tools/aapt2/flatten/TableFlattener.cpp

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "ResourceTable.h"
#include "ResourceValues.h"
#include "ValueVisitor.h"

#include "flatten/ChunkWriter.h"
#include "flatten/ResourceTypeExtensions.h"
#include "flatten/TableFlattener.h"
#include "util/BigBuffer.h"

#include <android-base/macros.h>
#include <type_traits>
#include <numeric>

using namespace android;

namespace aapt {

namespace {

template <typename T>
static bool cmpIds(const T* a, const T* b) {
    return a->id.value() < b->id.value();
}

static void strcpy16_htod(uint16_t* dst, size_t len, const StringPiece16& src) {
    if (len == 0) {
        return;
    }

    size_t i;
    const char16_t* srcData = src.data();
    for (i = 0; i < len - 1 && i < src.size(); i++) {
        dst[i] = util::hostToDevice16((uint16_t) srcData[i]);
    }
    dst[i] = 0;
}

struct FlatEntry {
    ResourceEntry* entry;
    Value* value;

    // The entry string pool index to the entry's name.
    uint32_t entryKey;

    // The source string pool index to the source file path.
    uint32_t sourcePathKey;
    uint32_t sourceLine;

    // The source string pool index to the comment.
    uint32_t commentKey;
};

class SymbolWriter {
public:
    struct Entry {
        StringPool::Ref name;
        size_t offset;
    };

    std::vector<Entry> symbols;

    explicit SymbolWriter(StringPool* pool) : mPool(pool) {
    }

    void addSymbol(const Reference& ref, size_t offset) {
        const ResourceName& name = ref.name.value();
        std::u16string fullName;
        if (ref.privateReference) {
            fullName += u"*";
        }

        if (!name.package.empty()) {
            fullName += name.package + u":";
        }
        fullName += toString(name.type).toString() + u"/" + name.entry;
        symbols.push_back(Entry{ mPool->makeRef(fullName), offset });
    }

    void shiftAllOffsets(size_t offset) {
        for (Entry& entry : symbols) {
            entry.offset += offset;
        }
    }

private:
    StringPool* mPool;
};

struct MapFlattenVisitor : public RawValueVisitor {
    using RawValueVisitor::visit;

    SymbolWriter* mSymbols;
    FlatEntry* mEntry;
    BigBuffer* mBuffer;
    StringPool* mSourcePool;
    StringPool* mCommentPool;
    bool mUseExtendedChunks;

    size_t mEntryCount = 0;
    const Reference* mParent = nullptr;

    MapFlattenVisitor(SymbolWriter* symbols, FlatEntry* entry, BigBuffer* buffer,
                      StringPool* sourcePool, StringPool* commentPool,
                      bool useExtendedChunks) :
            mSymbols(symbols), mEntry(entry), mBuffer(buffer), mSourcePool(sourcePool),
            mCommentPool(commentPool), mUseExtendedChunks(useExtendedChunks) {
    }

    void flattenKey(Reference* key, ResTable_map* outEntry) {
        if (!key->id || (key->privateReference && mUseExtendedChunks)) {
            assert(key->name && "reference must have a name");

            outEntry->name.ident = util::hostToDevice32(0);
            mSymbols->addSymbol(*key, (mBuffer->size() - sizeof(ResTable_map)) +
                                    offsetof(ResTable_map, name));
        } else {
            outEntry->name.ident = util::hostToDevice32(key->id.value().id);
        }
    }

    void flattenValue(Item* value, ResTable_map* outEntry) {
        bool privateRef = false;
        if (Reference* ref = valueCast<Reference>(value)) {
            privateRef = ref->privateReference && mUseExtendedChunks;
            if (!ref->id || privateRef) {
                assert(ref->name && "reference must have a name");

                mSymbols->addSymbol(*ref, (mBuffer->size() - sizeof(ResTable_map)) +
                                        offsetof(ResTable_map, value) + offsetof(Res_value, data));
            }
        }

        bool result = value->flatten(&outEntry->value);
        if (privateRef) {
            outEntry->value.data = 0;
        }
        assert(result && "flatten failed");
    }

    void flattenEntry(Reference* key, Item* value) {
        ResTable_map* outEntry = mBuffer->nextBlock<ResTable_map>();
        flattenKey(key, outEntry);
        flattenValue(value, outEntry);
        outEntry->value.size = util::hostToDevice16(sizeof(outEntry->value));
        mEntryCount++;
    }

    void flattenMetaData(Value* value) {
        if (!mUseExtendedChunks) {
            return;
        }

