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Avoid using data descriptors in ZIP files when possible.

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These add 16 bytes per ZIP entry, and are usually avoidable.  APKs contain thousands of
deflated entries, so this overhead adds up to tens of kilobytes.

Bug: 135470635
Change-Id: Ib928aa41dd55cacc41f7394c218c4340d3bbd570
This commit is contained in:
Donald Chai 2019-07-02 17:25:03 -07:00
parent b3fc1b7441
commit e170d7fe85
4 changed files with 39 additions and 2 deletions
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4
libziparchive/Android.bp
View file

@ -76,6 +76,10 @@ cc_defaults {
"liblog",
],
// for FRIEND_TEST
static_libs: ["libgtest_prod"],
export_static_lib_headers: ["libgtest_prod"],
export_include_dirs: ["include"],
}

4
libziparchive/include/ziparchive/zip_writer.h
View file

@ -19,6 +19,7 @@
#include <cstdio>
#include <ctime>
#include <gtest/gtest_prod.h>
#include <memory>
#include <string>
#include <string_view>
@ -165,6 +166,7 @@ class ZipWriter {
int32_t StoreBytes(FileEntry* file, const void* data, uint32_t len);
int32_t CompressBytes(FileEntry* file, const void* data, uint32_t len);
int32_t FlushCompressedBytes(FileEntry* file);
bool ShouldUseDataDescriptor() const;
enum class State {
kWritingZip,
@ -182,4 +184,6 @@ class ZipWriter {
std::unique_ptr<z_stream, void (*)(z_stream*)> z_stream_;
std::vector<uint8_t> buffer_;
FRIEND_TEST(zipwriter, WriteToUnseekableFile);
};

9
libziparchive/zip_writer.cc
View file

@ -455,6 +455,11 @@ int32_t ZipWriter::FlushCompressedBytes(FileEntry* file) {
return kNoError;
}
bool ZipWriter::ShouldUseDataDescriptor() const {
// Only use a trailing "data descriptor" if the output isn't seekable.
return !seekable_;
}
int32_t ZipWriter::FinishEntry() {
if (state_ != State::kWritingEntry) {
return kInvalidState;
@ -467,7 +472,7 @@ int32_t ZipWriter::FinishEntry() {
}
}
if ((current_file_entry_.compression_method & kCompressDeflated) || !seekable_) {
if (ShouldUseDataDescriptor()) {
// Some versions of ZIP don't allow STORED data to have a trailing DataDescriptor.
// If this file is not seekable, or if the data is compressed, write a DataDescriptor.
const uint32_t sig = DataDescriptor::kOptSignature;
@ -515,7 +520,7 @@ int32_t ZipWriter::Finish() {
for (FileEntry& file : files_) {
CentralDirectoryRecord cdr = {};
cdr.record_signature = CentralDirectoryRecord::kSignature;
if ((file.compression_method & kCompressDeflated) || !seekable_) {
if (ShouldUseDataDescriptor()) {
cdr.gpb_flags |= kGPBDDFlagMask;
}
cdr.compression_method = file.compression_method;

24
libziparchive/zip_writer_test.cc
View file

@ -243,6 +243,7 @@ TEST_F(zipwriter, WriteCompressedZipWithOneFile) {
ZipEntry data;
ASSERT_EQ(0, FindEntry(handle, "file.txt", &data));
EXPECT_EQ(kCompressDeflated, data.method);
EXPECT_EQ(0u, data.has_data_descriptor);
ASSERT_EQ(4u, data.uncompressed_length);
ASSERT_TRUE(AssertFileEntryContentsEq("helo", handle, &data));
@ -351,6 +352,29 @@ TEST_F(zipwriter, BackupRemovesTheLastFile) {
CloseArchive(handle);
}
TEST_F(zipwriter, WriteToUnseekableFile) {
const char* expected = "hello";
ZipWriter writer(file_);
writer.seekable_ = false;
ASSERT_EQ(0, writer.StartEntry("file.txt", 0));
ASSERT_EQ(0, writer.WriteBytes(expected, strlen(expected)));
ASSERT_EQ(0, writer.FinishEntry());
ASSERT_EQ(0, writer.Finish());
ASSERT_GE(0, lseek(fd_, 0, SEEK_SET));
ZipArchiveHandle handle;
ASSERT_EQ(0, OpenArchiveFd(fd_, "temp", &handle, false));
ZipEntry data;
ASSERT_EQ(0, FindEntry(handle, "file.txt", &data));
EXPECT_EQ(kCompressStored, data.method);
EXPECT_EQ(1u, data.has_data_descriptor);
EXPECT_EQ(strlen(expected), data.compressed_length);
ASSERT_EQ(strlen(expected), data.uncompressed_length);
ASSERT_TRUE(AssertFileEntryContentsEq(expected, handle, &data));
CloseArchive(handle);
}
TEST_F(zipwriter, TruncateFileAfterBackup) {
ZipWriter writer(file_);