path: root/third_party/nix/src/libstore/nar-accessor.cc

#include "nar-accessor.hh"

#include <algorithm>
#include <map>
#include <nlohmann/json.hpp>
#include <stack>
#include <utility>

#include "archive.hh"
#include "json.hh"

namespace nix {

struct NarMember {
  FSAccessor::Type type = FSAccessor::Type::tMissing;

  bool isExecutable = false;

  /* If this is a regular file, position of the contents of this
     file in the NAR. */
  size_t start = 0, size = 0;

  std::string target;

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

struct NarAccessor : public FSAccessor {
  std::shared_ptr<const std::string> nar;

  GetNarBytes getNarBytes;

  NarMember root;

  struct NarIndexer : ParseSink, StringSource {
    NarAccessor& acc;

    std::stack<NarMember*> parents;

    std::string currentStart;
    bool isExec = false;

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

    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()) {
        acc.root = std::move(member);
        parents.push(&acc.root);
      } else {
        if (parents.top()->type != FSAccessor::Type::tDirectory) {
          throw Error("NAR file missing parent directory of path '%s'", 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});
    }
  };

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

  NarAccessor(const std::string& listing, GetNarBytes getNarBytes)
      : getNarBytes(std::move(getNarBytes)) {
    using json = nlohmann::json;

    std::function<void(NarMember&, json&)> recurse;

    recurse = [&](NarMember& member, json& v) {
      std::string type = v["type"];

      if (type == "directory") {
        member.type = FSAccessor::Type::tDirectory;
        for (auto i = v["entries"].begin(); i != v["entries"].end(); ++i) {
          std::string name = i.key();
          recurse(member.children[name], i.value());
        }
      } else if (type == "regular") {
        member.type = FSAccessor::Type::tRegular;
        member.size = v["size"];
        member.isExecutable = v.value("executable", false);
        member.start = v["narOffset"];
      } else if (type == "symlink") {
        member.type = FSAccessor::Type::tSymlink;
        member.target = v.value("target", "");
      } else {
        return;
      }
    };

    json v = json::parse(listing);
    recurse(root, v);
  }

  NarMember* find(const Path& path) {
    Path canon = path.empty() ? "" : 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& get(const Path& path) {
    auto result = find(path);
    if (result == nullptr) {
      throw Error("NAR file does not contain path '%1%'", path);
    }
    return *result;
  }

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

  StringSet readDirectory(const Path& path) override {
    auto i = get(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 = get(path);
    if (i.type != FSAccessor::Type::tRegular) {
      throw Error(format("path '%1%' inside NAR file is not a regular file") %
                  path);
    }

    if (getNarBytes) {
      return getNarBytes(i.start, i.size);
    }

    assert(nar);
    return std::string(*nar, i.start, i.size);
  }

  std::string readLink(const Path& path) override {
    auto i = get(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);
}

ref<FSAccessor> makeLazyNarAccessor(const std::string& listing,
                                    GetNarBytes getNarBytes) {
  return make_ref<NarAccessor>(listing, getNarBytes);
}

void listNar(JSONPlaceholder& res, ref<FSAccessor> accessor, const Path& path,
             bool recurse) {
  auto st = accessor->stat(path);

  auto obj = res.object();

  switch (st.type) {
    case FSAccessor::Type::tRegular:
      obj.attr("type", "regular");
      obj.attr("size", st.fileSize);
      if (st.isExecutable) {
        obj.attr("executable", true);
      }
      if (st.narOffset != 0u) {
        obj.attr("narOffset", st.narOffset);
      }
      break;
    case FSAccessor::Type::tDirectory:
      obj.attr("type", "directory");
      {
        auto res2 = obj.object("entries");
        for (auto& name : accessor->readDirectory(path)) {
          if (recurse) {
            auto res3 = res2.placeholder(name);
            listNar(res3, accessor, path + "/" + name, true);
          } else {
            res2.object(name);
          }
        }
      }
      break;
    case FSAccessor::Type::tSymlink:
      obj.attr("type", "symlink");
      obj.attr("target", accessor->readLink(path));
      break;
    default:
      throw Error("path '%s' does not exist in NAR", path);
  }
}

}  // namespace nix