        Reference key(ResourceId{ ExtendedResTableMapTypes::ATTR_SOURCE_PATH });
        StringPool::Ref sourcePathRef = mSourcePool->makeRef(
                util::utf8ToUtf16(value->getSource().path));
        BinaryPrimitive val(Res_value::TYPE_INT_DEC,
                            static_cast<uint32_t>(sourcePathRef.getIndex()));
        flattenEntry(&key, &val);

        if (value->getSource().line) {
            key.id = ResourceId(ExtendedResTableMapTypes::ATTR_SOURCE_LINE);
            val.value.data = static_cast<uint32_t>(value->getSource().line.value());
            flattenEntry(&key, &val);
        }

        if (!value->getComment().empty()) {
            key.id = ResourceId(ExtendedResTableMapTypes::ATTR_COMMENT);
            StringPool::Ref commentRef = mCommentPool->makeRef(value->getComment());
            val.value.data = static_cast<uint32_t>(commentRef.getIndex());
            flattenEntry(&key, &val);
        }
    }

    void visit(Attribute* attr) override {
        {
            Reference key(ResourceId{ ResTable_map::ATTR_TYPE });
            BinaryPrimitive val(Res_value::TYPE_INT_DEC, attr->typeMask);
            flattenEntry(&key, &val);
        }

        if (attr->minInt != std::numeric_limits<int32_t>::min()) {
            Reference key(ResourceId{ ResTable_map::ATTR_MIN });
            BinaryPrimitive val(Res_value::TYPE_INT_DEC, static_cast<uint32_t>(attr->minInt));
            flattenEntry(&key, &val);
        }

        if (attr->maxInt != std::numeric_limits<int32_t>::max()) {
            Reference key(ResourceId{ ResTable_map::ATTR_MAX });
            BinaryPrimitive val(Res_value::TYPE_INT_DEC, static_cast<uint32_t>(attr->maxInt));
            flattenEntry(&key, &val);
        }

        for (Attribute::Symbol& s : attr->symbols) {
            BinaryPrimitive val(Res_value::TYPE_INT_DEC, s.value);
            flattenEntry(&s.symbol, &val);
        }
    }

    static bool cmpStyleEntries(const Style::Entry& a, const Style::Entry& b) {
        if (a.key.id) {
            if (b.key.id) {
                return a.key.id.value() < b.key.id.value();
            }
            return true;
        } else if (!b.key.id) {
            return a.key.name.value() < b.key.name.value();
        }
        return false;
    }

    void visit(Style* style) override {
        if (style->parent) {
            // Parents are treated a bit differently, so record the existence and move on.
            mParent = &style->parent.value();
        }

        // Sort the style.
        std::sort(style->entries.begin(), style->entries.end(), cmpStyleEntries);

        for (Style::Entry& entry : style->entries) {
            flattenEntry(&entry.key, entry.value.get());
            flattenMetaData(&entry.key);
        }
    }

    void visit(Styleable* styleable) override {
        for (auto& attrRef : styleable->entries) {
            BinaryPrimitive val(Res_value{});
            flattenEntry(&attrRef, &val);
            flattenMetaData(&attrRef);
        }
    }

    void visit(Array* array) override {
        for (auto& item : array->items) {
            ResTable_map* outEntry = mBuffer->nextBlock<ResTable_map>();
            flattenValue(item.get(), outEntry);
            outEntry->value.size = util::hostToDevice16(sizeof(outEntry->value));
            mEntryCount++;
            flattenMetaData(item.get());
        }
    }

    void visit(Plural* plural) override {
        const size_t count = plural->values.size();
        for (size_t i = 0; i < count; i++) {
            if (!plural->values[i]) {
                continue;
            }

