Android 构建工具--AAPT2源码解析（一）

一、什么是AAPT2

二、AAPT2如何工作

aapt2 compile path-to-input-files [options] -o output-directory/

aapt2 compile path-to-input-files1 path-to-input-files2 [options] -o output-directory/

aapt2 compile --dir .../res [options] -o output-directory/resource.ap_

// Top level message representing a resource table.message ResourceTable {    // 字符串池    StringPool source_pool = 1;    // 用于生成资源id    repeated Package package = 2;    // 资源叠加层相关    repeated Overlayable overlayable = 3;    // 工具版本    repeated ToolFingerprint tool_fingerprint = 4;}

message StringPool {  bytes data = 1;}

// 资源id的包id部分，在 [0x00, 0xff] 范围内message PackageId {  uint32 id = 1;}// 资源id的命名规则message Package {  // [0x02, 0x7f) 简单的说，由系统使用  // 0x7f 应用使用  // (0x7f, 0xff] 预留Id  PackageId package_id = 1;  // 包名  string package_name = 2;  // 资源类型，对应string, layout, xml, dimen, attr等，其对应的资源id区间为[0x01, 0xff]  repeated Type type = 3;}

int main(int argc, char** argv) {#ifdef _WIN32    ......    //参数格式转换    argv = utf8_argv.get();#endif    //具体的实现MainImpl中    return MainImpl(argc, argv);}

int MainImpl(int argc, char** argv) {    if (argc < 1) {        return -1;    }    // 从下标1开始的输入，保存在args中    std::vector<StringPiece> args;    for (int i = 1; i < argc; i++) {        args.push_back(argv[i]);    }    //省略部分代码，这部分代码用于打印信息和错误处理    //创建一个MainCommand    aapt::MainCommand main_command(&printer, &diagnostics);    // aapt2的守护进程模式，    main_command.AddOptionalSubcommand( aapt::util::make_unique<aapt::DaemonCommand>(&fout, &diagnostics));    // 调用Execute方法执行命令    return main_command.Execute(args, &std::cerr);}

explicit MainCommand(text::Printer* printer, IDiagnostics* diagnostics) : Command("aapt2"), diagnostics_(diagnostics) {    //对应Compile 命令    AddOptionalSubcommand(util::make_unique<CompileCommand>(diagnostics));    //对应link 命令    AddOptionalSubcommand(util::make_unique<LinkCommand>(diagnostics));    AddOptionalSubcommand(util::make_unique<DumpCommand>(printer, diagnostics));    AddOptionalSubcommand(util::make_unique<DiffCommand>());    AddOptionalSubcommand(util::make_unique<OptimizeCommand>());    AddOptionalSubcommand(util::make_unique<ConvertCommand>());    AddOptionalSubcommand(util::make_unique<VersionCommand>());}

void Command::AddOptionalSubcommand(std::unique_ptr<Command>&& subcommand, bool experimental) {    subcommand->full_subcommand_name_ = StringPrintf("%s %s", name_.data(), subcommand->name_.data());    if (experimental) {        experimental_subcommands_.push_back(std::move(subcommand));    } else {    subcommands_.push_back(std::move(subcommand));    }}

int Command::Execute(const std::vector<StringPiece>& args, std::ostream* out_error) {    TRACE_NAME_ARGS("Command::Execute", args);    std::vector<std::string> file_args;    for (size_t i = ; i < args.size(); i++) {        const StringPiece& arg = args[i];        // 参数不是 '-'        if (*(arg.data()) != '-') {        //是个参数        if (i == ) {            for (auto& subcommand : subcommands_) {                //判断是否是子命令                if (arg == subcommand->name_ || (!subcommand->short_name_.empty() && arg == subcommand->short_name_)) {                //执行子命令的Execute 方法，传入参数向后移动一位                return subcommand->Execute( std::vector<StringPiece>(args.begin() + 1, args.end()), out_error);            }        }        //省略部分代码    //调用Action方法，在执行二级命令时，file_args保存的是位移后的参数    return Action(file_args);}

