Libraries: Move to Userland/Libraries/

Userland/Libraries/LibCompress/CMakeLists.txt

@@ -0,0 +1,8 @@
+set(SOURCES
+    Deflate.cpp
+    Zlib.cpp
+    Gzip.cpp
+)
+
+serenity_lib(LibCompress compression)
+target_link_libraries(LibCompress LibC LibCrypto)

Userland/Libraries/LibCompress/Deflate.cpp

@@ -0,0 +1,452 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Array.h>
+#include <AK/Assertions.h>
+#include <AK/BinarySearch.h>
+#include <AK/LogStream.h>
+#include <AK/MemoryStream.h>
+
+#include <LibCompress/Deflate.h>
+
+namespace Compress {
+
+const CanonicalCode& CanonicalCode::fixed_literal_codes()
+{
+    static CanonicalCode code;
+    static bool initialized = false;
+
+    if (initialized)
+        return code;
+
+    Array<u8, 288> data;
+    data.span().slice(0, 144 - 0).fill(8);
+    data.span().slice(144, 256 - 144).fill(9);
+    data.span().slice(256, 280 - 256).fill(7);
+    data.span().slice(280, 288 - 280).fill(8);
+
+    code = CanonicalCode::from_bytes(data).value();
+    initialized = true;
+
+    return code;
+}
+
+const CanonicalCode& CanonicalCode::fixed_distance_codes()
+{
+    static CanonicalCode code;
+    static bool initialized = false;
+
+    if (initialized)
+        return code;
+
+    Array<u8, 32> data;
+    data.span().fill(5);
+
+    code = CanonicalCode::from_bytes(data).value();
+    initialized = true;
+
+    return code;
+}
+
+Optional<CanonicalCode> CanonicalCode::from_bytes(ReadonlyBytes bytes)
+{
+    // FIXME: I can't quite follow the algorithm here, but it seems to work.
+
+    CanonicalCode code;
+
+    auto next_code = 0;
+    for (size_t code_length = 1; code_length <= 15; ++code_length) {
+        next_code <<= 1;
+        auto start_bit = 1 << code_length;
+
+        for (size_t symbol = 0; symbol < bytes.size(); ++symbol) {
+            if (bytes[symbol] != code_length)
+                continue;
+
+            if (next_code > start_bit)
+                return {};
+
+            code.m_symbol_codes.append(start_bit | next_code);
+            code.m_symbol_values.append(symbol);
+
+            next_code++;
+        }
+    }
+
+    if (next_code != (1 << 15)) {
+        return {};
+    }
+
+    return code;
+}
+
+u32 CanonicalCode::read_symbol(InputBitStream& stream) const
+{
+    u32 code_bits = 1;
+
+    for (;;) {
+        code_bits = code_bits << 1 | stream.read_bits(1);
+        ASSERT(code_bits < (1 << 16));
+
+        // FIXME: This is very inefficent and could greatly be improved by implementing this
+        //        algorithm: https://www.hanshq.net/zip.html#huffdec
+        size_t index;
+        if (AK::binary_search(m_symbol_codes.span(), code_bits, &index))
+            return m_symbol_values[index];
+    }
+}
+
+DeflateDecompressor::CompressedBlock::CompressedBlock(DeflateDecompressor& decompressor, CanonicalCode literal_codes, Optional<CanonicalCode> distance_codes)
+    : m_decompressor(decompressor)
+    , m_literal_codes(literal_codes)
+    , m_distance_codes(distance_codes)
+{
+}
+
+bool DeflateDecompressor::CompressedBlock::try_read_more()
+{
+    if (m_eof == true)
+        return false;
+
+    const auto symbol = m_literal_codes.read_symbol(m_decompressor.m_input_stream);
+
+    if (symbol < 256) {
+        m_decompressor.m_output_stream << static_cast<u8>(symbol);
+        return true;
+    } else if (symbol == 256) {
+        m_eof = true;
+        return false;
+    } else {
+        if (!m_distance_codes.has_value()) {
+            m_decompressor.set_fatal_error();
+            return false;
+        }
+
+        const auto length = m_decompressor.decode_length(symbol);
+        const auto distance = m_decompressor.decode_distance(m_distance_codes.value().read_symbol(m_decompressor.m_input_stream));
+
+        for (size_t idx = 0; idx < length; ++idx) {
+            u8 byte = 0;
+            m_decompressor.m_output_stream.read({ &byte, sizeof(byte) }, distance);
+            m_decompressor.m_output_stream << byte;
+        }
+
+        return true;
+    }
+}
+
+DeflateDecompressor::UncompressedBlock::UncompressedBlock(DeflateDecompressor& decompressor, size_t length)
+    : m_decompressor(decompressor)
+    , m_bytes_remaining(length)
+{
+}
+
+bool DeflateDecompressor::UncompressedBlock::try_read_more()
+{
+    if (m_bytes_remaining == 0)
+        return false;
+