            ResourceId q;
            switch (i) {
            case Plural::Zero:
                q.id = android::ResTable_map::ATTR_ZERO;
                break;

            case Plural::One:
                q.id = android::ResTable_map::ATTR_ONE;
                break;

            case Plural::Two:
                q.id = android::ResTable_map::ATTR_TWO;
                break;

            case Plural::Few:
                q.id = android::ResTable_map::ATTR_FEW;
                break;

            case Plural::Many:
                q.id = android::ResTable_map::ATTR_MANY;
                break;

            case Plural::Other:
                q.id = android::ResTable_map::ATTR_OTHER;
                break;

            default:
                assert(false);
                break;
            }

            Reference key(q);
            flattenEntry(&key, plural->values[i].get());
            flattenMetaData(plural->values[i].get());
        }
    }
};

class PackageFlattener {
public:
    PackageFlattener(IDiagnostics* diag, TableFlattenerOptions options,
                     ResourceTablePackage* package, SymbolWriter* symbolWriter,
                     StringPool* sourcePool) :
            mDiag(diag), mOptions(options), mPackage(package), mSymbols(symbolWriter),
            mSourcePool(sourcePool) {
    }

    bool flattenPackage(BigBuffer* buffer) {
        ChunkWriter pkgWriter(buffer);
        ResTable_package* pkgHeader = pkgWriter.startChunk<ResTable_package>(
                RES_TABLE_PACKAGE_TYPE);
        pkgHeader->id = util::hostToDevice32(mPackage->id.value());

        if (mPackage->name.size() >= arraysize(pkgHeader->name)) {
            mDiag->error(DiagMessage() <<
                         "package name '" << mPackage->name << "' is too long");
            return false;
        }

        // Copy the package name in device endianness.
        strcpy16_htod(pkgHeader->name, arraysize(pkgHeader->name), mPackage->name);

        // Serialize the types. We do this now so that our type and key strings
        // are populated. We write those first.
        BigBuffer typeBuffer(1024);
        flattenTypes(&typeBuffer);

        pkgHeader->typeStrings = util::hostToDevice32(pkgWriter.size());
        StringPool::flattenUtf16(pkgWriter.getBuffer(), mTypePool);

        pkgHeader->keyStrings = util::hostToDevice32(pkgWriter.size());
        StringPool::flattenUtf16(pkgWriter.getBuffer(), mKeyPool);

        // Add the ResTable_package header/type/key strings to the offset.
        mSymbols->shiftAllOffsets(pkgWriter.size());

        // Append the types.
        buffer->appendBuffer(std::move(typeBuffer));

        pkgWriter.finish();
        return true;
    }

private:
    IDiagnostics* mDiag;
    TableFlattenerOptions mOptions;
    ResourceTablePackage* mPackage;
    StringPool mTypePool;
    StringPool mKeyPool;
    SymbolWriter* mSymbols;
    StringPool* mSourcePool;

    template <typename T, bool IsItem>
    T* writeEntry(FlatEntry* entry, BigBuffer* buffer) {
        static_assert(std::is_same<ResTable_entry, T>::value ||
                      std::is_same<ResTable_entry_ext, T>::value,
                      "T must be ResTable_entry or ResTable_entry_ext");

        T* result = buffer->nextBlock<T>();
        ResTable_entry* outEntry = (ResTable_entry*)(result);
        if (entry->entry->symbolStatus.state == SymbolState::kPublic) {
            outEntry->flags |= ResTable_entry::FLAG_PUBLIC;
        }

        if (entry->value->isWeak()) {
            outEntry->flags |= ResTable_entry::FLAG_WEAK;
        }

        if (!IsItem) {
            outEntry->flags |= ResTable_entry::FLAG_COMPLEX;
        }

        outEntry->key.index = util::hostToDevice32(entry->entryKey);
        outEntry->size = sizeof(T);

