bind9/doc/man/isc/isc_socket.3

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.\" $Id: isc_socket.3,v 1.2 2000/07/27 09:43:12 tale Exp $
.\" 
.Dd Jun 30, 2000
.Dt ISC_SOCKET 3
.Os BIND9 9
.ds vT BIND9 Programmer's Manual
.Sh NAME
.Nm isc_socket_create ,
.Nm isc_socket_attach ,
.Nm isc_socket_detach ,
.Nm isc_socketmgr_create ,
.Nm isc_socketmgr_destroy ,
.Nm isc_socket_recvv ,
.Nm isc_socket_recv ,
.Nm isc_socket_send ,
.Nm isc_socket_sendto ,
.Nm isc_socket_sendv ,
.Nm isc_socket_sendtov ,
.Nm isc_socket_bind ,
.Nm isc_socket_listen ,
.Nm isc_socket_accept ,
.Nm isc_socket_connect ,
.Nm isc_socket_getpeername ,
.Nm isc_socket_getsockname ,
.Nm isc_socket_cancel ,
.Nm isc_socket_recvmark ,
.Nm isc_socket_sendmark ,
.Nm isc_socket_gettype ,
.Nm isc_socket_isbound
.Nd name server network I/O
.Sh SYNOPSIS
.Fd #include <config.h>
.Fd 
.Fd #include <sys/param.h>
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Fd #include <sys/time.h>
.Fd #include <sys/uio.h>
.Fd 
.Fd #include <errno.h>
.Fd #include <stddef.h>
.Fd #include <stdlib.h>
.Fd #include <string.h>
.Fd #include <unistd.h>
.Fd #include <fcntl.h>
.Fd 
.Fd #include <isc/buffer.h>
.Fd #include <isc/bufferlist.h>
.Fd #include <isc/condition.h>
.Fd #include <isc/list.h>
.Fd #include <isc/log.h>
.Fd #include <isc/mem.h>
.Fd #include <isc/net.h>
.Fd #include <isc/print.h>
.Fd #include <isc/region.h>
.Fd #include <isc/socket.h>
.Fd #include <isc/task.h>
.Fd #include <isc/thread.h>
.Fd #include <isc/util.h>
.Fd 
.Ft isc_result_t
.Fo isc_socket_create
.Fa "isc_socketmgr_t *manager"
.Fa "int pf"
.Fa "isc_sockettype_t type"
.Fa "isc_socket_t **socketp"
.Fc
.Ft void
.Fo isc_socket_attach
.Fa "isc_socket_t *sock"
.Fa "isc_socket_t **socketp"
.Fc
.Ft void 
.Fo isc_socket_detach
.Fa "isc_socket_t **socketp"
.Fc
.Ft isc_result_t
.Fo isc_socketmgr_create
.Fa "isc_mem_t *mctx"
.Fa "isc_socketmgr_t **managerp"
.Fc
.Ft void
.Fo isc_socketmgr_destroy
.Fa "isc_socketmgr_t **managerp"
.Fc
.Ft isc_result_t
.Fo isc_socket_recvv
.Fa "isc_socket_t *sock"
.Fa "isc_bufferlist_t *buflist"
.Fa "unsigned int minimum"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_result_t
.Fo isc_socket_recv
.Fa "isc_socket_t *sock"
.Fa "isc_region_t *region"
.Fa "unsigned int minimum"
.Fa "sc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_result_t
.Fo isc_socket_send
.Fa "isc_socket_t *sock"
.Fa "isc_region_t *region"
.Fa "sc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_result_t
.Fo isc_socket_sendto
.Fa "isc_socket_t *sock"
.Fa "isc_region_t *region"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fa "isc_sockaddr_t *address"
.Fa "struct in6_pktinfo *pktinfo"
.Fc
.Ft isc_result_t
.Fo isc_socket_sendv
.Fa "isc_socket_t *sock"
.Fa "isc_bufferlist_t *buflist"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_result_t
.Fo isc_socket_sendtov
.Fa "isc_socket_t *sock"
.Fa "isc_bufferlist_t *buflist"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fa "isc_sockaddr_t *address"
.Fa "struct in6_pktinfo *pktinfo"
.Fc
.Ft isc_result_t
.Fo isc_socket_bind
.Fa "isc_socket_t *sock"
.Fa "isc_sockaddr_t *sockaddr"
.Fc
.Ft isc_result_t
.Fo isc_socket_listen
.Fa "isc_socket_t *sock"
.Fa "unsigned int backlog"
.Fc
.Ft isc_result_t
.Fo isc_socket_accept
.Fa "isc_socket_t *sock"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_result_t
.Fo isc_socket_connect
.Fa "isc_socket_t *sock"
.Fa "isc_sockaddr_t *addr"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_result_t
.Fo isc_socket_getpeername
.Fa "isc_socket_t *sock"
.Fa "isc_sockaddr_t *addressp"
.Fc
.Ft isc_result_t
.Fo isc_socket_getsockname
.Fa "isc_socket_t *sock"
.Fa "isc_sockaddr_t *addressp"
.Fc
.Ft void
.Fo isc_socket_cancel
.Fa "isc_socket_t *sock"
.Fa "isc_task_t *task"
.Fa "unsigned int how"
.Fc
.Ft isc_result_t
.Fo isc_socket_recvmark
.Fa "isc_socket_t *sock"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_result_t
.Fo isc_socket_sendmark
.Fa "isc_socket_t *sock"
.Fa "isc_task_t *task"
.Fa "isc_taskaction_t action"
.Fa "void *arg"
.Fc
.Ft isc_sockettype_t
.Fo isc_socket_gettype
.Fa "isc_socket_t *sock"
.Fc
.Ft isc_boolean_t
.Fo isc_socket_isbound
.Fa "isc_socket_t *sock"
.Fc
.Sh DESCRIPTION
Applications using the BIND9 library should use the following
functions for interfacing with the operating system's networking
subsystem.
These functions make extensive make use of the two data
structures below which are abstractions from the
.Xr socket 2
interface provided by most
.Ux
systems.
The contents of these structures should not be manipulated directly.
They should be altered using the functions described below.
.Bd -literal -offset indent
struct isc_socket {
        /* Not locked. */
        unsigned int            magic;
        isc_socketmgr_t        *manager;
        isc_mutex_t             lock;
        isc_sockettype_t        type;
 
        /* Locked by socket lock. */
        unsigned int            references;
        int                     fd;
        isc_result_t            recv_result;
        isc_result_t            send_result;
 
        ISC_LIST(isc_socketevent_t)             send_list;
        ISC_LIST(isc_socketevent_t)             recv_list;
        ISC_LIST(isc_socket_newconnev_t)        accept_list;
        isc_socket_connev_t                    *connect_ev;
 
        /*
         * Internal events.  Posted when a descriptor is readable or
         * writable.  These are statically allocated and never freed.
         * They will be set to non-purgable before use.
         */
        intev_t                 readable_ev;
        intev_t                 writable_ev;
 
        isc_sockaddr_t          address;  /* remote address */
 
        unsigned int            pending_recv : 1,
                                pending_send : 1,
                                pending_accept : 1,
                                listener : 1, /* listener socket */
                                connected : 1,
                                connecting : 1, /* connect pending */
                                bound : 1; /* bound to local addr */
 
#ifdef ISC_NET_RECVOVERFLOW
        unsigned char           overflow; /* used for MSG_TRUNC fake */
#endif
#ifdef USE_CMSG
        unsigned char          *cmsg;
        unsigned int            cmsglen;
#endif
};

typedef struct isc_socket isc_socket_t;
.Ed
.Bd -literal -offset indent
struct isc_socketmgr {
        /* Not locked. */
        unsigned int            magic;
        isc_mem_t              *mctx;
        isc_mutex_t             lock;
        /* Locked by manager lock. */
        unsigned int            nsockets;  /* sockets managed */
        isc_thread_t            watcher;
        isc_condition_t         shutdown_ok;
        fd_set                  read_fds;
        fd_set                  write_fds;
        isc_socket_t           *fds[FD_SETSIZE];
        int                     fdstate[FD_SETSIZE];
        int                     maxfd;
        int                     pipe_fds[2];
};

typedef struct isc_socketmgr isc_socketmgr_t;
.Ed
.Pp
.Fn isc_socket_create
creates a new socket of protocol family
.Fa pf 
which is either
.Dv PF_INET
or
.Dv PF_INET6 .
The socket manager
.Fa manager
will be used to control the socket.
.Fa manager
must be a valid socket manager and
.Fa socketp
should be a pointer to a NULL pointer.
The newly-created socket is returned through
.Fa *socketp .
.Pp
.Fn isc_socket_attach
increments the reference count to
to the socket
.Fa sock
and attaches
.Fa *socketp
to socket
.Fa sock .
.Fa sock
must be a pointer to a valid socket.
The reference count on a socket is decremented by calling
.Fn isc_socket_detach .
.Fa *socketp
must be a valid socket pointer.
When the socket's last reference is removed, its reference count
will be zero.
The socket will then be destroyed and any resources associated with it
will be discarded.
.Pp
Socket manager structures
.Dv "struct isc_socketmgr"
are set up and torn down by
.Fn isc_socketmgr_create
and
.Fn isc_socketmgr_destroy
respectively.
Memory from context
.Fa mctx
is allocated for the structure and
.Fa managerp
should point to a NULL
.Dv isc_socketmgr_t .
If
.Fn isc_socketmgr_create
succeeds,
.Fa *managerp
will be a pointer to the created
.Dv "struct isc_socketmgr" .
Calls to
.Fn isc_socketmgr_destroy
will block until there are no sockets left in the manager referenced
by
.Fa *managerp .
If the caller uses this manager to hold any socket references, it will
deadlock itself.
Therefore those sockets should be detached by calling
.Xr isc_socket_detach 3 
before invoking
.Fn isc_socketmgr_destroy .
.Pp
Reading data from a socket is performed by
.Fn isc_socket_recvv
and
.Fn isc_socket_recv .
.Fn isc_socket_recv
reads data into a single region,
.Fa region
while
.Fn isc_socket_recvv
uses a list of buffers
.Fa buflist
for storing the data.
.Fa minimum
indicates how many bytes should be read.
A read done event -
.Dv ISC_SOCKEVENT_RECVDONE
- with the given action
.Fa action
and argument
.Fa arg
gets  posted to the event queue of task
.Fa task .
When
.Fa minimum
is non-zero, the completion event will be posted
when at least that number of bytes have been read from the socket
.Fa sock .
If
.Fa minimum
is zero, the completion event is posted when the exact number of bytes
in
.Fa region
or
.Fa buflist
have been read.
This only makes sense for TCP sockets where there is a reasonable guarantee
that a predictable number of bytes can be received.
For UDP sockets,
.Fa minimum
is always set to 1.
The read completes when the requested number of bytes have been
received or if either an error or end of input occurs.
Buffers or regions passed to
.Fn isc_socket_recv
or
.Fn isc_socket_recvv
or any data they refer to
should not be modified by the caller until the completion event has
been received.
When a successful call to
.Fn isc_socket_recvv 
completes,
.Fa *buflist
will be empty.
The list of buffers that store the data which has been read are
returned in the done event's
.Dv bufferlist .
.Fa *buflist is unchanged if
.Fn isc_socket_recvv
returns an error.
.Pp
A number of assertion checks are performed by
.Fn isc_socket_recv
and
.Fn isc_socket_recvv .
For both functions,
.Fa sock
should be a valid socket and
.Fa task
should be a valid task.
.Fa action
has to be a valid action.
It must not be NULL.
.Fn isc_socket_recv
checks that
.Fa region
is a valid region.
.Fn isc_socket_recvv
demands that
.Fa buflist
is not NULL and that there is at least one buffer in
.Fa *buflist .
.Pp
The functions
.Fn isc_socket_send ,
.Fn isc_socket_sendto ,
.Fn isc_socket_sendv
and 
.Fn isc_socket_sendtov
are used to send data to the peer for socket
.Fa sock .
The data to be sent are held in either the region
.Fa region
or in multiple buffers referenced through
.Fa buflist .
The contents of the
.Fa region
and
.Fa buflist
structures and their underlying buffers must not be modified by the
caller until the completion event has been received.
A send done event
.Dv ISC_SOCKEVENT_SENDDONE
with action
.Fa action
and argument
.Fa arg
is quueued for task
.Fa task
when the data have been sent.
If
.Fa action
is NULL, no completion event is posted.
.Pp 
For
.Fn isc_socket_sendto
and
.Fn isc_socket_sendtov ,
.Fa address
is a pointer to the
.Dv "struct isc_sockaddr"
containing the destination address.
If
.Fa sock
is an IPv6 socket (protocol family
.Dv PF_INET6 )
.Fa pktinfo
is a pointer to the packet info structure
.Dv "struct in6_pktinfo"
for the socket.
.Pp
When
.Fn isc_socket_sendv
or
.Fn isc_socket_sendtov
complete successfully,
.Fa *buflist
will be empty.
The done event's
.Dv bufferlist
will contain the list of the buffers that were used.
.Fa *buflist
is not altered if an error occurs in
.Fn isc_socket_sendv
or
.Fn isc_socket_sendtov .
.Pp
These functions perform a number of assertion checks.
.Fa task
has to be a valid task and
.Fa sock
must be a valid, bound socket.
\fBCONFIRM THIS! Recall recent discussion/bug report about OSes that
don't allow sending data on unnamed sockets - JR\fP
.Fa action
must be either NULL or a valid action.
.Fn isc_socket_send
and
.Fn isc_socket_sendto
insist that
.Fa region
is a valid region.
.Fn isc_socket_sendv
and
.Fn isc_socket_sendtov
check that
.Fa buflist
is non-NULL and that there is at least one buffer in
.Fa *buflist .
.Pp
.Fn isc_socket_send
is a trivial "wrapper" function to
.Fn isc_socket_sendto
while
.Fn isc_socket_sendv
offers a similar service for calls to
.Fn isc_socket_sendtov .
If a task is shut down while it has any writes pending, the outcome is
system-dependent.
Data that has not yet been sent may be discarded or successfully written
to the socket's peer.
.Pp
.Fn isc_socket_bind
associates a name with socket
.Fa sock .
The name that is bound to the socket is given by
.Fa *addressp .
.Pp
To put a socket into listen mode,
.Fn isc_socket_listen
is called.
.Fa sock
must be a valid socket.
Once the socket
.Fa sock
is in listen mode, it can only be used in calls to
.Fn isc_socket_accept ,
.Fn isc_socket_attach
and
.Fn isc_socket_detach .
.Fa backlog
has the usual meaning for the
.Xr listen 2
system call in
.Ux .
It specifies the maximum number of pending connections that can be
queued waiting for the application to
.Xr accept 2
them.
If
.Fa backlog
is zero, a reasonable system default is used, typically
.Dv SOMAXCONN .
The value of
.Fa backlog
may be ignored on other operating systems. 
.Pp
.Fn isc_socket_accept
is used to queue an accept event when an incoming connection request
is made.
Task
.Fa task
gets a
.Dv ISC_SOCKEVENT_NEWCONN
event with the sender set to socket
.Fa sock
which was previously put into listen mode by
.Fn isc_socket_listen .
The new socket structure is attached to task
.Fa task
It is made available through the
.Dv isc_socket_newconnev_t
event type.
The function has assertion checks to ensure that
.Fa sock
is a valid socket and is in listen mode.