+    const auto nread = min(m_bytes_remaining, m_decompressor.m_output_stream.remaining_contigous_space());
+    m_bytes_remaining -= nread;
+
+    m_decompressor.m_input_stream >> m_decompressor.m_output_stream.reserve_contigous_space(nread);
+
+    return true;
+}
+
+DeflateDecompressor::DeflateDecompressor(InputStream& stream)
+    : m_input_stream(stream)
+{
+}
+
+DeflateDecompressor::~DeflateDecompressor()
+{
+    if (m_state == State::ReadingCompressedBlock)
+        m_compressed_block.~CompressedBlock();
+    if (m_state == State::ReadingUncompressedBlock)
+        m_uncompressed_block.~UncompressedBlock();
+}
+
+size_t DeflateDecompressor::read(Bytes bytes)
+{
+    if (has_any_error())
+        return 0;
+
+    if (m_state == State::Idle) {
+        if (m_read_final_bock)
+            return 0;
+
+        m_read_final_bock = m_input_stream.read_bit();
+        const auto block_type = m_input_stream.read_bits(2);
+
+        if (block_type == 0b00) {
+            m_input_stream.align_to_byte_boundary();
+
+            LittleEndian<u16> length, negated_length;
+            m_input_stream >> length >> negated_length;
+
+            if ((length ^ 0xffff) != negated_length) {
+                set_fatal_error();
+                return 0;
+            }
+
+            m_state = State::ReadingUncompressedBlock;
+            new (&m_uncompressed_block) UncompressedBlock(*this, length);
+
+            return read(bytes);
+        }
+
+        if (block_type == 0b01) {
+            m_state = State::ReadingCompressedBlock;
+            new (&m_compressed_block) CompressedBlock(*this, CanonicalCode::fixed_literal_codes(), CanonicalCode::fixed_distance_codes());
+
+            return read(bytes);
+        }
+
+        if (block_type == 0b10) {
+            CanonicalCode literal_codes;
+            Optional<CanonicalCode> distance_codes;
+            decode_codes(literal_codes, distance_codes);
+
+            m_state = State::ReadingCompressedBlock;
+            new (&m_compressed_block) CompressedBlock(*this, literal_codes, distance_codes);
+
+            return read(bytes);
+        }
+
+        set_fatal_error();
+        return 0;
+    }
+
+    if (m_state == State::ReadingCompressedBlock) {
+        auto nread = m_output_stream.read(bytes);
+
+        while (nread < bytes.size() && m_compressed_block.try_read_more()) {
+            nread += m_output_stream.read(bytes.slice(nread));
+        }
+
+        if (nread == bytes.size())
+            return nread;
+
+        m_compressed_block.~CompressedBlock();
+        m_state = State::Idle;
+
+        return nread + read(bytes.slice(nread));
+    }
+
+    if (m_state == State::ReadingUncompressedBlock) {
+        auto nread = m_output_stream.read(bytes);
+
+        while (nread < bytes.size() && m_uncompressed_block.try_read_more()) {
+            nread += m_output_stream.read(bytes.slice(nread));
+        }
+
+        if (nread == bytes.size())
+            return nread;
+
+        m_uncompressed_block.~UncompressedBlock();
+        m_state = State::Idle;
+
+        return nread + read(bytes.slice(nread));
+    }
+
+    ASSERT_NOT_REACHED();
+}
+
+bool DeflateDecompressor::read_or_error(Bytes bytes)
+{
+    if (read(bytes) < bytes.size()) {
+        set_fatal_error();
+        return false;
+    }
+
+    return true;
+}
+
+bool DeflateDecompressor::discard_or_error(size_t count)
+{
+    u8 buffer[4096];
+
+    size_t ndiscarded = 0;
+    while (ndiscarded < count) {
+        if (unreliable_eof()) {
+            set_fatal_error();
+            return false;
+        }
+
+        ndiscarded += read({ buffer, min<size_t>(count - ndiscarded, 4096) });
+    }
+
+    return true;
+}
+
+bool DeflateDecompressor::unreliable_eof() const { return m_state == State::Idle && m_read_final_bock; }
+
+Optional<ByteBuffer> DeflateDecompressor::decompress_all(ReadonlyBytes bytes)
+{
+    InputMemoryStream memory_stream { bytes };
+    DeflateDecompressor deflate_stream { memory_stream };
+    DuplexMemoryStream output_stream;
+
+    u8 buffer[4096];
+    while (!deflate_stream.has_any_error() && !deflate_stream.unreliable_eof()) {
+        const auto nread = deflate_stream.read({ buffer, sizeof(buffer) });
+        output_stream.write_or_error({ buffer, nread });
+    }
+
+    if (deflate_stream.handle_any_error())
+        return {};
+