SetDescription("Compiles resources to be linked into an apk.");AddRequiredFlag("-o", "Output path", &options_.output_path, Command::kPath);AddOptionalFlag("--dir", "Directory to scan for resources", &options_.res_dir, Command::kPath);AddOptionalFlag("--zip", "Zip file containing the res directory to scan for resources", &options_.res_zip, Command::kPath);AddOptionalFlag("--output-text-symbols", "Generates a text file containing the resource symbols in the\n" "specified file", &options_.generate_text_symbols_path, Command::kPath);AddOptionalSwitch("--pseudo-localize", "Generate resources for pseudo-locales " "(en-XA and ar-XB)", &options_.pseudolocalize);AddOptionalSwitch("--no-crunch", "Disables PNG processing", &options_.no_png_crunch);AddOptionalSwitch("--legacy", "Treat errors that used to be valid in AAPT as warnings", &options_.legacy_mode);AddOptionalSwitch("--preserve-visibility-of-styleables", "If specified, apply the same visibility rules for\n" "styleables as are used for all other resources.\n" "Otherwise, all stylesables will be made public.", &options_.preserve_visibility_of_styleables);AddOptionalFlag("--visibility", "Sets the visibility of the compiled resources to the specified\n" "level. Accepted levels: public, private, default", &visibility_);AddOptionalSwitch("-v", "Enables verbose logging", &options_.verbose);AddOptionalFlag("--trace-folder", "Generate systrace json trace fragment to specified folder.", &trace_folder_);

int CompileCommand::Action(const std::vector<std::string>& args) {    //省略部分代码....    std::unique_ptr<io::IFileCollection> file_collection;    //加载输入资源，简化逻辑，下面会省略掉校验的代码    if (options_.res_dir && options_.res_zip) {        context.GetDiagnostics()->Error(DiagMessage() << "only one of --dir and --zip can be specified");        return 1;    } else if (options_.res_dir) {        //加载目录下的资源文件...        file_collection = io::FileCollection::Create(options_.res_dir.value(), &err);        //...    }else if (options_.res_zip) {        //加载压缩包格式的资源文件...        file_collection = io::ZipFileCollection::Create(options_.res_zip.value(), &err);        //...    } else {        //也是FileCollection，先定义collection，通过循环依次添加输入文件，再拷贝到file_collection        file_collection = std::move(collection);    }    std::unique_ptr<IArchiveWriter> archive_writer;    //产物输出文件类型    file::FileType output_file_type = file::GetFileType(options_.output_path);    if (output_file_type == file::FileType::kDirectory) {        //输出到文件目录        archive_writer = CreateDirectoryArchiveWriter(context.GetDiagnostics(), options_.output_path);    } else {        //输出到压缩包        archive_writer = CreateZipFileArchiveWriter(context.GetDiagnostics(), options_.output_path);    }    if (!archive_writer) {        return 1;    }    return Compile(&context, file_collection.get(), archive_writer.get(), options_);}

