simplify protocol

doc/protocol.md

@@ -8,11 +8,7 @@ Session::=
   Server: Accept ->
   Client: Connect ->
   OR (
-    (
-      Client: Hello ->
-      Procedure ->
-      Client: Disconnect
-    ),
+    Procedure,
     Client: Shutdown
   )
 

src/client.c

@@ -16,8 +16,6 @@
 /// \note Needs to stay in sync with `server.cxx`
 enum {
   SIONFWD_MESSAGE_TYPE_SHUTDOWN, ///< instruct the server to shut down
-  SIONFWD_MESSAGE_TYPE_HELLO, ///< greet the server after establishing a connection
-  SIONFWD_MESSAGE_TYPE_DISCONNECT, ///< disconnect from the server
   SIONFWD_MESSAGE_TYPE_OPEN, ///< open a file
   SIONFWD_MESSAGE_TYPE_CLOSE, ///< close a file
   SIONFWD_MESSAGE_TYPE_PWRITE, ///< write at position
@@ -51,8 +49,6 @@ static MPI_Comm sionfwd_connect(void) {
   MPI_Comm connection;
   MPI_Comm_connect(port, MPI_INFO_NULL, 0, MPI_COMM_SELF, &connection);
 
-  MPI_Ssend(&(int){ SIONFWD_MESSAGE_TYPE_HELLO }, 1, MPI_INT, 0, 0, connection);
-
   return connection;
 }
 
@@ -64,7 +60,6 @@ static MPI_Comm sionfwd_connect(void) {
 ///
 /// \param[in,out] comm The connection to tear down, set to `MPI_COMM_NULL` on return
 static void sionfwd_disconnect(MPI_Comm *comm) {
-  MPI_Ssend(&(int){ SIONFWD_MESSAGE_TYPE_DISCONNECT }, 1, MPI_INT, 0, 0, *comm);
   MPI_Comm_disconnect(comm);
   assert(*comm == MPI_COMM_NULL);
 }

src/server.cxx

@@ -50,8 +50,6 @@ enum {
 /// \note Needs to stay in sync with `client.c`
 enum class MessageType : int {
   Shutdown,
-  Hello,
-  Disconnect,
   Open,
   Close,
   Pwrite,
@@ -114,12 +112,6 @@ private:
 /// \brief An instruction to shut down
 struct Shutdown {};
 
-/// \brief A greeting from the client
-struct Hello {};
-
-/// \brief A farewell from a disconnecting client
-struct Disconnect {};
-
 /// \brief Instruction to open a file
 struct Open {
   /// \brief Constructs from a partially decoded message
@@ -275,8 +267,6 @@ struct Unknown {};
 /// \brief Messages of various kinds
 using Message = std::variant<
   Shutdown,
-  Hello,
-  Disconnect,
   Open,
   Close,
   Pwrite,
@@ -335,10 +325,6 @@ struct Communicator {
     switch (MessageType{type}) {
       case MessageType::Shutdown:
         return Shutdown{};
-      case MessageType::Hello:
-        return Hello{};
-      case MessageType::Disconnect:
-        return Disconnect{};
       case MessageType::Open:
         return Open{std::move(decoder)};
       case MessageType::Close:
@@ -388,21 +374,61 @@ private:
   MPI_Comm comm_;
 };
 
-/// \brief Receives (and handles) messages from a client until the client disconnects
-struct CommunicatorReceiver {
+/// \brief An MPI port that can accept new connections
+struct Port {
+  /// \brief Open a port
+  Port() noexcept {
+    std::array<char, MPI_MAX_PORT_NAME> name;
+    MPI_Open_port(MPI_INFO_NULL, name.data());
+    name_ = name.data();
+  }
+
+  /// \brief Copying not allowed
+  Port(const Port&) = delete;
+  /// \brief Construct by moving
+  Port(Port&& other) noexcept : name_{std::move(other.name_)} {
+    other.name_.clear();
+  }
+
+  /// \brief Copying not allowed
+  Port& operator=(const Port&) = delete;
+  /// \brief Assign by moving
+  Port& operator=(Port&& other) noexcept {
+    std::string temp{std::move(other.name_)};
+    other.name_.clear();
+    if (!name_.empty()) { MPI_Close_port(name_.c_str()); }
+    name_ = std::move(temp);
+    return *this;
+  }
+
+  /// \brief Close the port at end of life time
+  ~Port() {
+    if (!name_.empty()) { MPI_Close_port(name_.c_str()); }
+  }
+
+  /// \brief Name of the port, used for connecting
+  [[nodiscard]] const std::string& name() const {
+    return this->name_;
+  }
+
+  /// \brief Accept a new connection from a client
+  [[nodiscard]] Communicator accept() const {
+    MPI_Comm comm;
+    MPI_Comm_accept(name_.c_str(), MPI_INFO_NULL, 0, MPI_COMM_SELF, &comm);
+    return Communicator{comm};
+  }
+
+private:
+    std::string name_;
+};
+
+/// \brief Accepts new client connections on an open port
+struct PortAcceptor {
   /// \brief Performs actions based on a message from the client
   struct MessageVisitor {
     /// \brief Construct from a \ref Communicator
     explicit MessageVisitor(Communicator& communicator) noexcept : communicator_{communicator} {}
 