+    return output_stream.copy_into_contiguous_buffer();
+}
+
+u32 DeflateDecompressor::decode_length(u32 symbol)
+{
+    // FIXME: I can't quite follow the algorithm here, but it seems to work.
+
+    if (symbol <= 264)
+        return symbol - 254;
+
+    if (symbol <= 284) {
+        auto extra_bits = (symbol - 261) / 4;
+        return (((symbol - 265) % 4 + 4) << extra_bits) + 3 + m_input_stream.read_bits(extra_bits);
+    }
+
+    if (symbol == 285)
+        return 258;
+
+    ASSERT_NOT_REACHED();
+}
+
+u32 DeflateDecompressor::decode_distance(u32 symbol)
+{
+    // FIXME: I can't quite follow the algorithm here, but it seems to work.
+
+    if (symbol <= 3)
+        return symbol + 1;
+
+    if (symbol <= 29) {
+        auto extra_bits = (symbol / 2) - 1;
+        return ((symbol % 2 + 2) << extra_bits) + 1 + m_input_stream.read_bits(extra_bits);
+    }
+
+    ASSERT_NOT_REACHED();
+}
+
+void DeflateDecompressor::decode_codes(CanonicalCode& literal_code, Optional<CanonicalCode>& distance_code)
+{
+    auto literal_code_count = m_input_stream.read_bits(5) + 257;
+    auto distance_code_count = m_input_stream.read_bits(5) + 1;
+    auto code_length_count = m_input_stream.read_bits(4) + 4;
+
+    // First we have to extract the code lengths of the code that was used to encode the code lengths of
+    // the code that was used to encode the block.
+
+    u8 code_lengths_code_lengths[19] = { 0 };
+    for (size_t i = 0; i < code_length_count; ++i) {
+        static const size_t indices[] { 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 };
+        code_lengths_code_lengths[indices[i]] = m_input_stream.read_bits(3);
+    }
+
+    // Now we can extract the code that was used to encode the code lengths of the code that was used to
+    // encode the block.
+
+    auto code_length_code_result = CanonicalCode::from_bytes({ code_lengths_code_lengths, sizeof(code_lengths_code_lengths) });
+    if (!code_length_code_result.has_value()) {
+        set_fatal_error();
+        return;
+    }
+    const auto code_length_code = code_length_code_result.value();
+
+    // Next we extract the code lengths of the code that was used to encode the block.
+
+    Vector<u8> code_lengths;
+    while (code_lengths.size() < literal_code_count + distance_code_count) {
+        auto symbol = code_length_code.read_symbol(m_input_stream);
+
+        if (symbol <= 15) {
+            code_lengths.append(static_cast<u8>(symbol));
+            continue;
+        } else if (symbol == 17) {
+            auto nrepeat = 3 + m_input_stream.read_bits(3);
+            for (size_t j = 0; j < nrepeat; ++j)
+                code_lengths.append(0);
+            continue;
+        } else if (symbol == 18) {
+            auto nrepeat = 11 + m_input_stream.read_bits(7);
+            for (size_t j = 0; j < nrepeat; ++j)
+                code_lengths.append(0);
+            continue;
+        } else {
+            ASSERT(symbol == 16);
+
+            if (code_lengths.is_empty()) {
+                set_fatal_error();
+                return;
+            }
+
+            auto nrepeat = 3 + m_input_stream.read_bits(2);
+            for (size_t j = 0; j < nrepeat; ++j)
+                code_lengths.append(code_lengths.last());
+        }
+    }
+
+    if (code_lengths.size() != literal_code_count + distance_code_count) {
+        set_fatal_error();
+        return;
+    }
+
+    // Now we extract the code that was used to encode literals and lengths in the block.
+
+    auto literal_code_result = CanonicalCode::from_bytes(code_lengths.span().trim(literal_code_count));
+    if (!literal_code_result.has_value()) {
+        set_fatal_error();
+        return;
+    }
+    literal_code = literal_code_result.value();
+
+    // Now we extract the code that was used to encode distances in the block.
+
+    if (distance_code_count == 1) {
+        auto length = code_lengths[literal_code_count];
+
+        if (length == 0) {
+            return;
+        } else if (length != 1) {
+            set_fatal_error();
+            return;
+        }
+    }
+
+    auto distance_code_result = CanonicalCode::from_bytes(code_lengths.span().slice(literal_code_count));
+    if (!distance_code_result.has_value()) {
+        set_fatal_error();
+        return;
+    }
+    distance_code = distance_code_result.value();
+}
+
+}