int Compile(IAaptContext* context, io::IFileCollection* inputs, IArchiveWriter* output_writer, CompileOptions& options) {    TRACE_CALL();    bool error = false;    // 编译输入的资源文件    auto file_iterator  = inputs->Iterator();    while (file_iterator->HasNext()) {        // 省略部分代码（文件校验相关...）        std::string err_str;        ResourcePathData path_data;        // 获取path全名，用于后续文件类型判断        if (auto maybe_path_data = ExtractResourcePathData(path, inputs->GetDirSeparator(), &err_str)) {            path_data = maybe_path_data.value();        } else {            context->GetDiagnostics()->Error(DiagMessage(file->GetSource()) << err_str);            error = true;            continue;        }         // 根据文件类型，选择编译方法，这里的 CompileFile 是函数指针，指向一个编译方法。        // 使用使用设置为CompileFile方法        auto compile_func = &CompileFile;        // 如果是values目录下的xml资源，使用 CompileTable 方法编译，并修改扩展名为arsc        if (path_data.resource_dir == "values" && path_data.extension == "xml") {            compile_func = &CompileTable;            // We use a different extension (not necessary anymore, but avoids altering the existing // build system logic).            path_data.extension = "arsc";        } else if (const ResourceType* type = ParseResourceType(path_data.resource_dir)) {            // 解析资源类型，如果kRaw类型，执行默认的编译方法，否则执行如下代码。            if (*type != ResourceType::kRaw) {                //xml路径或者文件扩展为.xml                if (*type == ResourceType::kXml || path_data.extension == "xml") {                    // xml类，使用CompileXml方法编译                    compile_func = &CompileXml;                } else if ((!options.no_png_crunch && path_data.extension == "png") || path_data.extension == "9.png") { //如果后缀名是.png并且开启png优化或者是点9图类型                    // png类，使用CompilePng方法编译                    compile_func = &CompilePng;                }            }        } else {            // 不合法的类型，输出错误信息，继续循环            context->GetDiagnostics()->Error(DiagMessage() << "invalid file path '" << path_data.source << "'");            error = true;            continue;        }         // 校验文件名中是否有.        if (compile_func != &CompileFile && !options.legacy_mode && std::count(path_data.name.begin(), path_data.name.end(), '.') != ) {            error = true;            context->GetDiagnostics()->Error(DiagMessage(file->GetSource()) << "file name cannot contain '.' other than for" << " specifying the extension");            continue;        }        // 生成产物文件名，这个方法会生成完成的flat文件名，例如上文demo中的 drawable-hdpi_ic_launcher.png.flat        const std::string out_path = BuildIntermediateContainerFilename(path_data);        // 执行编译方法        if (!compile_func(context, options, path_data, file, output_writer, out_path)) {            context->GetDiagnostics()->Error(DiagMessage(file->GetSource()) << "file failed to compile"); error = true;        }    }    return error ? 1 : ;}

static bool CompileFile(IAaptContext* context, const CompileOptions& options, const ResourcePathData& path_data, io::IFile* file, IArchiveWriter* writer, const std::string& output_path) {    TRACE_CALL();    if (context->IsVerbose()) {        context->GetDiagnostics()->Note(DiagMessage(path_data.source) << "compiling file");    }    // 定义ResourceFile 对象，保存config，source等信息    ResourceFile res_file;    res_file.name = ResourceName({}, *ParseResourceType(path_data.resource_dir), path_data.name);    res_file.config = path_data.config;    res_file.source = path_data.source;    res_file.type = ResourceFile::Type::kUnknown; //这类型下可能有xml，png或者其他的什么，统一设置类型为unknow。    // 原始文件数据    auto data = file->OpenAsData();    if (!data) {        context->GetDiagnostics()->Error(DiagMessage(path_data.source) << "failed to open file ");        return false;    }    return WriteHeaderAndDataToWriter(output_path, res_file, data.get(), writer, context->GetDiagnostics());}

static bool WriteHeaderAndDataToWriter(const StringPiece& output_path, const ResourceFile& file, io::KnownSizeInputStream* in, IArchiveWriter* writer, IDiagnostics* diag) {    // 打开文件    if (!writer->StartEntry(output_path, )) {        diag->Error(DiagMessage(output_path) << "failed to open file");        return false;    }    // Make sure CopyingOutputStreamAdaptor is deleted before we call writer->FinishEntry().    {        // 对write做一层包装，用来写protobuf数据        CopyingOutputStreamAdaptor copying_adaptor(writer);        ContainerWriter container_writer(©ing_adaptor, 1u);        //把file按照protobuf格式序列化，序列化后的文件是 pb_compiled_file，这里的file文件是ResourceFile文件，包含了原始文件的路径，配置等信息        pb::internal::CompiledFile pb_compiled_file;        SerializeCompiledFileToPb(file, &pb_compiled_file);        // 再把pb_compiled_file 和 in（原始文件） 写入到产物文件中        if (!container_writer.AddResFileEntry(pb_compiled_file, in)) {            diag->Error(DiagMessage(output_path) << "failed to write entry data");            return false;        }    }    // 退出写状态    if (!writer->FinishEntry()) {        diag->Error(DiagMessage(output_path) << "failed to finish writing data");        return false;    }    return true;}

