[sgt/putty] / windows / winnet.c

/*
 * Windows networking abstraction.
 *
 * For the IPv6 code in here I am indebted to Jeroen Massar and
 * unfix.org.
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

#define DEFINE_PLUG_METHOD_MACROS
#include "putty.h"
#include "network.h"
#include "tree234.h"

#include <ws2tcpip.h>

#ifndef NO_IPV6
const struct in6_addr in6addr_any = IN6ADDR_ANY_INIT;
const struct in6_addr in6addr_loopback = IN6ADDR_LOOPBACK_INIT;
#endif

#define ipv4_is_loopback(addr) \
        ((p_ntohl(addr.s_addr) & 0xFF000000L) == 0x7F000000L)

/*
 * We used to typedef struct Socket_tag *Socket.
 *
 * Since we have made the networking abstraction slightly more
 * abstract, Socket no longer means a tcp socket (it could mean
 * an ssl socket).  So now we must use Actual_Socket when we know
 * we are talking about a tcp socket.
 */
typedef struct Socket_tag *Actual_Socket;

/*
 * Mutable state that goes with a SockAddr: stores information
 * about where in the list of candidate IP(v*) addresses we've
 * currently got to.
 */
typedef struct SockAddrStep_tag SockAddrStep;
struct SockAddrStep_tag {
#ifndef NO_IPV6
    struct addrinfo *ai;               /* steps along addr->ais */
#endif
    int curraddr;
};

struct Socket_tag {
    const struct socket_function_table *fn;
    /* the above variable absolutely *must* be the first in this structure */
    char *error;
    SOCKET s;
    Plug plug;
    void *private_ptr;
    bufchain output_data;
    int connected;
    int writable;
    int frozen; /* this causes readability notifications to be ignored */
    int frozen_readable; /* this means we missed at least one readability
                          * notification while we were frozen */
    int localhost_only;                /* for listening sockets */
    char oobdata[1];
    int sending_oob;
    int oobinline, nodelay, keepalive, privport;
    enum { EOF_NO, EOF_PENDING, EOF_SENT } outgoingeof;
    SockAddr addr;
    SockAddrStep step;
    int port;
    int pending_error;                 /* in case send() returns error */
    /*
     * We sometimes need pairs of Socket structures to be linked:
     * if we are listening on the same IPv6 and v4 port, for
     * example. So here we define `parent' and `child' pointers to
     * track this link.
     */
    Actual_Socket parent, child;
};

struct SockAddr_tag {
    int refcount;
    char *error;
    int resolved;
#ifndef NO_IPV6
    struct addrinfo *ais;              /* Addresses IPv6 style. */
#endif
    unsigned long *addresses;          /* Addresses IPv4 style. */
    int naddresses;
    char hostname[512];                /* Store an unresolved host name. */
};

/*
 * Which address family this address belongs to. AF_INET for IPv4;
 * AF_INET6 for IPv6; AF_UNSPEC indicates that name resolution has
 * not been done and a simple host name is held in this SockAddr
 * structure.
 */
#ifndef NO_IPV6
#define SOCKADDR_FAMILY(addr, step) \
    (!(addr)->resolved ? AF_UNSPEC : \
     (step).ai ? (step).ai->ai_family : AF_INET)
#else
#define SOCKADDR_FAMILY(addr, step) \
    (!(addr)->resolved ? AF_UNSPEC : AF_INET)
#endif

/*
 * Start a SockAddrStep structure to step through multiple
 * addresses.
 */
#ifndef NO_IPV6
#define START_STEP(addr, step) \
    ((step).ai = (addr)->ais, (step).curraddr = 0)
#else
#define START_STEP(addr, step) \
    ((step).curraddr = 0)
#endif

static tree234 *sktree;

static int cmpfortree(void *av, void *bv)
{
    Actual_Socket a = (Actual_Socket) av, b = (Actual_Socket) bv;
    unsigned long as = (unsigned long) a->s, bs = (unsigned long) b->s;
    if (as < bs)
        return -1;
    if (as > bs)
        return +1;
    if (a < b)
        return -1;
    if (a > b)
        return +1;
    return 0;
}

static int cmpforsearch(void *av, void *bv)
{
    Actual_Socket b = (Actual_Socket) bv;
    unsigned long as = (unsigned long) av, bs = (unsigned long) b->s;
    if (as < bs)
        return -1;
    if (as > bs)
        return +1;
    return 0;
}

