nix-gh/src/libstore/nar-accessor.cc

#include "nar-accessor.hh"
#include "archive.hh"

#include <map>
#include <stack>
#include <algorithm>

namespace nix {

struct NarMember
{
    FSAccessor::Type type;

    bool isExecutable;

    /* If this is a regular file, position of the contents of this
       file in the NAR. */
    size_t start, size;

    std::string target;

    /* If this is a directory, all the children of the directory. */
    std::map<std::string, NarMember> children;
};

struct NarIndexer : ParseSink, StringSource
{
    NarMember root;
    std::stack<NarMember*> parents;

    std::string currentStart;
    bool isExec = false;

    NarIndexer(const std::string & nar) : StringSource(nar)
    {
    }

    void createMember(const Path & path, NarMember member) {
        size_t level = std::count(path.begin(), path.end(), '/');
        while(parents.size() > level) {
            parents.pop();
        }

        if(parents.empty()) {
            root = std::move(member);
            parents.push(&root);
        } else {
            if(parents.top()->type != FSAccessor::Type::tDirectory) {
                throw Error(format("NAR file missing parent directory of path '%1%'") % path);
            }
            auto result = parents.top()->children.emplace(baseNameOf(path), std::move(member));
            parents.push(&result.first->second);
        }
    }

    void createDirectory(const Path & path) override
    {
        createMember(path, {FSAccessor::Type::tDirectory, false, 0, 0 });
    }

    void createRegularFile(const Path & path) override
    {
        createMember(path, {FSAccessor::Type::tRegular, false, 0, 0 });
    }

    void isExecutable() override
    {
        parents.top()->isExecutable = true;
    }

    void preallocateContents(unsigned long long size) override
    {
        currentStart = string(s, pos, 16);
        assert(size <= std::numeric_limits<size_t>::max());
        parents.top()->size = (size_t)size;
        parents.top()->start = pos;
    }

    void receiveContents(unsigned char * data, unsigned int len) override
    {
        // Sanity check
        if (!currentStart.empty()) {
            assert(len < 16 || currentStart == string((char *) data, 16));
            currentStart.clear();
        }
    }

    void createSymlink(const Path & path, const string & target) override
    {
        createMember(path,
            NarMember{FSAccessor::Type::tSymlink, false, 0, 0, target});
    }

    NarMember* find(const Path & path)
    {
        Path canon = path == "" ? "" : canonPath(path);
        NarMember* current = &root;
        auto end = path.end();
        for(auto it = path.begin(); it != end; ) {
            // because it != end, the remaining component is non-empty so we need
            // a directory
            if(current->type != FSAccessor::Type::tDirectory) return nullptr;

            // skip slash (canonPath above ensures that this is always a slash)
            assert(*it == '/');
            it += 1;

            // lookup current component
            auto next = std::find(it, end, '/');
            auto child = current->children.find(std::string(it, next));
            if(child == current->children.end()) return nullptr;
            current = &child->second;

            it = next;
        }

        return current;
    }

    NarMember& at(const Path & path) {
        auto result = find(path);
        if(result == nullptr) {
            throw Error(format("NAR file does not contain path '%1%'") % path);
        }
        return *result;
    }
};

struct NarAccessor : public FSAccessor
{
    ref<const std::string> nar;
    NarIndexer indexer;

    NarAccessor(ref<const std::string> nar) : nar(nar), indexer(*nar)
    {
        parseDump(indexer, indexer);
    }

    Stat stat(const Path & path) override
    {
        auto i = indexer.find(path);
        if (i == nullptr)
            return {FSAccessor::Type::tMissing, 0, false};
        return {i->type, i->size, i->isExecutable};
    }

    StringSet readDirectory(const Path & path) override
    {
        auto i = indexer.at(path);

        if (i.type != FSAccessor::Type::tDirectory)
            throw Error(format("path '%1%' inside NAR file is not a directory") % path);

        StringSet res;
        for(auto&& child : i.children) {
            res.insert(child.first);

        }
        return res;
    }

    std::string readFile(const Path & path) override
    {
        auto i = indexer.at(path);
        if (i.type != FSAccessor::Type::tRegular)
            throw Error(format("path '%1%' inside NAR file is not a regular file") % path);
        return std::string(*nar, i.start, i.size);
    }

    std::string readLink(const Path & path) override
    {
        auto i = indexer.at(path);
        if (i.type != FSAccessor::Type::tSymlink)
            throw Error(format("path '%1%' inside NAR file is not a symlink") % path);
        return i.target;
    }
};

ref<FSAccessor> makeNarAccessor(ref<const std::string> nar)
{
    return make_ref<NarAccessor>(nar);
}

}