Celestin Apprentice 5/Apprentice-Release5.iso/Source Code/Libraries/CW GUSI 1.6.4/doc/pod/GUSI_Common.pod

Text File | 1995-04-20 | 15.9 KB | 594 lines | [TEXT/CWIE]

=head1 Overview

This section discusses the routines common to all, or almost all
communication domains. These routines return C<-1> if an error occurred,
and set the variable C<errno> to an error code. On success, the routines return C<0>
or some positive value.

Here's a list of all error codes and their typical explanations. The most important
of them are repeated for the individual calls.

=over 4

=item C<EACCES>

Permission denied: An attempt was made to access a file in a way forbidden by its
file access permissions, e.g., to C<open()> a locked file for writing.

=item C<EADDRINUSE>

Address already in use: C<bind()> was called with an address already in use
by another socket.

=item C<EADDRNOTAVAIL>

Can't assign requested address: C<bind()> was called with an address which this
socket can't assume, e.g., a TCP/IP address whose C<in_addr> specifies a different
host.

=item C<EAFNOSUPPORT>

Address family not supported: You haven't linked with this socket family or have
specified a nonexisting family, e.g., AF_CHAOS.

=item C<EALREADY>

Operation already in progress, e.g., C<connect()> was called twice in a row for a
nonblocking socket.

=item C<EBADF>

Bad file descriptor: The file descriptor you specified is not open.

=item C<EBUSY>

Request for a system resource already in incompatible use, e.g., attempt to delete
an open file.

=item C<ECONNREFUSED>

Connection refused, e.g. you specified an unused port for a C<connect()>

=item C<EEXIST>

File exists, and you tried to open it with C<O_EXCL>.

=item C<EHOSTDOWN>

Remote host is down.

=item C<EHOSTUNREACH>

No route to host.

=item C<EINPROGRESS>

Operation now in progress. This is *not* an error, but returned from nonblocking
operations, e.g., nonblocking C<connect()>.

=item C<EINTR>

Interrupted system call: The user pressed Command-. or C<alarm()> timed out.

=item C<EINVAL>

Invalid argument or various other error conditions.

=item C<EIO>

Input/output error.

=item C<EISCONN>

Socket is already connected.

=item C<EISDIR>

Is a directory, e.g. you tried to C<open()> a directory.

=item C<EMFILE>

Too many open files.

=item C<EMSGSIZE>

Message too long, e.g. for an UDP C<send()>.

=item C<ENAMETOOLONG>

File name too long.

=item C<ENETDOWN>

Network is down, e.g., Appletalk is turned off in the chooser.

=item C<ENFILE>

Too many open files in system.

=item C<ENOBUFS>

No buffer space available.

=item C<ENOENT>

No such file or directory.

=item C<ENOEXEC>

Severe error with the PowerPC standard library.

=item C<ENOMEM>

Cannot allocate memory.

=item C<ENOSPC>

No space left on device.

=item C<ENOTCONN>

Socket is not connected, e.g., neither C<connect()> nor C<accept()> has been called
successfully for it.

=item C<ENOTDIR>

Not a directory.

=item C<ENOTEMPTY>

Directory not empty, e.g., attempt to delete nonempty directory.

=item C<ENXIO>

Device not configured, e.g., MacTCP control panel misconfigured.

=item C<EOPNOTSUPP>

Operation not supported on socket, e.g., C<sendto()> on a stream socket.

=item C<EPFNOSUPPORT>

Protocol family not supported, i.e., attempted use of ADSP on a machine that has
AppleTalk but not ADSP.

=item C<EPROTONOSUPPORT>

Protocol not supported, e.g., you called C<getprotobyname()> with neither "tcp" nor
"udp" specified.

=item C<ERANGE>

Result too large, e.g., C<getcwd()> called with insufficient buffer.

=item C<EROFS>

Read-only file system.

=item C<ESHUTDOWN>

Can't send after socket shutdown.

=item C<ESOCKTNOSUPPORT>

Socket type not supported, e.g., datagram PPC toolbox sockets.

=item C<ESPIPE>

Illegal seek, e.g., C<lseek()> called for a TCP socket.