DECL_WINDOWS_FUNCTION(static, int, WSAStartup, (WORD, LPWSADATA));
DECL_WINDOWS_FUNCTION(static, int, WSACleanup, (void));
DECL_WINDOWS_FUNCTION(static, int, closesocket, (SOCKET));
DECL_WINDOWS_FUNCTION(static, u_long, ntohl, (u_long));
DECL_WINDOWS_FUNCTION(static, u_long, htonl, (u_long));
DECL_WINDOWS_FUNCTION(static, u_short, htons, (u_short));
DECL_WINDOWS_FUNCTION(static, u_short, ntohs, (u_short));
DECL_WINDOWS_FUNCTION(static, int, gethostname, (char *, int));
DECL_WINDOWS_FUNCTION(static, struct hostent FAR *, gethostbyname,
                      (const char FAR *));
DECL_WINDOWS_FUNCTION(static, struct servent FAR *, getservbyname,
                      (const char FAR *, const char FAR *));
DECL_WINDOWS_FUNCTION(static, unsigned long, inet_addr, (const char FAR *));
DECL_WINDOWS_FUNCTION(static, char FAR *, inet_ntoa, (struct in_addr));
DECL_WINDOWS_FUNCTION(static, int, connect,
                      (SOCKET, const struct sockaddr FAR *, int));
DECL_WINDOWS_FUNCTION(static, int, bind,
                      (SOCKET, const struct sockaddr FAR *, int));
DECL_WINDOWS_FUNCTION(static, int, setsockopt,
                      (SOCKET, int, int, const char FAR *, int));
DECL_WINDOWS_FUNCTION(static, SOCKET, socket, (int, int, int));
DECL_WINDOWS_FUNCTION(static, int, listen, (SOCKET, int));
DECL_WINDOWS_FUNCTION(static, int, send, (SOCKET, const char FAR *, int, int));
DECL_WINDOWS_FUNCTION(static, int, shutdown, (SOCKET, int));
DECL_WINDOWS_FUNCTION(static, int, ioctlsocket,
                      (SOCKET, long, u_long FAR *));
DECL_WINDOWS_FUNCTION(static, SOCKET, accept,
                      (SOCKET, struct sockaddr FAR *, int FAR *));
DECL_WINDOWS_FUNCTION(static, int, recv, (SOCKET, char FAR *, int, int));
DECL_WINDOWS_FUNCTION(static, int, WSAIoctl,
                      (SOCKET, DWORD, LPVOID, DWORD, LPVOID, DWORD,
                       LPDWORD, LPWSAOVERLAPPED,
                       LPWSAOVERLAPPED_COMPLETION_ROUTINE));
#ifndef NO_IPV6
DECL_WINDOWS_FUNCTION(static, int, getaddrinfo,
                      (const char *nodename, const char *servname,
                       const struct addrinfo *hints, struct addrinfo **res));
DECL_WINDOWS_FUNCTION(static, void, freeaddrinfo, (struct addrinfo *res));
DECL_WINDOWS_FUNCTION(static, int, getnameinfo,
                      (const struct sockaddr FAR * sa, socklen_t salen,
                       char FAR * host, size_t hostlen, char FAR * serv,
                       size_t servlen, int flags));
DECL_WINDOWS_FUNCTION(static, char *, gai_strerror, (int ecode));
DECL_WINDOWS_FUNCTION(static, int, WSAAddressToStringA,
                      (LPSOCKADDR, DWORD, LPWSAPROTOCOL_INFO,
                       LPSTR, LPDWORD));
#endif

static HMODULE winsock_module = NULL;
static WSADATA wsadata;
#ifndef NO_IPV6
static HMODULE winsock2_module = NULL;
static HMODULE wship6_module = NULL;
#endif

int sk_startup(int hi, int lo)
{
    WORD winsock_ver;

    winsock_ver = MAKEWORD(hi, lo);

    if (p_WSAStartup(winsock_ver, &wsadata)) {
        return FALSE;
    }

    if (LOBYTE(wsadata.wVersion) != LOBYTE(winsock_ver)) {
        return FALSE;
    }

#ifdef NET_SETUP_DIAGNOSTICS
    {
        char buf[80];
        sprintf(buf, "Using WinSock %d.%d", hi, lo);
        logevent(NULL, buf);
    }
#endif
    return TRUE;
}

void sk_init(void)
{
#ifndef NO_IPV6
    winsock2_module =
#endif
        winsock_module = load_system32_dll("ws2_32.dll");
    if (!winsock_module) {
        winsock_module = load_system32_dll("wsock32.dll");
    }
    if (!winsock_module)
        fatalbox("Unable to load any WinSock library");