        if (mOptions.useExtendedChunks) {
            // Write the extra source block. This will be ignored by the Android runtime.
            ResTable_entry_source* sourceBlock = buffer->nextBlock<ResTable_entry_source>();
            sourceBlock->path.index = util::hostToDevice32(entry->sourcePathKey);
            sourceBlock->line = util::hostToDevice32(entry->sourceLine);
            sourceBlock->comment.index = util::hostToDevice32(entry->commentKey);
            outEntry->size += sizeof(*sourceBlock);
        }

        outEntry->flags = util::hostToDevice16(outEntry->flags);
        outEntry->size = util::hostToDevice16(outEntry->size);
        return result;
    }

    bool flattenValue(FlatEntry* entry, BigBuffer* buffer) {
        if (Item* item = valueCast<Item>(entry->value)) {
            writeEntry<ResTable_entry, true>(entry, buffer);
            bool privateRef = false;
            if (Reference* ref = valueCast<Reference>(entry->value)) {
                // If there is no ID or the reference is private and we allow extended chunks,
                // write out a 0 and mark the symbol table with the name of the reference.
                privateRef = (ref->privateReference && mOptions.useExtendedChunks);
                if (!ref->id || privateRef) {
                    assert(ref->name && "reference must have at least a name");
                    mSymbols->addSymbol(*ref, buffer->size() + offsetof(Res_value, data));
                }
            }
            Res_value* outValue = buffer->nextBlock<Res_value>();
            bool result = item->flatten(outValue);
            assert(result && "flatten failed");
            if (privateRef) {
                // Force the value of 0 so we look up the symbol at unflatten time.
                outValue->data = 0;
            }
            outValue->size = util::hostToDevice16(sizeof(*outValue));
        } else {
            const size_t beforeEntry = buffer->size();
            ResTable_entry_ext* outEntry = writeEntry<ResTable_entry_ext, false>(entry, buffer);
            MapFlattenVisitor visitor(mSymbols, entry, buffer, mSourcePool, mSourcePool,
                                      mOptions.useExtendedChunks);
            entry->value->accept(&visitor);
            outEntry->count = util::hostToDevice32(visitor.mEntryCount);
            if (visitor.mParent) {
                const bool forceSymbol = visitor.mParent->privateReference &&
                        mOptions.useExtendedChunks;
                if (!visitor.mParent->id || forceSymbol) {
                    assert(visitor.mParent->name && "reference must have a name");
                    mSymbols->addSymbol(*visitor.mParent,
                                        beforeEntry + offsetof(ResTable_entry_ext, parent));
                } else {
                    outEntry->parent.ident = util::hostToDevice32(visitor.mParent->id.value().id);
                }
            }
        }
        return true;
    }

    bool flattenConfig(const ResourceTableType* type, const ConfigDescription& config,
                       std::vector<FlatEntry>* entries, BigBuffer* buffer) {
        ChunkWriter typeWriter(buffer);
        ResTable_type* typeHeader = typeWriter.startChunk<ResTable_type>(RES_TABLE_TYPE_TYPE);
        typeHeader->id = type->id.value();
        typeHeader->config = config;
        typeHeader->config.swapHtoD();

        auto maxAccum = [](uint32_t max, const std::unique_ptr<ResourceEntry>& a) -> uint32_t {
            return std::max(max, (uint32_t) a->id.value());
        };

        // Find the largest entry ID. That is how many entries we will have.
        const uint32_t entryCount =
                std::accumulate(type->entries.begin(), type->entries.end(), 0, maxAccum) + 1;

        typeHeader->entryCount = util::hostToDevice32(entryCount);
        uint32_t* indices = typeWriter.nextBlock<uint32_t>(entryCount);

        assert((size_t) entryCount <= std::numeric_limits<uint16_t>::max() + 1);
        memset(indices, 0xff, entryCount * sizeof(uint32_t));

        typeHeader->entriesStart = util::hostToDevice32(typeWriter.size());