.Pp
.Fn isc_socket_connect
connects socket
.Fa sock
to the peer with address
.Fa addr .
When the connection completes - either on success or if an error
occurs - a
.Dv ISC_SOCKEVENT_CONNECT
event with action
.Fa action
and argument
.Fa arg is posted to the event queue for task
.Fa task .
The function's assertion checks ensure that
.Fa sock
is a valid TCP socket and
.Fa addressp
points to a valid
.Dv "struct isc_sockaddr" .
The checks also make sure that
.Fa task
and
.Fa action
are valid tasks and actions respectively.
.Pp
.Fn isc_socket_getpeername
returns the name of the peer connected to socket
.Fa sock .
and copies it to
.Fa addressp .
.Fn isc_socket_getsockname
gets the name of socket
.Fa sock
and copies it to
.Fa addressp .
Both functions have assertion checks to ensure that
.Fa sock 
is a valid socket
and that
.Fa *addressp
is not NULL.
.Pp
Socket events that hav been queued for some task can be cancelled using
.Fn isc_socket_cancel .
.Fa sock
and
.Fa task
are a valid socket and task pointers respectively.
.Fa how 
is a bitmask of the events that are to be cancelled.
Possible values for
.Fa how
are any combination of
.Dv ISC_SOCKCANCEL_RECV ,
.Dv ISC_SOCKCANCEL_SEND ,
.Dv ISC_SOCKCANCEL_ACCEPT 
and
.Dv ISC_SOCKCANCEL_CONNECT .
When the events are cancelled,
.Fn isc_socket_cancel
attempts to remove it from the task's queue.
If this fails, the event is marked as cancelled and the task
is expected to clean it up later.
A done event with status
.Dv ISC_R_CANCELED
is posted for each cancelled event and any necessary state information
is reset.
.Pp
.Fn isc_socket_recvmark
and
.Fn isc_socket_sendmark
insert a receive or send marker for socket
.Fa sock .
The marker gets processed when all I/O requests in the the task
.Fa task 's
queue have been processed.
If that queue is empty, the event is posted immediately to that task.
Both functions check that
.Fa sock ,
.Fa task
and
.Fa action
are a valid socket, task and action respectively.
.Pp
When the event handler returns, its
.Dv result
member can sometimes contain useful information. 
Depending on the marker type, the event's
.Dv result member
will contain the same error that the last
.Fn isc_socket_recv ,
.Fn isc_socket_send
.Fn isc_socket_sendto
if the mark was processed after a fatal error.
.Pp
.Fn isc_socket_gettype
returns the type of socket - UDP or TCP - for
.Fa sock ,
which must be a valid socket.
.Fn isc_socket_isbound
returns
.Er ISC_TRUE
or
.Er ISC_FALSE
depending on whether the socket
.Fa sock
has been bound to a name or not: in other words if
.Fn isc_socket_bind
has been successfully invoked on the socket.
.Sh RETURN VALUES
A successful call to
.Fn isc_socket_create
returns
.Er ISC_R_SUCCESS .
.Er ISC_R_NORESOURCES
if the operating system was unable to allocate resources for the
socket: typically buffers or file descriptors.
If the
.Fn isc_socket_create
is unable to allocate memory for the socket,
.Er ISC_R_NOMEMORY
is returned.
Unexpected errors - for instance when setting options on the new
socket -  return
.Er ISC_R_UNEXPECTED .
.Pp
.Fn isc_socketmgr_create
returns
.Er ISC_R_SUCCESS
on success.
The function returns
.Er ISC_R_NOMEMORY
if the BIND9 library was unable to allocate memory for the socket
manager structure.
.Er ISC_R_UNEXPECTED
is returned if it was not possible to initialise the
.Dv "struct isc_socketmgr" .
.Pp
Successful calls to
.Fn isc_socket_recv
and
.Fn isc_socket_recvv
return
.Er ISC_R_SUCCESS .
