The .ZIP File Format Specification is found here: https://pkwaredownloads.blob.core.windows.net/pem/APPNOTE.txt
Note that this file uses the abbreviation "cd" for "central directory"
//! The .ZIP File Format Specification is found here:
//! https://pkwaredownloads.blob.core.windows.net/pem/APPNOTE.txt
//!
//! Note that this file uses the abbreviation "cd" for "central directory"
const builtin = @import("builtin");
const is_le = builtin.target.cpu.arch.endian() == .little;
const std = @import("std");
const Io = std.Io;
const File = std.Io.File;
const Writer = std.Io.Writer;
const Reader = std.Io.Reader;
const flate = std.compress.flate;
pub const CompressionMethod = enum(u16) {
store = 0,
deflate = 8,
_,
};
pub const central_file_header_sig = [4]u8{ 'P', 'K', 1, 2 };
pub const local_file_header_sig = [4]u8{ 'P', 'K', 3, 4 };
pub const end_record_sig = [4]u8{ 'P', 'K', 5, 6 };
pub const end_record64_sig = [4]u8{ 'P', 'K', 6, 6 };
pub const end_locator64_sig = [4]u8{ 'P', 'K', 6, 7 };
pub const ExtraHeader = enum(u16) {
zip64_info = 0x1,
_,
};
const GeneralPurposeFlags = packed struct(u16) {
encrypted: bool,
_: u15,
};
pub const LocalFileHeader = extern struct {
signature: [4]u8 align(1),
version_needed_to_extract: u16 align(1),
flags: GeneralPurposeFlags align(1),
compression_method: CompressionMethod align(1),
last_modification_time: u16 align(1),
last_modification_date: u16 align(1),
crc32: u32 align(1),
compressed_size: u32 align(1),
uncompressed_size: u32 align(1),
filename_len: u16 align(1),
extra_len: u16 align(1),
};
pub const CentralDirectoryFileHeader = extern struct {
signature: [4]u8 align(1),
version_made_by: u16 align(1),
version_needed_to_extract: u16 align(1),
flags: GeneralPurposeFlags align(1),
compression_method: CompressionMethod align(1),
last_modification_time: u16 align(1),
last_modification_date: u16 align(1),
crc32: u32 align(1),
compressed_size: u32 align(1),
uncompressed_size: u32 align(1),
filename_len: u16 align(1),
extra_len: u16 align(1),
comment_len: u16 align(1),
disk_number: u16 align(1),
internal_file_attributes: u16 align(1),
external_file_attributes: u32 align(1),
local_file_header_offset: u32 align(1),
};
pub const EndRecord64 = extern struct {
signature: [4]u8 align(1),
end_record_size: u64 align(1),
version_made_by: u16 align(1),
version_needed_to_extract: u16 align(1),
disk_number: u32 align(1),
central_directory_disk_number: u32 align(1),
record_count_disk: u64 align(1),
record_count_total: u64 align(1),
central_directory_size: u64 align(1),
central_directory_offset: u64 align(1),
};
pub const EndLocator64 = extern struct {
signature: [4]u8 align(1),
zip64_disk_count: u32 align(1),
record_file_offset: u64 align(1),
total_disk_count: u32 align(1),
};
pub const EndRecord = extern struct {
signature: [4]u8 align(1),
disk_number: u16 align(1),
central_directory_disk_number: u16 align(1),
record_count_disk: u16 align(1),
record_count_total: u16 align(1),
central_directory_size: u32 align(1),
central_directory_offset: u32 align(1),
comment_len: u16 align(1),
pub fn need_zip64(self: EndRecord) bool {
return isMaxInt(self.record_count_disk) or
isMaxInt(self.record_count_total) or
isMaxInt(self.central_directory_size) or
isMaxInt(self.central_directory_offset);
}
pub const FindBufferError = error{ ZipNoEndRecord, ZipTruncated };
/// TODO audit this logic
pub fn findBuffer(buffer: []const u8) FindBufferError!EndRecord {
const pos = std.mem.lastIndexOf(u8, buffer, &end_record_sig) orelse return error.ZipNoEndRecord;
if (pos + @sizeOf(EndRecord) > buffer.len) return error.EndOfStream;
const record_ptr: *EndRecord = @ptrCast(buffer[pos..][0..@sizeOf(EndRecord)]);
