add compatibility for ancient Rubies

[kgio.git] / ext / kgio / kgio_ext.c

#include <ruby.h>
#ifdef HAVE_RUBY_IO_H
#  include <ruby/io.h>
#else
#  include <rubyio.h>
#endif
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <assert.h>

#include "missing/accept4.h"
#include "missing/ancient_ruby.h"
#include "nonblock.h"
#include "my_fileno.h"
#include "sock_for_fd.h"

#if defined(__linux__)
/*
 * we know MSG_DONTWAIT works properly on all stream sockets under Linux
 * we can define this macro for other platforms as people care and
 * notice.
 */
#  define USE_MSG_DONTWAIT
static int accept4_flags = A4_SOCK_CLOEXEC;
#else /* ! linux */
static int accept4_flags = A4_SOCK_CLOEXEC | A4_SOCK_NONBLOCK;
#endif /* ! linux */

static VALUE cSocket;
static VALUE localhost;
static VALUE mKgio_WaitReadable, mKgio_WaitWritable;
static ID io_wait_rd, io_wait_wr;
static ID iv_kgio_addr;

struct io_args {
        VALUE io;
        VALUE buf;
        char *ptr;
        long len;
        int fd;
};

struct accept_args {
        int fd;
        struct sockaddr *addr;
        socklen_t *addrlen;
};

static void wait_readable(VALUE io, int fd)
{
        if (io_wait_rd) {
                (void)rb_funcall(io, io_wait_rd, 0, 0);
        } else {
                if (!rb_io_wait_readable(fd))
                        rb_sys_fail("wait readable");
        }
}

static void wait_writable(VALUE io, int fd)
{
        if (io_wait_wr) {
                (void)rb_funcall(io, io_wait_wr, 0, 0);
        } else {
                if (!rb_io_wait_writable(fd))
                        rb_sys_fail("wait writable");
        }
}

static void prepare_read(struct io_args *a, int argc, VALUE *argv, VALUE io)
{
        VALUE length;

        a->io = io;
        a->fd = my_fileno(io);
        rb_scan_args(argc, argv, "11", &length, &a->buf);
        a->len = NUM2LONG(length);
        if (NIL_P(a->buf)) {
                a->buf = rb_str_new(NULL, a->len);
        } else {
                StringValue(a->buf);
                rb_str_resize(a->buf, a->len);
        }
        a->ptr = RSTRING_PTR(a->buf);
}

static int read_check(struct io_args *a, long n, const char *msg, int io_wait)
{
        if (n == -1) {
                if (errno == EINTR)
                        return -1;
                rb_str_set_len(a->buf, 0);
                if (errno == EAGAIN) {
                        if (io_wait) {
                                wait_readable(a->io, a->fd);

                                /* buf may be modified in other thread/fiber */
                                rb_str_resize(a->buf, a->len);
                                a->ptr = RSTRING_PTR(a->buf);
                                return -1;
                        } else {
                                a->buf = mKgio_WaitReadable;
                                return 0;
                        }
                }
                rb_sys_fail(msg);
        }
        rb_str_set_len(a->buf, n);
        if (n == 0)
                a->buf = Qnil;
        return 0;
}

static VALUE my_read(int io_wait, int argc, VALUE *argv, VALUE io)
{
        struct io_args a;
        long n;

        prepare_read(&a, argc, argv, io);
        set_nonblocking(a.fd);
retry:
        n = (long)read(a.fd, a.ptr, a.len);
        if (read_check(&a, n, "read", io_wait) != 0)
                goto retry;
        return a.buf;
}

/*
 * call-seq:
 *
 *      io.kgio_read(maxlen)           ->  buffer
 *      io.kgio_read(maxlen, buffer)   ->  buffer
 *
 * Reads at most maxlen bytes from the stream socket.  Returns with a
 * newly allocated buffer, or may reuse an existing buffer if supplied.
 *
 * Calls the method assigned to Kgio.wait_readable, or blocks in a
 * thread-safe manner for writability.
 *
 * Returns nil on EOF.
 *
 * This behaves like read(2) and IO#readpartial, NOT fread(3) or
 * IO#read which possess read-in-full behavior.
 */
static VALUE kgio_read(int argc, VALUE *argv, VALUE io)
{
        return my_read(1, argc, argv, io);
}