They return
.Er ISC_R_NOMEMORY
if it was not possible to allocate memory for a
socket event handler.
The handler that is invoked for
the
.Dv ISC_SOCKEVENT_RECVDONE
when the socket read 
completes will return
.Er ISC_R_SUCCESS
on success or
.Er ISC_R_UNEXPECTED
if it encounters an error.
.Pp
The functions
.Fn isc_socket_sendto ,
.Fn isc_socket_sendtov ,
.Fn isc_socket_send 
and
.Fn isc_socket_sendv 
all return
.Er ISC_R_SUCCESS
on success.
If these four functions are unable to allocate memory when setting up
an event handler, they return 
.Er ISC_R_NOMEMORY .
The event handler that is invoked when a
.Dv ISC_SOCKEVENT_SENDDONE
event is posted when socket write
completes returns
.Er ISC_R_SUCCESS
on success.
It returns
.Er ISC_R_UNEXPECTED
if an error occurs.
.Pp
Successful calls to
.Fn isc_socket_bind
return
.Er ISC_R_SUCCESS .
The function returns
.Er ISC_R_NOPERM
if the requested address needs a privileged port, and the current user
does no have sufficient permission to access it.
.Er ISC_R_ADDRNOTAVAIL
is returned if the specified address is not available.
.Fn isc_socket_bind
returns 
.Er ISC_R_ADDRINUSE
if the address is already in use and
.Er ISC_R_BOUND
if
.Fa sock had already been bound to an address.
.Er ISC_R_UNEXPECTED
is returned for any other error conditions that are reported by
.Xr bind 2 
and an error message printed on
.Dv stderr .
.Pp
.Fn isc_socket_listen
returns 
.Er ISC_R_SUCCESS
on success.
.Er ISC_R_UNEXPECTED
is returned and an error message printed on
.Dv stderr
if the
.Xr listen 2
system call fails.
.Pp
.Er ISC_R_NOMEMORY
is returned by
.Fn isc_socket_accept
if it was unable to allocate memory for the new socket or the event
handler.
.Er ISC_R_SUCCESS
is returned on success.
.Pp
.Fn isc_socket_connect
returns
.Er ISC_R_NOMEMORY
if there was a memory allocation problem
or
.Er ISC_R_UNEXPECTED
if the call to
.Xr connect 2
fails.
.Er ISC_R_SUCCESS
is returned otherwise.
The event handler returns
.Er ISC_R_SUCCESS
when the connection attempt completes successfully.
It returns
.Er ISC_R_TIMEDOUT 
when the connection attempt times out or
.Er ISC_R_CONNREFUSED
if the peer 
.Fa addr
refused the connection.
An error of
.Er ISC_R_NETUNREACH
if the peer's network isn't reachable.
Other error conditions from
.Xr connect 2
return
.Er ISC_R_UNEXPECTED .
.Pp
If the socket
.Fa sock
is connected,
.Fa isc_socket_getpeername
returns
.Er ISC_R_SUCCESS
and
.Er ISC_R_NOTCONNECTED
otherwise.
.Fn isc_socket_getsockname
normally returns
.Er ISC_R_SUCCESS.
It returns
.Er ISC_R_NOTBOUND
if
.Fa sock
is not bound.
.Er ISC_R_UNEXPECTED
is returned and an error message logged on
.Dv stderr
if
.Xr getsockname 2
failed
.Pp
.Fn isc_socket_recvmark
and
.Fn isc_socket_sendmark
always return
.Er ISC_R_SUCCESS
unless they were unable to set up an event handler, in which case they
return
.Er ISC_R_NOMEMORY .
.Sh SEE ALSO
.Xr socket 2 ,
.Xr readv 2
.Xr recv 2 ,
.Xr writev 2 ,
.Xr send 2 ,
.Xr sendto 2 ,
.Xr bind 2 ,
.Xr listen 2 ,
.Xr accept 2 ,
.Xr connect 2 ,
.Xr getpeername 2 ,
.Xr getsockname 2 .