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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                         G N A T . S O C K E T S                          --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                     Copyright (C) 2001-2009, AdaCore                     --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 2,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT;  see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, USA.                                              --

--                                                                          --

-- As a special exception,  if other files  instantiate  generics from this --

-- unit, or you link  this unit with other files  to produce an executable, --

-- this  unit  does not  by itself cause  the resulting  executable  to  be --

-- covered  by the  GNU  General  Public  License.  This exception does not --

-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

--  This package provides an interface to the sockets communication facility

--  provided on many operating systems. This is implemented on the following

--  platforms:

--     All native ports, with restrictions as follows

--       Multicast is available only on systems which provide support for this

--       feature, so it is not available if Multicast is not supported, or not

--       installed.

--       The VMS implementation was implemented using the DECC RTL Socket API,

--       and is thus subject to limitations in the implementation of this API.

--     VxWorks cross ports fully implement this package

--     This package is not yet implemented on LynxOS or other cross ports

with Ada.Exceptions;

with Ada.Streams;

with Ada.Unchecked_Deallocation;

with Interfaces.C;

with System.OS_Constants;

with System.Storage_Elements;

package GNAT.Sockets is

   --  Sockets are designed to provide a consistent communication facility

   --  between applications. This package provides an Ada binding to the

   --  the de-facto standard BSD sockets API. The documentation below covers

   --  only the specific binding provided by this package. It assumes that

   --  the reader is already familiar with general network programming and

   --  sockets usage. A useful reference on this matter is W. Richard Stevens'

   --  "UNIX Network Programming: The Sockets Networking API"

   --  (ISBN: 0131411551).

   --  GNAT.Sockets has been designed with several ideas in mind

   --  This is a system independent interface. Therefore, we try as much as

   --  possible to mask system incompatibilities. Some functionalities are not

   --  available because there are not fully supported on some systems.

   --  This is a thick binding. For instance, a major effort has been done to

   --  avoid using memory addresses or untyped ints. We preferred to define

   --  streams and enumeration types. Errors are not returned as returned

   --  values but as exceptions.

   --  This package provides a POSIX-compliant interface (between two

   --  different implementations of the same routine, we adopt the one closest

   --  to the POSIX specification). For instance, using select(), the

   --  notification of an asynchronous connect failure is delivered in the

   --  write socket set (POSIX) instead of the exception socket set (NT).

   --  The example below demonstrates various features of GNAT.Sockets:

   --  with GNAT.Sockets; use GNAT.Sockets;

   --  with Ada.Text_IO;

   --  with Ada.Exceptions; use Ada.Exceptions;

   --  procedure PingPong is

   --     Group : constant String := "239.255.128.128";

   --     --  Multicast group: administratively scoped IP address

   --     task Pong is

   --        entry Start;

   --        entry Stop;

   --     end Pong;

   --     task body Pong is

   --        Address  : Sock_Addr_Type;

   --        Server   : Socket_Type;

   --        Socket   : Socket_Type;

   --        Channel  : Stream_Access;

   --     begin

   --        accept Start;

   --

   --        --  Get an Internet address of a host (here the local host name).

   --        --  Note that a host can have several addresses. Here we get

   --        --  the first one which is supposed to be the official one.

   --        Address.Addr := Addresses (Get_Host_By_Name (Host_Name), 1);

   --        --  Get a socket address that is an Internet address and a port

   --        Address.Port := 5876;

   --        --  The first step is to create a socket. Once created, this

   --        --  socket must be associated to with an address. Usually only a

   --        --  server (Pong here) needs to bind an address explicitly. Most

   --        --  of the time clients can skip this step because the socket

   --        --  routines will bind an arbitrary address to an unbound socket.

   --        Create_Socket (Server);

   --        --  Allow reuse of local addresses

   --        Set_Socket_Option

   --          (Server,

   --           Socket_Level,

   --           (Reuse_Address, True));

   --        Bind_Socket (Server, Address);

   --        --  A server marks a socket as willing to receive connect events

   --        Listen_Socket (Server);

   --        --  Once a server calls Listen_Socket, incoming connects events

   --        --  can be accepted. The returned Socket is a new socket that

   --        --  represents the server side of the connection. Server remains

   --        --  available to receive further connections.