/*
 * call-seq:
 *
 *      io.kgio_tryread(maxlen)           ->  buffer
 *      io.kgio_tryread(maxlen, buffer)   ->  buffer
 *
 * Reads at most maxlen bytes from the stream socket.  Returns with a
 * newly allocated buffer, or may reuse an existing buffer if supplied.
 *
 * Returns nil on EOF.
 *
 * Returns Kgio::WaitReadable if EAGAIN is encountered.
 */
static VALUE kgio_tryread(int argc, VALUE *argv, VALUE io)
{
        return my_read(0, argc, argv, io);
}

#ifdef USE_MSG_DONTWAIT
static VALUE my_recv(int io_wait, int argc, VALUE *argv, VALUE io)
{
        struct io_args a;
        long n;

        prepare_read(&a, argc, argv, io);
retry:
        n = (long)recv(a.fd, a.ptr, a.len, MSG_DONTWAIT);
        if (read_check(&a, n, "recv", io_wait) != 0)
                goto retry;
        return a.buf;
}

/*
 * This method may be optimized on some systems (e.g. GNU/Linux) to use
 * MSG_DONTWAIT to avoid explicitly setting the O_NONBLOCK flag via fcntl.
 * Otherwise this is the same as Kgio::PipeMethods#kgio_read
 */
static VALUE kgio_recv(int argc, VALUE *argv, VALUE io)
{
        return my_recv(1, argc, argv, io);
}

/*
 * This method may be optimized on some systems (e.g. GNU/Linux) to use
 * MSG_DONTWAIT to avoid explicitly setting the O_NONBLOCK flag via fcntl.
 * Otherwise this is the same as Kgio::PipeMethods#kgio_tryread
 */
static VALUE kgio_tryrecv(int argc, VALUE *argv, VALUE io)
{
        return my_recv(0, argc, argv, io);
}
#else /* ! USE_MSG_DONTWAIT */
#  define kgio_recv kgio_read
#  define kgio_tryrecv kgio_tryread
#endif /* USE_MSG_DONTWAIT */

static void prepare_write(struct io_args *a, VALUE io, VALUE str)
{
        a->buf = (TYPE(str) == T_STRING) ? str : rb_obj_as_string(str);
        a->ptr = RSTRING_PTR(a->buf);
        a->len = RSTRING_LEN(a->buf);
        a->io = io;
        a->fd = my_fileno(io);
}

static int write_check(struct io_args *a, long n, const char *msg, int io_wait)
{
        if (a->len == n) {
done:
                a->buf = Qnil;
        } else if (n == -1) {
                if (errno == EINTR)
                        return -1;
                if (errno == EAGAIN) {
                        if (io_wait) {
                                long written = RSTRING_LEN(a->buf) - a->len;

                                wait_writable(a->io, a->fd);

                                /* buf may be modified in other thread/fiber */
                                a->len = RSTRING_LEN(a->buf) - written;
                                if (a->len <= 0)
                                        goto done;
                                a->ptr = RSTRING_PTR(a->buf) + written;
                                return -1;
                        } else {
                                a->buf = mKgio_WaitWritable;
                                return 0;
                        }
                }
                rb_sys_fail(msg);
        } else {
                assert(n >= 0 && n < a->len && "write/send syscall broken?");
                if (io_wait) {
                        a->ptr += n;
                        a->len -= n;
                        return -1;
                }
                a->buf = rb_str_new(a->ptr + n, a->len - n);
        }
        return 0;
}

static VALUE my_write(VALUE io, VALUE str, int io_wait)
{
        struct io_args a;
        long n;

        prepare_write(&a, io, str);
        set_nonblocking(a.fd);
retry:
        n = (long)write(a.fd, a.ptr, a.len);
        if (write_check(&a, n, "write", io_wait) != 0)
                goto retry;
        return a.buf;
}

/*
 * call-seq:
 *
 *      io.kgio_write(str)      -> nil
 *
 * Returns nil when the write completes.
 *
 * Calls the method Kgio.wait_writable if it is set.  Otherwise this
 * blocks in a thread-safe manner until all data is written or a
 * fatal error occurs.
 */
static VALUE kgio_write(VALUE io, VALUE str)
{
        return my_write(io, str, 1);
}

/*
 * call-seq:
 *
 *      io.kgio_trywrite(str)   -> nil or Kgio::WaitWritable
 *
 * Returns nil if the write was completed in full.
 *
 * Returns a String containing the unwritten portion if there was a
 * partial write.
 *
 * Returns Kgio::WaitWritable if EAGAIN is encountered.
 */
static VALUE kgio_trywrite(VALUE io, VALUE str)
{
        return my_write(io, str, 0);
}

