fill(0) will fill all bytes in bit reader. If bit reader is aligned to
the byte, as it is at the end of the stream this ensures no overshoot
when reading footer. Footer is 4 bytes (zlib) or 8 bytes (gzip). For
zlib we will use 4 bytes BitReader and 8 for gzip. After align and fill
we will read those bytes and leave BitReader empty after that.
Follow up to #19079, which made test names fully qualified.
This fixes tests that now-redundant information in their test names. For example here's a fully qualified test name before the changes in this commit:
"priority_queue.test.std.PriorityQueue: shrinkAndFree"
and the same test's name after the changes in this commit:
"priority_queue.test.shrinkAndFree"
This commit works around #18967 by adding an `AccumulatingReader`, which
accumulates data read from the underlying packfile, and by keeping track
of the position in the packfile and hash/checksum information separately
rather than using reader composition. That is, the packfile position and
hashes/checksums are updated with the accumulated read history data only
after we can determine what data has actually been used by the
decompressor rather than merely being buffered.
The only addition to the standard library APIs to support this change is
the `unreadBytes` function in `std.compress.flate.Inflate`, which allows
the user to determine how many bytes have been read only for buffering
and not used as part of compressed data.
These changes can be reverted if #18967 is resolved with a decompressor
that reads precisely only the number of bytes needed for decompression.
Until now literal and distance code lengths where treated as two
different arrays. But according to rfc they can overlap:
The code length repeat codes can cross from HLIT + 257 to the
HDIST + 1 code lengths. In other words, all code lengths form
a single sequence of HLIT + HDIST + 258 values.
Now code lengths are decoded in single array which is then split
to literal and distance part.
It was usefull during development.
From andrewrk code review comment:
In fact, Zig does not guarantee the @sizeOf structs, and so these tests are not valid.
Zig deflate compression/decompression implementation. It supports compression and decompression of gzip, zlib and raw deflate format.
Fixes#18062.
This PR replaces current compress/gzip and compress/zlib packages. Deflate package is renamed to flate. Flate is common name for deflate/inflate where deflate is compression and inflate decompression.
There are breaking change. Methods signatures are changed because of removal of the allocator, and I also unified API for all three namespaces (flate, gzip, zlib).
Currently I put old packages under v1 namespace they are still available as compress/v1/gzip, compress/v1/zlib, compress/v1/deflate. Idea is to give users of the current API little time to postpone analyzing what they had to change. Although that rises question when it is safe to remove that v1 namespace.
Here is current API in the compress package:
```Zig
// deflate
fn compressor(allocator, writer, options) !Compressor(@TypeOf(writer))
fn Compressor(comptime WriterType) type
fn decompressor(allocator, reader, null) !Decompressor(@TypeOf(reader))
fn Decompressor(comptime ReaderType: type) type
// gzip
fn compress(allocator, writer, options) !Compress(@TypeOf(writer))
fn Compress(comptime WriterType: type) type
fn decompress(allocator, reader) !Decompress(@TypeOf(reader))
fn Decompress(comptime ReaderType: type) type
// zlib
fn compressStream(allocator, writer, options) !CompressStream(@TypeOf(writer))
fn CompressStream(comptime WriterType: type) type
fn decompressStream(allocator, reader) !DecompressStream(@TypeOf(reader))
fn DecompressStream(comptime ReaderType: type) type
// xz
fn decompress(allocator: Allocator, reader: anytype) !Decompress(@TypeOf(reader))
fn Decompress(comptime ReaderType: type) type
// lzma
fn decompress(allocator, reader) !Decompress(@TypeOf(reader))
fn Decompress(comptime ReaderType: type) type
// lzma2
fn decompress(allocator, reader, writer !void
// zstandard:
fn DecompressStream(ReaderType, options) type
fn decompressStream(allocator, reader) DecompressStream(@TypeOf(reader), .{})
struct decompress
```
The proposed naming convention:
- Compressor/Decompressor for functions which return type, like Reader/Writer/GeneralPurposeAllocator
- compressor/compressor for functions which are initializers for that type, like reader/writer/allocator
- compress/decompress for one shot operations, accepts reader/writer pair, like read/write/alloc
```Zig
/// Compress from reader and write compressed data to the writer.
fn compress(reader: anytype, writer: anytype, options: Options) !void
/// Create Compressor which outputs the writer.
fn compressor(writer: anytype, options: Options) !Compressor(@TypeOf(writer))
/// Compressor type
fn Compressor(comptime WriterType: type) type
/// Decompress from reader and write plain data to the writer.
fn decompress(reader: anytype, writer: anytype) !void
/// Create Decompressor which reads from reader.
fn decompressor(reader: anytype) Decompressor(@TypeOf(reader)
/// Decompressor type
fn Decompressor(comptime ReaderType: type) type
```
Comparing this implementation with the one we currently have in Zig's standard library (std).
