPDF("QPDFPageObjectHelper::getFormXObjectForPage called with a direct object")
            .newStream();
    QPDFObjectHandle newdict = result.getDict();
    newdict.replaceKey("/Type", QPDFObjectHandle::newName("/XObject"));
    newdict.replaceKey("/Subtype", QPDFObjectHandle::newName("/Form"));
    newdict.replaceKey("/Resources", getAttribute("/Resources", false).shallowCopy());
    newdict.replaceKey("/Group", getAttribute("/Group", false).shallowCopy());
    QPDFObjectHandle bbox = getTrimBox(false).shallowCopy();
    if (!bbox.isRectangle()) {
        this->oh.warnIfPossible("bounding box is invalid; form"
                                " XObject created from page will not work");
    }
    newdict.replaceKey("/BBox", bbox);
    auto provider =
        std::shared_ptr<QPDFObjectHandle::StreamDataProvider>(new ContentProvider(this->oh));
    result.replaceStreamData(provider, QPDFObjectHandle::newNull(), QPDFObjectHandle::newNull());
    QPDFObjectHandle rotate_obj = getAttribute("/Rotate", false);
    QPDFObjectHandle scale_obj = getAttribute("/UserUnit", false);
    if (handle_transformations && (!(rotate_obj.isNull() && scale_obj.isNull()))) {
        newdict.replaceKey("/Matrix", QPDFObjectHandle::newArray(getMatrixForTransformations()));
    }

    return result;
}

QPDFMatrix
QPDFPageObjectHelper::getMatrixForFormXObjectPlacement(
    QPDFObjectHandle fo,
    QPDFObjectHandle::Rectangle rect,
    bool invert_transformations,
    bool allow_shrink,
    bool allow_expand)
{
    // Calculate the transformation matrix that will place the given form XObject fully inside the
    // given rectangle, center and shrinking or expanding as needed if requested.

    // When rendering a form XObject, the transformation in the graphics state (cm) is applied first
    // (of course -- when it is applied, the PDF interpreter doesn't even know we're going to be
    // drawing a form XObject yet), and then the object's matrix (M) is applied. The resulting
    // matrix, when applied to the form XObject's bounding box, will generate a new rectangle. We
    // want to create a transformation matrix that make the form XObject's bounding box land in
    // exactly the right spot.

    QPDFObjectHandle fdict = fo.getDict();
    QPDFObjectHandle bbox_obj = fdict.getKey("/BBox");
    if (!bbox_obj.isRectangle()) {
        return {};
    }

    QPDFMatrix wmatrix; // work matrix
    QPDFMatrix tmatrix; // "to" matrix
    QPDFMatrix fmatrix; // "from" matrix
    if (invert_transformations) {
        // tmatrix inverts scaling and rotation of the destination page. Applying this matrix allows
        // the overlaid form XObject's to be absolute rather than relative to properties of the
        // destination page. tmatrix is part of the computed transformation matrix.
        tmatrix = QPDFMatrix(getMatrixForTransformations(true));
        wmatrix.concat(tmatrix);
    }
    if (fdict.getKey("/Matrix").isMatrix()) {
        // fmatrix is the transformation matrix that is applied to the form XObject itself. We need
        // this for calculations, but we don't explicitly use it in the final result because the PDF
        // rendering system automatically applies this last before
        // drawing the form XObject.
        fmatrix = QPDFMatrix(fdict.getKey("/Matrix").getArrayAsMatrix());
        wmatrix.concat(fmatrix);
    }

    // The current wmatrix handles transformation from the form xobject and, if requested, the
    // destination page. Next, we have to adjust this for scale and position.

    // Step 1: figure out what scale factor we need to make the form XObject's bounding box fit
    // within the destination rectangle.

    // Transform bounding box
    QPDFObjectHandle::Rectangle bbox = bbox_obj.getArrayAsRectangle();
    QPDFObjectHandle::Rectangle T = wmatrix.transformRectangle(bbox);

    // Calculate a scale factor, if needed. Shrink or expand if needed and allowed.
    if ((T.urx == T.llx) || (T.ury == T.lly)) {
        // avoid division by zero
        return {};
    }
    double rect_w = rect.urx - rect.llx;
    double rect_h = rect.ury - rect.lly;
    double t_w = T.urx - T.llx;
    double t_h = T.ury - T.lly;
    double xscale = rect_w / t_w;
    double yscale = rect_h / t_h;
    double scale = (xscale < yscale ? xscale : yscale);
    if (scale > 1.0) {
        if (!allow_expand) {
            scale = 1.0;
        }
    } else if (scale < 1.0) {
        if (!allow_shrink) {
            scale = 1.0;
        }
    }