var record = record_ptr.*;
if (!is_le) std.mem.byteSwapAllFields(EndRecord, &record);
return record;
}
pub const FindFileError = File.Reader.SizeError || File.SeekError || File.Reader.Error || error{
ZipNoEndRecord,
EndOfStream,
ReadFailed,
};
pub fn findFile(fr: *File.Reader) FindFileError!EndRecord {
const end_pos = try fr.getSize();
var buf: [@sizeOf(EndRecord) + std.math.maxInt(u16)]u8 = undefined;
const record_len_max = @min(end_pos, buf.len);
var loaded_len: u32 = 0;
var comment_len: u16 = 0;
while (true) {
const record_len: u32 = @as(u32, comment_len) + @sizeOf(EndRecord);
if (record_len > record_len_max)
return error.ZipNoEndRecord;
if (record_len > loaded_len) {
const new_loaded_len = @min(loaded_len + 300, record_len_max);
const read_len = new_loaded_len - loaded_len;
try fr.seekTo(end_pos - @as(u64, new_loaded_len));
const read_buf: []u8 = buf[buf.len - new_loaded_len ..][0..read_len];
fr.interface.readSliceAll(read_buf) catch |err| switch (err) {
error.ReadFailed => return fr.err.?,
error.EndOfStream => |e| return e,
};
loaded_len = new_loaded_len;
}
const record_bytes = buf[buf.len - record_len ..][0..@sizeOf(EndRecord)];
if (std.mem.eql(u8, record_bytes[0..4], &end_record_sig) and
std.mem.readInt(u16, record_bytes[20..22], .little) == comment_len)
{
const record: *align(1) EndRecord = @ptrCast(record_bytes.ptr);
if (!is_le) std.mem.byteSwapAllFields(EndRecord, record);
return record.*;
}
if (comment_len == std.math.maxInt(u16))
return error.ZipNoEndRecord;
comment_len += 1;
}
}
};
fn isBadFilename(filename: []const u8) bool {
if (filename.len == 0 or filename[0] == '/')
return true;
var it = std.mem.splitScalar(u8, filename, '/');
while (it.next()) |part| {
if (std.mem.eql(u8, part, ".."))
return true;
}
return false;
}
fn isMaxInt(uint: anytype) bool {
return uint == std.math.maxInt(@TypeOf(uint));
}
const FileExtents = struct {
uncompressed_size: u64,
compressed_size: u64,
local_file_header_offset: u64,
};
fn readZip64FileExtents(comptime T: type, header: T, extents: *FileExtents, data: []u8) !void {
var data_offset: usize = 0;
if (isMaxInt(header.uncompressed_size)) {
if (data_offset + 8 > data.len)
return error.ZipBadCd64Size;
extents.uncompressed_size = std.mem.readInt(u64, data[data_offset..][0..8], .little);
data_offset += 8;
}
if (isMaxInt(header.compressed_size)) {
if (data_offset + 8 > data.len)
return error.ZipBadCd64Size;
extents.compressed_size = std.mem.readInt(u64, data[data_offset..][0..8], .little);
data_offset += 8;
}
switch (T) {
CentralDirectoryFileHeader => {
if (isMaxInt(header.local_file_header_offset)) {
if (data_offset + 8 > data.len)
return error.ZipBadCd64Size;
extents.local_file_header_offset = std.mem.readInt(u64, data[data_offset..][0..8], .little);
data_offset += 8;
}
if (isMaxInt(header.disk_number)) {
if (data_offset + 4 > data.len)
return error.ZipInvalid;
const disk_number = std.mem.readInt(u32, data[data_offset..][0..4], .little);
if (disk_number != 0)
return error.ZipMultiDiskUnsupported;
data_offset += 4;
}
if (data_offset > data.len)
return error.ZipBadCd64Size;
},
else => {},
}
}
pub const Iterator = struct {
input: *File.Reader,
cd_record_count: u64,
cd_zip_offset: u64,
cd_size: u64,
cd_record_index: u64 = 0,
cd_record_offset: u64 = 0,
pub fn init(input: *File.Reader) !Iterator {
const end_record = try EndRecord.findFile(input);
if (!isMaxInt(end_record.record_count_disk) and end_record.record_count_disk > end_record.record_count_total)
return error.ZipDiskRecordCountTooLarge;
if (end_record.disk_number != 0 or end_record.central_directory_disk_number != 0)
return error.ZipMultiDiskUnsupported;
{
const counts_valid = !isMaxInt(end_record.record_count_disk) and !isMaxInt(end_record.record_count_total);
