Merge branch 'libarchive-decompress' of https://github.com/serokell/nix

6 files changed, 231 insertions, 368 deletions

diff --git a/src/libutil/compression.cc b/src/libutil/compression.cc
index 986ba2976..8ba536000 100644
--- a/src/libutil/compression.cc
+++ b/src/libutil/compression.cc
@@ -1,10 +1,13 @@
 #include "compression.hh"
+#include "tarfile.hh"
 #include "util.hh"
 #include "finally.hh"
 #include "logging.hh"
 
 #include <lzma.h>
 #include <bzlib.h>
+#include <archive.h>
+#include <archive_entry.h>
 #include <cstdio>
 #include <cstring>
 
@@ -35,177 +38,86 @@ struct ChunkedCompressionSink : CompressionSink
     virtual void writeInternal(std::string_view data) = 0;
 };
 
-struct NoneSink : CompressionSink
-{
-    Sink & nextSink;
-    NoneSink(Sink & nextSink) : nextSink(nextSink) { }
-    void finish() override { flush(); }
-    void write(std::string_view data) override { nextSink(data); }
-};
-
-struct GzipDecompressionSink : CompressionSink
+struct ArchiveDecompressionSource : Source
 {
-    Sink & nextSink;
-    z_stream strm;
-    bool finished = false;
-    uint8_t outbuf[BUFSIZ];
-
-    GzipDecompressionSink(Sink & nextSink) : nextSink(nextSink)
-    {
-        strm.zalloc = Z_NULL;
-        strm.zfree = Z_NULL;
-        strm.opaque = Z_NULL;
-        strm.avail_in = 0;
-        strm.next_in = Z_NULL;
-        strm.next_out = outbuf;
-        strm.avail_out = sizeof(outbuf);
-
-        // Enable gzip and zlib decoding (+32) with 15 windowBits
-        int ret = inflateInit2(&strm,15+32);
-        if (ret != Z_OK)
-            throw CompressionError("unable to initialise gzip encoder");
-    }
-
-    ~GzipDecompressionSink()
-    {
-        inflateEnd(&strm);
-    }
-
-    void finish() override
-    {
-        CompressionSink::flush();
-        write({});
-    }
-
-    void write(std::string_view data) override
-    {
-        assert(data.size() <= std::numeric_limits<decltype(strm.avail_in)>::max());
-
-        strm.next_in = (Bytef *) data.data();
-        strm.avail_in = data.size();
-
-        while (!finished && (!data.data() || strm.avail_in)) {
-            checkInterrupt();
-
-            int ret = inflate(&strm,Z_SYNC_FLUSH);
-            if (ret != Z_OK && ret != Z_STREAM_END)
-                throw CompressionError("error while decompressing gzip file: %d (%d, %d)",
-                    zError(ret), data.size(), strm.avail_in);
-
-            finished = ret == Z_STREAM_END;
-
-            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink({(char *) outbuf, sizeof(outbuf) - strm.avail_out});
-                strm.next_out = (Bytef *) outbuf;
-                strm.avail_out = sizeof(outbuf);
+    std::unique_ptr<TarArchive> archive = 0;
+    Source & src;
+    ArchiveDecompressionSource(Source & src) : src(src) {}
+    ~ArchiveDecompressionSource() override {}
+    size_t read(char * data, size_t len) override {
+        struct archive_entry* ae;
+        if (!archive) {
+            archive = std::make_unique<TarArchive>(src, true);
+            this->archive->check(archive_read_next_header(this->archive->archive, &ae), "Failed to read header (%s)");
+            if (archive_filter_count(this->archive->archive) < 2) {
+                throw CompressionError("Input compression not recognized.");
             }
         }
+        ssize_t result = archive_read_data(this->archive->archive, data, len);
+        if (result > 0) return result;
+        if (result == 0) {
+            throw EndOfFile("reached end of compressed file");
+        }
+        this->archive->check(result, "Failed to read compressed data (%s)");
+        return result;
     }
 };
-
-struct XzDecompressionSink : CompressionSink
+struct ArchiveCompressionSink : CompressionSink
 {
     Sink & nextSink;
-    uint8_t outbuf[BUFSIZ];
-    lzma_stream strm = LZMA_STREAM_INIT;
-    bool finished = false;
-
-    XzDecompressionSink(Sink & nextSink) : nextSink(nextSink)