    // Step 2: figure out what translation is required to get the rectangle to the right spot:
    // centered within the destination.
    wmatrix = QPDFMatrix();
    wmatrix.scale(scale, scale);
    wmatrix.concat(tmatrix);
    wmatrix.concat(fmatrix);

    T = wmatrix.transformRectangle(bbox);
    double t_cx = (T.llx + T.urx) / 2.0;
    double t_cy = (T.lly + T.ury) / 2.0;
    double r_cx = (rect.llx + rect.urx) / 2.0;
    double r_cy = (rect.lly + rect.ury) / 2.0;
    double tx = r_cx - t_cx;
    double ty = r_cy - t_cy;

    // Now we can calculate the final matrix. The final matrix does not include fmatrix because that
    // is applied automatically by the PDF interpreter.
    QPDFMatrix cm;
    cm.translate(tx, ty);
    cm.scale(scale, scale);
    cm.concat(tmatrix);
    return cm;
}

std::string
QPDFPageObjectHelper::placeFormXObject(
    QPDFObjectHandle fo,
    std::string const& name,
    QPDFObjectHandle::Rectangle rect,
    bool invert_transformations,
    bool allow_shrink,
    bool allow_expand)
{
    QPDFMatrix cm;
    return placeFormXObject(fo, name, rect, cm, invert_transformations, allow_shrink, allow_expand);
}

std::string
QPDFPageObjectHelper::placeFormXObject(
    QPDFObjectHandle fo,
    std::string const& name,
    QPDFObjectHandle::Rectangle rect,
    QPDFMatrix& cm,
    bool invert_transformations,
    bool allow_shrink,
    bool allow_expand)
{
    cm = getMatrixForFormXObjectPlacement(
        fo, rect, invert_transformations, allow_shrink, allow_expand);
    return ("q\n" + cm.unparse() + " cm\n" + name + " Do\n" + "Q\n");
}

void
QPDFPageObjectHelper::flattenRotation(QPDFAcroFormDocumentHelper* afdh)
{
    QPDF& qpdf =
        this->oh.getQPDF("QPDFPageObjectHelper::flattenRotation called with a direct object");
    auto rotate_oh = this->oh.getKey("/Rotate");
    int rotate = 0;
    if (rotate_oh.isInteger()) {
        rotate = rotate_oh.getIntValueAsInt();
    }
    if (!((rotate == 90) || (rotate == 180) || (rotate == 270))) {
        return;
    }
    auto mediabox = this->oh.getKey("/MediaBox");
    if (!mediabox.isRectangle()) {
        return;
    }
    auto media_rect = mediabox.getArrayAsRectangle();

    std::vector<std::string> boxes = {
        "/MediaBox",
        "/CropBox",
        "/BleedBox",
        "/TrimBox",
        "/ArtBox",
    };
    for (auto const& boxkey: boxes) {
        auto box = this->oh.getKey(boxkey);
        if (!box.isRectangle()) {
            continue;
        }
        auto rect = box.getArrayAsRectangle();
        decltype(rect) new_rect;

        // How far are the edges of our rectangle from the edges of the media box?
        auto left_x = rect.llx - media_rect.llx;
        auto right_x = media_rect.urx - rect.urx;
        auto bottom_y = rect.lly - media_rect.lly;
        auto top_y = media_rect.ury - rect.ury;

        // Rotating the page 180 degrees does not change /MediaBox. Rotating 90 or 270 degrees
        // reverses llx and lly and also reverse urx and ury. For all the other boxes, we want the
        // corners to be the correct distance away from the corners of the mediabox.
        switch (rotate) {
        case 90:
            new_rect.llx = media_rect.lly + bottom_y;
            new_rect.urx = media_rect.ury - top_y;
            new_rect.lly = media_rect.llx + right_x;
            new_rect.ury = media_rect.urx - left_x;
            break;

        case 180:
            new_rect.llx = media_rect.llx + right_x;
            new_rect.urx = media_rect.urx - left_x;
            new_rect.lly = media_rect.lly + top_y;
            new_rect.ury = media_rect.ury - bottom_y;
            break;

        case 270:
            new_rect.llx = media_rect.lly + top_y;
            new_rect.urx = media_rect.ury - bottom_y;
            new_rect.lly = media_rect.llx + left_x;
            new_rect.ury = media_rect.urx - right_x;
            break;