-    /// \brief Handle \ref Disconnect message
-    bool operator()(Disconnect&& args) {
-      if (debug) {
-        std::cerr << "got a disconnect message" << std::endl;
-      }
-      return false;
-    }
-
     /// \brief Handle \ref Open message
     bool operator()(Open&& args) {
       if (debug) {
@@ -521,6 +547,14 @@ struct CommunicatorReceiver {
       return true;
     }
 
+    /// \brief Handle \ref Shutdown message
+    bool operator()(Shutdown&& args) {
+      if (debug) {
+        std::cerr << "got a shutdown message" << std::endl;
+      }
+      return false;
+    }
+
     /// \brief Handle an unexpected message
     template<typename T>
     bool operator()(T&& args) {
@@ -531,76 +565,6 @@ struct CommunicatorReceiver {
     Communicator& communicator_;
   };
 
-  /// \brief Construct from a \ref Communicator
-  explicit CommunicatorReceiver(Communicator&& communicator) noexcept : communicator_{std::move(communicator)} {
-    if (debug) {
-      std::cerr << "launching a CommunicatorReceiver" << std::endl;
-    }
-  }
-
-  /// \brief Receive (and handle) messages
-  void operator()() {
-    bool go_on;
-    do {
-      Message message{communicator_.receive()};
-      go_on = std::visit(MessageVisitor{communicator_}, std::move(message));
-    } while (go_on);
-  }
-
-private:
-  Communicator communicator_;
-};
-
-/// \brief An MPI port that can accept new connections
-struct Port {
-  /// \brief Open a port
-  Port() noexcept {
-    std::array<char, MPI_MAX_PORT_NAME> name;
-    MPI_Open_port(MPI_INFO_NULL, name.data());
-    name_ = name.data();
-  }
-
-  /// \brief Copying not allowed
-  Port(const Port&) = delete;
-  /// \brief Construct by moving
-  Port(Port&& other) noexcept : name_{std::move(other.name_)} {
-    other.name_.clear();
-  }
-
-  /// \brief Copying not allowed
-  Port& operator=(const Port&) = delete;
-  /// \brief Assign by moving
-  Port& operator=(Port&& other) noexcept {
-    std::string temp{std::move(other.name_)};
-    other.name_.clear();
-    if (!name_.empty()) { MPI_Close_port(name_.c_str()); }
-    name_ = std::move(temp);
-    return *this;
-  }
-
-  /// \brief Close the port at end of life time
-  ~Port() {
-    if (!name_.empty()) { MPI_Close_port(name_.c_str()); }
-  }
-
-  /// \brief Name of the port, used for connecting
-  [[nodiscard]] const std::string& name() const {
-    return this->name_;
-  }
-
-  /// \brief Accept a new connection from a client
-  [[nodiscard]] Communicator accept() const {
-    MPI_Comm comm;
-    MPI_Comm_accept(name_.c_str(), MPI_INFO_NULL, 0, MPI_COMM_SELF, &comm);
-    return Communicator{comm};
-  }
-
-private:
-    std::string name_;
-};
-
-/// \brief Accepts new client connections on an open port
-struct PortAcceptor {
   /// \brief Construct from an open \ref Port
   explicit PortAcceptor(Port&& port) noexcept : port_{std::move(port)} {
     if (debug) {
@@ -610,18 +574,15 @@ struct PortAcceptor {
 
   /// \brief Accept new connections until \ref Shutdown \ref Message is received
   void operator()() {
-    while (true) {
+    bool go_on;
+    do {
       if (debug) {
         std::cerr << "accepting new connections" << std::endl;
       }
       Communicator client{port_.accept()};
       Message message{client.receive()};
-      if (std::holds_alternative<Shutdown>(message)) { break; }
-      if (!std::holds_alternative<Hello>(message)) {
-        throw std::runtime_error{"unexpected message type"};
-      }
-      CommunicatorReceiver{std::move(client)}();
-    }
+      go_on = std::visit(MessageVisitor{client}, std::move(message));
+    } while (go_on);
   }
 
 private: