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\chapter{The SOCKETS unit.}
\label{ch:socketsunit}

\FPCexampledir{sockex}
This chapter describes the SOCKETS unit for Free Pascal. 
it was written for \linux by Micha\"el Van Canneyt, and ported to \windows
by Florian Kl\"ampfl.
The chapter is divided in 2 sections:
\begin{itemize}
\item The first section lists types, constants and variables from the
interface part of the unit.
\item The second section describes the functions defined in the unit.
\end{itemize}
\section {Types, Constants and variables : }
The following constants identify the different socket types, as needed in
the \seef{Socket} call.
\begin{verbatim}
SOCK_STREAM     = 1; { stream (connection) socket   }
SOCK_DGRAM      = 2; { datagram (conn.less) socket  }
SOCK_RAW        = 3; { raw socket                   }
SOCK_RDM        = 4; { reliably-delivered message   }
SOCK_SEQPACKET  = 5; { sequential packet socket     }
SOCK_PACKET     =10;
\end{verbatim}
The following constants determine the socket domain, they are used in the
\seef{Socket} call.
\begin{verbatim}
AF_UNSPEC       = 0;
AF_UNIX         = 1; { Unix domain sockets          }
AF_INET         = 2; { Internet IP Protocol         }
AF_AX25         = 3; { Amateur Radio AX.25          }
AF_IPX          = 4; { Novell IPX                   }
AF_APPLETALK    = 5; { Appletalk DDP                }
AF_NETROM       = 6; { Amateur radio NetROM         }
AF_BRIDGE       = 7; { Multiprotocol bridge         }
AF_AAL5         = 8; { Reserved for Werner's ATM    }
AF_X25          = 9; { Reserved for X.25 project    }
AF_INET6        = 10; { IP version 6                 }
AF_MAX          = 12;
\end{verbatim}
The following constants determine the protocol family, they are used in the
\seef{Socket} call.
\begin{verbatim} 
PF_UNSPEC       = AF_UNSPEC;
PF_UNIX         = AF_UNIX;
PF_INET         = AF_INET;
PF_AX25         = AF_AX25;
PF_IPX          = AF_IPX;
PF_APPLETALK    = AF_APPLETALK;
PF_NETROM       = AF_NETROM;
PF_BRIDGE       = AF_BRIDGE;
PF_AAL5         = AF_AAL5;
PF_X25          = AF_X25;
PF_INET6        = AF_INET6;
PF_MAX          = AF_MAX;   
\end{verbatim}
The following types are used to store different kinds of eddresses for the
\seef{Bind}, \seef{Recv} and \seef{Send} calls.
\begin{verbatim}  
TSockAddr = packed Record
  family:word;
  data  :array [0..13] of char;
  end;
TUnixSockAddr = packed Record
  family:word;
  path:array[0..108] of char;
  end;
TInetSockAddr = packed Record
  family:Word;
  port  :Word;
  addr  :Cardinal;
  pad   :array [1..8] of byte; 
  end;
\end{verbatim}
The following type is returned by the \seef{SocketPair} call.
\begin{verbatim}
TSockArray = Array[1..2] of Longint;
\end{verbatim}
\section {Functions and Procedures}
\begin{function}{Accept}
\Declaration
Function Accept (Sock:Longint;Var Addr;Var Addrlen:Longint) : Longint;

\Description
\var{Accept} accepts a connection from a socket \var{Sock}, which was
listening for a connection. If a connection is accepted, a file descriptor
is returned. On error \var{-1} is returned. The returned socket may NOT 
be used to accept more connections.  The original socket remains open.

The \var{Accept} call fills the address of the connecting entity in 
\var{Addr}, and sets its length in \var{Addrlen}. \var{Addr} should 
be pointing to enough space, and \var{Addrlen} should be set to the 
amount of space available, prior to the call.

\Errors
On error, \var{-1} is returned, and errors are reported in 
\var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF]  The socket descriptor is invalid.
\item[SYS\_ENOTSOCK]  The descriptor is not a socket.
\item[SYS\_EOPNOTSUPP]  The socket type doesn't support the \var{Listen}
operation.
\item[SYS\_EFAULT]  \var{Addr} points outside your address space.
\item[SYS\_EWOULDBLOCK]  The requested operation would block the process.
\end{description}

\SeeAlso
\seef{Listen}, \seef{Connect}
\end{function}

\FPCexample{socksvr}

\begin{functionl}{Accept}{AltAAccept}
\Declaration
Function Accept (Sock:longint;var addr:string;var SockIn,SockOut:text) : Boolean;

\Description
This is an alternate form of the \seef{Accept} command. It is equivalent
to subsequently calling the regular \seef{Accept}
function and the \seep{Sock2Text} function.
The function returns \var{True} if successfull, \var{False} otherwise.

\Errors
The errors are those of \seef{Accept}.
\SeeAlso
\seef{Accept}
\end{functionl}
\begin{functionl}{Accept}{AltBAccept}
\Declaration
Function Accept (Sock:longint;var addr:string;var SockIn,SockOut:File) : Boolean;

\Description
 This is an alternate form of the \seef{Accept} command. 
It is equivalent
to subsequently calling the regular \seef{Accept} function and the 
\seep{Sock2File} function.
The \var{Addr} parameter contains the name of the unix socket file to be
opened. 
The function returns \var{True} if successfull, \var{False} otherwise.

\Errors
The errors are those of \seef{Accept}.
\SeeAlso
\seef{Accept}
\end{functionl}
\begin{functionl}{Accept}{AltCAccept}
\Declaration
Function Accept (Sock:longint;var addr:TInetSockAddr;var SockIn,SockOut:File) : Boolean;
\Description
 This is an alternate form of the \seef{Accept} command. 
It is equivalent
to subsequently calling the regular \seef{Accept} function and the 
\seep{Sock2File} function.
The \var{Addr} parameter contains the parameters of the internet socket that
should be opened.
The function returns \var{True} if successfull, \var{False} otherwise.

\Errors
The errors are those of \seef{Accept}.
\SeeAlso
\seef{Accept}
\end{functionl}
\begin{function}{Bind}
\Declaration
Function Bind (Sock:Longint;Var Addr;AddrLen:Longint) : Boolean;

\Description
\var{Bind} binds the socket \var{Sock} to address \var{Addr}. \var{Addr}
has length \var{Addrlen}.
The function returns \var{True} if the call was succesful, \var{False} if
not.

\Errors
Errors are returned in \var{SocketError} and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_EINVAL] The socket is already bound to an address,
\item[SYS\_EACCESS] Address is protected and you don't have permission to
open it.
\end{description}
More arrors can be found in the Unix man pages.

\SeeAlso
\seef{Socket}
\end{function}
\begin{functionl}{Bind}{AltBind}
\Declaration
Function Bind (Sock:longint;const addr:string) : boolean;

\Description
This is an alternate form of the \var{Bind} command.
This form of the \var{Bind} command is equivalent to subsequently 
calling \seep{Str2UnixSockAddr} and the regular \seef{Bind} function.
The function returns \var{True} if successfull, \var{False} otherwise.

\Errors
Errors are those of the regular \seef{Bind} command.
\SeeAlso
\seef{Bind}
\end{functionl}
\begin{function}{Connect}
\Declaration
Function Connect (Sock:Longint;Var Addr;Addrlen:Longint) : Longint;

\Description
\var{Connect} opens a connection to a peer, whose address is described by
\var{Addr}. \var{AddrLen} contains the length of the address.
The type of \var{Addr} depends on the kind of connection you're trying to
make, but is generally one of \var{TSockAddr} or \var{TUnixSockAddr}.

The \var{Connect} function returns a file descriptor if the call
was successfull, \var{-1} in case of error.
\Errors
On error, \var{-1} is returned and errors are reported in 
\var{SocketError}.
\SeeAlso
\seef{Listen}, \seef{Bind},\seef{Accept}
\end{function}
\FPCexample{sockcli}
\begin{functionl}{Connect}{AltAConnect}
\Declaration
Function Connect (Sock:longint;const addr:string;var SockIn,SockOut:text) : Boolean;

\Description
 This is an alternate form of the \seef{Connect} command. 
It is equivalent to subsequently calling the regular \seef{Connect} 
function and the  \seep{Sock2Text} function.
The function returns \var{True} if successfull, \var{False} otherwise.

\Errors
The errors are those of \seef{Connect}.
\SeeAlso
\seef{Connect}
\end{functionl}
\begin{functionl}{Connect}{AltBConnect}
\Declaration
Function Connect (Sock:longint;const addr:string;var SockIn,SockOut:file) : Boolean;

\Description
 This is an alternate form of the \seef{Connect} command. The parameter
\var{addr} contains the name of the unix socket file to be opened. 
It is equivalent to subsequently calling the regular \seef{Connect} 
function and the  \seep{Sock2File} function.
The function returns \var{True} if successfull, \var{False} otherwise.

\Errors
The errors are those of \seef{Connect}.
\SeeAlso
\seef{Connect}
\end{functionl}
\begin{functionl}{Connect}{AltCConnect}
\Declaration
Function Connect (Sock:longint;const addr: TInetSockAddr;var SockIn,SockOut:file) : Boolean;

\Description
 This is another alternate form of the \seef{Connect} command. 
It is equivalent
to subsequently calling the regular \seef{Connect} function and the 
\seep{Sock2File} function. The \var{Addr} parameter contains the parameters
of the internet socket to connect to.
The function returns \var{True} if successfull, \var{False} otherwise.

\Errors
The errors are those of \seef{Connect}.
\SeeAlso
\seef{Connect}
\end{functionl}
\FPCexample{pfinger}

\begin{function}{GetPeerName}
\Declaration
Function GetPeerName (Sock:Longint;Var Addr;Var Addrlen:Longint) : Longint;

\Description
\var{GetPeerName} returns the name of the entity connected to the 
specified socket \var{Sock}. The Socket must be connected for this call to
work. 
\var{Addr} should point to enough space to store the name, the
amount of space pointed to should be set in \var{Addrlen}. 
When the function returns succesfully, \var{Addr} will be filled with the 
name, and \var{Addrlen} will be set to the length of \var{Addr}.

\Errors
Errors are reported in \var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOBUFS] The system doesn't have enough buffers to perform the
operation.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\item[SYS\_EFAULT] \var{Addr} points outside your address space.
\item[SYS\_ENOTCONN] The socket isn't connected.
\end{description}

\SeeAlso
\seef{Connect}, \seef{Socket}, \seem{connect}{2}
\end{function}
\begin{function}{GetSocketName}
\Declaration
Function GetSocketName (Sock:Longint;Var Addr;Var Addrlen:Longint) : Longint;

\Description
\var{GetSockName} returns the current name of the specified socket
\var{Sock}. \var{Addr} should point to enough space to store the name, the
amount of space pointed to should be set in \var{Addrlen}. 
When the function returns succesfully, \var{Addr} will be filled with the 
name, and \var{Addrlen} will be set to the length of \var{Addr}.
\Errors
Errors are reported in \var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOBUFS] The system doesn't have enough buffers to perform the
operation.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\item[SYS\_EFAULT] \var{Addr} points outside your address space.
\end{description}

\SeeAlso
\seef{Bind}
\end{function}
\begin{function}{GetSocketOptions}
\Declaration
Function GetSocketOptions (Sock,Level,OptName:Longint;Var OptVal;optlen:longint) : Longint;

\Description
\var{GetSocketOptions} gets the connection options for socket \var{Sock}.
The socket may be obtained from different levels, indicated by \var{Level},
which can be one of the following:
\begin{description}
\item[SOL\_SOCKET] From the socket itself. 
\item[XXX] set \var{Level} to \var{XXX}, the protocol number of the protocol
which should interprete the option.
 \end{description}
For more information on this call, refer to the unix manual page \seem{getsockopt}{2}.

\Errors
Errors are reported in \var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\item[SYS\_EFAULT] \var{OptVal} points outside your address space.
\end{description}

\SeeAlso
\seef{GetSocketOptions}
\end{function}
\begin{function}{Listen}
\Declaration
Function Listen (Sock,MaxConnect:Longint) : Boolean;

\Description
\var{Listen} listens for up to \var{MaxConnect} connections from socket
\var{Sock}. The socket \var{Sock} must be of type \var{SOCK\_STREAM} or
\var{Sock\_SEQPACKET}.
The function returns \var{True} if a connection was accepted, \var{False} 
if an error occurred.

\Errors
Errors are reported in \var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\item[SYS\_EOPNOTSUPP] The socket type doesn't support the \var{Listen}
operation.
\end{description}

\SeeAlso
\seef{Socket}, \seef{Bind}, \seef{Connect}
\end{function}
\begin{function}{Recv}
\Declaration
Function Recv (Sock:Longint;Var Addr;AddrLen,Flags:Longint) : Longint;

\Description
\var{Recv} reads at most \var{Addrlen} bytes from socket \var{Sock} into
address \var{Addr}. The socket must be in a connected state.
\var{Flags} can be one of the following:
\begin{description}
\item [1] : Process out-of band data.
\item [4] : Bypass routing, use a direct interface.
\item [??] : Wait for full request or report an error.
\end{description}
The functions returns the number of bytes actually read from the socket, or
-1 if a detectable error occurred.
\Errors
Errors are reported in \var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOTCONN] The socket isn't connected.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\item[SYS\_EFAULT] The address is outside your address space.
\item[SYS\_EMSGSIZE] The message cannot be sent atomically.
\item[SYS\_EWOULDBLOCK] The requested operation would block the process.
\item[SYS\_ENOBUFS] The system doesn't have enough free buffers available.
\end{description}

\SeeAlso
\seef{Send}
\end{function}
\begin{function}{Send}
\Declaration
Function Send (Sock:Longint;Var Addr;AddrLen,Flags:Longint) : Longint;

\Description
\var{Send} sends \var{AddrLen} bytes starting from address \var{Addr}
to socket \var{Sock}. \var{Sock} must be in a connected state.
The function returns the number of bytes sent, or -1 if a detectable 
error occurred.
\var{Flags} can be one of the following:
\begin{description}
\item [1] : Process out-of band data.
\item [4] : Bypass routing, use a direct interface.
\end{description}

\Errors
Errors are reported in \var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\item[SYS\_EFAULT] The address is outside your address space.
\item[SYS\_EMSGSIZE] The message cannot be sent atomically.
\item[SYS\_EWOULDBLOCK] The requested operation would block the process.
\item[SYS\_ENOBUFS] The system doesn't have enough free buffers available.
\end{description}

\SeeAlso
\seef{Recv}, \seem{send}{2}
\end{function}
\begin{function}{SetSocketOptions}
\Declaration
Function SetSocketOptions (Sock,Level,OptName:Longint;Var OptVal;optlen:longint) : Longint;

\Description
\var{SetSocketOptions} sets the connection options for socket \var{Sock}.
The socket may be manipulated at different levels, indicated by \var{Level},
which can be one of the following:
\begin{description}
\item[SOL\_SOCKET] To manipulate the socket itself. 
\item[XXX] set \var{Level} to \var{XXX}, the protocol number of the protocol
which should interprete the option.
 \end{description}
For more information on this call, refer to the unix manual page \seem{setsockopt}{2}.

\Errors
Errors are reported in \var{SocketError}, and include the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\item[SYS\_EFAULT] \var{OptVal} points outside your address space.
\end{description}

\SeeAlso
\seef{GetSocketOptions}
\end{function}
\begin{function}{Shutdown}
\Declaration
Function Shutdown (Sock:Longint;How:Longint) : Longint;

\Description
\var{ShutDown} closes one end of a full duplex socket connection, described
by \var{Sock}. \var{How} determines how the connection will be shut down,
and can be one of the following:
\begin{description}
\item[0] : Further receives are disallowed.
\item[1] : Further sends are disallowed.
\item[2] : Sending nor receiving are allowed.
\end{description}
On succes, the function returns 0, on error -1 is returned.

\Errors
\var{SocketError} is used to report errors, and includes the following:
\begin{description}
\item[SYS\_EBADF] The socket descriptor is invalid.
\item[SYS\_ENOTCONN] The socket isn't connected.
\item[SYS\_ENOTSOCK] The descriptor is not a socket.
\end{description}

\SeeAlso
\seef{Socket}, \seef{Connect}
\end{function}
\begin{procedure}{Sock2File}
\Declaration
Procedure Sock2File (Sock:Longint;Var SockIn,SockOut:File);

\Description
\var{Sock2File} transforms a socket \var{Sock} into 2 Pascal file
descriptors of type \var{File}, one for reading from the socket
(\var{SockIn}), one for writing to the socket (\var{SockOut}).
\Errors
None.
\SeeAlso
\seef{Socket}, \seep{Sock2Text}
\end{procedure}
\begin{procedure}{Sock2Text}
\Declaration
Procedure Sock2Text (Sock:Longint;Var SockIn,SockOut: Text);

\Description
\var{Sock2Text} transforms a socket \var{Sock} into 2 Pascal file
descriptors of type \var{Text}, one for reading from the socket
(\var{SockIn}), one for writing to the socket (\var{SockOut}).
\Errors
None.
\SeeAlso
\seef{Socket}, \seep{Sock2File}
\end{procedure}
\begin{function}{Socket}
\Declaration
Function Socket (Domain,SocketType,Protocol:Longint) : Longint;

\Description
\var{Socket} creates a new socket in domain \var{Domain}, from type
\var{SocketType} using protocol \var{Protocol}.
The Domain, Socket type and Protocol can be specified using predefined
constants (see the section on constants for available constants)
If succesfull, the function returns a socket descriptor, which can be passed
to a subsequent \seef{Bind} call. If unsuccesfull, the function returns -1.

\Errors
Errors are returned in \var{SocketError}, and include the follwing:
\begin{description}
\item[SYS\_EPROTONOSUPPORT]
The protocol type or the specified protocol is not
supported within this domain.
\item[SYS\_EMFILE]
The per-process descriptor table is full.
\item[SYS\_ENFILE]
The system file table is full.
\item[SYS\_EACCESS]
 Permission  to  create  a  socket of the specified
 type and/or protocol is denied.
\item[SYS\_ENOBUFS]
 Insufficient  buffer  space  is  available.    The
 socket   cannot   be   created   until  sufficient
 resources are freed.
\end{description}
\SeeAlso
\seef{SocketPair}, \seem{socket}{2}
\end{function}

for an example, see \seef{Accept}.

\begin{function}{SocketPair}
\Declaration
Function SocketPair (Domain,SocketType,Protocol:Longint;var Pair:TSockArray) : Longint;
\Description
\var{SocketPair} creates 2 sockets in domain \var{Domain}, from type
\var{SocketType} and using protocol \var{Protocol}.
The pair is returned in \var{Pair}, and they are indistinguishable.
The function returns -1 upon error and 0 upon success.
\Errors
Errors are reported in \var{SocketError}, and are the same as in \seef{Socket}
\SeeAlso
\seep{Str2UnixSockAddr}
\end{function}

\begin{procedure}{Str2UnixSockAddr}
\Declaration
Procedure Str2UnixSockAddr(const addr:string;var t:TUnixSockAddr;var len:longint)
\Description
\var{Str2UnixSockAddr} transforms a Unix socket address in a string to a
\var{TUnixSockAddr} structure which can be passed to the \seef{Bind} call.
\Errors
None.
\SeeAlso
\seef{Socket}, \seef{Bind}
\end{procedure}