   --        Accept_Socket (Server, Socket, Address);

   --        --  Return a stream associated to the connected socket

   --        Channel := Stream (Socket);

   --        --  Force Pong to block

   --        delay 0.2;

   --        --  Receive and print message from client Ping

   --        declare

   --           Message : String := String'Input (Channel);

   --        begin

   --           Ada.Text_IO.Put_Line (Message);

   --           --  Send same message back to client Ping

   --           String'Output (Channel, Message);

   --        end;

   --        Close_Socket (Server);

   --        Close_Socket (Socket);

   --        --  Part of the multicast example

   --        --  Create a datagram socket to send connectionless, unreliable

   --        --  messages of a fixed maximum length.

   --        Create_Socket (Socket, Family_Inet, Socket_Datagram);

   --        --  Allow reuse of local addresses

   --        Set_Socket_Option

   --          (Socket,

   --           Socket_Level,

   --           (Reuse_Address, True));

   --        --  Controls the live time of the datagram to avoid it being

   --        --  looped forever due to routing errors. Routers decrement

   --        --  the TTL of every datagram as it traverses from one network

   --        --  to another and when its value reaches 0 the packet is

   --        --  dropped. Default is 1.

   --        Set_Socket_Option

   --          (Socket,

   --           IP_Protocol_For_IP_Level,

   --           (Multicast_TTL, 1));

   --        --  Want the data you send to be looped back to your host

   --        Set_Socket_Option

   --          (Socket,

   --           IP_Protocol_For_IP_Level,

   --           (Multicast_Loop, True));

   --        --  If this socket is intended to receive messages, bind it

   --        --  to a given socket address.

   --        Address.Addr := Any_Inet_Addr;

   --        Address.Port := 55505;

   --        Bind_Socket (Socket, Address);

   --        --  Join a multicast group

   --        --  Portability note: On Windows, this option may be set only

   --        --  on a bound socket.

   --        Set_Socket_Option

   --          (Socket,

   --           IP_Protocol_For_IP_Level,

   --           (Add_Membership, Inet_Addr (Group), Any_Inet_Addr));

   --        --  If this socket is intended to send messages, provide the

   --        --  receiver socket address.

   --        Address.Addr := Inet_Addr (Group);

   --        Address.Port := 55506;

   --        Channel := Stream (Socket, Address);

   --        --  Receive and print message from client Ping

   --        declare

   --           Message : String := String'Input (Channel);

   --        begin

   --           --  Get the address of the sender

   --           Address := Get_Address (Channel);

   --           Ada.Text_IO.Put_Line (Message & " from " & Image (Address));

   --           --  Send same message back to client Ping

   --           String'Output (Channel, Message);

   --        end;

   --        Close_Socket (Socket);

   --        accept Stop;

   --     exception when E : others =>

   --        Ada.Text_IO.Put_Line

   --          (Exception_Name (E) & ": " & Exception_Message (E));

   --     end Pong;

   --     task Ping is

   --        entry Start;

   --        entry Stop;

   --     end Ping;

   --     task body Ping is

   --        Address  : Sock_Addr_Type;

   --        Socket   : Socket_Type;

   --        Channel  : Stream_Access;

   --     begin

   --        accept Start;

   --        --  See comments in Ping section for the first steps

   --        Address.Addr := Addresses (Get_Host_By_Name (Host_Name), 1);

   --        Address.Port := 5876;

   --        Create_Socket (Socket);

   --        Set_Socket_Option

   --          (Socket,

   --           Socket_Level,

   --           (Reuse_Address, True));

   --        --  Force Pong to block

   --        delay 0.2;

   --        --  If the client's socket is not bound, Connect_Socket will

   --        --  bind to an unused address. The client uses Connect_Socket to

   --        --  create a logical connection between the client's socket and

   --        --  a server's socket returned by Accept_Socket.

