added crow

include/crow/middlewares/session.h

@@ -0,0 +1,564 @@
+#pragma once
+
+#include "crow/http_request.h"
+#include "crow/http_response.h"
+#include "crow/json.h"
+#include "crow/utility.h"
+#include "crow/middlewares/cookie_parser.h"
+
+#include <unordered_map>
+#include <unordered_set>
+#include <set>
+#include <queue>
+
+#include <memory>
+#include <string>
+#include <cstdio>
+#include <mutex>
+
+#include <fstream>
+#include <sstream>
+
+#include <type_traits>
+#include <functional>
+#include <chrono>
+
+#include <variant>
+
+namespace
+{
+    // convert all integer values to int64_t
+    template<typename T>
+    using wrap_integral_t = typename std::conditional<
+      std::is_integral<T>::value && !std::is_same<bool, T>::value
+        // except for uint64_t because that could lead to overflow on conversion
+        && !std::is_same<uint64_t, T>::value,
+      int64_t, T>::type;
+
+    // convert char[]/char* to std::string
+    template<typename T>
+    using wrap_char_t = typename std::conditional<
+      std::is_same<typename std::decay<T>::type, char*>::value,
+      std::string, T>::type;
+
+    // Upgrade to correct type for multi_variant use
+    template<typename T>
+    using wrap_mv_t = wrap_char_t<wrap_integral_t<T>>;
+} // namespace
+
+namespace crow
+{
+    namespace session
+    {
+
+        using multi_value_types = black_magic::S<bool, int64_t, double, std::string>;
+
+        /// A multi_value is a safe variant wrapper with json conversion support
+        struct multi_value
+        {
+            json::wvalue json() const
+            {
+                // clang-format off
+                return std::visit([](auto arg) {
+                    return json::wvalue(arg);
+                }, v_);
+                // clang-format on
+            }
+
+            static multi_value from_json(const json::rvalue&);
+
+            std::string string() const
+            {
+                // clang-format off
+                return std::visit([](auto arg) {
+                    if constexpr (std::is_same_v<decltype(arg), std::string>)
+                        return arg;
+                    else
+                        return std::to_string(arg);
+                }, v_);
+                // clang-format on
+            }
+
+            template<typename T, typename RT = wrap_mv_t<T>>
+            RT get(const T& fallback)
+            {
+                if (const RT* val = std::get_if<RT>(&v_)) return *val;
+                return fallback;
+            }
+
+            template<typename T, typename RT = wrap_mv_t<T>>
+            void set(T val)
+            {
+                v_ = RT(std::move(val));
+            }
+
+            typename multi_value_types::rebind<std::variant> v_;
+        };
+
+        inline multi_value multi_value::from_json(const json::rvalue& rv)
+        {
+            using namespace json;
+            switch (rv.t())
+            {
+                case type::Number:
+                {
+                    if (rv.nt() == num_type::Floating_point || rv.nt() == num_type::Double_precision_floating_point)
+                        return multi_value{rv.d()};
+                    else if (rv.nt() == num_type::Unsigned_integer)
+                        return multi_value{int64_t(rv.u())};
+                    else
+                        return multi_value{rv.i()};
+                }
+                case type::False: return multi_value{false};
+                case type::True: return multi_value{true};
+                case type::String: return multi_value{std::string(rv)};
+                default: return multi_value{false};
+            }
+        }
+
+        /// Expiration tracker keeps track of soonest-to-expire keys
+        struct ExpirationTracker
+        {
+            using DataPair = std::pair<uint64_t /*time*/, std::string /*key*/>;
+
+            /// Add key with time to tracker.