bool StartEntry(const StringPiece& path, uint32_t flags) override {    if (file_) {        return false;    }    std::string full_path = dir_;    file::AppendPath(&full_path, path);    file::mkdirs(file::GetStem(full_path).to_string());    //打开文件    file_ = {::android::base::utf8::fopen(full_path.c_str(), "wb"), fclose};    if (!file_) {        error_ = SystemErrorCodeToString(errno);        return false;    }    return true;}

bool FinishEntry() override {    if (!file_) {        return false;    }    file_.reset(nullptr);    return true;}

// 在类的构造方法中，写入文件头的信息ContainerWriter::ContainerWriter(ZeroCopyOutputStream* out, size_t entry_count)  : out_(out), total_entry_count_(entry_count), current_entry_count_(0u) {    CodedOutputStream coded_out(out_);    // 魔法数据，kContainerFormatMagic = 0x54504141u    coded_out.WriteLittleEndian32(kContainerFormatMagic);      // 版本号，kContainerFormatVersion = 1u    coded_out.WriteLittleEndian32(kContainerFormatVersion);    // 容器中包含的条目数 total_entry_count_是在ContainerReader构造时赋值，值由外部传入    coded_out.WriteLittleEndian32(static_cast<uint32_t>(total_entry_count_));    if (coded_out.HadError()) {        error_ = "failed writing container format header";    }}

// file:protobuf格式的信息文件，in：原始文件bool ContainerWriter::AddResFileEntry(const pb::internal::CompiledFile& file, io::KnownSizeInputStream* in) {    // 判断条目数量，大于设定数量就直接报错    if (current_entry_count_ >= total_entry_count_) {        error_ = "too many entries being serialized";        return false;    }    // 条目++    current_entry_count_++;    constexpr const static int kResFileEntryHeaderSize = 12; 、    //输出流    CodedOutputStream coded_out(out_);    //写入资源类型    coded_out.WriteLittleEndian32(kResFile);     const ::google::protobuf::uint32    // ResourceFile 文件长度 ，该部分包含了当前文件的路径，类型，配置等信息    header_size = file.ByteSize();    const int header_padding = CalculatePaddingForAlignment(header_size);    // 原始文件长度    const ::google::protobuf::uint64 data_size = in->TotalSize();    const int data_padding = CalculatePaddingForAlignment(data_size);    // 写入数据长度，计算公式：kResFileEntryHeaderSize（固定12） + ResourceFile文件长度 + header_padding + 原始文件长度 + data_padding    coded_out.WriteLittleEndian64(kResFileEntryHeaderSize + header_size + header_padding + data_size + data_padding);     // 写入文件头长度    coded_out.WriteLittleEndian32(header_size);    // 写入数据长度    coded_out.WriteLittleEndian64(data_size);    // 写入“头信息”    file.SerializeToCodedStream(&coded_out);    // 对齐    WritePadding(header_padding, &coded_out);    // 使用Copy之前需要调用Trim（至于为什么，其实也不太清楚，好在我们学习AAPT2，了解底层API的功能即可。如果有读者知道，希望赐教）    coded_out.Trim();    // 异常判断    if (coded_out.HadError()) {        error_ = "failed writing to output"; return false;    } if (!io::Copy(out_, in)) {  //资源数据（源码中也叫payload，可能是png，xml，或者XmlNode）        if (in->HadError()) {            std::ostringstream error;            error << "failed reading from input: " << in->GetError();            error_ = error.str();        } else {            error_ = "failed writing to output";        }        return false;    }    // 对其    WritePadding(data_padding, &coded_out);    if (coded_out.HadError()) {        error_ = "failed writing to output";        return false;    }    return true;}