   --        Connect_Socket (Socket, Address);

   --        Channel := Stream (Socket);

   --        --  Send message to server Pong

   --        String'Output (Channel, "Hello world");

   --        --  Force Ping to block

   --        delay 0.2;

   --        --  Receive and print message from server Pong

   --        Ada.Text_IO.Put_Line (String'Input (Channel));

   --        Close_Socket (Socket);

   --        --  Part of multicast example. Code similar to Pong's one

   --        Create_Socket (Socket, Family_Inet, Socket_Datagram);

   --        Set_Socket_Option

   --          (Socket,

   --           Socket_Level,

   --           (Reuse_Address, True));

   --        Set_Socket_Option

   --          (Socket,

   --           IP_Protocol_For_IP_Level,

   --           (Multicast_TTL, 1));

   --        Set_Socket_Option

   --          (Socket,

   --           IP_Protocol_For_IP_Level,

   --           (Multicast_Loop, True));

   --        Address.Addr := Any_Inet_Addr;

   --        Address.Port := 55506;

   --        Bind_Socket (Socket, Address);

   --        Set_Socket_Option

   --          (Socket,

   --           IP_Protocol_For_IP_Level,

   --           (Add_Membership, Inet_Addr (Group), Any_Inet_Addr));

   --        Address.Addr := Inet_Addr (Group);

   --        Address.Port := 55505;

   --        Channel := Stream (Socket, Address);

   --        --  Send message to server Pong

   --        String'Output (Channel, "Hello world");

   --        --  Receive and print message from server Pong

   --        declare

   --           Message : String := String'Input (Channel);

   --        begin

   --           Address := Get_Address (Channel);

   --           Ada.Text_IO.Put_Line (Message & " from " & Image (Address));

   --        end;

   --        Close_Socket (Socket);

   --        accept Stop;

   --     exception when E : others =>

   --        Ada.Text_IO.Put_Line

   --          (Exception_Name (E) & ": " & Exception_Message (E));

   --     end Ping;

   --  begin

   --     Initialize;

   --     Ping.Start;

   --     Pong.Start;

   --     Ping.Stop;

   --     Pong.Stop;

   --     Finalize;

   --  end PingPong;

   package SOSC renames System.OS_Constants;

   --  Renaming used to provide short-hand notations throughout the sockets

   --  binding. Note that System.OS_Constants is an internal unit, and the

   --  entities declared therein are not meant for direct access by users,

   --  including through this renaming.

   procedure Initialize;

   pragma Obsolescent

     (Entity  => Initialize,

      Message => "explicit initialization is no longer required");

   --  Initialize must be called before using any other socket routines.

   --  Note that this operation is a no-op on UNIX platforms, but applications

   --  should make sure to call it if portability is expected: some platforms

   --  (such as Windows) require initialization before any socket operation.

   --  This is now a no-op (initialization and finalization are done

   --  automatically).

   procedure Initialize (Process_Blocking_IO : Boolean);

   pragma Obsolescent

     (Entity  => Initialize,

      Message => "passing a parameter to Initialize is no longer supported");

   --  Previous versions of GNAT.Sockets used to require the user to indicate

   --  whether socket I/O was process- or thread-blocking on the platform.

   --  This property is now determined automatically when the run-time library

   --  is built. The old version of Initialize, taking a parameter, is kept

   --  for compatibility reasons, but this interface is obsolete (and if the

   --  value given is wrong, an exception will be raised at run time).

   --  This is now a no-op (initialization and finalization are done

   --  automatically).

   procedure Finalize;

   pragma Obsolescent

     (Entity  => Finalize,

      Message => "explicit finalization is no longer required");

   --  After Finalize is called it is not possible to use any routines

   --  exported in by this package. This procedure is idempotent.