Userland/Libraries/LibCompress/Deflate.h

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/BitStream.h>
+#include <AK/ByteBuffer.h>
+#include <AK/CircularDuplexStream.h>
+#include <AK/Endian.h>
+#include <AK/Vector.h>
+
+namespace Compress {
+
+class CanonicalCode {
+public:
+    CanonicalCode() = default;
+    u32 read_symbol(InputBitStream&) const;
+
+    static const CanonicalCode& fixed_literal_codes();
+    static const CanonicalCode& fixed_distance_codes();
+
+    static Optional<CanonicalCode> from_bytes(ReadonlyBytes);
+
+private:
+    Vector<u32> m_symbol_codes;
+    Vector<u32> m_symbol_values;
+};
+
+class DeflateDecompressor final : public InputStream {
+private:
+    class CompressedBlock {
+    public:
+        CompressedBlock(DeflateDecompressor&, CanonicalCode literal_codes, Optional<CanonicalCode> distance_codes);
+
+        bool try_read_more();
+
+    private:
+        bool m_eof { false };
+
+        DeflateDecompressor& m_decompressor;
+        CanonicalCode m_literal_codes;
+        Optional<CanonicalCode> m_distance_codes;
+    };
+
+    class UncompressedBlock {
+    public:
+        UncompressedBlock(DeflateDecompressor&, size_t);
+
+        bool try_read_more();
+
+    private:
+        DeflateDecompressor& m_decompressor;
+        size_t m_bytes_remaining;
+    };
+
+    enum class State {
+        Idle,
+        ReadingCompressedBlock,
+        ReadingUncompressedBlock
+    };
+
+public:
+    friend CompressedBlock;
+    friend UncompressedBlock;
+
+    DeflateDecompressor(InputStream&);
+    ~DeflateDecompressor();
+
+    size_t read(Bytes) override;
+    bool read_or_error(Bytes) override;
+    bool discard_or_error(size_t) override;
+
+    bool unreliable_eof() const override;
+
+    static Optional<ByteBuffer> decompress_all(ReadonlyBytes);
+
+private:
+    u32 decode_length(u32);
+    u32 decode_distance(u32);
+    void decode_codes(CanonicalCode& literal_code, Optional<CanonicalCode>& distance_code);
+
+    bool m_read_final_bock { false };
+
+    State m_state { State::Idle };
+    union {
+        CompressedBlock m_compressed_block;
+        UncompressedBlock m_uncompressed_block;
+    };
+
+    InputBitStream m_input_stream;
+    CircularDuplexStream<32 * 1024> m_output_stream;
+};
+
+}