#ifdef USE_MSG_DONTWAIT
/*
 * This method behaves like Kgio::PipeMethods#kgio_write, except
 * it will use send(2) with the MSG_DONTWAIT flag on sockets to
 * avoid unnecessary calls to fcntl(2).
 */
static VALUE my_send(VALUE io, VALUE str, int io_wait)
{
        struct io_args a;
        long n;

        prepare_write(&a, io, str);
retry:
        n = (long)send(a.fd, a.ptr, a.len, MSG_DONTWAIT);
        if (write_check(&a, n, "send", io_wait) != 0)
                goto retry;
        return a.buf;
}

/*
 * This method may be optimized on some systems (e.g. GNU/Linux) to use
 * MSG_DONTWAIT to avoid explicitly setting the O_NONBLOCK flag via fcntl.
 * Otherwise this is the same as Kgio::PipeMethods#kgio_write
 */
static VALUE kgio_send(VALUE io, VALUE str)
{
        return my_send(io, str, 1);
}

/*
 * This method may be optimized on some systems (e.g. GNU/Linux) to use
 * MSG_DONTWAIT to avoid explicitly setting the O_NONBLOCK flag via fcntl.
 * Otherwise this is the same as Kgio::PipeMethods#kgio_trywrite
 */
static VALUE kgio_trysend(VALUE io, VALUE str)
{
        return my_send(io, str, 0);
}
#else /* ! USE_MSG_DONTWAIT */
#  define kgio_send kgio_write
#  define kgio_trysend kgio_trywrite
#endif /* ! USE_MSG_DONTWAIT */

/*
 * call-seq:
 *
 *      Kgio.wait_readable = :method_name
 *      Kgio.wait_readable = nil
 *
 * Sets a method for kgio_read to call when a read would block.
 * This is useful for non-blocking frameworks that use Fibers,
 * as the method referred to this may cause the current Fiber
 * to yield execution.
 *
 * A special value of nil will cause Ruby to wait using the
 * rb_io_wait_readable() function.
 */
static VALUE set_wait_rd(VALUE mod, VALUE sym)
{
        switch (TYPE(sym)) {
        case T_SYMBOL:
                io_wait_rd = SYM2ID(sym);
                return sym;
        case T_NIL:
                io_wait_rd = 0;
                return sym;
        }
        rb_raise(rb_eTypeError, "must be a symbol or nil");
        return sym;
}

/*
 * call-seq:
 *
 *      Kgio.wait_writable = :method_name
 *      Kgio.wait_writable = nil
 *
 * Sets a method for kgio_write to call when a read would block.
 * This is useful for non-blocking frameworks that use Fibers,
 * as the method referred to this may cause the current Fiber
 * to yield execution.
 *
 * A special value of nil will cause Ruby to wait using the
 * rb_io_wait_writable() function.
 */
static VALUE set_wait_wr(VALUE mod, VALUE sym)
{
        switch (TYPE(sym)) {
        case T_SYMBOL:
                io_wait_wr = SYM2ID(sym);
                return sym;
        case T_NIL:
                io_wait_wr = 0;
                return sym;
        }
        rb_raise(rb_eTypeError, "must be a symbol or nil");
        return sym;
}

/*
 * call-seq:
 *
 *      Kgio.wait_writable      -> Symbol or nil
 *
 * Returns the symbolic method name of the method assigned to
 * call when EAGAIN is occurs on a Kgio::PipeMethods#kgio_write
 * or Kgio::SocketMethods#kgio_write call
 */
static VALUE wait_wr(VALUE mod)
{
        return io_wait_wr ? ID2SYM(io_wait_wr) : Qnil;
}

/*
 * call-seq:
 *
 *      Kgio.wait_readable      -> Symbol or nil
 *
 * Returns the symbolic method name of the method assigned to
 * call when EAGAIN is occurs on a Kgio::PipeMethods#kgio_read
 * or Kgio::SocketMethods#kgio_read call.
 */
static VALUE wait_rd(VALUE mod)
{
        return io_wait_rd ? ID2SYM(io_wait_rd) : Qnil;
}

static VALUE xaccept(void *ptr)
{
        struct accept_args *a = ptr;

        return (VALUE)accept4(a->fd, a->addr, a->addrlen, accept4_flags);
}

#ifdef HAVE_RB_THREAD_BLOCKING_REGION
#  include <time.h>
/*
 * Try to use a (real) blocking accept() since that can prevent
 * thundering herds under Linux:
 * http://www.citi.umich.edu/projects/linux-scalability/reports/accept.html
 *
 * So we periodically disable non-blocking, but not too frequently
 * because other processes may set non-blocking (especially during
 * a process upgrade) with Rainbows! concurrency model changes.
 */
static int thread_accept(struct accept_args *a, int force_nonblock)
{
        if (force_nonblock)
                set_nonblocking(a->fd);
        return (int)rb_thread_blocking_region(xaccept, a, RUBY_UBF_IO, 0);
}

