doos 0.1.0: user-level overlayfs containers with slirp networking

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/util.hpp

@@ -0,0 +1,57 @@
+#pragma once
+#include <cerrno>
+#include <filesystem>
+#include <stdexcept>
+#include <string>
+
+namespace doos {
+
+class SysError : public std::runtime_error {
+public:
+    explicit SysError(const std::string& what, int err = errno);
+    int code() const { return code_; }
+
+private:
+    int code_;
+};
+
+class Fd {
+public:
+    Fd() = default;
+    explicit Fd(int fd) : fd_(fd) {}
+    Fd(Fd&& o) noexcept : fd_(o.release()) {}
+    Fd& operator=(Fd&& o) noexcept;
+    Fd(const Fd&) = delete;
+    Fd& operator=(const Fd&) = delete;
+    ~Fd() { reset(); }
+    int get() const { return fd_; }
+    int release();
+    void reset(int fd = -1);
+    bool valid() const { return fd_ >= 0; }
+
+private:
+    int fd_ = -1;
+};
+
+// flock(2) on a file for the lifetime of the object, bounded wait.
+class FileLock {
+public:
+    FileLock(const std::filesystem::path& file, int timeoutMs);
+    ~FileLock() = default;
+    void unlock() { fd_.reset(); }
+    int fd() const { return fd_.get(); }
+
+private:
+    Fd fd_;
+};
+
+namespace fsutil {
+void mkdirs(const std::filesystem::path& p, mode_t mode = 0755);
+void writeFile(const std::filesystem::path& p, const std::string& content);
+std::string readFile(const std::filesystem::path& p);
+// Removes a tree without following symlinks; bounded depth.
+void removeTree(const std::filesystem::path& p, std::size_t depth = 0);
+std::size_t countEntries(const std::filesystem::path& p, std::size_t cap);
+}  // namespace fsutil
+
+}  // namespace doos