Userland/Libraries/LibCompress/Gzip.cpp

@@ -0,0 +1,183 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibCompress/Gzip.h>
+
+#include <AK/MemoryStream.h>
+#include <AK/String.h>
+
+namespace Compress {
+
+bool GzipDecompressor::BlockHeader::valid_magic_number() const
+{
+    return identification_1 == 0x1f && identification_2 == 0x8b;
+}
+
+bool GzipDecompressor::BlockHeader::supported_by_implementation() const
+{
+    if (compression_method != 0x08) {
+        // RFC 1952 does not define any compression methods other than deflate.
+        return false;
+    }
+
+    if (flags > Flags::MAX) {
+        // RFC 1952 does not define any more flags.
+        return false;
+    }
+
+    if (flags & Flags::FHCRC) {
+        TODO();
+    }
+
+    return true;
+}
+
+GzipDecompressor::GzipDecompressor(InputStream& stream)
+    : m_input_stream(stream)
+{
+}
+
+GzipDecompressor::~GzipDecompressor()
+{
+    m_current_member.clear();
+}
+
+// FIXME: Again, there are surely a ton of bugs because the code doesn't check for read errors.
+size_t GzipDecompressor::read(Bytes bytes)
+{
+    if (has_any_error() || m_eof)
+        return 0;
+
+    if (m_current_member.has_value()) {
+        size_t nread = current_member().m_stream.read(bytes);
+        current_member().m_checksum.update(bytes.trim(nread));
+        current_member().m_nread += nread;
+
+        if (nread < bytes.size()) {
+            LittleEndian<u32> crc32, input_size;
+            m_input_stream >> crc32 >> input_size;
+
+            if (crc32 != current_member().m_checksum.digest()) {
+                // FIXME: Somehow the checksum is incorrect?
+
+                set_fatal_error();
+                return 0;
+            }
+
+            if (input_size != current_member().m_nread) {
+                set_fatal_error();
+                return 0;
+            }
+
+            m_current_member.clear();
+
+            return nread + read(bytes.slice(nread));
+        }
+
+        return nread;
+    } else {
+        BlockHeader header;
+        m_input_stream >> Bytes { &header, sizeof(header) };
+
+        if (m_input_stream.handle_any_error()) {
+            m_eof = true;
+            return 0;
+        }
+
+        if (!header.valid_magic_number() || !header.supported_by_implementation()) {
+            set_fatal_error();
+            return 0;
+        }
+
+        if (header.flags & Flags::FEXTRA) {
+            LittleEndian<u16> subfield_id, length;
+            m_input_stream >> subfield_id >> length;
+            m_input_stream.discard_or_error(length);
+        }
+
+        if (header.flags & Flags::FNAME) {
+            String original_filename;
+            m_input_stream >> original_filename;
+        }
+
+        if (header.flags & Flags::FCOMMENT) {
+            String comment;
+            m_input_stream >> comment;
+        }
+
+        m_current_member.emplace(header, m_input_stream);
+        return read(bytes);
+    }
+}
+
+bool GzipDecompressor::read_or_error(Bytes bytes)
+{
+    if (read(bytes) < bytes.size()) {
+        set_fatal_error();
+        return false;
+    }
+
+    return true;
+}
+
+bool GzipDecompressor::discard_or_error(size_t count)
+{
+    u8 buffer[4096];
+
+    size_t ndiscarded = 0;
+    while (ndiscarded < count) {
+        if (unreliable_eof()) {
+            set_fatal_error();
+            return false;
+        }
+
+        ndiscarded += read({ buffer, min<size_t>(count - ndiscarded, sizeof(buffer)) });
+    }
+
+    return true;
+}
+
+Optional<ByteBuffer> GzipDecompressor::decompress_all(ReadonlyBytes bytes)
+{
+    InputMemoryStream memory_stream { bytes };
+    GzipDecompressor gzip_stream { memory_stream };
+    DuplexMemoryStream output_stream;
+
+    u8 buffer[4096];
+    while (!gzip_stream.has_any_error() && !gzip_stream.unreliable_eof()) {
+        const auto nread = gzip_stream.read({ buffer, sizeof(buffer) });
+        output_stream.write_or_error({ buffer, nread });
+    }
+
+    if (gzip_stream.handle_any_error())
+        return {};
+
+    return output_stream.copy_into_contiguous_buffer();
+}
+
+bool GzipDecompressor::unreliable_eof() const { return m_eof; }
+
+}