+            /// If the key is already present, it will be updated
+            void add(std::string key, uint64_t time)
+            {
+                auto it = times_.find(key);
+                if (it != times_.end()) remove(key);
+                times_[key] = time;
+                queue_.insert({time, std::move(key)});
+            }
+
+            void remove(const std::string& key)
+            {
+                auto it = times_.find(key);
+                if (it != times_.end())
+                {
+                    queue_.erase({it->second, key});
+                    times_.erase(it);
+                }
+            }
+
+            /// Get expiration time of soonest-to-expire entry
+            uint64_t peek_first() const
+            {
+                if (queue_.empty()) return std::numeric_limits<uint64_t>::max();
+                return queue_.begin()->first;
+            }
+
+            std::string pop_first()
+            {
+                auto it = times_.find(queue_.begin()->second);
+                auto key = it->first;
+                times_.erase(it);
+                queue_.erase(queue_.begin());
+                return key;
+            }
+
+            using iterator = typename std::set<DataPair>::const_iterator;
+
+            iterator begin() const { return queue_.cbegin(); }
+
+            iterator end() const { return queue_.cend(); }
+
+        private:
+            std::set<DataPair> queue_;
+            std::unordered_map<std::string, uint64_t> times_;
+        };
+
+        /// CachedSessions are shared across requests
+        struct CachedSession
+        {
+            std::string session_id;
+            std::string requested_session_id; // session hasn't been created yet, but a key was requested
+
+            std::unordered_map<std::string, multi_value> entries;
+            std::unordered_set<std::string> dirty; // values that were changed after last load
+
+            void* store_data;
+            bool requested_refresh;
+
+            // number of references held - used for correctly destroying the cache.
+            // No need to be atomic, all SessionMiddleware accesses are synchronized
+            int referrers;
+            std::recursive_mutex mutex;
+        };
+    } // namespace session
+
+    // SessionMiddleware allows storing securely and easily small snippets of user information
+    template<typename Store>
+    struct SessionMiddleware
+    {
+        using lock = std::scoped_lock<std::mutex>;
+        using rc_lock = std::scoped_lock<std::recursive_mutex>;
+
+        struct context
+        {
+            // Get a mutex for locking this session
+            std::recursive_mutex& mutex()
+            {
+                check_node();
+                return node->mutex;
+            }
+
+            // Check whether this session is already present
+            bool exists() { return bool(node); }
+
+            // Get a value by key or fallback if it doesn't exist or is of another type
+            template<typename F>
+            auto get(const std::string& key, const F& fallback = F())
+              // This trick lets the multi_value deduce the return type from the fallback
+              // which allows both:
+              //   context.get<std::string>("key")
+              //   context.get("key", "") -> char[] is transformed into string by multivalue
+              // to return a string
+              -> decltype(std::declval<session::multi_value>().get<F>(std::declval<F>()))
+            {
+                if (!node) return fallback;
+                rc_lock l(node->mutex);
+
+                auto it = node->entries.find(key);
+                if (it != node->entries.end()) return it->second.get<F>(fallback);
+                return fallback;
+            }
+
+            // Set a value by key
+            template<typename T>
+            void set(const std::string& key, T value)
+            {
+                check_node();
+                rc_lock l(node->mutex);
+
+                node->dirty.insert(key);
+                node->entries[key].set(std::move(value));
+            }
+
+            bool contains(const std::string& key)
+            {
+                if (!node) return false;
+                return node->entries.find(key) != node->entries.end();
+            }
+
+            // Atomically mutate a value with a function
+            template<typename Func>
+            void apply(const std::string& key, const Func& f)
+            {
+                using traits = utility::function_traits<Func>;
+                using arg = typename std::decay<typename traits::template arg<0>>::type;
+                using retv = typename std::decay<typename traits::result_type>::type;
+                check_node();
+                rc_lock l(node->mutex);
+                node->dirty.insert(key);
+                node->entries[key].set<retv>(f(node->entries[key].get(arg{})));
+            }
+
+            // Remove a value from the session
+            void remove(const std::string& key)
+            {
+                if (!node) return;
+                rc_lock l(node->mutex);
+                node->dirty.insert(key);
+                node->entries.erase(key);
+            }
+
+            // Format value by key as a string
+            std::string string(const std::string& key)
+            {