        const size_t entryStart = typeWriter.getBuffer()->size();
        for (FlatEntry& flatEntry : *entries) {
            assert(flatEntry.entry->id.value() < entryCount);
            indices[flatEntry.entry->id.value()] = util::hostToDevice32(
                    typeWriter.getBuffer()->size() - entryStart);
            if (!flattenValue(&flatEntry, typeWriter.getBuffer())) {
                mDiag->error(DiagMessage()
                             << "failed to flatten resource '"
                             << ResourceNameRef(mPackage->name, type->type, flatEntry.entry->name)
                             << "' for configuration '" << config << "'");
                return false;
            }
        }
        typeWriter.finish();
        return true;
    }

    std::vector<ResourceTableType*> collectAndSortTypes() {
        std::vector<ResourceTableType*> sortedTypes;
        for (auto& type : mPackage->types) {
            if (type->type == ResourceType::kStyleable && !mOptions.useExtendedChunks) {
                // Styleables aren't real Resource Types, they are represented in the R.java
                // file.
                continue;
            }

            assert(type->id && "type must have an ID set");

            sortedTypes.push_back(type.get());
        }
        std::sort(sortedTypes.begin(), sortedTypes.end(), cmpIds<ResourceTableType>);
        return sortedTypes;
    }

    std::vector<ResourceEntry*> collectAndSortEntries(ResourceTableType* type) {
        // Sort the entries by entry ID.
        std::vector<ResourceEntry*> sortedEntries;
        for (auto& entry : type->entries) {
            assert(entry->id && "entry must have an ID set");
            sortedEntries.push_back(entry.get());
        }
        std::sort(sortedEntries.begin(), sortedEntries.end(), cmpIds<ResourceEntry>);
        return sortedEntries;
    }

    bool flattenTypeSpec(ResourceTableType* type, std::vector<ResourceEntry*>* sortedEntries,
                         BigBuffer* buffer) {
        ChunkWriter typeSpecWriter(buffer);
        ResTable_typeSpec* specHeader = typeSpecWriter.startChunk<ResTable_typeSpec>(
                RES_TABLE_TYPE_SPEC_TYPE);
        specHeader->id = type->id.value();

        if (sortedEntries->empty()) {
            typeSpecWriter.finish();
            return true;
        }

        // We can't just take the size of the vector. There may be holes in the entry ID space.
        // Since the entries are sorted by ID, the last one will be the biggest.
        const size_t numEntries = sortedEntries->back()->id.value() + 1;

        specHeader->entryCount = util::hostToDevice32(numEntries);

        // Reserve space for the masks of each resource in this type. These
        // show for which configuration axis the resource changes.
        uint32_t* configMasks = typeSpecWriter.nextBlock<uint32_t>(numEntries);

        const size_t actualNumEntries = sortedEntries->size();
        for (size_t entryIndex = 0; entryIndex < actualNumEntries; entryIndex++) {
            ResourceEntry* entry = sortedEntries->at(entryIndex);

            // Populate the config masks for this entry.

            if (entry->symbolStatus.state == SymbolState::kPublic) {
                configMasks[entry->id.value()] |=
                        util::hostToDevice32(ResTable_typeSpec::SPEC_PUBLIC);
            }

            const size_t configCount = entry->values.size();
            for (size_t i = 0; i < configCount; i++) {
                const ConfigDescription& config = entry->values[i].config;
                for (size_t j = i + 1; j < configCount; j++) {
                    configMasks[entry->id.value()] |= util::hostToDevice32(
                            config.diff(entry->values[j].config));
                }
            }
        }
        typeSpecWriter.finish();
        return true;
    }

    bool flattenPublic(ResourceTableType* type, std::vector<ResourceEntry*>* sortedEntries,
                       BigBuffer* buffer) {
        ChunkWriter publicWriter(buffer);
        Public_header* publicHeader = publicWriter.startChunk<Public_header>(RES_TABLE_PUBLIC_TYPE);
        publicHeader->typeId = type->id.value();