if (counts_valid and end_record.record_count_disk != end_record.record_count_total)
return error.ZipMultiDiskUnsupported;
}
var result: Iterator = .{
.input = input,
.cd_record_count = end_record.record_count_total,
.cd_zip_offset = end_record.central_directory_offset,
.cd_size = end_record.central_directory_size,
};
if (!end_record.need_zip64()) return result;
const locator_end_offset: u64 = @as(u64, end_record.comment_len) + @sizeOf(EndRecord) + @sizeOf(EndLocator64);
const stream_len = try input.getSize();
if (locator_end_offset > stream_len)
return error.ZipTruncated;
try input.seekTo(stream_len - locator_end_offset);
const locator = input.interface.takeStruct(EndLocator64, .little) catch |err| switch (err) {
error.ReadFailed => return input.err.?,
error.EndOfStream => |e| return e,
};
if (!std.mem.eql(u8, &locator.signature, &end_locator64_sig))
return error.ZipBadLocatorSig;
if (locator.zip64_disk_count != 0)
return error.ZipUnsupportedZip64DiskCount;
if (locator.total_disk_count != 1)
return error.ZipMultiDiskUnsupported;
try input.seekTo(locator.record_file_offset);
const record64 = input.interface.takeStruct(EndRecord64, .little) catch |err| switch (err) {
error.ReadFailed => return input.err.?,
error.EndOfStream => |e| return e,
};
if (!std.mem.eql(u8, &record64.signature, &end_record64_sig))
return error.ZipBadEndRecord64Sig;
if (record64.end_record_size < @sizeOf(EndRecord64) - 12)
return error.ZipEndRecord64SizeTooSmall;
if (record64.end_record_size > @sizeOf(EndRecord64) - 12)
return error.ZipEndRecord64UnhandledExtraData;
if (record64.version_needed_to_extract > 45)
return error.ZipUnsupportedVersion;
{
const is_multidisk = record64.disk_number != 0 or
record64.central_directory_disk_number != 0 or
record64.record_count_disk != record64.record_count_total;
if (is_multidisk)
return error.ZipMultiDiskUnsupported;
}
if (isMaxInt(end_record.record_count_total)) {
result.cd_record_count = record64.record_count_total;
} else if (end_record.record_count_total != record64.record_count_total)
return error.Zip64RecordCountTotalMismatch;
if (isMaxInt(end_record.central_directory_offset)) {
result.cd_zip_offset = record64.central_directory_offset;
} else if (end_record.central_directory_offset != record64.central_directory_offset)
return error.Zip64CentralDirectoryOffsetMismatch;
if (isMaxInt(end_record.central_directory_size)) {
result.cd_size = record64.central_directory_size;
} else if (end_record.central_directory_size != record64.central_directory_size)
return error.Zip64CentralDirectorySizeMismatch;
return result;
}
pub fn next(self: *Iterator) !?Entry {
if (self.cd_record_index == self.cd_record_count) {
if (self.cd_record_offset != self.cd_size)
return if (self.cd_size > self.cd_record_offset)
error.ZipCdOversized
else
error.ZipCdUndersized;
return null;
}
const header_zip_offset = self.cd_zip_offset + self.cd_record_offset;
const input = self.input;
try input.seekTo(header_zip_offset);
const header = input.interface.takeStruct(CentralDirectoryFileHeader, .little) catch |err| switch (err) {
error.ReadFailed => return input.err.?,
error.EndOfStream => |e| return e,
};
if (!std.mem.eql(u8, &header.signature, ¢ral_file_header_sig))
return error.ZipBadCdOffset;
self.cd_record_index += 1;
self.cd_record_offset += @sizeOf(CentralDirectoryFileHeader) + header.filename_len + header.extra_len + header.comment_len;
// Note: checking the version_needed_to_extract doesn't seem to be helpful, i.e. the zip file
// at https://github.com/ninja-build/ninja/releases/download/v1.12.0/ninja-linux.zip
// has an undocumented version 788 but extracts just fine.