+                if (!node) return "";
+                rc_lock l(node->mutex);
+
+                auto it = node->entries.find(key);
+                if (it != node->entries.end()) return it->second.string();
+                return "";
+            }
+
+            // Get a list of keys present in session
+            std::vector<std::string> keys()
+            {
+                if (!node) return {};
+                rc_lock l(node->mutex);
+
+                std::vector<std::string> out;
+                for (const auto& p : node->entries)
+                    out.push_back(p.first);
+                return out;
+            }
+
+            // Delay expiration by issuing another cookie with an updated expiration time
+            // and notifying the store
+            void refresh_expiration()
+            {
+                if (!node) return;
+                node->requested_refresh = true;
+            }
+
+        private:
+            friend struct SessionMiddleware;
+
+            void check_node()
+            {
+                if (!node) node = std::make_shared<session::CachedSession>();
+            }
+
+            std::shared_ptr<session::CachedSession> node;
+        };
+
+        template<typename... Ts>
+        SessionMiddleware(
+          CookieParser::Cookie cookie,
+          int id_length,
+          Ts... ts):
+          id_length_(id_length),
+          cookie_(cookie),
+          store_(std::forward<Ts>(ts)...), mutex_(new std::mutex{})
+        {}
+
+        template<typename... Ts>
+        SessionMiddleware(Ts... ts):
+          SessionMiddleware(
+            CookieParser::Cookie("session").path("/").max_age(/*month*/ 30 * 24 * 60 * 60),
+            /*id_length */ 20, // around 10^34 possible combinations, but small enough to fit into SSO
+            std::forward<Ts>(ts)...)
+        {}
+
+        template<typename AllContext>
+        void before_handle(request& /*req*/, response& /*res*/, context& ctx, AllContext& all_ctx)
+        {
+            lock l(*mutex_);
+
+            auto& cookies = all_ctx.template get<CookieParser>();
+            auto session_id = load_id(cookies);
+            if (session_id == "") return;
+
+            // search entry in cache
+            auto it = cache_.find(session_id);
+            if (it != cache_.end())
+            {
+                it->second->referrers++;
+                ctx.node = it->second;
+                return;
+            }
+
+            // check this is a valid entry before loading
+            if (!store_.contains(session_id)) return;
+
+            auto node = std::make_shared<session::CachedSession>();
+            node->session_id = session_id;
+            node->referrers = 1;
+
+            try
+            {
+                store_.load(*node);
+            }
+            catch (...)
+            {
+                CROW_LOG_ERROR << "Exception occurred during session load";
+                return;
+            }
+
+            ctx.node = node;
+            cache_[session_id] = node;
+        }
+
+        template<typename AllContext>
+        void after_handle(request& /*req*/, response& /*res*/, context& ctx, AllContext& all_ctx)
+        {
+            lock l(*mutex_);
+            if (!ctx.node || --ctx.node->referrers > 0) return;
+            ctx.node->requested_refresh |= ctx.node->session_id == "";
+
+            // generate new id
+            if (ctx.node->session_id == "")
+            {
+                // check for requested id
+                ctx.node->session_id = std::move(ctx.node->requested_session_id);
+                if (ctx.node->session_id == "")
+                {
+                    ctx.node->session_id = utility::random_alphanum(id_length_);
+                }
+            }
+            else
+            {
+                cache_.erase(ctx.node->session_id);
+            }
+
+            if (ctx.node->requested_refresh)
+            {
+                auto& cookies = all_ctx.template get<CookieParser>();
+                store_id(cookies, ctx.node->session_id);
+            }
+
+            try
+            {
+                store_.save(*ctx.node);
+            }
+            catch (...)
+            {
+                CROW_LOG_ERROR << "Exception occurred during session save";
+                return;
+            }
+        }
+
+    private:
+        std::string next_id()
+        {
+            std::string id;
+            do
+            {
+                id = utility::random_alphanum(id_length_);
+            } while (store_.contains(id));
+            return id;
+        }
+
+        std::string load_id(const CookieParser::context& cookies)
+        {
+            return cookies.get_cookie(cookie_.name());
+        }
+
+        void store_id(CookieParser::context& cookies, const std::string& session_id)
+        {
+            cookie_.value(session_id);
+            cookies.set_cookie(cookie_);
+        }
+
+    private:
+        int id_length_;
+
+        // prototype for cookie
+        CookieParser::Cookie cookie_;
+
+        Store store_;
+
+        // mutexes are immovable
+        std::unique_ptr<std::mutex> mutex_;
+        std::unordered_map<std::string, std::shared_ptr<session::CachedSession>> cache_;
+    };
+
+    /// InMemoryStore stores all entries in memory
+    struct InMemoryStore
+    {
+        // Load a value into the session cache.