static bool CompilePng(IAaptContext* context, const CompileOptions& options, const ResourcePathData& path_data, io::IFile* file, IArchiveWriter* writer, const std::string& output_path) {    //..省略部分校验代码    BigBuffer buffer(4096);   // 基本一样的代码，区别是type不一样    ResourceFile res_file;    res_file.name = ResourceName({}, *ParseResourceType(path_data.resource_dir), path_data.name);    res_file.config = path_data.config;    res_file.source = path_data.source;    res_file.type = ResourceFile::Type::kPng;     {        // 读取资源内容到data中        auto data = file->OpenAsData();        // 读取结果校验        if (!data) {            context->GetDiagnostics()->Error(DiagMessage(path_data.source) << "failed to open file ");            return false;        }        // 用来保存输出流        BigBuffer crunched_png_buffer(4096);        io::BigBufferOutputStream crunched_png_buffer_out(&crunched_png_buffer);         // 对PNG图片做优化        const StringPiece content(reinterpret_cast<const char*>(Liberation Mono', Menlo, Courier, monospace;">        PngChunkFilter png_chunk_filter(content);        std::unique_ptr<Image> image = ReadPng(context, path_data.source, &png_chunk_filter);        if (!image) {            return false;        }                 // 处理.9图        std::unique_ptr<NinePatch> nine_patch;        if (path_data.extension == "9.png") {            std::string err;            nine_patch = NinePatch::Create(image->rows.get(), image->width, image->height, &err);            if (!nine_patch) {                context->GetDiagnostics()->Error(DiagMessage() << err); return false;            }            // 移除1像素的边框            image->width -= 2;            image->height -= 2;            memmove(image->rows.get(), image->rows.get() + 1, image->height * sizeof(uint8_t**));            for (int32_t h = ; h < image->height; h++) {                memmove(image->rows[h], image->rows[h] + 4, image->width * 4);            } if (context->IsVerbose()) {                context->GetDiagnostics()->Note(DiagMessage(path_data.source) << "9-patch: " << *nine_patch);            }        }         // 保存处理后的png到 &crunched_png_buffer_out        if (!WritePng(context, image.get(), nine_patch.get(), &crunched_png_buffer_out, {})) {            return false;        }         // ...省略部分图片校验代码,这部分代码会比较优化后的图片和原图片的大小，如果优化后比原图片大，则使用原图片。（PNG优化后是有可能比原图片还大的）    }    io::BigBufferInputStream buffer_in(&buffer);    // 和 CompileFile 调用相同的方法，写入flat文件，资源文件内容是    return WriteHeaderAndDataToWriter(output_path, res_file, &buffer_in, writer, context->GetDiagnostics());}

static bool CompileXml(IAaptContext* context, const CompileOptions& options,                       const ResourcePathData& path_data, io::IFile* file, IArchiveWriter* writer,                       const std::string& output_path) {  // ...省略校验代码  std::unique_ptr<xml::XmlResource> xmlres;  {    // 打开xml文件    auto fin = file->OpenInputStream();    // ...省略校验代码    // 解析XML    xmlres = xml::Inflate(fin.get(), context->GetDiagnostics(), path_data.source);    if (!xmlres) {      return false;    }  }  //  xmlres->file.name = ResourceName({}, *ParseResourceType(path_data.resource_dir), path_data.name);  xmlres->file.config = path_data.config;  xmlres->file.source = path_data.source;  xmlres->file.type = ResourceFile::Type::kProtoXml;   // 判断id类型的资源是否有id合法（是否有id异常，如果有提示“has an invalid entry name”）  XmlIdCollector collector;  if (!collector.Consume(context, xmlres.get())) {    return false;  }   // 处理aapt:attr内嵌资源  InlineXmlFormatParser inline_xml_format_parser;  if (!inline_xml_format_parser.Consume(context, xmlres.get())) {    return false;  }   // 打开输出文件  if (!writer->StartEntry(output_path, )) {    context->GetDiagnostics()->Error(DiagMessage(output_path) << "failed to open file");    return false;  }   std::vector<std::unique_ptr<xml::XmlResource>>& inline_documents =      inline_xml_format_parser.GetExtractedInlineXmlDocuments();   {    // 和CompileFile 类似，创建可处理protobuf格式的writer，用于protobuf格式序列化    CopyingOutputStreamAdaptor copying_adaptor(writer);    ContainerWriter container_writer(©ing_adaptor, 1u + inline_documents.size());     if (!FlattenXmlToOutStream(output_path, *xmlres, &container_writer,                               context->GetDiagnostics())) {      return false;    }    // 处理内嵌的元素（aapt:attr）    for (const std::unique_ptr<xml::XmlResource>& inline_xml_doc : inline_documents) {      if (!FlattenXmlToOutStream(output_path, *inline_xml_doc, &container_writer,                                 context->GetDiagnostics())) {        return false;      }    }  }  // 释放内存  if (!writer->FinishEntry()) {    context->GetDiagnostics()->Error(DiagMessage(output_path) << "failed to finish writing data");    return false;  }  // 编译选项部分，省略  return true;}

