nix-super/src/libutil/compression.cc

#include "compression.hh"
#include "util.hh"

#include <lzma.h>
#include <cstdio>

namespace nix {

/* RAII wrapper around lzma_stream. */
struct LzmaStream
{
    lzma_stream strm;
    LzmaStream() : strm(LZMA_STREAM_INIT) { };
    ~LzmaStream() { lzma_end(&strm); };
    lzma_stream & operator()() { return strm; }
};

static ref<std::string> compressXZ(const std::string & in)
{
    LzmaStream strm;

    // FIXME: apply the x86 BCJ filter?

    lzma_ret ret = lzma_easy_encoder(
        &strm(), 6, LZMA_CHECK_CRC64);
    if (ret != LZMA_OK)
        throw Error("unable to initialise lzma encoder");

    lzma_action action = LZMA_RUN;
    uint8_t outbuf[BUFSIZ];
    ref<std::string> res = make_ref<std::string>();
    strm().next_in = (uint8_t *) in.c_str();
    strm().avail_in = in.size();
    strm().next_out = outbuf;
    strm().avail_out = sizeof(outbuf);

    while (true) {
        checkInterrupt();

        if (strm().avail_in == 0)
            action = LZMA_FINISH;

        lzma_ret ret = lzma_code(&strm(), action);

        if (strm().avail_out == 0 || ret == LZMA_STREAM_END) {
            res->append((char *) outbuf, sizeof(outbuf) - strm().avail_out);
            strm().next_out = outbuf;
            strm().avail_out = sizeof(outbuf);
        }

        if (ret == LZMA_STREAM_END)
            return res;

        if (ret != LZMA_OK)
            throw Error("error while decompressing xz file");
    }
}

static ref<std::string> decompressXZ(const std::string & in)
{
    LzmaStream strm;

    lzma_ret ret = lzma_stream_decoder(
        &strm(), UINT64_MAX, LZMA_CONCATENATED);
    if (ret != LZMA_OK)
        throw Error("unable to initialise lzma decoder");

    lzma_action action = LZMA_RUN;
    uint8_t outbuf[BUFSIZ];
    ref<std::string> res = make_ref<std::string>();
    strm().next_in = (uint8_t *) in.c_str();
    strm().avail_in = in.size();
    strm().next_out = outbuf;
    strm().avail_out = sizeof(outbuf);

    while (true) {
        checkInterrupt();

        if (strm().avail_in == 0)
            action = LZMA_FINISH;

        lzma_ret ret = lzma_code(&strm(), action);

        if (strm().avail_out == 0 || ret == LZMA_STREAM_END) {
            res->append((char *) outbuf, sizeof(outbuf) - strm().avail_out);
            strm().next_out = outbuf;
            strm().avail_out = sizeof(outbuf);
        }

        if (ret == LZMA_STREAM_END)
            return res;

        if (ret != LZMA_OK)
            throw Error("error while decompressing xz file");
    }
}

ref<std::string> compress(const std::string & method, ref<std::string> in)
{
    if (method == "none")
        return in;
    else if (method == "xz")
        return compressXZ(*in);
    else
        throw UnknownCompressionMethod(format("unknown compression method ‘%s’") % method);
}

ref<std::string> decompress(const std::string & method, ref<std::string> in)
{
    if (method == "none")
        return in;
    else if (method == "xz")
        return decompressXZ(*in);
    else
        throw UnknownCompressionMethod(format("unknown compression method ‘%s’") % method);
}

}