   --  This is now a no-op (initialization and finalization are done

   --  automatically).

   type Socket_Type is private;

   --  Sockets are used to implement a reliable bi-directional point-to-point,

   --  stream-based connections between hosts. No_Socket provides a special

   --  value to denote uninitialized sockets.

   No_Socket : constant Socket_Type;

   type Selector_Type is limited private;

   type Selector_Access is access all Selector_Type;

   --  Selector objects are used to wait for i/o events to occur on sockets

   --  Timeval_Duration is a subtype of Standard.Duration because the full

   --  range of Standard.Duration cannot be represented in the equivalent C

   --  structure. Moreover, negative values are not allowed to avoid system

   --  incompatibilities.

   Immediate : constant Duration := 0.0;

   Timeval_Forever : constant := 2.0 ** (SOSC.SIZEOF_tv_sec * 8 - 1) - 1.0;

   Forever         : constant Duration :=

                       Duration'Min (Duration'Last, Timeval_Forever);

   subtype Timeval_Duration is Duration range Immediate .. Forever;

   subtype Selector_Duration is Timeval_Duration;

   --  Timeout value for selector operations

   type Selector_Status is (Completed, Expired, Aborted);

   --  Completion status of a selector operation, indicated as follows:

   --    Complete: one of the expected events occurred

   --    Expired:  no event occurred before the expiration of the timeout

   --    Aborted:  an external action cancelled the wait operation before

   --              any event occurred.

   Socket_Error : exception;

   --  There is only one exception in this package to deal with an error during

   --  a socket routine. Once raised, its message contains a string describing

   --  the error code.

   function Image (Socket : Socket_Type) return String;

   --  Return a printable string for Socket

   function To_C (Socket : Socket_Type) return Integer;

   --  Return a file descriptor to be used by external subprograms. This is

   --  useful for C functions that are not yet interfaced in this package.

   type Family_Type is (Family_Inet, Family_Inet6);

   --  Address family (or protocol family) identifies the communication domain

   --  and groups protocols with similar address formats. IPv6 will soon be

   --  supported.

   type Mode_Type is (Socket_Stream, Socket_Datagram);

   --  Stream sockets provide connection-oriented byte streams. Datagram

   --  sockets support unreliable connectionless message based communication.

   type Shutmode_Type is (Shut_Read, Shut_Write, Shut_Read_Write);

   --  When a process closes a socket, the policy is to retain any data queued

   --  until either a delivery or a timeout expiration (in this case, the data

   --  are discarded). A finer control is available through shutdown. With

   --  Shut_Read, no more data can be received from the socket. With_Write, no

   --  more data can be transmitted. Neither transmission nor reception can be

   --  performed with Shut_Read_Write.

   type Port_Type is new Natural;

   --  Classical port definition. No_Port provides a special value to

   --  denote uninitialized port. Any_Port provides a special value

   --  enabling all ports.

   Any_Port : constant Port_Type;

   No_Port  : constant Port_Type;

   type Inet_Addr_Type (Family : Family_Type := Family_Inet) is private;

   --  An Internet address depends on an address family (IPv4 contains 4 octets

   --  and IPv6 contains 16 octets). Any_Inet_Addr is a special value treated

   --  like a wildcard enabling all addresses. No_Inet_Addr provides a special

   --  value to denote uninitialized inet addresses.

   Any_Inet_Addr       : constant Inet_Addr_Type;

   No_Inet_Addr        : constant Inet_Addr_Type;

   Broadcast_Inet_Addr : constant Inet_Addr_Type;

   Loopback_Inet_Addr  : constant Inet_Addr_Type;

   --  Useful constants for IPv4 multicast addresses

   Unspecified_Group_Inet_Addr : constant Inet_Addr_Type;

   All_Hosts_Group_Inet_Addr   : constant Inet_Addr_Type;

   All_Routers_Group_Inet_Addr : constant Inet_Addr_Type;

   type Sock_Addr_Type (Family : Family_Type := Family_Inet) is record

      Addr : Inet_Addr_Type (Family);

      Port : Port_Type;

   end record;

   --  Socket addresses fully define a socket connection with protocol family,

   --  an Internet address and a port. No_Sock_Addr provides a special value

   --  for uninitialized socket addresses.