=item C<EWOULDBLOCK>

Nonblocking operation would block.

=item C<EXDEV>

Cross-device link, e.g. C<FSpSmartMove()> attempted to move file to a different
volume.

=back

=head2 Creating and destroying sockets

A socket is created with C<socket()> and destroyed
with C<close()>.

C<int socket(int af, int type, int protocol)> creates an endpoint for communication
and returns a descriptor. C<af> specifies the communication domain to be used. Valid
values are:

=over 4

=item C<AF_UNIX>

Communication internal to a single Mac.

=item C<AF_INET>

TCP/IP, using C<MacTCP>.

=item C<AF_APPLETALK>

Appletalk, using ADSP.

=item C<AF_PPC>

The Program-to-Program Communication Toolbox.

=back

C<type> specifies the semantics of the communication. The following two types are
available:

=over 4

=item C<SOCK_STREAM>

A two way, reliable, connection based byte stream.

=item C<SOCK_DGRAM>

Connectionless, unreliable messages of a fixed maximum length.

=back

C<protocol> would be used to specify an alternate protocol to be used with a socket.
In C<GUSI>, however, this parameter is always ignored.

Error codes:

=over 4

=item C<EINVAL>

The C<af> you specified doesn't exist.

=item C<EMFILE>

The descriptor table is full.

=back

C<void close(int fd)> removes the access path associated with the descriptor, and
closes the file or socket if the last access path referring to it was removed.

=head2 Prompting the user for an address

To give the user the opportunity of entering
an address for a socket to be bound or connected to, the C<choose()> routine was
introduced in C<GUSI>. This routine has no counterpart in UNIX implementations.

C<int choose(int dom, int type, char * prompt, void * constraint, int flags,
void * name, int * nlen)> puts up a modal dialog prompting the user to
choose an address. C<dom> specifies the communication domain, like in C<socket>.
C<type> may be used by future communication domains to further differentiate
within a domain, but is ignored by current domains. C<prompt> is a message that will
appear in the dialog. C<constraint> may be used to restrict the types of acceptable
addresses (For more information, consult the section of the communication domain).
The following two C<flags> are defined for most socket types:

=over 4

=item C<CHOOSE_DEFAULT>

Offer the contents passed in C<name> as the default choice.

=item C<CHOOSE_NEW>

Prompt for a new address, suitable for passing to C<bind()>. Default
is prompting for an existing address, to be used by C<connect()>.

=back

C<name> on input contains a default address if C<CHOOSE_DEFAULT> is set. On output, it
is set to the address chosen.

Error codes:

=over 4

=item C<EINVAL>

One of the C<flags> is not (yet) supported by this communications
domain. This error is never reported for C<CHOOSE_DEFAULT>, which might get silently
ignored.

=item C<EINTR>

The user chose "Cancel" in the dialog.

=back

=head2 Establishing connections between sockets

Before you can transmit data on a
stream socket, it must be connected to a peer socket. Connection establishment is
asymmetrical: The server socket registers its address with C<bind()>, calls C<listen()>
to indicate its willingness to accept connections and accepts them by calling
C<accept()>. The client socket, after possibly having registered its address with
C<bind()> (This is not necessary for all socket families as some will automatically
assign an address) calls C<connect()> to establish a connection with a server.

It is possible, but not required, to call C<connect()> for datagram sockets.

C<int bind(int s, const struct sockaddr *name, int namelen)> binds a socket to its address. The
format of the address is different for every socket family. For some families, you
may ask the user for an address by calling C<choose()>.

Error codes:

=over 4

=item C<EAFNOSUPPORT>

C<name> specifies an illegal address family for this socket.

=item C<EADDRINUSE>

There is already another socket with this address.

=back

C<int listen(int s, int qlen)> turns a socket into a listener. C<qlen> determines
how many sockets can concurrently wait for a connection, but is ignored for almost
all socket families.

C<int accept(int s, struct sockaddr *addr, int *addrlen)> accepts a connection for a socket
I<on a new socket> and returns the descriptor of the new socket. If C<addr> is not
C<NULL>, the address of the connecting socket will be assigned to it.