-    {
-        lzma_ret ret = lzma_stream_decoder(
-            &strm, UINT64_MAX, LZMA_CONCATENATED);
-        if (ret != LZMA_OK)
-            throw CompressionError("unable to initialise lzma decoder");
-
-        strm.next_out = outbuf;
-        strm.avail_out = sizeof(outbuf);
+    struct archive* archive;
+    ArchiveCompressionSink(Sink & nextSink, std::string format, bool parallel) : nextSink(nextSink) {
+        archive = archive_write_new();
+        if (!archive) throw Error("failed to initialize libarchive");
+        check(archive_write_add_filter_by_name(archive, format.c_str()), "Couldn't initialize compression (%s)");
+        check(archive_write_set_format_raw(archive));
+        if (format == "xz" && parallel) {
+            check(archive_write_set_filter_option(archive, format.c_str(), "threads", "0"));
+        }
+        // disable internal buffering
+        check(archive_write_set_bytes_per_block(archive, 0));
+        // disable output padding
+        check(archive_write_set_bytes_in_last_block(archive, 1));
+        open();
     }
-
-    ~XzDecompressionSink()
-    {
-        lzma_end(&strm);
+    ~ArchiveCompressionSink() override {
+        if (archive) archive_write_free(archive);
     }
-
-    void finish() override
-    {
-        CompressionSink::flush();
-        write({});
+    void finish() override {
+        flush();
+        check(archive_write_close(archive));
     }
-
-    void write(std::string_view data) override
-    {
-        strm.next_in = (const unsigned char *) data.data();
-        strm.avail_in = data.size();
-
-        while (!finished && (!data.data() || strm.avail_in)) {
-            checkInterrupt();
-
-            lzma_ret ret = lzma_code(&strm, data.data() ? LZMA_RUN : LZMA_FINISH);
-            if (ret != LZMA_OK && ret != LZMA_STREAM_END)
-                throw CompressionError("error %d while decompressing xz file", ret);
-
-            finished = ret == LZMA_STREAM_END;
-
-            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink({(char *) outbuf, sizeof(outbuf) - strm.avail_out});
-                strm.next_out = outbuf;
-                strm.avail_out = sizeof(outbuf);
-            }
-        }
+    void check(int err, const char *reason="Failed to compress (%s)") {
+        if (err == ARCHIVE_EOF)
+            throw EndOfFile("reached end of archive");
+        else if (err != ARCHIVE_OK)
+            throw Error(reason, archive_error_string(this->archive));
     }
-};
-
-struct BzipDecompressionSink : ChunkedCompressionSink
-{
-    Sink & nextSink;
-    bz_stream strm;
-    bool finished = false;
-
-    BzipDecompressionSink(Sink & nextSink) : nextSink(nextSink)
-    {
-        memset(&strm, 0, sizeof(strm));
-        int ret = BZ2_bzDecompressInit(&strm, 0, 0);
-        if (ret != BZ_OK)
-            throw CompressionError("unable to initialise bzip2 decoder");
-
-        strm.next_out = (char *) outbuf;
-        strm.avail_out = sizeof(outbuf);
+    void write(std::string_view data) override {
+        ssize_t result = archive_write_data(archive, data.data(), data.length());
+        if (result <= 0) check(result);
     }
-
-    ~BzipDecompressionSink()
-    {
-        BZ2_bzDecompressEnd(&strm);
+private:
+    void open() {
+        check(archive_write_open(archive, this, NULL, ArchiveCompressionSink::callback_write, NULL));
+        struct archive_entry *ae = archive_entry_new();
+        archive_entry_set_filetype(ae, AE_IFREG);
+        check(archive_write_header(archive, ae));
+        archive_entry_free(ae);
     }
-
-    void finish() override
-    {
-        flush();
-        write({});
+    static ssize_t callback_write(struct archive *archive, void *_self, const void *buffer, size_t length) {
+        ArchiveCompressionSink *self = (ArchiveCompressionSink *)_self;
+        self->nextSink({(const char*)buffer, length});
+        return length;
     }
+};
 