static bool FlattenXmlToOutStream(const StringPiece& output_path, const xml::XmlResource& xmlres,                                  ContainerWriter* container_writer, IDiagnostics* diag) {  // 序列化CompiledFile部分  pb::internal::CompiledFile pb_compiled_file;  SerializeCompiledFileToPb(xmlres.file, &pb_compiled_file);   // 序列化XmlNode部分  pb::XmlNode pb_xml_node;  SerializeXmlToPb(*xmlres.root, &pb_xml_node);   // 专程string格式的流，这里可以再找源码看看  std::string serialized_xml = pb_xml_node.SerializeAsString();  io::StringInputStream serialized_in(serialized_xml);  // 保存到资源项中  if (!container_writer->AddResFileEntry(pb_compiled_file, &serialized_in)) {    diag->Error(DiagMessage(output_path) << "failed to write entry data");    return false;  }  return true;}

static bool CompileTable(IAaptContext* context, const CompileOptions& options,                         const ResourcePathData& path_data, io::IFile* file, IArchiveWriter* writer,                         const std::string& output_path) {  // Filenames starting with "donottranslate" are not localizable  bool translatable_file = path_data.name.find("donottranslate") != ;  ResourceTable table;  {    // 读取文件    auto fin = file->OpenInputStream();    if (fin->HadError()) {      context->GetDiagnostics()->Error(DiagMessage(path_data.source)          << "failed to open file: " << fin->GetError());      return false;    }     // 创建XmlPullParser，设置很多handler，用于xml解析    xml::XmlPullParser xml_parser(fin.get());         // 设置解析选项    ResourceParserOptions parser_options;    parser_options.error_on_positional_arguments = !options.legacy_mode;    parser_options.preserve_visibility_of_styleables = options.preserve_visibility_of_styleables;    parser_options.translatable = translatable_file;    parser_options.visibility = options.visibility;         // 创建ResourceParser，并把结果保存到ResourceTable中    ResourceParser res_parser(context->GetDiagnostics(), &table, path_data.source, path_data.config,        parser_options);    // 执行解析    if (!res_parser.Parse(&xml_parser)) {      return false;    }  }  // 省略部分校验代码   // 打开输出文件  if (!writer->StartEntry(output_path, )) {    context->GetDiagnostics()->Error(DiagMessage(output_path) << "failed to open");    return false;  }   {    // 和前面一样，创建ContainerWriter 用于写文件    CopyingOutputStreamAdaptor copying_adaptor(writer);    ContainerWriter container_writer(©ing_adaptor, 1u);     pb::ResourceTable pb_table;    // 把ResourceTable序列化为pb::ResourceTable    SerializeTableToPb(table, &pb_table, context->GetDiagnostics());    // 写入数据项pb::ResourceTable    if (!container_writer.AddResTableEntry(pb_table)) {      context->GetDiagnostics()->Error(DiagMessage(output_path) << "failed to write");      return false;    }  }   if (!writer->FinishEntry()) {    context->GetDiagnostics()->Error(DiagMessage(output_path) << "failed to finish entry");    return false;  }  // ...省略部分代码...  }   return true;}

三、问题和总结