if (header.flags.encrypted)
return error.ZipEncryptionUnsupported;
// TODO: check/verify more flags
if (header.disk_number != 0)
return error.ZipMultiDiskUnsupported;
var extents: FileExtents = .{
.uncompressed_size = header.uncompressed_size,
.compressed_size = header.compressed_size,
.local_file_header_offset = header.local_file_header_offset,
};
if (header.extra_len > 0) {
var extra_buf: [std.math.maxInt(u16)]u8 = undefined;
const extra = extra_buf[0..header.extra_len];
try input.seekTo(header_zip_offset + @sizeOf(CentralDirectoryFileHeader) + header.filename_len);
input.interface.readSliceAll(extra) catch |err| switch (err) {
error.ReadFailed => return input.err.?,
error.EndOfStream => |e| return e,
};
var extra_offset: usize = 0;
while (extra_offset + 4 <= extra.len) {
const header_id = std.mem.readInt(u16, extra[extra_offset..][0..2], .little);
const data_size = std.mem.readInt(u16, extra[extra_offset..][2..4], .little);
const end = extra_offset + 4 + data_size;
if (end > extra.len)
return error.ZipBadExtraFieldSize;
const data = extra[extra_offset + 4 .. end];
switch (@as(ExtraHeader, @fromBackingInt(@intCast(header_id)))) {
.zip64_info => try readZip64FileExtents(CentralDirectoryFileHeader, header, &extents, data),
else => {}, // ignore
}
extra_offset = end;
}
}
return .{
.version_needed_to_extract = header.version_needed_to_extract,
.flags = header.flags,
.compression_method = header.compression_method,
.last_modification_time = header.last_modification_time,
.last_modification_date = header.last_modification_date,
.header_zip_offset = header_zip_offset,
.crc32 = header.crc32,
.filename_len = header.filename_len,
.compressed_size = extents.compressed_size,
.uncompressed_size = extents.uncompressed_size,
.file_offset = extents.local_file_header_offset,
};
}
pub const Entry = struct {
version_needed_to_extract: u16,
flags: GeneralPurposeFlags,
compression_method: CompressionMethod,
last_modification_time: u16,
last_modification_date: u16,
header_zip_offset: u64,
crc32: u32,
filename_len: u32,
compressed_size: u64,
uncompressed_size: u64,
file_offset: u64,
pub fn getFilename(self: Entry, stream: *File.Reader, filename_buf: []u8, options: ExtractOptions) ![]u8 {
if (filename_buf.len < self.filename_len)
return error.ZipInsufficientBuffer;
switch (self.compression_method) {
.store, .deflate => {},
else => return error.UnsupportedCompressionMethod,
}
const filename = filename_buf[0..self.filename_len];
{
try stream.seekTo(self.header_zip_offset + @sizeOf(CentralDirectoryFileHeader));
try stream.interface.readSliceAll(filename);
}
if (options.allow_backslashes) {
std.mem.replaceScalar(u8, filename, '\\', '/');
} else {
if (std.mem.findScalar(u8, filename, '\\')) |_|
return error.ZipFilenameHasBackslash;
}
if (isBadFilename(filename))
return error.ZipBadFilename;
return filename;
}
pub fn extractTo(self: Entry, stream: *File.Reader, w: *Writer) !void {
switch (self.compression_method) {
.store, .deflate => {},
else => return error.UnsupportedCompressionMethod,
}
const local_data_header_offset: u64 = local_data_header_offset: {
const local_header = blk: {
try stream.seekTo(self.file_offset);
break :blk try stream.interface.takeStruct(LocalFileHeader, .little);
};
if (!std.mem.eql(u8, &local_header.signature, &local_file_header_sig))
return error.ZipBadFileOffset;
if (local_header.version_needed_to_extract != self.version_needed_to_extract)
return error.ZipMismatchVersionNeeded;
if (local_header.last_modification_time != self.last_modification_time)
return error.ZipMismatchModTime;
if (local_header.last_modification_date != self.last_modification_date)
return error.ZipMismatchModDate;
if (@as(u16, @bitCast(local_header.flags)) != @as(u16, @bitCast(self.flags)))
return error.ZipMismatchFlags;
if (local_header.crc32 != 0 and local_header.crc32 != self.crc32)
return error.ZipMismatchCrc32;
var extents: FileExtents = .{
