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//
// Decompressor for ZLIB data streams (RFC1950)
const std = @import("std");
const io = std.io;
const fs = std.fs;
const testing = std.testing;
const mem = std.mem;
const deflate = std.compress.deflate;
pub fn ZlibStream(comptime ReaderType: type) type {
return struct {
const Self = @This();
pub const Error = ReaderType.Error ||
deflate.Decompressor(ReaderType).Error ||
error{ WrongChecksum, Unsupported };
pub const Reader = io.Reader(*Self, Error, read);
allocator: mem.Allocator,
inflater: deflate.Decompressor(ReaderType),
in_reader: ReaderType,
hasher: std.hash.Adler32,
fn init(allocator: mem.Allocator, source: ReaderType) !Self {
// Zlib header format is specified in RFC1950
const header = try source.readBytesNoEof(2);
const CM = @truncate(u4, header[0]);
const CINFO = @truncate(u4, header[0] >> 4);
const FCHECK = @truncate(u5, header[1]);
_ = FCHECK;
const FDICT = @truncate(u1, header[1] >> 5);
if ((@as(u16, header[0]) << 8 | header[1]) % 31 != 0)
return error.BadHeader;
// The CM field must be 8 to indicate the use of DEFLATE
if (CM != 8) return error.InvalidCompression;
// CINFO is the base-2 logarithm of the LZ77 window size, minus 8.
// Values above 7 are unspecified and therefore rejected.
if (CINFO > 7) return error.InvalidWindowSize;
const dictionary = null;
// TODO: Support this case
if (FDICT != 0)
return error.Unsupported;
return Self{
.allocator = allocator,
.inflater = try deflate.decompressor(allocator, source, dictionary),
.in_reader = source,
.hasher = std.hash.Adler32.init(),
};
}
pub fn deinit(self: *Self) void {
self.inflater.deinit();
}
// Implements the io.Reader interface
pub fn read(self: *Self, buffer: []u8) Error!usize {
if (buffer.len == 0)
return 0;
// Read from the compressed stream and update the computed checksum
const r = try self.inflater.read(buffer);
if (r != 0) {
self.hasher.update(buffer[0..r]);
return r;
}
// We've reached the end of stream, check if the checksum matches
const hash = try self.in_reader.readIntBig(u32);
if (hash != self.hasher.final())
return error.WrongChecksum;
return 0;
}
pub fn reader(self: *Self) Reader {
return .{ .context = self };
}
};
}
pub fn zlibStream(allocator: mem.Allocator, reader: anytype) !ZlibStream(@TypeOf(reader)) {
return ZlibStream(@TypeOf(reader)).init(allocator, reader);
}
fn testReader(data: []const u8, expected: []const u8) !void {
var in_stream = io.fixedBufferStream(data);
var zlib_stream = try zlibStream(testing.allocator, in_stream.reader());
defer zlib_stream.deinit();
// Read and decompress the whole file
const buf = try zlib_stream.reader().readAllAlloc(testing.allocator, std.math.maxInt(usize));
defer testing.allocator.free(buf);
// Check against the reference
try testing.expectEqualSlices(u8, buf, expected);
}
// All the test cases are obtained by compressing the RFC1951 text
//
// https://tools.ietf.org/rfc/rfc1951.txt length=36944 bytes
// SHA256=5ebf4b5b7fe1c3a0c0ab9aa3ac8c0f3853a7dc484905e76e03b0b0f301350009
test "compressed data" {
const rfc1951_txt = @embedFile("rfc1951.txt");
// Compressed with compression level = 0
try testReader(
@embedFile("rfc1951.txt.z.0"),
rfc1951_txt,
);
// Compressed with compression level = 9
try testReader(
@embedFile("rfc1951.txt.z.9"),
rfc1951_txt,
);
// Compressed with compression level = 9 and fixed Huffman codes
try testReader(
@embedFile("rfc1951.txt.fixed.z.9"),
rfc1951_txt,
);
}
test "don't read past deflate stream's end" {
try testReader(&[_]u8{
0x08, 0xd7, 0x63, 0xf8, 0xcf, 0xc0, 0xc0, 0x00, 0xc1, 0xff,
0xff, 0x43, 0x30, 0x03, 0x03, 0xc3, 0xff, 0xff, 0xff, 0x01,
0x83, 0x95, 0x0b, 0xf5,
}, &[_]u8{
0x00, 0xff, 0x00, 0x00, 0x00, 0xff, 0x00, 0x00, 0x00, 0xff,
0x00, 0xff, 0xff, 0xff, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00,
0x00, 0x00, 0xff, 0xff, 0xff,
});
}
test "sanity checks" {
// Truncated header
try testing.expectError(
error.EndOfStream,
testReader(&[_]u8{0x78}, ""),
);
// Failed FCHECK check
try testing.expectError(
error.BadHeader,
testReader(&[_]u8{ 0x78, 0x9D }, ""),
);
// Wrong CM
try testing.expectError(
error.InvalidCompression,
testReader(&[_]u8{ 0x79, 0x94 }, ""),
);
// Wrong CINFO
try testing.expectError(
error.InvalidWindowSize,
testReader(&[_]u8{ 0x88, 0x98 }, ""),
);
// Wrong checksum
try testing.expectError(
error.WrongChecksum,
testReader(&[_]u8{ 0x78, 0xda, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00 }, ""),
);
// Truncated checksum
try testing.expectError(
error.EndOfStream,
testReader(&[_]u8{ 0x78, 0xda, 0x03, 0x00, 0x00 }, ""),
);
}
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