        for (ResourceEntry* entry : *sortedEntries) {
            if (entry->symbolStatus.state != SymbolState::kUndefined) {
                // Write the public status of this entry.
                Public_entry* publicEntry = publicWriter.nextBlock<Public_entry>();
                publicEntry->entryId = util::hostToDevice32(entry->id.value());
                publicEntry->key.index = util::hostToDevice32(mKeyPool.makeRef(
                        entry->name).getIndex());
                publicEntry->source.path.index = util::hostToDevice32(mSourcePool->makeRef(
                        util::utf8ToUtf16(entry->symbolStatus.source.path)).getIndex());
                if (entry->symbolStatus.source.line) {
                    publicEntry->source.line = util::hostToDevice32(
                            entry->symbolStatus.source.line.value());
                }
                publicEntry->source.comment.index = util::hostToDevice32(mSourcePool->makeRef(
                        entry->symbolStatus.comment).getIndex());

                switch (entry->symbolStatus.state) {
                case SymbolState::kPrivate:
                    publicEntry->state = Public_entry::kPrivate;
                    break;

                case SymbolState::kPublic:
                    publicEntry->state = Public_entry::kPublic;
                    break;

                case SymbolState::kUndefined:
                    publicEntry->state = Public_entry::kUndefined;
                    break;
                }

                // Don't hostToDevice until the last step.
                publicHeader->count += 1;
            }
        }

        publicHeader->count = util::hostToDevice32(publicHeader->count);
        publicWriter.finish();
        return true;
    }

    bool flattenTypes(BigBuffer* buffer) {
        // Sort the types by their IDs. They will be inserted into the StringPool in this order.
        std::vector<ResourceTableType*> sortedTypes = collectAndSortTypes();

        size_t expectedTypeId = 1;
        for (ResourceTableType* type : sortedTypes) {
            // If there is a gap in the type IDs, fill in the StringPool
            // with empty values until we reach the ID we expect.
            while (type->id.value() > expectedTypeId) {
                std::u16string typeName(u"?");
                typeName += expectedTypeId;
                mTypePool.makeRef(typeName);
                expectedTypeId++;
            }
            expectedTypeId++;
            mTypePool.makeRef(toString(type->type));

            std::vector<ResourceEntry*> sortedEntries = collectAndSortEntries(type);

            if (!flattenTypeSpec(type, &sortedEntries, buffer)) {
                return false;
            }

            if (mOptions.useExtendedChunks) {
                if (!flattenPublic(type, &sortedEntries, buffer)) {
                    return false;
                }
            }

            // The binary resource table lists resource entries for each configuration.
            // We store them inverted, where a resource entry lists the values for each
            // configuration available. Here we reverse this to match the binary table.
            std::map<ConfigDescription, std::vector<FlatEntry>> configToEntryListMap;
            for (ResourceEntry* entry : sortedEntries) {
                const uint32_t keyIndex = (uint32_t) mKeyPool.makeRef(entry->name).getIndex();

                // Group values by configuration.
                for (auto& configValue : entry->values) {
                    Value* value = configValue.value.get();

                    const StringPool::Ref sourceRef = mSourcePool->makeRef(
                            util::utf8ToUtf16(value->getSource().path));

                    uint32_t lineNumber = 0;
                    if (value->getSource().line) {
                        lineNumber = value->getSource().line.value();
                    }

                    const StringPool::Ref commentRef = mSourcePool->makeRef(value->getComment());

                    configToEntryListMap[configValue.config]
                            .push_back(FlatEntry{
                                    entry,
                                    value,
                                    keyIndex,
                                    (uint32_t) sourceRef.getIndex(),
                                    lineNumber,
                                    (uint32_t) commentRef.getIndex() });
                }
            }

            // Flatten a configuration value.
            for (auto& entry : configToEntryListMap) {
                if (!flattenConfig(type, entry.first, &entry.second, buffer)) {
                    return false;
                }
            }
        }
        return true;
    }
};

} // namespace

bool TableFlattener::consume(IAaptContext* context, ResourceTable* table) {
    // We must do this before writing the resources, since the string pool IDs may change.
    table->stringPool.sort([](const StringPool::Entry& a, const StringPool::Entry& b) -> bool {
        int diff = a.context.priority - b.context.priority;
        if (diff < 0) return true;
        if (diff > 0) return false;
        diff = a.context.config.compare(b.context.config);
        if (diff < 0) return true;
        if (diff > 0) return false;
        return a.value < b.value;
    });
    table->stringPool.prune();