.uncompressed_size = local_header.uncompressed_size,
.compressed_size = local_header.compressed_size,
.local_file_header_offset = 0,
};
if (local_header.extra_len > 0) {
var extra_buf: [std.math.maxInt(u16)]u8 = undefined;
const extra = extra_buf[0..local_header.extra_len];
{
try stream.seekTo(self.file_offset + @sizeOf(LocalFileHeader) + local_header.filename_len);
try stream.interface.readSliceAll(extra);
}
var extra_offset: usize = 0;
while (extra_offset + 4 <= local_header.extra_len) {
const header_id = std.mem.readInt(u16, extra[extra_offset..][0..2], .little);
const data_size = std.mem.readInt(u16, extra[extra_offset..][2..4], .little);
const end = extra_offset + 4 + data_size;
if (end > local_header.extra_len)
return error.ZipBadExtraFieldSize;
const data = extra[extra_offset + 4 .. end];
switch (@as(ExtraHeader, @fromBackingInt(@intCast(header_id)))) {
.zip64_info => try readZip64FileExtents(LocalFileHeader, local_header, &extents, data),
else => {}, // ignore
}
extra_offset = end;
}
}
if (extents.compressed_size != 0 and
extents.compressed_size != self.compressed_size)
return error.ZipMismatchCompLen;
if (extents.uncompressed_size != 0 and
extents.uncompressed_size != self.uncompressed_size)
return error.ZipMismatchUncompLen;
if (local_header.filename_len != self.filename_len)
return error.ZipMismatchFilenameLen;
break :local_data_header_offset @as(u64, local_header.filename_len) +
@as(u64, local_header.extra_len);
};
const local_data_file_offset: u64 =
@as(u64, self.file_offset) +
@as(u64, @sizeOf(LocalFileHeader)) +
local_data_header_offset;
try stream.seekTo(local_data_file_offset);
// TODO limit based on self.compressed_size
switch (self.compression_method) {
.store => {
stream.interface.streamExact64(w, self.uncompressed_size) catch |err| switch (err) {
error.ReadFailed => |e| return stream.err orelse e,
error.WriteFailed => |e| return e,
error.EndOfStream => return error.ZipDecompressTruncated,
};
},
.deflate => {
var flate_buffer: [flate.max_window_len]u8 = undefined;
var decompress: flate.Decompress = .init(&stream.interface, .raw, &flate_buffer);
decompress.reader.streamExact64(w, self.uncompressed_size) catch |err| switch (err) {
error.ReadFailed => |e| return decompress.err orelse (stream.err orelse e),
error.WriteFailed => |e| return e,
error.EndOfStream => return error.ZipDecompressTruncated,
};
},
else => return error.UnsupportedCompressionMethod,
}
}
pub fn extract(
self: Entry,
stream: *File.Reader,
options: ExtractOptions,
filename_buf: []u8,
dest: Io.Dir,
) !void {
const io = stream.io;
const filename = try self.getFilename(stream, filename_buf, options);
// All entries that end in '/' are directories
if (filename[filename.len - 1] == '/') {
if (self.uncompressed_size != 0)
return error.ZipBadDirectorySize;
try dest.createDirPath(io, filename[0 .. filename.len - 1]);
return;
}
const out_file = blk: {
if (std.fs.path.dirname(filename)) |dirname| {
var parent_dir = try dest.createDirPathOpen(io, dirname, .{});
defer parent_dir.close(io);
const basename = std.fs.path.basename(filename);
break :blk try parent_dir.createFile(io, basename, .{ .exclusive = true });
}
break :blk try dest.createFile(io, filename, .{ .exclusive = true });
};
defer out_file.close(io);
var out_file_buffer: [1024]u8 = undefined;
var file_writer = out_file.writer(io, &out_file_buffer);
self.extractTo(stream, &file_writer.interface) catch |err| switch (err) {
error.WriteFailed => |e| return file_writer.err orelse e,
else => return err,
};
try file_writer.end();
}
};
};
// returns true if `filename` starts with `root` followed by a forward slash
fn filenameInRoot(filename: []const u8, root: []const u8) bool {
return (filename.len >= root.len + 1) and
(filename[root.len] == '/') and
std.mem.eql(u8, filename[0..root.len], root);
}
pub const Diagnostics = struct {
allocator: std.mem.Allocator,
/// The common root directory for all extracted files if there is one.
