text: // Copyright (c) 2020-2020 The Wflscoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include <chainparams.h>
  #include <compat.h>
  #include <compat/endian.h>
  #include <crypto/sha256.h>
  #include <fs.h>
  #include <i2p.h>
  #include <logging.h>
  #include <netaddress.h>
  #include <netbase.h>
  #include <random.h>
  #include <util/strencodings.h>
  #include <tinyformat.h>
  #include <util/readwritefile.h>
  #include <util/sock.h>
  #include <util/spanparsing.h>
  #include <util/system.h>
  
  #include <chrono>
  #include <memory>
  #include <stdexcept>
  #include <string>
  
  namespace i2p {
  
  /**
   * Swap Standard Base64 <-> I2P Base64.
   * Standard Base64 uses `+` and `/` as last two characters of its alphabet.
   * I2P Base64 uses `-` and `~` respectively.
   * So it is easy to detect in which one is the input and convert to the other.
   * @param[in] from Input to convert.
   * @return converted `from`
   */
  static std::string SwapBase64(const std::string& from)
  {
      std::string to;
      to.resize(from.size());
      for (size_t i = 0; i < from.size(); ++i) {
          switch (from[i]) {
          case '-':
              to[i] = '+';
              break;
          case '~':
              to[i] = '/';
              break;
          case '+':
              to[i] = '-';
              break;
          case '/':
              to[i] = '~';
              break;
          default:
              to[i] = from[i];
              break;
          }
      }
      return to;
  }
  
  /**
   * Decode an I2P-style Base64 string.
   * @param[in] i2p_b64 I2P-style Base64 string.
   * @return decoded `i2p_b64`
   * @throw std::runtime_error if decoding fails
   */
  static Binary DecodeI2PBase64(const std::string& i2p_b64)
  {
      const std::string& std_b64 = SwapBase64(i2p_b64);
      bool invalid;
      Binary decoded = DecodeBase64(std_b64.c_str(), &invalid);
      if (invalid) {
          throw std::runtime_error(strprintf("Cannot decode Base64: \"%s\"", i2p_b64));
      }
      return decoded;
  }
  
  /**
   * Derive the .b32.i2p address of an I2P destination (binary).
   * @param[in] dest I2P destination.
   * @return the address that corresponds to `dest`
   * @throw std::runtime_error if conversion fails
   */
  static CNetAddr DestBinToAddr(const Binary& dest)
  {
      CSHA256 hasher;
      hasher.Write(dest.data(), dest.size());
      unsigned char hash[CSHA256::OUTPUT_SIZE];
      hasher.Finalize(hash);
  
      CNetAddr addr;
      const std::string addr_str = EncodeBase32(hash, false) + ".b32.i2p";
      if (!addr.SetSpecial(addr_str)) {
          throw std::runtime_error(strprintf("Cannot parse I2P address: \"%s\"", addr_str));
      }
  
      return addr;
  }
  
  /**
   * Derive the .b32.i2p address of an I2P destination (I2P-style Base64).
   * @param[in] dest I2P destination.
   * @return the address that corresponds to `dest`
   * @throw std::runtime_error if conversion fails
   */
  static CNetAddr DestB64ToAddr(const std::string& dest)
  {
      const Binary& decoded = DecodeI2PBase64(dest);
      return DestBinToAddr(decoded);
  }
  
  namespace sam {
  
  Session::Session(const fs::path& private_key_file,
                   const CService& control_host,
                   CThreadInterrupt* interrupt)
      : m_private_key_file(private_key_file), m_control_host(control_host), m_interrupt(interrupt),
        m_control_sock(std::make_unique<Sock>(INVALID_SOCKET))
  {
  }
  
  Session::~Session()
  {
      LOCK(m_mutex);
      Disconnect();
  }
  
  bool Session::Listen(Connection& conn)
  {
      try {
          LOCK(m_mutex);
          CreateIfNotCreatedAlready();
          conn.me = m_my_addr;
          conn.sock = StreamAccept();
          return true;
      } catch (const std::runtime_error& e) {
          Log("Error listening: %s", e.what());
          CheckControlSock();
      }
      return false;
  }
  
  bool Session::Accept(Connection& conn)
  {
      try {
          while (!*m_interrupt) {
              Sock::Event occurred;
              if (!conn.sock->Wait(MAX_WAIT_FOR_IO, Sock::RECV, &occurred)) {
                  throw std::runtime_error("wait on socket failed");
              }
  