    // Write the ResTable header.
    ChunkWriter tableWriter(mBuffer);
    ResTable_header* tableHeader = tableWriter.startChunk<ResTable_header>(RES_TABLE_TYPE);
    tableHeader->packageCount = util::hostToDevice32(table->packages.size());

    // Flatten the values string pool.
    StringPool::flattenUtf8(tableWriter.getBuffer(), table->stringPool);

    // If we have a reference to a symbol that doesn't exist, we don't know its resource ID.
    // We encode the name of the symbol along with the offset of where to include the resource ID
    // once it is found.
    StringPool symbolPool;
    std::vector<SymbolWriter::Entry> symbolOffsets;

    // String pool holding the source paths of each value.
    StringPool sourcePool;

    BigBuffer packageBuffer(1024);

    // Flatten each package.
    for (auto& package : table->packages) {
        const size_t beforePackageSize = packageBuffer.size();

        // All packages will share a single global symbol pool.
        SymbolWriter packageSymbolWriter(&symbolPool);

        PackageFlattener flattener(context->getDiagnostics(), mOptions, package.get(),
                                   &packageSymbolWriter, &sourcePool);
        if (!flattener.flattenPackage(&packageBuffer)) {
            return false;
        }

        // The symbols are offset only from their own Package start. Offset them from the
        // start of the packageBuffer.
        packageSymbolWriter.shiftAllOffsets(beforePackageSize);

        // Extract all the symbols to offset
        symbolOffsets.insert(symbolOffsets.end(),
                             std::make_move_iterator(packageSymbolWriter.symbols.begin()),
                             std::make_move_iterator(packageSymbolWriter.symbols.end()));
    }

    SymbolTable_entry* symbolEntryData = nullptr;
    if (mOptions.useExtendedChunks) {
        if (!symbolOffsets.empty()) {
            // Sort the offsets so we can scan them linearly.
            std::sort(symbolOffsets.begin(), symbolOffsets.end(),
                      [](const SymbolWriter::Entry& a, const SymbolWriter::Entry& b) -> bool {
                          return a.offset < b.offset;
                      });

            // Write the Symbol header.
            ChunkWriter symbolWriter(tableWriter.getBuffer());
            SymbolTable_header* symbolHeader = symbolWriter.startChunk<SymbolTable_header>(
                    RES_TABLE_SYMBOL_TABLE_TYPE);
            symbolHeader->count = util::hostToDevice32(symbolOffsets.size());

            symbolEntryData = symbolWriter.nextBlock<SymbolTable_entry>(symbolOffsets.size());
            StringPool::flattenUtf8(symbolWriter.getBuffer(), symbolPool);
            symbolWriter.finish();
        }

        if (sourcePool.size() > 0) {
            // Write out source pool.
            ChunkWriter srcWriter(tableWriter.getBuffer());
            srcWriter.startChunk<ResChunk_header>(RES_TABLE_SOURCE_POOL_TYPE);
            StringPool::flattenUtf8(srcWriter.getBuffer(), sourcePool);
            srcWriter.finish();
        }
    }

    const size_t beforePackagesSize = tableWriter.size();

    // Finally merge all the packages into the main buffer.
    tableWriter.getBuffer()->appendBuffer(std::move(packageBuffer));

    // Update the offsets to their final values.
    if (symbolEntryData) {
        for (SymbolWriter::Entry& entry : symbolOffsets) {
            symbolEntryData->name.index = util::hostToDevice32(entry.name.getIndex());

            // The symbols were all calculated with the packageBuffer offset. We need to
            // add the beginning of the output buffer.
            symbolEntryData->offset = util::hostToDevice32(entry.offset + beforePackagesSize);
            symbolEntryData++;
        }
    }

    tableWriter.finish();
    return true;
}

} // namespace aapt