static void set_blocking_or_block(int fd)
{
        static time_t last_set_blocking;
        time_t now = time(NULL);

        if (last_set_blocking == 0) {
                last_set_blocking = now;
                (void)rb_io_wait_readable(fd);
        } else if ((now - last_set_blocking) <= 5) {
                (void)rb_io_wait_readable(fd);
        } else {
                int flags = fcntl(fd, F_GETFL);
                if (flags == -1)
                        rb_sys_fail("fcntl(F_GETFL)");
                if (flags & O_NONBLOCK) {
                        flags = fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);
                        if (flags == -1)
                                rb_sys_fail("fcntl(F_SETFL)");
                }
                last_set_blocking = now;
        }
}
#else /* ! HAVE_RB_THREAD_BLOCKING_REGION */
#  include <rubysig.h>
static int thread_accept(struct accept_args *a, int force_nonblock)
{
        int rv;

        /* always use non-blocking accept() under 1.8 for green threads */
        set_nonblocking(a->fd);
        TRAP_BEG;
        rv = (int)xaccept(a);
        TRAP_END;
        return rv;
}
#define set_blocking_or_block(fd) (void)rb_io_wait_readable(fd)
#endif /* ! HAVE_RB_THREAD_BLOCKING_REGION */

static VALUE
my_accept(VALUE io, struct sockaddr *addr, socklen_t *addrlen, int nonblock)
{
        int client;
        struct accept_args a;

        a.fd = my_fileno(io);
        a.addr = addr;
        a.addrlen = addrlen;
retry:
        client = thread_accept(&a, nonblock);
        if (client == -1) {
                switch (errno) {
                case EAGAIN:
                        if (nonblock)
                                return Qnil;
                        set_blocking_or_block(a.fd);
#ifdef ECONNABORTED
                case ECONNABORTED:
#endif /* ECONNABORTED */
#ifdef EPROTO
                case EPROTO:
#endif /* EPROTO */
                case EINTR:
                        goto retry;
                case ENOMEM:
                case EMFILE:
                case ENFILE:
#ifdef ENOBUFS
                case ENOBUFS:
#endif /* ENOBUFS */
                        errno = 0;
                        rb_gc();
                        client = thread_accept(&a, nonblock);
                }
                if (client == -1) {
                        if (errno == EINTR)
                                goto retry;
                        rb_sys_fail("accept");
                }
        }
        return sock_for_fd(cSocket, client);
}

static void in_addr_set(VALUE io, struct sockaddr_in *addr)
{
        VALUE host = rb_str_new(0, INET_ADDRSTRLEN);
        socklen_t addrlen = (socklen_t)INET_ADDRSTRLEN;
        const char *name;

        name = inet_ntop(AF_INET, &addr->sin_addr, RSTRING_PTR(host), addrlen);
        if (name == NULL)
                rb_sys_fail("inet_ntop");
        rb_str_set_len(host, strlen(name));
        rb_ivar_set(io, iv_kgio_addr, host);
}

/*
 * call-seq:
 *
 *      server = Kgio::TCPServer.new('0.0.0.0', 80)
 *      server.kgio_tryaccept -> Kgio::Socket or nil
 *
 * Initiates a non-blocking accept and returns a generic Kgio::Socket
 * object with the kgio_addr attribute set to the IP address of the
 * connected client on success.
 *
 * Returns nil on EAGAIN, and raises on other errors.
 */
static VALUE tcp_tryaccept(VALUE io)
{
        struct sockaddr_in addr;
        socklen_t addrlen = sizeof(struct sockaddr_in);
        VALUE rv = my_accept(io, (struct sockaddr *)&addr, &addrlen, 1);

        if (!NIL_P(rv))
                in_addr_set(rv, &addr);
        return rv;
}

/*
 * call-seq:
 *
 *      server = Kgio::TCPServer.new('0.0.0.0', 80)
 *      server.kgio_accept -> Kgio::Socket or nil
 *
 * Initiates a blocking accept and returns a generic Kgio::Socket
 * object with the kgio_addr attribute set to the IP address of
 * the client on success.
 *
 * On Ruby implementations using native threads, this can use a blocking
 * accept(2) (or accept4(2)) system call to avoid thundering herds.
 */
static VALUE tcp_accept(VALUE io)
{
        struct sockaddr_in addr;
        socklen_t addrlen = sizeof(struct sockaddr_in);
        VALUE rv = my_accept(io, (struct sockaddr *)&addr, &addrlen, 0);

        in_addr_set(rv, &addr);
        return rv;
}

/*
 * call-seq:
 *
 *      server = Kgio::UNIXServer.new("/path/to/unix/socket")
 *      server.kgio_tryaccept -> Kgio::Socket or nil
 *
 * Initiates a non-blocking accept and returns a generic Kgio::Socket
 * object with the kgio_addr attribute set (to the value of
 * Kgio::LOCALHOST) on success.
 *
 * Returns nil on EAGAIN, and raises on other errors.
 */
static VALUE unix_tryaccept(VALUE io)
{
        VALUE rv = my_accept(io, NULL, NULL, 1);

        if (!NIL_P(rv))
                rb_ivar_set(rv, iv_kgio_addr, localhost);
        return rv;
}

/*
 * call-seq:
 *
 *      server = Kgio::UNIXServer.new("/path/to/unix/socket")
 *      server.kgio_accept -> Kgio::Socket or nil
 *
 * Initiates a blocking accept and returns a generic Kgio::Socket
 * object with the kgio_addr attribute set (to the value of
 * Kgio::LOCALHOST) on success.
 *
 * On Ruby implementations using native threads, this can use a blocking
 * accept(2) (or accept4(2)) system call to avoid thundering herds.
 */
static VALUE unix_accept(VALUE io)
{
        VALUE rv = my_accept(io, NULL, NULL, 0);

        rb_ivar_set(rv, iv_kgio_addr, localhost);
        return rv;
}

/*
 * call-seq:
 *
 *      Kgio.accept_cloexec? -> true or false
 *
 * Returns true if newly accepted Kgio::Sockets are created with the
 * FD_CLOEXEC file descriptor flag, false if not.
 */
static VALUE get_cloexec(VALUE mod)
{
        return (accept4_flags & A4_SOCK_CLOEXEC) ==
            A4_SOCK_CLOEXEC ? Qtrue : Qfalse;
}

/*
 *
 * call-seq:
 *
 *      Kgio.accept_nonblock? -> true or false
 *
 * Returns true if newly accepted Kgio::Sockets are created with the
 * O_NONBLOCK file status flag, false if not.
 */
static VALUE get_nonblock(VALUE mod)
{
        return (accept4_flags & A4_SOCK_NONBLOCK) ==
            A4_SOCK_NONBLOCK ? Qtrue : Qfalse;
}

/*
 * call-seq:
 *
 *      Kgio.accept_cloexec = true
 *      Kgio.accept_clocexec = false
 *
 * Sets whether or not Kgio::Socket objects created by
 * TCPServer#kgio_accept,
 * TCPServer#kgio_tryaccept,
 * UNIXServer#kgio_accept,
 * and UNIXServer#kgio_tryaccept
 * are created with the FD_CLOEXEC file descriptor flag.
 *
 * This is on by default, as there is little reason to deal to enable
 * it for client sockets on a socket server.
 */
static VALUE set_cloexec(VALUE mod, VALUE boolean)
{
        switch (TYPE(boolean)) {
        case T_TRUE:
                accept4_flags |= A4_SOCK_CLOEXEC;
                return boolean;
        case T_FALSE:
                accept4_flags &= ~A4_SOCK_CLOEXEC;
                return boolean;
        }
        rb_raise(rb_eTypeError, "not true or false");
        return Qnil;
}

/*
 * call-seq:
 *
 *      Kgio.accept_nonblock = true
 *      Kgio.accept_nonblock = false
 *
 * Sets whether or not Kgio::Socket objects created by
 * TCPServer#kgio_accept,
 * TCPServer#kgio_tryaccept,
 * UNIXServer#kgio_accept,
 * and UNIXServer#kgio_tryaccept
 * are created with the O_NONBLOCK file status flag.
 *
 * This defaults to +false+ for GNU/Linux where MSG_DONTWAIT is
 * available (and on newer GNU/Linux, accept4() may also set
 * the non-blocking flag.  This defaults to +true+ on non-GNU/Linux
 * systems.
 */
static VALUE set_nonblock(VALUE mod, VALUE boolean)
{
        switch (TYPE(boolean)) {
        case T_TRUE:
                accept4_flags |= A4_SOCK_NONBLOCK;
                return boolean;
        case T_FALSE:
                accept4_flags &= ~A4_SOCK_NONBLOCK;
                return boolean;
        }
        rb_raise(rb_eTypeError, "not true or false");
        return Qnil;
}

static void close_fail(int fd, const char *msg)
{
        int saved_errno = errno;
        (void)close(fd);
        errno = saved_errno;
        rb_sys_fail(msg);
}