root_dir: []const u8 = "",
saw_first_file: bool = false,
pub fn deinit(self: *Diagnostics) void {
self.allocator.free(self.root_dir);
self.* = undefined;
}
// This function assumes name is a filename from a zip file which has already been verified to
// not start with a slash, backslashes have been normalized to forward slashes, and directories
// always end in a slash.
pub fn nextFilename(self: *Diagnostics, name: []const u8) error{OutOfMemory}!void {
if (!self.saw_first_file) {
self.saw_first_file = true;
std.debug.assert(self.root_dir.len == 0);
const root_len = std.mem.findScalar(u8, name, '/') orelse return;
std.debug.assert(root_len > 0);
self.root_dir = try self.allocator.dupe(u8, name[0..root_len]);
} else if (self.root_dir.len > 0) {
if (!filenameInRoot(name, self.root_dir)) {
self.allocator.free(self.root_dir);
self.root_dir = "";
}
}
}
};
pub const ExtractOptions = struct {
/// Allow filenames within the zip to use backslashes. Back slashes are normalized
/// to forward slashes before forwarding them to platform APIs.
allow_backslashes: bool = false,
diagnostics: ?*Diagnostics = null,
verify_checksums: bool = false,
};
/// Extract the zipped files to the given `dest` directory.
pub fn extract(dest: Io.Dir, fr: *File.Reader, options: ExtractOptions) !void {
if (options.verify_checksums) @panic("TODO unimplemented");
var iter = try Iterator.init(fr);
var filename_buf: [std.fs.max_path_bytes]u8 = undefined;
while (try iter.next()) |entry| {
try entry.extract(fr, options, &filename_buf, dest);
if (options.diagnostics) |d| {
try d.nextFilename(filename_buf[0..entry.filename_len]);
}
}
}
const testing = std.testing;
test "extractTo" {
const io = testing.io;
var tmp = testing.tmpDir(.{});
defer tmp.cleanup();
try tmp.dir.writeFile(io, .{
.sub_path = "test.zip",
.data = @embedFile("zip/testdata/test.zip"),
});
var file = try tmp.dir.openFile(io, "test.zip", .{});
defer file.close(io);
var read_buf: [512]u8 = undefined;
var reader = file.reader(io, &read_buf);
const Expected = struct {
contents: []const u8,
compression: CompressionMethod,
};
const expected_map = std.StaticStringMap(Expected).initComptime(.{
.{ "deflate.txt", Expected{ .contents = "aaaaaaaaaaaaaaaaaaaaaaaa\n", .compression = .deflate } },
.{ "store.txt", Expected{ .contents = "hello world\n", .compression = .store } },
.{ "dir/", Expected{ .contents = "", .compression = .store } },
});
var iter = try Iterator.init(&reader);
var num_entries: usize = 0;
while (try iter.next()) |entry| {
var filename_buf: [256]u8 = undefined;
const filename = try entry.getFilename(&reader, &filename_buf, .{});
const expected = expected_map.get(filename) orelse {
std.debug.print("found unexpected filename: {f}\n", .{std.ascii.hexEscape(filename, .lower)});
return error.UnexpectedFilename;
};
var buf: [256]u8 = undefined;
var w: Writer = .fixed(&buf);
try entry.extractTo(&reader, &w);
try testing.expectEqualStrings(expected.contents, w.buffered());
try testing.expectEqual(expected.compression, entry.compression_method);
num_entries += 1;
}
try testing.expectEqual(expected_map.kvs.len, num_entries);
}
test "output buffers too small" {
const io = testing.io;
var tmp = testing.tmpDir(.{});
defer tmp.cleanup();
try tmp.dir.writeFile(io, .{
.sub_path = "test.zip",
.data = @embedFile("zip/testdata/test.zip"),
});
var file = try tmp.dir.openFile(io, "test.zip", .{});
defer file.close(io);
var read_buf: [512]u8 = undefined;
var reader = file.reader(io, &read_buf);
var iter = try Iterator.init(&reader);
var num_entries: usize = 0;
while (try iter.next()) |entry| {
try testing.expectError(
error.ZipInsufficientBuffer,
entry.getFilename(&reader, &.{}, .{}),
);
if (entry.uncompressed_size <= 1) continue;
var buf: [1]u8 = undefined;
var w: Writer = .fixed(&buf);
try testing.expectError(
error.WriteFailed,
entry.extractTo(&reader, &w),
);
num_entries += 1;
}
try std.testing.expect(num_entries > 0);
}