   No_Sock_Addr : constant Sock_Addr_Type;

   function Image (Value : Inet_Addr_Type) return String;

   --  Return an image of an Internet address. IPv4 notation consists in 4

   --  octets in decimal format separated by dots. IPv6 notation consists in

   --  16 octets in hexadecimal format separated by colons (and possibly

   --  dots).

   function Image (Value : Sock_Addr_Type) return String;

   --  Return inet address image and port image separated by a colon

   function Inet_Addr (Image : String) return Inet_Addr_Type;

   --  Convert address image from numbers-and-dots notation into an

   --  inet address.

   --  Host entries provide complete information on a given host: the official

   --  name, an array of alternative names or aliases and array of network

   --  addresses.

   type Host_Entry_Type

     (Aliases_Length, Addresses_Length : Natural) is private;

   function Official_Name (E : Host_Entry_Type) return String;

   --  Return official name in host entry

   function Aliases_Length (E : Host_Entry_Type) return Natural;

   --  Return number of aliases in host entry

   function Addresses_Length (E : Host_Entry_Type) return Natural;

   --  Return number of addresses in host entry

   function Aliases

     (E : Host_Entry_Type;

      N : Positive := 1) return String;

   --  Return N'th aliases in host entry. The first index is 1

   function Addresses

     (E : Host_Entry_Type;

      N : Positive := 1) return Inet_Addr_Type;

   --  Return N'th addresses in host entry. The first index is 1

   Host_Error : exception;

   --  Exception raised by the two following procedures. Once raised, its

   --  message contains a string describing the error code. This exception is

   --  raised when an host entry cannot be retrieved.

   function Get_Host_By_Address

     (Address : Inet_Addr_Type;

      Family  : Family_Type := Family_Inet) return Host_Entry_Type;

   --  Return host entry structure for the given Inet address. Note that no

   --  result will be returned if there is no mapping of this IP address to a

   --  host name in the system tables (host database, DNS or otherwise).

   function Get_Host_By_Name

     (Name : String) return Host_Entry_Type;

   --  Return host entry structure for the given host name. Here name is

   --  either a host name, or an IP address. If Name is an IP address, this

   --  is equivalent to Get_Host_By_Address (Inet_Addr (Name)).

   function Host_Name return String;

   --  Return the name of the current host

   type Service_Entry_Type (Aliases_Length : Natural) is private;

   --  Service entries provide complete information on a given service: the

   --  official name, an array of alternative names or aliases and the port

   --  number.

   function Official_Name (S : Service_Entry_Type) return String;

   --  Return official name in service entry

   function Port_Number (S : Service_Entry_Type) return Port_Type;

   --  Return port number in service entry

   function Protocol_Name (S : Service_Entry_Type) return String;

   --  Return Protocol in service entry (usually UDP or TCP)

   function Aliases_Length (S : Service_Entry_Type) return Natural;

   --  Return number of aliases in service entry

   function Aliases

     (S : Service_Entry_Type;

      N : Positive := 1) return String;

   --  Return N'th aliases in service entry (the first index is 1)

   function Get_Service_By_Name

     (Name     : String;

      Protocol : String) return Service_Entry_Type;

   --  Return service entry structure for the given service name

   function Get_Service_By_Port

     (Port     : Port_Type;

      Protocol : String) return Service_Entry_Type;

   --  Return service entry structure for the given service port number

   Service_Error : exception;

   --  Comment required ???

   --  Errors are described by an enumeration type. There is only one exception

   --  Socket_Error in this package to deal with an error during a socket

   --  routine. Once raised, its message contains the error code between

   --  brackets and a string describing the error code.