#ifdef SOCK_NONBLOCK
#  define MY_SOCK_STREAM (SOCK_STREAM|SOCK_NONBLOCK)
#else
#  define MY_SOCK_STREAM SOCK_STREAM
#endif /* ! SOCK_NONBLOCK */

static VALUE
my_connect(VALUE klass, int io_wait, int domain, void *addr, socklen_t addrlen)
{
        int fd = socket(domain, MY_SOCK_STREAM, 0);

        if (fd == -1) {
                switch (errno) {
                case EMFILE:
                case ENFILE:
#ifdef ENOBUFS
                case ENOBUFS:
#endif /* ENOBUFS */
                        errno = 0;
                        rb_gc();
                        fd = socket(domain, MY_SOCK_STREAM, 0);
                }
                if (fd == -1)
                        rb_sys_fail("socket");
        }

#ifndef SOCK_NONBLOCK
        if (fcntl(fd, F_SETFL, O_RDWR | O_NONBLOCK) == -1)
                close_fail(fd, "fcntl(F_SETFL, O_RDWR | O_NONBLOCK)");
#endif /* SOCK_NONBLOCK */

        if (connect(fd, addr, addrlen) == -1) {
                if (errno == EINPROGRESS) {
                        VALUE io = sock_for_fd(klass, fd);

                        if (io_wait) {
                                errno = EAGAIN;
                                wait_writable(io, fd);
                        }
                        return io;
                }
                close_fail(fd, "connect");
        }
        return sock_for_fd(klass, fd);
}

static VALUE tcp_connect(VALUE klass, VALUE ip, VALUE port, int io_wait)
{
        struct sockaddr_in addr = { 0 };

        addr.sin_family = AF_INET;
        addr.sin_port = htons((unsigned short)NUM2INT(port));

        switch (inet_pton(AF_INET, StringValuePtr(ip), &addr.sin_addr)) {
        case 1:
                return my_connect(klass, io_wait, PF_INET, &addr, sizeof(addr));
        case -1:
                rb_sys_fail("inet_pton");
        }
        rb_raise(rb_eArgError, "invalid address: %s", StringValuePtr(ip));

        return Qnil;
}

/*
 * call-seq:
 *
 *      Kgio::TCPSocket.new('127.0.0.1', 80) -> socket
 *
 * Creates a new Kgio::TCPSocket object and initiates a
 * non-blocking connection.
 *
 * This may block and call any method assigned to Kgio.wait_writable.
 *
 * Unlike the TCPSocket.new in Ruby, this does NOT perform DNS
 * lookups (which is subject to a different set of timeouts and
 * best handled elsewhere).
 */
static VALUE kgio_tcp_connect(VALUE klass, VALUE ip, VALUE port)
{
        return tcp_connect(klass, ip, port, 1);
}

/*
 * call-seq:
 *
 *      Kgio::TCPSocket.start('127.0.0.1', 80) -> socket
 *
 * Creates a new Kgio::TCPSocket object and initiates a
 * non-blocking connection.  The caller should select/poll
 * on the socket for writability before attempting to write
 * or optimistically attempt a write and handle Kgio::WaitWritable
 * or Errno::EAGAIN.
 *
 * Unlike the TCPSocket.new in Ruby, this does NOT perform DNS
 * lookups (which is subject to a different set of timeouts and
 * best handled elsewhere).
 */
static VALUE kgio_tcp_start(VALUE klass, VALUE ip, VALUE port)
{
        return tcp_connect(klass, ip, port, 0);
}

static VALUE unix_connect(VALUE klass, VALUE path, int io_wait)
{
        struct sockaddr_un addr = { 0 };
        long len;

        StringValue(path);
        len = RSTRING_LEN(path);
        if (sizeof(addr.sun_path) <= len)
                rb_raise(rb_eArgError,
                         "too long unix socket path (max: %dbytes)",
                         (int)sizeof(addr.sun_path)-1);

        memcpy(addr.sun_path, RSTRING_PTR(path), len);
        addr.sun_family = AF_UNIX;

        return my_connect(klass, io_wait, PF_UNIX, &addr, sizeof(addr));
}

/*
 * call-seq:
 *
 *      Kgio::UNIXSocket.new("/path/to/unix/socket") -> socket
 *
 * Creates a new Kgio::UNIXSocket object and initiates a
 * non-blocking connection.
 *
 * This may block and call any method assigned to Kgio.wait_writable.
 */
static VALUE kgio_unix_connect(VALUE klass, VALUE path)
{
        return unix_connect(klass, path, 1);
}