Std is roughly 1.2-1.4 times slower in decompression, and 1.1-1.2 times slower in compression. Compressed sizes are pretty much same in both cases.
More resutls in [this](https://github.com/ianic/flate) repo.
This library uses static allocations for all structures, doesn't require allocator. That makes sense especially for deflate where all structures, internal buffers are allocated to the full size. Little less for inflate where we std version uses less memory by not preallocating to theoretical max size array which are usually not fully used.
For deflate this library allocates 395K while std 779K.
For inflate this library allocates 74.5K while std around 36K.
Inflate difference is because we here use 64K history instead of 32K in std.
If merged existing usage of compress gzip/zlib/deflate need some changes. Here is example with necessary changes in comments:
```Zig
const std = @import("std");
// To get this file:
// wget -nc -O war_and_peace.txt https://www.gutenberg.org/ebooks/2600.txt.utf-8
const data = @embedFile("war_and_peace.txt");
pub fn main() !void {
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
defer std.debug.assert(gpa.deinit() == .ok);
const allocator = gpa.allocator();
try oldDeflate(allocator);
try new(std.compress.flate, allocator);
try oldZlib(allocator);
try new(std.compress.zlib, allocator);
try oldGzip(allocator);
try new(std.compress.gzip, allocator);
}
pub fn new(comptime pkg: type, allocator: std.mem.Allocator) !void {
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Compressor
var cmp = try pkg.compressor(buf.writer(), .{});
_ = try cmp.write(data);
try cmp.finish();
var fbs = std.io.fixedBufferStream(buf.items);
// Decompressor
var dcp = pkg.decompressor(fbs.reader());
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
pub fn oldDeflate(allocator: std.mem.Allocator) !void {
const deflate = std.compress.v1.deflate;
// Compressor
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Remove allocator
// Rename deflate -> flate
var cmp = try deflate.compressor(allocator, buf.writer(), .{});
_ = try cmp.write(data);
try cmp.close(); // Rename to finish
cmp.deinit(); // Remove
// Decompressor
var fbs = std.io.fixedBufferStream(buf.items);
// Remove allocator and last param
// Rename deflate -> flate
// Remove try
var dcp = try deflate.decompressor(allocator, fbs.reader(), null);
defer dcp.deinit(); // Remove
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
pub fn oldZlib(allocator: std.mem.Allocator) !void {
const zlib = std.compress.v1.zlib;
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Compressor
// Rename compressStream => compressor
// Remove allocator
var cmp = try zlib.compressStream(allocator, buf.writer(), .{});
_ = try cmp.write(data);
try cmp.finish();
cmp.deinit(); // Remove
var fbs = std.io.fixedBufferStream(buf.items);
// Decompressor
// decompressStream => decompressor
// Remove allocator
// Remove try
var dcp = try zlib.decompressStream(allocator, fbs.reader());
defer dcp.deinit(); // Remove
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
pub fn oldGzip(allocator: std.mem.Allocator) !void {
const gzip = std.compress.v1.gzip;
var buf = std.ArrayList(u8).init(allocator);
defer buf.deinit();
// Compressor
// Rename compress => compressor
// Remove allocator
var cmp = try gzip.compress(allocator, buf.writer(), .{});
_ = try cmp.write(data);
try cmp.close(); // Rename to finisho
cmp.deinit(); // Remove
var fbs = std.io.fixedBufferStream(buf.items);
// Decompressor
// Rename decompress => decompressor
// Remove allocator
// Remove try
var dcp = try gzip.decompress(allocator, fbs.reader());
defer dcp.deinit(); // Remove
const plain = try dcp.reader().readAllAlloc(allocator, std.math.maxInt(usize));
defer allocator.free(plain);
try std.testing.expectEqualSlices(u8, data, plain);
}
```