              if ((occurred & Sock::RECV) == 0) {
                  // Timeout, no incoming connections within MAX_WAIT_FOR_IO.
                  continue;
              }
  
              const std::string& peer_dest =
                  conn.sock->RecvUntilTerminator('\n', MAX_WAIT_FOR_IO, *m_interrupt, MAX_MSG_SIZE);
  
              conn.peer = CService(DestB64ToAddr(peer_dest), Params().GetDefaultPort());
  
              return true;
          }
      } catch (const std::runtime_error& e) {
          Log("Error accepting: %s", e.what());
          CheckControlSock();
      }
      return false;
  }
  
  bool Session::Connect(const CService& to, Connection& conn, bool& proxy_error)
  {
      proxy_error = true;
  
      std::string session_id;
      std::unique_ptr<Sock> sock;
      conn.peer = to;
  
      try {
          {
              LOCK(m_mutex);
              CreateIfNotCreatedAlready();
              session_id = m_session_id;
              conn.me = m_my_addr;
              sock = Hello();
          }
  
          const Reply& lookup_reply =
              SendRequestAndGetReply(*sock, strprintf("NAMING LOOKUP NAME=%s", to.ToStringIP()));
  
          const std::string& dest = lookup_reply.Get("VALUE");
  
          const Reply& connect_reply = SendRequestAndGetReply(
              *sock, strprintf("STREAM CONNECT ID=%s DESTINATION=%s SILENT=false", session_id, dest),
              false);
  
          const std::string& result = connect_reply.Get("RESULT");
  
          if (result == "OK") {
              conn.sock = std::move(sock);
              return true;
          }
  
          if (result == "INVALID_ID") {
              LOCK(m_mutex);
              Disconnect();
              throw std::runtime_error("Invalid session id");
          }
  
          if (result == "CANT_REACH_PEER" || result == "TIMEOUT") {
              proxy_error = false;
          }
  
          throw std::runtime_error(strprintf("\"%s\"", connect_reply.full));
      } catch (const std::runtime_error& e) {
          Log("Error connecting to %s: %s", to.ToString(), e.what());
          CheckControlSock();
          return false;
      }
  }
  
  // Private methods
  
  std::string Session::Reply::Get(const std::string& key) const
  {
      const auto& pos = keys.find(key);
      if (pos == keys.end() || !pos->second.has_value()) {
          throw std::runtime_error(
              strprintf("Missing %s= in the reply to \"%s\": \"%s\"", key, request, full));
      }
      return pos->second.value();
  }
  
  template <typename... Args>
  void Session::Log(const std::string& fmt, const Args&... args) const
  {
      LogPrint(BCLog::I2P, "I2P: %s\n", tfm::format(fmt, args...));
  }
  
  Session::Reply Session::SendRequestAndGetReply(const Sock& sock,
                                                 const std::string& request,
                                                 bool check_result_ok) const
  {
      sock.SendComplete(request + "\n", MAX_WAIT_FOR_IO, *m_interrupt);
  
      Reply reply;
  
      // Don't log the full "SESSION CREATE ..." because it contains our private key.
      reply.request = request.substr(0, 14) == "SESSION CREATE" ? "SESSION CREATE ..." : request;
  
      // It could take a few minutes for the I2P router to reply as it is querying the I2P network
      // (when doing name lookup, for example). Notice: `RecvUntilTerminator()` is checking
      // `m_interrupt` more often, so we would not be stuck here for long if `m_interrupt` is
      // signaled.
      static constexpr auto recv_timeout = 3min;
  
      reply.full = sock.RecvUntilTerminator('\n', recv_timeout, *m_interrupt, MAX_MSG_SIZE);
  
      for (const auto& kv : spanparsing::Split(reply.full, ' ')) {
          const auto& pos = std::find(kv.begin(), kv.end(), '=');
          if (pos != kv.end()) {
              reply.keys.emplace(std::string{kv.begin(), pos}, std::string{pos + 1, kv.end()});
          } else {
              reply.keys.emplace(std::string{kv.begin(), kv.end()}, std::nullopt);
          }
      }
  
      if (check_result_ok && reply.Get("RESULT") != "OK") {
          throw std::runtime_error(
              strprintf("Unexpected reply to \"%s\": \"%s\"", request, reply.full));
      }
  
      return reply;
  }
  
  std::unique_ptr<Sock> Session::Hello() const
  {
      auto sock = CreateSock(m_control_host);
  
      if (!sock) {
          throw std::runtime_error("Cannot create socket");
      }
  
      if (!ConnectSocketDirectly(m_control_host, *sock, nConnectTimeout, true)) {
          throw std::runtime_error(strprintf("Cannot connect to %s", m_control_host.ToString()));
      }
  