/*
 * call-seq:
 *
 *      Kgio::UNIXSocket.start("/path/to/unix/socket") -> socket
 *
 * Creates a new Kgio::UNIXSocket object and initiates a
 * non-blocking connection.  The caller should select/poll
 * on the socket for writability before attempting to write
 * or optimistically attempt a write and handle Kgio::WaitWritable
 * or Errno::EAGAIN.
 */
static VALUE kgio_unix_start(VALUE klass, VALUE path)
{
        return unix_connect(klass, path, 0);
}

static VALUE stream_connect(VALUE klass, VALUE addr, int io_wait)
{
        int domain;
        socklen_t addrlen;
        struct sockaddr *sockaddr;

        if (TYPE(addr) == T_STRING) {
                sockaddr = (struct sockaddr *)(RSTRING_PTR(addr));
                addrlen = (socklen_t)RSTRING_LEN(addr);
        } else {
                rb_raise(rb_eTypeError, "invalid address");
        }
        switch (((struct sockaddr_in *)(sockaddr))->sin_family) {
        case AF_UNIX: domain = PF_UNIX; break;
        case AF_INET: domain = PF_INET; break;
#ifdef AF_INET6 /* IPv6 support incomplete */
        case AF_INET6: domain = PF_INET6; break;
#endif /* AF_INET6 */
        default:
                rb_raise(rb_eArgError, "invalid address family");
        }

        return my_connect(klass, io_wait, domain, sockaddr, addrlen);
}

/* call-seq:
 *
 *      addr = Socket.pack_sockaddr_in(80, 'example.com')
 *      Kgio::Socket.connect(addr) -> socket
 *
 *      addr = Socket.pack_sockaddr_un("/path/to/unix/socket")
 *      Kgio::Socket.connect(addr) -> socket
 *
 * Creates a generic Kgio::Socket object and initiates a
 * non-blocking connection.
 *
 * This may block and call any method assigned to Kgio.wait_writable.
 */
static VALUE kgio_connect(VALUE klass, VALUE addr)
{
        return stream_connect(klass, addr, 1);
}

/* call-seq:
 *
 *      addr = Socket.pack_sockaddr_in(80, 'example.com')
 *      Kgio::Socket.start(addr) -> socket
 *
 *      addr = Socket.pack_sockaddr_un("/path/to/unix/socket")
 *      Kgio::Socket.start(addr) -> socket
 *
 * Creates a generic Kgio::Socket object and initiates a
 * non-blocking connection.  The caller should select/poll
 * on the socket for writability before attempting to write
 * or optimistically attempt a write and handle Kgio::WaitWritable
 * or Errno::EAGAIN.
 */
static VALUE kgio_start(VALUE klass, VALUE addr)
{
        return stream_connect(klass, addr, 0);
}

void Init_kgio_ext(void)
{
        VALUE mKgio = rb_define_module("Kgio");
        VALUE mPipeMethods, mSocketMethods;
        VALUE cUNIXServer, cTCPServer, cUNIXSocket, cTCPSocket;

        rb_require("socket");

        /*
         * Document-module: Kgio::Socket
         *
         * A generic socket class with Kgio::SocketMethods included.
         * This is returned by all Kgio methods that accept(2) a connected
         * stream socket.
         */
        cSocket = rb_const_get(rb_cObject, rb_intern("Socket"));
        cSocket = rb_define_class_under(mKgio, "Socket", cSocket);

        localhost = rb_str_new2("127.0.0.1");

        /*
         * The IPv4 address of UNIX domain sockets, useful for creating
         * Rack (and CGI) servers that also serve HTTP traffic over
         * UNIX domain sockets.
         */
        rb_const_set(mKgio, rb_intern("LOCALHOST"), localhost);

        /*
         * Document-module: Kgio::WaitReadable
         *
         * PipeMethods#kgio_tryread and SocketMethods#kgio_tryread will
         * return this constant when waiting for a read is required.
         */
        mKgio_WaitReadable = rb_define_module_under(mKgio, "WaitReadable");