Userland/Libraries/LibCompress/Gzip.h

@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibCompress/Deflate.h>
+#include <LibCrypto/Checksum/CRC32.h>
+
+namespace Compress {
+
+class GzipDecompressor final : public InputStream {
+public:
+    GzipDecompressor(InputStream&);
+    ~GzipDecompressor();
+
+    size_t read(Bytes) override;
+    bool read_or_error(Bytes) override;
+    bool discard_or_error(size_t) override;
+
+    bool unreliable_eof() const override;
+
+    static Optional<ByteBuffer> decompress_all(ReadonlyBytes);
+
+private:
+    struct [[gnu::packed]] BlockHeader {
+        u8 identification_1;
+        u8 identification_2;
+        u8 compression_method;
+        u8 flags;
+        LittleEndian<u32> modification_time;
+        u8 extra_flags;
+        u8 operating_system;
+
+        bool valid_magic_number() const;
+        bool supported_by_implementation() const;
+    };
+
+    struct Flags {
+        static constexpr u8 FTEXT = 1 << 0;
+        static constexpr u8 FHCRC = 1 << 1;
+        static constexpr u8 FEXTRA = 1 << 2;
+        static constexpr u8 FNAME = 1 << 3;
+        static constexpr u8 FCOMMENT = 1 << 4;
+
+        static constexpr u8 MAX = FTEXT | FHCRC | FEXTRA | FNAME | FCOMMENT;
+    };
+
+    class Member {
+    public:
+        Member(BlockHeader header, InputStream& stream)
+            : m_header(header)
+            , m_stream(stream)
+        {
+        }
+
+        BlockHeader m_header;
+        DeflateDecompressor m_stream;
+        Crypto::Checksum::CRC32 m_checksum;
+        size_t m_nread { 0 };
+    };
+
+    const Member& current_member() const { return m_current_member.value(); }
+    Member& current_member() { return m_current_member.value(); }
+
+    InputStream& m_input_stream;
+    Optional<Member> m_current_member;
+
+    bool m_eof { false };
+};
+
+}

Userland/Libraries/LibCompress/Zlib.cpp

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Assertions.h>
+#include <AK/Span.h>
+#include <AK/Types.h>
+#include <AK/Vector.h>
+#include <LibCompress/Deflate.h>
+#include <LibCompress/Zlib.h>
+
+namespace Compress {
+
+Zlib::Zlib(ReadonlyBytes data)
+{
+    m_input_data = data;
+
+    u8 compression_info = data.at(0);
+    u8 flags = data.at(1);
+
+    m_compression_method = compression_info & 0xF;
+    m_compression_info = (compression_info >> 4) & 0xF;
+    m_check_bits = flags & 0xF;
+    m_has_dictionary = (flags >> 5) & 0x1;
+    m_compression_level = (flags >> 6) & 0x3;
+    m_checksum = 0;
+
+    ASSERT(m_compression_method == 8);
+    ASSERT(m_compression_info == 7);
+    ASSERT(!m_has_dictionary);
+    ASSERT((compression_info * 256 + flags) % 31 == 0);
+
+    m_data_bytes = data.slice(2, data.size() - 2 - 4);
+}
+
+Optional<ByteBuffer> Zlib::decompress()
+{
+    return DeflateDecompressor::decompress_all(m_data_bytes);
+}
+
+Optional<ByteBuffer> Zlib::decompress_all(ReadonlyBytes bytes)
+{
+    Zlib zlib { bytes };
+    return zlib.decompress();
+}
+
+u32 Zlib::checksum()
+{
+    if (!m_checksum) {
+        auto bytes = m_input_data.slice(m_input_data.size() - 4, 4);
+        m_checksum = bytes.at(0) << 24 | bytes.at(1) << 16 | bytes.at(2) << 8 || bytes.at(3);
+    }
+
+    return m_checksum;
+}
+
+}

Userland/Libraries/LibCompress/Zlib.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/Span.h>
+#include <AK/Types.h>
+
+namespace Compress {
+
+class Zlib {
+public:
+    Zlib(ReadonlyBytes data);
+
+    Optional<ByteBuffer> decompress();
+    u32 checksum();
+
+    static Optional<ByteBuffer> decompress_all(ReadonlyBytes);
+
+private:
+    u8 m_compression_method;
+    u8 m_compression_info;
+    u8 m_check_bits;
+    u8 m_has_dictionary;
+    u8 m_compression_level;
+
+    u32 m_checksum;
+    ReadonlyBytes m_input_data;
+    ReadonlyBytes m_data_bytes;
+};
+
+}