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//
// Decompressor for GZIP data streams (RFC1952)
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;
// Flags for the FLG field in the header
const FTEXT = 1 << 0;
const FHCRC = 1 << 1;
const FEXTRA = 1 << 2;
const FNAME = 1 << 3;
const FCOMMENT = 1 << 4;
pub fn GzipStream(comptime ReaderType: type) type {
return struct {
const Self = @This();
pub const Error = ReaderType.Error ||
deflate.Decompressor(ReaderType).Error ||
error{ CorruptedData, WrongChecksum };
pub const Reader = io.Reader(*Self, Error, read);
allocator: mem.Allocator,
inflater: deflate.Decompressor(ReaderType),
in_reader: ReaderType,
hasher: std.hash.Crc32,
read_amt: usize,
info: struct {
filename: ?[]const u8,
comment: ?[]const u8,
modification_time: u32,
},
fn init(allocator: mem.Allocator, source: ReaderType) !Self {
// gzip header format is specified in RFC1952
const header = try source.readBytesNoEof(10);
// Check the ID1/ID2 fields
if (header[0] != 0x1f or header[1] != 0x8b)
return error.BadHeader;
const CM = header[2];
// The CM field must be 8 to indicate the use of DEFLATE
if (CM != 8) return error.InvalidCompression;
// Flags
const FLG = header[3];
// Modification time, as a Unix timestamp.
// If zero there's no timestamp available.
const MTIME = mem.readIntLittle(u32, header[4..8]);
// Extra flags
const XFL = header[8];
// Operating system where the compression took place
const OS = header[9];
_ = XFL;
_ = OS;
if (FLG & FEXTRA != 0) {
// Skip the extra data, we could read and expose it to the user
// if somebody needs it.
const len = try source.readIntLittle(u16);
try source.skipBytes(len, .{});
}
var filename: ?[]const u8 = null;
if (FLG & FNAME != 0) {
filename = try source.readUntilDelimiterAlloc(
allocator,
0,
std.math.maxInt(usize),
);
}
errdefer if (filename) |p| allocator.free(p);
var comment: ?[]const u8 = null;
if (FLG & FCOMMENT != 0) {
comment = try source.readUntilDelimiterAlloc(
allocator,
0,
std.math.maxInt(usize),
);
}
errdefer if (comment) |p| allocator.free(p);
if (FLG & FHCRC != 0) {
// TODO: Evaluate and check the header checksum. The stdlib has
// no CRC16 yet :(
_ = try source.readIntLittle(u16);
}
return Self{
.allocator = allocator,
.inflater = try deflate.decompressor(allocator, source, null),
.in_reader = source,
.hasher = std.hash.Crc32.init(),
.info = .{
.filename = filename,
.comment = comment,
.modification_time = MTIME,
},
.read_amt = 0,
};
}
pub fn deinit(self: *Self) void {
self.inflater.deinit();
if (self.info.filename) |filename|
self.allocator.free(filename);
if (self.info.comment) |comment|
self.allocator.free(comment);
}
// 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]);
self.read_amt += r;
return r;
}
// We've reached the end of stream, check if the checksum matches
const hash = try self.in_reader.readIntLittle(u32);
if (hash != self.hasher.final())
return error.WrongChecksum;
// The ISIZE field is the size of the uncompressed input modulo 2^32
const input_size = try self.in_reader.readIntLittle(u32);
if (self.read_amt & 0xffffffff != input_size)
return error.CorruptedData;
return 0;
}
pub fn reader(self: *Self) Reader {
return .{ .context = self };
}
};
}
pub fn gzipStream(allocator: mem.Allocator, reader: anytype) !GzipStream(@TypeOf(reader)) {
return GzipStream(@TypeOf(reader)).init(allocator, reader);
}
fn testReader(data: []const u8, comptime expected: []const u8) !void {
var in_stream = io.fixedBufferStream(data);
var gzip_stream = try gzipStream(testing.allocator, in_stream.reader());
defer gzip_stream.deinit();
// Read and decompress the whole file
const buf = try gzip_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 RFC1952 text
//
// https://tools.ietf.org/rfc/rfc1952.txt length=25037 bytes
// SHA256=164ef0897b4cbec63abf1b57f069f3599bd0fb7c72c2a4dee21bd7e03ec9af67
test "compressed data" {
try testReader(
@embedFile("rfc1952.txt.gz"),
@embedFile("rfc1952.txt"),
);
}
test "sanity checks" {
// Truncated header
try testing.expectError(
error.EndOfStream,
testReader(&[_]u8{ 0x1f, 0x8B }, ""),
);
// Wrong CM
try testing.expectError(
error.InvalidCompression,
testReader(&[_]u8{
0x1f, 0x8b, 0x09, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x03,
}, ""),
);
// Wrong checksum
try testing.expectError(
error.WrongChecksum,
testReader(&[_]u8{
0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x03, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01,
0x00, 0x00, 0x00, 0x00,
}, ""),
);
// Truncated checksum
try testing.expectError(
error.EndOfStream,
testReader(&[_]u8{
0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x03, 0x03, 0x00, 0x00, 0x00, 0x00,
}, ""),
);
// Wrong initial size
try testing.expectError(
error.CorruptedData,
testReader(&[_]u8{
0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x03, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x01,
}, ""),
);
// Truncated initial size field
try testing.expectError(
error.EndOfStream,
testReader(&[_]u8{
0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x03, 0x03, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00,
}, ""),
);
}
|