        /*
         * Document-module: Kgio::WaitWritable
         *
         * PipeMethods#kgio_trywrite and SocketMethods#kgio_trywrite will
         * return this constant when waiting for a read is required.
         */
        mKgio_WaitWritable = rb_define_module_under(mKgio, "WaitWritable");

        rb_define_singleton_method(mKgio, "wait_readable=", set_wait_rd, 1);
        rb_define_singleton_method(mKgio, "wait_writable=", set_wait_wr, 1);
        rb_define_singleton_method(mKgio, "wait_readable", wait_rd, 0);
        rb_define_singleton_method(mKgio, "wait_writable", wait_wr, 0);
        rb_define_singleton_method(mKgio, "accept_cloexec?", get_cloexec, 0);
        rb_define_singleton_method(mKgio, "accept_cloexec=", set_cloexec, 1);
        rb_define_singleton_method(mKgio, "accept_nonblock?", get_nonblock, 0);
        rb_define_singleton_method(mKgio, "accept_nonblock=", set_nonblock, 1);

        /*
         * Document-module: Kgio::PipeMethods
         *
         * This module may be used used to create classes that respond to
         * various Kgio methods for reading and writing.  This is included
         * in Kgio::Pipe by default.
         */
        mPipeMethods = rb_define_module_under(mKgio, "PipeMethods");
        rb_define_method(mPipeMethods, "kgio_read", kgio_read, -1);
        rb_define_method(mPipeMethods, "kgio_write", kgio_write, 1);
        rb_define_method(mPipeMethods, "kgio_tryread", kgio_tryread, -1);
        rb_define_method(mPipeMethods, "kgio_trywrite", kgio_trywrite, 1);

        /*
         * Document-module: Kgio::SocketMethods
         *
         * This method behaves like Kgio::PipeMethods, but contains
         * optimizations for sockets on certain operating systems
         * (e.g. GNU/Linux).
         */
        mSocketMethods = rb_define_module_under(mKgio, "SocketMethods");
        rb_define_method(mSocketMethods, "kgio_read", kgio_recv, -1);
        rb_define_method(mSocketMethods, "kgio_write", kgio_send, 1);
        rb_define_method(mSocketMethods, "kgio_tryread", kgio_tryrecv, -1);
        rb_define_method(mSocketMethods, "kgio_trywrite", kgio_trysend, 1);

        /*
         * Returns the client IPv4 address of the socket in dotted quad
         * form as a string.  This is always the value of the
         * Kgio::LOCALHOST constant for UNIX domain sockets.
         */
        rb_define_attr(mSocketMethods, "kgio_addr", 1, 1);

        rb_include_module(cSocket, mSocketMethods);
        rb_define_singleton_method(cSocket, "new", kgio_connect, 1);
        rb_define_singleton_method(cSocket, "start", kgio_start, 1);

        cUNIXServer = rb_const_get(rb_cObject, rb_intern("UNIXServer"));
        cUNIXServer = rb_define_class_under(mKgio, "UNIXServer", cUNIXServer);
        rb_define_method(cUNIXServer, "kgio_tryaccept", unix_tryaccept, 0);
        rb_define_method(cUNIXServer, "kgio_accept", unix_accept, 0);

        cTCPServer = rb_const_get(rb_cObject, rb_intern("TCPServer"));
        cTCPServer = rb_define_class_under(mKgio, "TCPServer", cTCPServer);
        rb_define_method(cTCPServer, "kgio_tryaccept", tcp_tryaccept, 0);
        rb_define_method(cTCPServer, "kgio_accept", tcp_accept, 0);

        cTCPSocket = rb_const_get(rb_cObject, rb_intern("TCPSocket"));
        cTCPSocket = rb_define_class_under(mKgio, "TCPSocket", cTCPSocket);
        rb_include_module(cTCPSocket, mSocketMethods);
        rb_define_singleton_method(cTCPSocket, "new", kgio_tcp_connect, 2);
        rb_define_singleton_method(cTCPSocket, "start", kgio_tcp_start, 2);

        cUNIXSocket = rb_const_get(rb_cObject, rb_intern("UNIXSocket"));
        cUNIXSocket = rb_define_class_under(mKgio, "UNIXSocket", cUNIXSocket);
        rb_include_module(cUNIXSocket, mSocketMethods);
        rb_define_singleton_method(cUNIXSocket, "new", kgio_unix_connect, 1);
        rb_define_singleton_method(cUNIXSocket, "start", kgio_unix_start, 1);

        iv_kgio_addr = rb_intern("@kgio_addr");
        init_sock_for_fd();
}