        default:
            // ignore
            break;
        }

        this->oh.replaceKey(boxkey, QPDFObjectHandle::newFromRectangle(new_rect));
    }

    // When we rotate the page, pivot about the point 0, 0 and then translate so the page is visible
    // with the origin point being the same offset from the lower left corner of the media box.
    // These calculations have been verified empirically with various
    // PDF readers.
    QPDFMatrix cm(0, 0, 0, 0, 0, 0);
    switch (rotate) {
    case 90:
        cm.b = -1;
        cm.c = 1;
        cm.f = media_rect.urx + media_rect.llx;
        break;

    case 180:
        cm.a = -1;
        cm.d = -1;
        cm.e = media_rect.urx + media_rect.llx;
        cm.f = media_rect.ury + media_rect.lly;
        break;

    case 270:
        cm.b = 1;
        cm.c = -1;
        cm.e = media_rect.ury + media_rect.lly;
        break;

    default:
        break;
    }
    std::string cm_str = std::string("q\n") + cm.unparse() + " cm\n";
    this->oh.addPageContents(QPDFObjectHandle::newStream(&qpdf, cm_str), true);
    this->oh.addPageContents(qpdf.newStream("\nQ\n"), false);
    this->oh.removeKey("/Rotate");
    QPDFObjectHandle rotate_obj = getAttribute("/Rotate", false);
    if (!rotate_obj.isNull()) {
        QTC::TC("qpdf", "QPDFPageObjectHelper flatten inherit rotate");
        this->oh.replaceKey("/Rotate", QPDFObjectHandle::newInteger(0));
    }

    QPDFObjectHandle annots = this->oh.getKey("/Annots");
    if (annots.isArray()) {
        std::vector<QPDFObjectHandle> new_annots;
        std::vector<QPDFObjectHandle> new_fields;
        std::set<QPDFObjGen> old_fields;
        std::shared_ptr<QPDFAcroFormDocumentHelper> afdhph;
        if (!afdh) {
            afdhph = std::make_shared<QPDFAcroFormDocumentHelper>(qpdf);
            afdh = afdhph.get();
        }
        afdh->transformAnnotations(annots, new_annots, new_fields, old_fields, cm);
        afdh->removeFormFields(old_fields);
        for (auto const& f: new_fields) {
            afdh->addFormField(QPDFFormFieldObjectHelper(f));
        }
        this->oh.replaceKey("/Annots", QPDFObjectHandle::newArray(new_annots));
    }
}

void
QPDFPageObjectHelper::copyAnnotations(
    QPDFPageObjectHelper from_page,
    QPDFMatrix const& cm,
    QPDFAcroFormDocumentHelper* afdh,
    QPDFAcroFormDocumentHelper* from_afdh)
{
    auto old_annots = from_page.getObjectHandle().getKey("/Annots");
    if (!old_annots.isArray()) {
        return;
    }

    QPDF& from_qpdf = from_page.getObjectHandle().getQPDF(
        "QPDFPageObjectHelper::copyAnnotations: from page is a direct object");
    QPDF& this_qpdf =
        this->oh.getQPDF("QPDFPageObjectHelper::copyAnnotations: this page is a direct object");

    std::vector<QPDFObjectHandle> new_annots;
    std::vector<QPDFObjectHandle> new_fields;
    std::set<QPDFObjGen> old_fields;
    std::shared_ptr<QPDFAcroFormDocumentHelper> afdhph;
    std::shared_ptr<QPDFAcroFormDocumentHelper> from_afdhph;
    if (!afdh) {
        afdhph = std::make_shared<QPDFAcroFormDocumentHelper>(this_qpdf);
        afdh = afdhph.get();
    }
    if (&this_qpdf == &from_qpdf) {
        from_afdh = afdh;
    } else if (from_afdh) {
        if (from_afdh->getQPDF().getUniqueId() != from_qpdf.getUniqueId()) {
            throw std::logic_error("QPDFAcroFormDocumentHelper::copyAnnotations: from_afdh"
                                   " is not from the same QPDF as from_page");
        }
    } else {
        from_afdhph = std::make_shared<QPDFAcroFormDocumentHelper>(from_qpdf);
        from_afdh = from_afdhph.get();
    }

    afdh->transformAnnotations(
        old_annots, new_annots, new_fields, old_fields, cm, &from_qpdf, from_afdh);
    afdh->addAndRenameFormFields(new_fields);
    auto annots = this->oh.getKey("/Annots");
    if (!annots.isArray()) {
        annots = this->oh.replaceKeyAndGetNew("/Annots", QPDFObjectHandle::newArray());
    }
    for (auto const& annot: new_annots) {
        annots.appendItem(annot);
    }
}