ladybird/Libraries/LibCore/CGzip.cpp

#include "CGzip.h"

#include <AK/ByteBuffer.h>
#include <AK/Optional.h>
#include <limits.h>
#include <stddef.h>

#include <LibDraw/puff.h>

bool CGzip::is_compressed(const ByteBuffer& data)
{
    return data.size() > 2 && data[0] == 0x1F && data[1] == 0x8b;
}

// skips the gzip header
// see: https://tools.ietf.org/html/rfc1952#page-5
static Optional<ByteBuffer> get_gzip_payload(const ByteBuffer& data)
{
    int current = 0;
    auto read_byte = [&]() {
        if (current >= data.size()) {
            ASSERT_NOT_REACHED();
            return (u8)0;
        }
        // dbg() << "read_byte: " << String::format("%x", data[current]);
        return data[current++];
    };

    dbg() << "get_gzip_payload: Skipping over gzip header.";

    // Magic Header
    if (read_byte() != 0x1F || read_byte() != 0x8B) {
        dbg() << "get_gzip_payload: Wrong magic number.";
        return Optional<ByteBuffer>();
    }

    // Compression method
    auto method = read_byte();
    if (method != 8) {
        dbg() << "get_gzip_payload: Wrong compression method = " << method;
        return Optional<ByteBuffer>();
    }

    u8 flags = read_byte();

    // Timestamp, Extra flags, OS
    current += 6;

    // FEXTRA
    if (flags & 4) {
        u16 length = read_byte() & read_byte() << 8;
        dbg() << "get_gzip_payload: Header has FEXTRA flag set. Length = " << length;
        current += length;
    }

    // FNAME
    if (flags & 8) {
        dbg() << "get_gzip_payload: Header has FNAME flag set.";
        while (read_byte() != '\0')
            ;
    }

    // FCOMMENT
    if (flags & 16) {
        dbg() << "get_gzip_payload: Header has FCOMMENT flag set.";
        while (read_byte() != '\0')
            ;
    }

    // FHCRC
    if (flags & 2) {
        dbg() << "get_gzip_payload: Header has FHCRC flag set.";
        current += 2;
    }

    auto new_size = data.size() - current;
    dbg() << "get_gzip_payload: Returning slice from " << current << " with size " << new_size;
    return data.slice(current, new_size);
}

Optional<ByteBuffer> CGzip::decompress(const ByteBuffer& data)
{
    ASSERT(is_compressed(data));

    dbg() << "Gzip::decompress: Decompressing gzip compressed data. Size = " << data.size();
    auto optional_payload = get_gzip_payload(data);
    if (!optional_payload.has_value()) {
        return Optional<ByteBuffer>();
    }

    auto source = optional_payload.value();
    unsigned long source_len = source.size();
    auto destination = ByteBuffer::create_uninitialized(1024);
    while (true) {
        unsigned long destination_len = destination.size();
        // FIXME: dbg() cannot take ulong?
        // dbg() << "Gzip::decompress: Calling puff()\n"
        //       << "  destination_data = " << destination.data() << "\n"
        //       << "  destination_len = " << (int)destination_len << "\n"
        //       << "  source_data = " << source.data() << "\n"
        //       << "  source_len = " << (int)source_len;

        auto puff_ret = puff(
            destination.data(), &destination_len,
            source.data(), &source_len);

        if (puff_ret == 0) {
            dbg() << "Gzip::decompress: Decompression success.";
            break;
        } 
        
        if (puff_ret == 1) {
            // FIXME: Find a better way of decompressing without needing to try over and over again.
            dbg() << "Gzip::decompress: Output buffer exhausted. Growing.";
            destination.grow(destination.size() * 2);
        } else {
            dbg() << "Gzip::decompress: Error. puff() returned: " << puff_ret;
            ASSERT_NOT_REACHED();
        }
    }

    return destination;
}