   --  The name of the enumeration constant documents the error condition

   --  Note that on some platforms, a single error value is used for both

   --  EWOULDBLOCK and EAGAIN. Both errors are therefore always reported as

   --  Resource_Temporarily_Unavailable.

   type Error_Type is

     (Success,

      Permission_Denied,

      Address_Already_In_Use,

      Cannot_Assign_Requested_Address,

      Address_Family_Not_Supported_By_Protocol,

      Operation_Already_In_Progress,

      Bad_File_Descriptor,

      Software_Caused_Connection_Abort,

      Connection_Refused,

      Connection_Reset_By_Peer,

      Destination_Address_Required,

      Bad_Address,

      Host_Is_Down,

      No_Route_To_Host,

      Operation_Now_In_Progress,

      Interrupted_System_Call,

      Invalid_Argument,

      Input_Output_Error,

      Transport_Endpoint_Already_Connected,

      Too_Many_Symbolic_Links,

      Too_Many_Open_Files,

      Message_Too_Long,

      File_Name_Too_Long,

      Network_Is_Down,

      Network_Dropped_Connection_Because_Of_Reset,

      Network_Is_Unreachable,

      No_Buffer_Space_Available,

      Protocol_Not_Available,

      Transport_Endpoint_Not_Connected,

      Socket_Operation_On_Non_Socket,

      Operation_Not_Supported,

      Protocol_Family_Not_Supported,

      Protocol_Not_Supported,

      Protocol_Wrong_Type_For_Socket,

      Cannot_Send_After_Transport_Endpoint_Shutdown,

      Socket_Type_Not_Supported,

      Connection_Timed_Out,

      Too_Many_References,

      Resource_Temporarily_Unavailable,

      Broken_Pipe,

      Unknown_Host,

      Host_Name_Lookup_Failure,

      Non_Recoverable_Error,

      Unknown_Server_Error,

      Cannot_Resolve_Error);

   --  Get_Socket_Options and Set_Socket_Options manipulate options associated

   --  with a socket. Options may exist at multiple protocol levels in the

   --  communication stack. Socket_Level is the uppermost socket level.

   type Level_Type is (

     Socket_Level,

     IP_Protocol_For_IP_Level,

     IP_Protocol_For_UDP_Level,

     IP_Protocol_For_TCP_Level);

   --  There are several options available to manipulate sockets. Each option

   --  has a name and several values available. Most of the time, the value is

   --  a boolean to enable or disable this option.

   type Option_Name is (

     Keep_Alive,          -- Enable sending of keep-alive messages

     Reuse_Address,       -- Allow bind to reuse local address

     Broadcast,           -- Enable datagram sockets to recv/send broadcasts

     Send_Buffer,         -- Set/get the maximum socket send buffer in bytes

     Receive_Buffer,      -- Set/get the maximum socket recv buffer in bytes

     Linger,              -- Shutdown wait for msg to be sent or timeout occur

     Error,               -- Get and clear the pending socket error

     No_Delay,            -- Do not delay send to coalesce data (TCP_NODELAY)

     Add_Membership,      -- Join a multicast group

     Drop_Membership,     -- Leave a multicast group

     Multicast_If,        -- Set default out interface for multicast packets

     Multicast_TTL,       -- Set the time-to-live of sent multicast packets

     Multicast_Loop,      -- Sent multicast packets are looped to local socket

     Receive_Packet_Info, -- Receive low level packet info as ancillary data

     Send_Timeout,        -- Set timeout value for output

     Receive_Timeout);    -- Set timeout value for input

   type Option_Type (Name : Option_Name := Keep_Alive) is record

      case Name is

         when Keep_Alive          |

              Reuse_Address       |

              Broadcast           |

              Linger              |

              No_Delay            |

              Receive_Packet_Info |

              Multicast_Loop      =>

            Enabled : Boolean;

            case Name is

               when Linger    =>

                  Seconds : Natural;

               when others    =>

                  null;

            end case;

         when Send_Buffer     |

              Receive_Buffer  =>

            Size : Natural;

         when Error           =>

            Error : Error_Type;

         when Add_Membership  |

              Drop_Membership =>

            Multicast_Address : Inet_Addr_Type;