-    void writeInternal(std::string_view data) override
-    {
-        assert(data.size() <= std::numeric_limits<decltype(strm.avail_in)>::max());
-
-        strm.next_in = (char *) data.data();
-        strm.avail_in = data.size();
-
-        while (strm.avail_in) {
-            checkInterrupt();
-
-            int ret = BZ2_bzDecompress(&strm);
-            if (ret != BZ_OK && ret != BZ_STREAM_END)
-                throw CompressionError("error while decompressing bzip2 file");
-
-            finished = ret == BZ_STREAM_END;
-
-            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink({(char *) outbuf, sizeof(outbuf) - strm.avail_out});
-                strm.next_out = (char *) outbuf;
-                strm.avail_out = sizeof(outbuf);
-            }
-        }
-    }
+struct NoneSink : CompressionSink
+{
+    Sink & nextSink;
+    NoneSink(Sink & nextSink) : nextSink(nextSink) { }
+    void finish() override { flush(); }
+    void write(std::string_view data) override { nextSink(data); }
 };
 
 struct BrotliDecompressionSink : ChunkedCompressionSink
@@ -261,161 +173,32 @@ struct BrotliDecompressionSink : ChunkedCompressionSink
 
 ref<std::string> decompress(const std::string & method, const std::string & in)
 {
-    StringSink ssink;
-    auto sink = makeDecompressionSink(method, ssink);
-    (*sink)(in);
-    sink->finish();
-    return ssink.s;
+    if (method == "br") {
+        StringSink ssink;
+        auto sink = makeDecompressionSink(method, ssink);
+        (*sink)(in);
+        sink->finish();
+        return ssink.s;
+    } else {
+        StringSource ssrc(in);
+        auto src = makeDecompressionSource(ssrc);
+        return make_ref<std::string>(src->drain());
+    }
 }
 
-ref<CompressionSink> makeDecompressionSink(const std::string & method, Sink & nextSink)
+std::unique_ptr<FinishSink> makeDecompressionSink(const std::string & method, Sink & nextSink)
 {
     if (method == "none" || method == "")
-        return make_ref<NoneSink>(nextSink);
-    else if (method == "xz")
-        return make_ref<XzDecompressionSink>(nextSink);
-    else if (method == "bzip2")
-        return make_ref<BzipDecompressionSink>(nextSink);
-    else if (method == "gzip")
-        return make_ref<GzipDecompressionSink>(nextSink);
+        return std::make_unique<NoneSink>(nextSink);
     else if (method == "br")
-        return make_ref<BrotliDecompressionSink>(nextSink);
+        return std::make_unique<BrotliDecompressionSink>(nextSink);
     else
-        throw UnknownCompressionMethod("unknown compression method '%s'", method);
+		return sourceToSink([&](Source & source) {
+			auto decompressionSource = makeDecompressionSource(source);
+			decompressionSource->drainInto(nextSink);
+		});
 }
 