+        // A load is always followed by a save, no loads happen consecutively
+        void load(session::CachedSession& cn)
+        {
+            // load & stores happen sequentially, so moving is safe
+            cn.entries = std::move(entries[cn.session_id]);
+        }
+
+        // Persist session data
+        void save(session::CachedSession& cn)
+        {
+            entries[cn.session_id] = std::move(cn.entries);
+            // cn.dirty is a list of changed keys since the last load
+        }
+
+        bool contains(const std::string& key)
+        {
+            return entries.count(key) > 0;
+        }
+
+        std::unordered_map<std::string, std::unordered_map<std::string, session::multi_value>> entries;
+    };
+
+    // FileStore stores all data as json files in a folder.
+    // Files are deleted after expiration. Expiration refreshes are automatically picked up.
+    struct FileStore
+    {
+        FileStore(const std::string& folder, uint64_t expiration_seconds = /*month*/ 30 * 24 * 60 * 60):
+          path_(folder), expiration_seconds_(expiration_seconds)
+        {
+            std::ifstream ifs(get_filename(".expirations", false));
+
+            auto current_ts = chrono_time();
+            std::string key;
+            uint64_t time;
+            while (ifs >> key >> time)
+            {
+                if (current_ts > time)
+                {
+                    evict(key);
+                }
+                else if (contains(key))
+                {
+                    expirations_.add(key, time);
+                }
+            }
+        }
+
+        ~FileStore()
+        {
+            std::ofstream ofs(get_filename(".expirations", false), std::ios::trunc);
+            for (const auto& p : expirations_)
+                ofs << p.second << " " << p.first << "\n";
+        }
+
+        // Delete expired entries
+        // At most 3 to prevent freezes
+        void handle_expired()
+        {
+            int deleted = 0;
+            auto current_ts = chrono_time();
+            while (current_ts > expirations_.peek_first() && deleted < 3)
+            {
+                evict(expirations_.pop_first());
+                deleted++;
+            }
+        }
+
+        void load(session::CachedSession& cn)
+        {
+            handle_expired();
+
+            std::ifstream file(get_filename(cn.session_id));
+
+            std::stringstream buffer;
+            buffer << file.rdbuf() << std::endl;
+
+            for (const auto& p : json::load(buffer.str()))
+                cn.entries[p.key()] = session::multi_value::from_json(p);
+        }
+
+        void save(session::CachedSession& cn)
+        {
+            if (cn.requested_refresh)
+                expirations_.add(cn.session_id, chrono_time() + expiration_seconds_);
+            if (cn.dirty.empty()) return;
+
+            std::ofstream file(get_filename(cn.session_id));
+            json::wvalue jw;
+            for (const auto& p : cn.entries)
+                jw[p.first] = p.second.json();
+            file << jw.dump() << std::flush;
+        }
+
+        std::string get_filename(const std::string& key, bool suffix = true)
+        {
+            return utility::join_path(path_, key + (suffix ? ".json" : ""));
+        }
+
+        bool contains(const std::string& key)
+        {
+            std::ifstream file(get_filename(key));
+            return file.good();
+        }
+
+        void evict(const std::string& key)
+        {
+            std::remove(get_filename(key).c_str());
+        }
+
+        uint64_t chrono_time() const
+        {
+            return std::chrono::duration_cast<std::chrono::seconds>(
+                     std::chrono::steady_clock::now().time_since_epoch())
+              .count();
+        }
+
+        std::string path_;
+        uint64_t expiration_seconds_;
+        session::ExpirationTracker expirations_;
+    };
+
+} // namespace crow