            Local_Interface   : Inet_Addr_Type;

         when Multicast_If    =>

            Outgoing_If : Inet_Addr_Type;

         when Multicast_TTL   =>

            Time_To_Live : Natural;

         when Send_Timeout |

              Receive_Timeout =>

            Timeout : Timeval_Duration;

      end case;

   end record;

   --  There are several controls available to manipulate sockets. Each option

   --  has a name and several values available. These controls differ from the

   --  socket options in that they are not specific to sockets but are

   --  available for any device.

   type Request_Name is (

      Non_Blocking_IO,  --  Cause a caller not to wait on blocking operations.

      N_Bytes_To_Read); --  Return the number of bytes available to read

   type Request_Type (Name : Request_Name := Non_Blocking_IO) is record

      case Name is

         when Non_Blocking_IO =>

            Enabled : Boolean;

         when N_Bytes_To_Read =>

            Size : Natural;

      end case;

   end record;

   --  A request flag allows to specify the type of message transmissions or

   --  receptions. A request flag can be combination of zero or more

   --  predefined request flags.

   type Request_Flag_Type is private;

   No_Request_Flag : constant Request_Flag_Type;

   --  This flag corresponds to the normal execution of an operation

   Process_Out_Of_Band_Data : constant Request_Flag_Type;

   --  This flag requests that the receive or send function operates on

   --  out-of-band data when the socket supports this notion (e.g.

   --  Socket_Stream).

   Peek_At_Incoming_Data : constant Request_Flag_Type;

   --  This flag causes the receive operation to return data from the beginning

   --  of the receive queue without removing that data from the queue. A

   --  subsequent receive call will return the same data.

   Wait_For_A_Full_Reception : constant Request_Flag_Type;

   --  This flag requests that the operation block until the full request is

   --  satisfied. However, the call may still return less data than requested

   --  if a signal is caught, an error or disconnect occurs, or the next data

   --  to be received is of a different type than that returned. Note that

   --  this flag depends on support in the underlying sockets implementation,

   --  and is not supported under Windows.

   Send_End_Of_Record : constant Request_Flag_Type;

   --  This flag indicates that the entire message has been sent and so this

   --  terminates the record.

   function "+" (L, R : Request_Flag_Type) return Request_Flag_Type;

   --  Combine flag L with flag R

   type Stream_Element_Reference is access all Ada.Streams.Stream_Element;

   type Vector_Element is record

      Base   : Stream_Element_Reference;

      Length : Ada.Streams.Stream_Element_Count;

   end record;

   type Vector_Type is array (Integer range <>) of Vector_Element;

   procedure Create_Socket

     (Socket : out Socket_Type;

      Family : Family_Type := Family_Inet;

      Mode   : Mode_Type   := Socket_Stream);

   --  Create an endpoint for communication. Raises Socket_Error on error

   procedure Accept_Socket

     (Server  : Socket_Type;

      Socket  : out Socket_Type;

      Address : out Sock_Addr_Type);

   --  Extracts the first connection request on the queue of pending

   --  connections, creates a new connected socket with mostly the same

   --  properties as Server, and allocates a new socket. The returned Address

   --  is filled in with the address of the connection. Raises Socket_Error on

   --  error.

   procedure Accept_Socket

     (Server   : Socket_Type;

      Socket   : out Socket_Type;

      Address  : out Sock_Addr_Type;

      Timeout  : Selector_Duration;

      Selector : access Selector_Type := null;

      Status   : out Selector_Status);

   --  Accept a new connection on Server using Accept_Socket, waiting no longer

   --  than the given timeout duration. Status is set to indicate whether the

   --  operation completed successfully, timed out, or was aborted. If Selector

   --  is not null, the designated selector is used to wait for the socket to

   --  become available, else a private selector object is created by this

   --  procedure and destroyed before it returns.

   procedure Bind_Socket

     (Socket  : Socket_Type;

      Address : Sock_Addr_Type);