-struct XzCompressionSink : CompressionSink
-{
-    Sink & nextSink;
-    uint8_t outbuf[BUFSIZ];
-    lzma_stream strm = LZMA_STREAM_INIT;
-    bool finished = false;
-
-    XzCompressionSink(Sink & nextSink, bool parallel) : nextSink(nextSink)
-    {
-        lzma_ret ret;
-        bool done = false;
-
-        if (parallel) {
-#ifdef HAVE_LZMA_MT
-            lzma_mt mt_options = {};
-            mt_options.flags = 0;
-            mt_options.timeout = 300; // Using the same setting as the xz cmd line
-            mt_options.preset = LZMA_PRESET_DEFAULT;
-            mt_options.filters = NULL;
-            mt_options.check = LZMA_CHECK_CRC64;
-            mt_options.threads = lzma_cputhreads();
-            mt_options.block_size = 0;
-            if (mt_options.threads == 0)
-                mt_options.threads = 1;
-            // FIXME: maybe use lzma_stream_encoder_mt_memusage() to control the
-            // number of threads.
-            ret = lzma_stream_encoder_mt(&strm, &mt_options);
-            done = true;
-#else
-            printMsg(lvlError, "warning: parallel XZ compression requested but not supported, falling back to single-threaded compression");
-#endif
-        }
-
-        if (!done)
-            ret = lzma_easy_encoder(&strm, 6, LZMA_CHECK_CRC64);
-
-        if (ret != LZMA_OK)
-            throw CompressionError("unable to initialise lzma encoder");
-
-        // FIXME: apply the x86 BCJ filter?
-
-        strm.next_out = outbuf;
-        strm.avail_out = sizeof(outbuf);
-    }
-
-    ~XzCompressionSink()
-    {
-        lzma_end(&strm);
-    }
-
-    void finish() override
-    {
-        CompressionSink::flush();
-        write({});
-    }
-
-    void write(std::string_view data) override
-    {
-        strm.next_in = (const unsigned char *) data.data();
-        strm.avail_in = data.size();
-
-        while (!finished && (!data.data() || strm.avail_in)) {
-            checkInterrupt();
-
-            lzma_ret ret = lzma_code(&strm, data.data() ? LZMA_RUN : LZMA_FINISH);
-            if (ret != LZMA_OK && ret != LZMA_STREAM_END)
-                throw CompressionError("error %d while compressing xz file", ret);
-
-            finished = ret == LZMA_STREAM_END;
-
-            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink({(const char *) outbuf, sizeof(outbuf) - strm.avail_out});
-                strm.next_out = outbuf;
-                strm.avail_out = sizeof(outbuf);
-            }
-        }
-    }
-};
-
-struct BzipCompressionSink : ChunkedCompressionSink
-{
-    Sink & nextSink;
-    bz_stream strm;
-    bool finished = false;
-
-    BzipCompressionSink(Sink & nextSink) : nextSink(nextSink)
-    {
-        memset(&strm, 0, sizeof(strm));
-        int ret = BZ2_bzCompressInit(&strm, 9, 0, 30);
-        if (ret != BZ_OK)
-            throw CompressionError("unable to initialise bzip2 encoder");
-
-        strm.next_out = (char *) outbuf;
-        strm.avail_out = sizeof(outbuf);
-    }
-
-    ~BzipCompressionSink()
-    {
-        BZ2_bzCompressEnd(&strm);
-    }
-
-    void finish() override
-    {
-        flush();
-        writeInternal({});
-    }
-
-    void writeInternal(std::string_view data) override
-    {
-        assert(data.size() <= std::numeric_limits<decltype(strm.avail_in)>::max());
-
-        strm.next_in = (char *) data.data();
-        strm.avail_in = data.size();
-
-        while (!finished && (!data.data() || strm.avail_in)) {
-            checkInterrupt();
-
-            int ret = BZ2_bzCompress(&strm, data.data() ? BZ_RUN : BZ_FINISH);
-            if (ret != BZ_RUN_OK && ret != BZ_FINISH_OK && ret != BZ_STREAM_END)
-                throw CompressionError("error %d while compressing bzip2 file", ret);
-
-            finished = ret == BZ_STREAM_END;
-
-            if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink({(const char *) outbuf, sizeof(outbuf) - strm.avail_out});
-                strm.next_out = (char *) outbuf;
-                strm.avail_out = sizeof(outbuf);
-            }
-        }
-    }
-};
-
 struct BrotliCompressionSink : ChunkedCompressionSink
 {
     Sink & nextSink;
@@ -468,15 +251,20 @@ struct BrotliCompressionSink : ChunkedCompressionSink
         }
     }
 };
+std::unique_ptr<Source> makeDecompressionSource(Source & prev) {
+    return std::unique_ptr<Source>(new ArchiveDecompressionSource(prev));
+}
 
 ref<CompressionSink> makeCompressionSink(const std::string & method, Sink & nextSink, const bool parallel)
 {
+    std::vector<std::string> la_supports = {
+        "bzip2", "compress", "grzip", "gzip", "lrzip", "lz4", "lzip", "lzma", "lzop", "xz", "zstd"
+    };
+    if (std::find(la_supports.begin(), la_supports.end(), method) != la_supports.end()) {
+        return make_ref<ArchiveCompressionSink>(nextSink, method, parallel);
+    }
     if (method == "none")
         return make_ref<NoneSink>(nextSink);
-    else if (method == "xz")
-        return make_ref<XzCompressionSink>(nextSink, parallel);
-    else if (method == "bzip2")
-        return make_ref<BzipCompressionSink>(nextSink);
     else if (method == "br")
         return make_ref<BrotliCompressionSink>(nextSink);
     else
diff --git a/src/libutil/compression.hh b/src/libutil/compression.hh
index dd666a4e1..192cb3e91 100644
--- a/src/libutil/compression.hh
+++ b/src/libutil/compression.hh
@@ -8,14 +8,18 @@
 
 namespace nix {
 
-struct CompressionSink : BufferedSink
+struct CompressionSink : BufferedSink, FinishSink
 {
-    virtual void finish() = 0;
+	using BufferedSink::operator ();
+	using BufferedSink::write;
+	using FinishSink::finish;
 };
 
+std::unique_ptr<Source> makeDecompressionSource(Source & prev);
+
 ref<std::string> decompress(const std::string & method, const std::string & in);
 
-ref<CompressionSink> makeDecompressionSink(const std::string & method, Sink & nextSink);
+std::unique_ptr<FinishSink> makeDecompressionSink(const std::string & method, Sink & nextSink);
 
 ref<std::string> compress(const std::string & method, const std::string & in, const bool parallel = false);
 
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index d1a16b6ba..374b48d79 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -201,6 +201,61 @@ static DefaultStackAllocator defaultAllocatorSingleton;
 StackAllocator *StackAllocator::defaultAllocator = &defaultAllocatorSingleton;
 
 
+std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun)
+{
+    struct SourceToSink : FinishSink
+    {
+        typedef boost::coroutines2::coroutine<bool> coro_t;
+
+        std::function<void(Source &)> fun;
+        std::optional<coro_t::push_type> coro;
+
+        SourceToSink(std::function<void(Source &)> fun) : fun(fun)
+        {
+        }
+
+        std::string_view cur;
+
+        void operator () (std::string_view in) override
+        {
+            if (in.empty()) return;
+            cur = in;
+
+            if (!coro)
+                coro = coro_t::push_type(VirtualStackAllocator{}, [&](coro_t::pull_type & yield) {
+                    LambdaSource source([&](char *out, size_t out_len) {
+                        if (cur.empty()) {
+                            yield();
+                            if (yield.get()) {
+                                return (size_t)0;
+                            }
+                        }
+
+                        size_t n = std::min(cur.size(), out_len);
+                        memcpy(out, cur.data(), n);
+                        cur.remove_prefix(n);
+                        return n;
+                    });
+                    fun(source);
+                });
+
+            if (!*coro) { abort(); }
+
+            if (!cur.empty()) (*coro)(false);
+        }
+
+        void finish() {
+            if (!coro) return;
+            if (!*coro) abort();
+            (*coro)(true);
+            if (*coro) abort();
+        }
+    };
+
+    return std::make_unique<SourceToSink>(fun);
+}
+
+
 std::unique_ptr<Source> sinkToSource(
     std::function<void(Sink &)> fun,
     std::function<void()> eof)
@@ -212,7 +267,6 @@ std::unique_ptr<Source> sinkToSource(
         std::function<void(Sink &)> fun;
         std::function<void()> eof;
         std::optional<coro_t::pull_type> coro;
-        bool started = false;
 
         SinkToSource(std::function<void(Sink &)> fun, std::function<void()> eof)
             : fun(fun), eof(eof)
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 5bbbc7ce3..0fe6e8332 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -25,6 +25,13 @@ struct NullSink : Sink
     { }
 };
 
+
+struct FinishSink : virtual Sink
+{
+    virtual void finish() = 0;
+};
+
+
 /* A buffered abstract sink. Warning: a BufferedSink should not be
    used from multiple threads concurrently. */
 struct BufferedSink : virtual Sink
@@ -281,6 +288,7 @@ struct ChainSource : Source
     size_t read(char * data, size_t len) override;
 };
 
+std::unique_ptr<FinishSink> sourceToSink(std::function<void(Source &)> fun);
 
 /* Convert a function that feeds data into a Sink into a Source. The
    Source executes the function as a coroutine. */
diff --git a/src/libutil/tarfile.cc b/src/libutil/tarfile.cc
index 2da169ba7..b5e1cb4c0 100644
--- a/src/libutil/tarfile.cc
+++ b/src/libutil/tarfile.cc
@@ -2,83 +2,73 @@
 #include <archive_entry.h>
 
 #include "serialise.hh"
+#include "tarfile.hh"
 
 namespace nix {
+static int callback_open(struct archive *, void *self) {
+    return ARCHIVE_OK;
+}
+
+static ssize_t callback_read(struct archive * archive, void * _self, const void * * buffer) {
+    TarArchive *self = (TarArchive *)_self;
+    *buffer = self->buffer.data();
 
-struct TarArchive {
-    struct archive * archive;
-    Source * source;
-    std::vector<unsigned char> buffer;
+    try {
+        return self->source->read((char *) self->buffer.data(), 4096);
+    } catch (EndOfFile &) {
+        return 0;
+    } catch (std::exception &err) {
+        archive_set_error(archive, EIO, "Source threw exception: %s", err.what());
+
+        return -1;
+    }
+}
+
+static int callback_close(struct archive *, void *self) {
+    return ARCHIVE_OK;
+}
 
-    void check(int err, const char * reason = "failed to extract archive: %s")
-    {
+void TarArchive::check(int err, const char *reason)
+{
         if (err == ARCHIVE_EOF)
             throw EndOfFile("reached end of archive");
         else if (err != ARCHIVE_OK)
             throw Error(reason, archive_error_string(this->archive));
     }
 
-    TarArchive(Source & source) : buffer(4096)
-    {
-        this->archive = archive_read_new();
-        this->source = &source;
+TarArchive::TarArchive(Source& source, bool raw) : buffer(4096)
+{
+    this->archive = archive_read_new();
+    this->source = &source;
 
+    if (!raw) {
         archive_read_support_filter_all(archive);
         archive_read_support_format_all(archive);
-        check(archive_read_open(archive,
-                (void *)this,
-                TarArchive::callback_open,
-                TarArchive::callback_read,
-                TarArchive::callback_close),
-            "failed to open archive: %s");
-    }
-
-    TarArchive(const Path & path)
-    {
-        this->archive = archive_read_new();
-
+    } else {
         archive_read_support_filter_all(archive);
-        archive_read_support_format_all(archive);
-        check(archive_read_open_filename(archive, path.c_str(), 16384), "failed to open archive: %s");
-    }
-
-    TarArchive(const TarArchive &) = delete;
-
-    void close()
-    {
-        check(archive_read_close(archive), "failed to close archive: %s");
+        archive_read_support_format_raw(archive);
+        archive_read_support_format_empty(archive);
     }
+    check(archive_read_open(archive, (void *)this, callback_open, callback_read, callback_close), "Failed to open archive (%s)");
+}
 
-    ~TarArchive()
-    {
-        if (this->archive) archive_read_free(this->archive);
-    }
 
-private:
+TarArchive::TarArchive(const Path &path)
+{
+    this->archive = archive_read_new();
 
-    static int callback_open(struct archive *, void * self) {
-        return ARCHIVE_OK;
-    }
+    archive_read_support_filter_all(archive);
+    archive_read_support_format_all(archive);
+    check(archive_read_open_filename(archive, path.c_str(), 16384), "failed to open archive: %s");
+}
 
-    static ssize_t callback_read(struct archive * archive, void * _self, const void * * buffer)
-    {
-        auto self = (TarArchive *)_self;
-        *buffer = self->buffer.data();
-
-        try {
-            return self->source->read((char *) self->buffer.data(), 4096);
-        } catch (EndOfFile &) {
-            return 0;
-        } catch (std::exception & err) {
-            archive_set_error(archive, EIO, "source threw exception: %s", err.what());
-            return -1;
-        }
-    }
+void TarArchive::close() {
+    check(archive_read_close(this->archive), "Failed to close archive (%s)");
+}
 
-    static int callback_close(struct archive *, void * self) {
-        return ARCHIVE_OK;
-    }
-};
+TarArchive::~TarArchive() {
+    if (this->archive) archive_read_free(this->archive);
+}
 
 static void extract_archive(TarArchive & archive, const Path & destDir)
 {
diff --git a/src/libutil/tarfile.hh b/src/libutil/tarfile.hh
index 89a024f1d..18adf3490 100644
--- a/src/libutil/tarfile.hh
+++ b/src/libutil/tarfile.hh
@@ -1,7 +1,26 @@
 #include "serialise.hh"
+#include <archive.h>
 
 namespace nix {
 
+struct TarArchive {
+    struct archive *archive;
+    Source *source;
+    std::vector<unsigned char> buffer;
+
+    void check(int err, const char *reason = "Failed to extract archive (%s)");
+
+    TarArchive(Source& source, bool raw = false);
+
+    TarArchive(const Path &path);
+
+    // disable copy constructor
+    TarArchive(const TarArchive&) = delete;
+
+    void close();
+
+    ~TarArchive();
+};
 void unpackTarfile(Source & source, const Path & destDir);
 
 void unpackTarfile(const Path & tarFile, const Path & destDir);