      SendRequestAndGetReply(*sock, "HELLO VERSION MIN=3.1 MAX=3.1");
  
      return sock;
  }
  
  void Session::CheckControlSock()
  {
      LOCK(m_mutex);
  
      std::string errmsg;
      if (!m_control_sock->IsConnected(errmsg)) {
          Log("Control socket error: %s", errmsg);
          Disconnect();
      }
  }
  
  void Session::DestGenerate(const Sock& sock)
  {
      // https://geti2p.net/spec/common-structures#key-certificates
      // "7" or "EdDSA_SHA512_Ed25519" - "Recent Router Identities and Destinations".
      // Use "7" because i2pd <2.24.0 does not recognize the textual form.
      const Reply& reply = SendRequestAndGetReply(sock, "DEST GENERATE SIGNATURE_TYPE=7", false);
  
      m_private_key = DecodeI2PBase64(reply.Get("PRIV"));
  }
  
  void Session::GenerateAndSavePrivateKey(const Sock& sock)
  {
      DestGenerate(sock);
  
      // umask is set to 077 in init.cpp, which is ok (unless -sysperms is given)
      if (!WriteBinaryFile(m_private_key_file,
                           std::string(m_private_key.begin(), m_private_key.end()))) {
          throw std::runtime_error(
              strprintf("Cannot save I2P private key to %s", m_private_key_file));
      }
  }
  
  Binary Session::MyDestination() const
  {
      // From https://geti2p.net/spec/common-structures#destination:
      // "They are 387 bytes plus the certificate length specified at bytes 385-386, which may be
      // non-zero"
      static constexpr size_t DEST_LEN_BASE = 387;
      static constexpr size_t CERT_LEN_POS = 385;
  
      uint16_t cert_len;
      memcpy(&cert_len, &m_private_key.at(CERT_LEN_POS), sizeof(cert_len));
      cert_len = be16toh(cert_len);
  
      const size_t dest_len = DEST_LEN_BASE + cert_len;
  
      return Binary{m_private_key.begin(), m_private_key.begin() + dest_len};
  }
  
  void Session::CreateIfNotCreatedAlready()
  {
      std::string errmsg;
      if (m_control_sock->IsConnected(errmsg)) {
          return;
      }
  
      Log("Creating SAM session with %s", m_control_host.ToString());
  
      auto sock = Hello();
  
      const auto& [read_ok, data] = ReadBinaryFile(m_private_key_file);
      if (read_ok) {
          m_private_key.assign(data.begin(), data.end());
      } else {
          GenerateAndSavePrivateKey(*sock);
      }
  
      const std::string& session_id = GetRandHash().GetHex().substr(0, 10); // full is an overkill, too verbose in the logs
      const std::string& private_key_b64 = SwapBase64(EncodeBase64(m_private_key));
  
      SendRequestAndGetReply(*sock, strprintf("SESSION CREATE STYLE=STREAM ID=%s DESTINATION=%s",
                                              session_id, private_key_b64));
  
      m_my_addr = CService(DestBinToAddr(MyDestination()), Params().GetDefaultPort());
      m_session_id = session_id;
      m_control_sock = std::move(sock);
  
      LogPrintf("I2P: SAM session created: session id=%s, my address=%s\n", m_session_id,
                m_my_addr.ToString());
  }
  
  std::unique_ptr<Sock> Session::StreamAccept()
  {
      auto sock = Hello();
  
      const Reply& reply = SendRequestAndGetReply(
          *sock, strprintf("STREAM ACCEPT ID=%s SILENT=false", m_session_id), false);
  
      const std::string& result = reply.Get("RESULT");
  
      if (result == "OK") {
          return sock;
      }
  
      if (result == "INVALID_ID") {
          // If our session id is invalid, then force session re-creation on next usage.
          Disconnect();
      }
  
      throw std::runtime_error(strprintf("\"%s\"", reply.full));
  }
  
  void Session::Disconnect()
  {
      if (m_control_sock->Get() != INVALID_SOCKET) {
          if (m_session_id.empty()) {
              Log("Destroying incomplete session");
          } else {
              Log("Destroying session %s", m_session_id);
          }
      }
      m_control_sock->Reset();
      m_session_id.clear();
  }
  } // namespace sam
  } // namespace i2p
  