You can find out if a connection is pending by calling C<select()> to find out if
the socket is ready for I<reading>.

Error codes:

=over 4

=item C<ENOTCONN>

You did not call C<listen()> for this socket.

=item C<EWOULDBLOCK>

The socket is nonblocking and no socket is trying to connect.

=back

C<int connect(int s, const struct sockaddr *addr, int addrlen)> tries to connect to the socket whose
address is in C<addr>. If the socket is nonblocking and the connection cannot be
made immediately, C<connect()> returns C<EINPROGRESS>. You can find out if the
connection has been established by calling C<select()> to find out if
the socket is ready for I<writing>.

Error codes:

=over 4

=item C<EAFNOSUPPORT>

C<name> specifies an illegal address family for this socket.

=item C<EISCONN>

The socket is already connected.

=item C<EADDRNOAVAIL>

There is no socket with the given address.

=item C<ECONNREFUSED>

The socket refused the connection.

=item C<EINPROGRESS>

The socket is nonblocking and the connection is being established.

=back

=head2 Transmitting data between sockets

You can write data to a socket using C<write()>,
C<writev()>, C<send()>, C<sendto()>, or C<sendmsg()>. You can read data from a socket
using C<read()>, C<readv()>, C<recv()>, C<recvfrom()>, or C<recvmsg()>.

C<int read(int s, char *buffer, unsigned buflen)> reads up to C<buflen> bytes from
the socket. C<read()> for sockets differs from C<read()> for files mainly in that it
may read fewer than the requested number of bytes without waiting for the rest to
arrive.

Error codes:

=over 4

=item C<EWOULDBLOCK>

The socket is nonblocking and there is no data immediately available.

=back

C<int readv(int s, const struct iovec *iov, int count)> performs the same
action, but scatters the input data into the C<count> buffers of the C<iov> array, always
filling one buffer completely before proceeding to the next. C<iovec> is defined as
follows:

    struct iovec {
      caddr_t  iov_base;   /* Address of this buffer */
      int   iov_len;       /* Length of the buffer */
    };

C<int recv(int s, void *buffer, int buflen, int flags)> is identical to C<read()>,
except for the C<flags> parameter. If the C<MSG_OOB> flag is set for a stream socket
that supports out-of-band data, C<recv()> reads out-of-band data.

C<int recvfrom(int s, void *buffer, int buflen, int flags, void *from, int *fromlen)>
is the equivalent of C<recv()> for unconnected datagram sockets. If C<from> is not
C<NULL>, it will be set to the address of the sender of the message.

C<int recvmsg(int s, struct msghdr *msg, int flags)> is the most general routine,
combining the possibilities of C<readv()> and C<recvfrom()>. C<msghdr> is defined as
follows:

    struct msghdr {
      caddr_t  msg_name;            /* Like from in recvfrom() */
      int      msg_namelen;         /* Like fromlen in recvfrom() */
      struct   iovec *msg_iov;      /* Scatter/gather array */
      int      msg_iovlen;          /* Number of elements in msg_iov */
      caddr_t  msg_accrights;       /* Access rights sent/received. Not used in GUSI */
      int      msg_accrightslen;
    };

C<int write(int s, char *buffer, unsigned buflen)> writes up to C<buflen> bytes to
the socket. As opposed to C<read()>, C<write()> for nonblocking sockets always blocks
until all bytes are written or an error occurs.


Error codes:

=over 4

=item C<EWOULDBLOCK>

The socket is nonblocking and data can't be immediately written.

=back

C<int writev(int s, const struct iovec *iov, int count)> performs the same
action, but gathers the output data from the C<count> buffers of the C<iov> array, always
sending one buffer completely before proceeding to the next.

C<int send(int s, void *buffer, int buflen, int flags)> is identical to C<write()>,
except for the C<flags> parameter. If the C<MSG_OOB> flag is set for a stream socket
that supports out-of-band data, C<send()> sends an out-of-band message.

C<int sendto(int s, void *buffer, int buflen, int flags, void *to, int *tolen)>
is the equivalent of C<send()> for unconnected datagram sockets. The message will
be sent to the socket whose address is given in C<to>.

C<int sendmsg(int s, const struct msghdr *msg, int flags)> combines the possibilities
of C<writev()> and C<sendto()>.

=head2 I/O multiplexing


int select(int width, fd_set *readfds, fd_set *writefds,
fd_set *exceptfds, struct timeval *timeout) examines the I/O descriptors specified
by the bit masks C<readfs>, C<writefs>, and C<exceptfs> to see if they are ready for
reading, writing, or have an exception pending. C<width> is the number of significant
bits in the bit mask. C<select()> replaces the bit masks with masks of those descriptors
which are ready and returns the total number of ready descriptors. C<timeout>, if
not C<NULL>, specifies the maximum time to wait for a descriptor to become ready. If
C<timeout> is C<NULL>, C<select()> waits indefinitely. To do a poll, pass a pointer to
a zero C<timeval> value in C<timeout>. Any of C<readfds>, C<writefds>, or C<exceptfds>
may be given as C<NULL> if no descriptors are of interest.

Error codes:

=over 4

=item C<EBADF>

One of the bit masks specified an invalid descriptor.

=back

The descriptor bit masks can be manipulated with the following macros:


    FD_ZERO(fds);    /* Clear all bits in *fds */
    FD_SET(n, fds);  /* Set bit n in *fds */
    FD_CLR(n, fds);  /* Clear bit n in *fds */
    FD_ISSET(n, fds);   /* Return 1 if bit n in *fds is set, else 0 */

=head2 Getting and changing properties of sockets

You can obtain the address of a
socket and the socket it is connected to by calling C<getsockname()> and
C<getpeername()> respectively. You can query and manipulate other properties of a
socket by calling C<ioctl()>, C<fcntl()>, C<getsockopt()>, and C<setsockopt()>. You
can create additional descriptors for a socket by calling C<dup()> or C<dup2()>.

C<int getsockname(int s, struct sockaddr *name, int *namelen)> returns in C<*name> the address
the socket is bound to. C<*namelen> should be set to the maximum length of C<name> and
will be set by C<getsockname()> to the actual length of the name.

C<int getpeername(int s, struct sockaddr *name, int *namelen)> returns in C<*name> the address
of the socket that this socket is connected to. C<*namelen> should be set to the
maximum length of C<name> and will be set by C<getpeername()> to the actual length
of the name.

C<int ioctl(int d, unsigned int request, long *argp)> performs various operations
on the socket, depending on the C<request>. The following codes are valid for all
socket families:

=over 4

=item C<FIONBIO>

Make the socket blocking if the C<long> pointed to by argp is C<0>, else
make it nonblocking.

=item C<FIONREAD>

Set C<*argp> to the number of bytes waiting to be read.

=back

Error codes:

=over 4

=item C<EOPNOTSUPP>

The operation you requested with C<request> is not supported by this
socket family.

=back

C<int fcntl(int s, unsigned int cmd, int arg)> provides additional control over a
socket. The following values of C<cmd> are defined for all socket families:

=over 4

=item C<F_DUPFD>

Return a new descriptor greater than or equal to C<arg> which refers to the same socket.

=item C<F_GETFL>

Return descriptor status flags.

=item C<F_SETFL>

Set descriptor status flags to C<arg>.

=back

The only status flag implemented is C<FNDELAY> which is true if the socket is
nonblocking.

Error codes:

=over 4

=item C<EOPNOTSUPP>

The operation you requested with C<cmd> is not supported by this
socket family.

=back

C<int getsockopt(int s, int level, int optname, void *optval, int * optlen)> is
used to request information about sockets. It is not implemented in C<GUSI>.

C<int setsockopt(int s, int level, int optname, void *optval, int optlen)> is used
to set options associated with a socket. It is not implemented in C<GUSI>.

C<int dup(int fd)> returns a new descriptor referring to the same socket as C<fd>.
The old and new descriptors are indistinguishible. The new descriptor will always
be the smallest free descriptor.

C<int dup2(int oldfd, int newfd)> closes C<newfd> if it was open and makes it
a duplicate of C<oldfd>. The old and new descriptors are indistinguishible.