#ifndef NO_IPV6
    /* Check if we have getaddrinfo in Winsock */
    if (GetProcAddress(winsock_module, "getaddrinfo") != NULL) {
#ifdef NET_SETUP_DIAGNOSTICS
        logevent(NULL, "Native WinSock IPv6 support detected");
#endif
        GET_WINDOWS_FUNCTION(winsock_module, getaddrinfo);
        GET_WINDOWS_FUNCTION(winsock_module, freeaddrinfo);
        GET_WINDOWS_FUNCTION(winsock_module, getnameinfo);
        GET_WINDOWS_FUNCTION(winsock_module, gai_strerror);
    } else {
        /* Fall back to wship6.dll for Windows 2000 */
        wship6_module = load_system32_dll("wship6.dll");
        if (wship6_module) {
#ifdef NET_SETUP_DIAGNOSTICS
            logevent(NULL, "WSH IPv6 support detected");
#endif
            GET_WINDOWS_FUNCTION(wship6_module, getaddrinfo);
            GET_WINDOWS_FUNCTION(wship6_module, freeaddrinfo);
            GET_WINDOWS_FUNCTION(wship6_module, getnameinfo);
            GET_WINDOWS_FUNCTION(wship6_module, gai_strerror);
        } else {
#ifdef NET_SETUP_DIAGNOSTICS
            logevent(NULL, "No IPv6 support detected");
#endif
        }
    }
    GET_WINDOWS_FUNCTION(winsock2_module, WSAAddressToStringA);
#else
#ifdef NET_SETUP_DIAGNOSTICS
    logevent(NULL, "PuTTY was built without IPv6 support");
#endif
#endif

    GET_WINDOWS_FUNCTION(winsock_module, WSAAsyncSelect);
    GET_WINDOWS_FUNCTION(winsock_module, WSAEventSelect);
    GET_WINDOWS_FUNCTION(winsock_module, select);
    GET_WINDOWS_FUNCTION(winsock_module, WSAGetLastError);
    GET_WINDOWS_FUNCTION(winsock_module, WSAEnumNetworkEvents);
    GET_WINDOWS_FUNCTION(winsock_module, WSAStartup);
    GET_WINDOWS_FUNCTION(winsock_module, WSACleanup);
    GET_WINDOWS_FUNCTION(winsock_module, closesocket);
    GET_WINDOWS_FUNCTION(winsock_module, ntohl);
    GET_WINDOWS_FUNCTION(winsock_module, htonl);
    GET_WINDOWS_FUNCTION(winsock_module, htons);
    GET_WINDOWS_FUNCTION(winsock_module, ntohs);
    GET_WINDOWS_FUNCTION(winsock_module, gethostname);
    GET_WINDOWS_FUNCTION(winsock_module, gethostbyname);
    GET_WINDOWS_FUNCTION(winsock_module, getservbyname);
    GET_WINDOWS_FUNCTION(winsock_module, inet_addr);
    GET_WINDOWS_FUNCTION(winsock_module, inet_ntoa);
    GET_WINDOWS_FUNCTION(winsock_module, connect);
    GET_WINDOWS_FUNCTION(winsock_module, bind);
    GET_WINDOWS_FUNCTION(winsock_module, setsockopt);
    GET_WINDOWS_FUNCTION(winsock_module, socket);
    GET_WINDOWS_FUNCTION(winsock_module, listen);
    GET_WINDOWS_FUNCTION(winsock_module, send);
    GET_WINDOWS_FUNCTION(winsock_module, shutdown);
    GET_WINDOWS_FUNCTION(winsock_module, ioctlsocket);
    GET_WINDOWS_FUNCTION(winsock_module, accept);
    GET_WINDOWS_FUNCTION(winsock_module, recv);
    GET_WINDOWS_FUNCTION(winsock_module, WSAIoctl);

    /* Try to get the best WinSock version we can get */
    if (!sk_startup(2,2) &&
        !sk_startup(2,0) &&
        !sk_startup(1,1)) {
        fatalbox("Unable to initialise WinSock");
    }

    sktree = newtree234(cmpfortree);
}

void sk_cleanup(void)
{
    Actual_Socket s;
    int i;

    if (sktree) {
        for (i = 0; (s = index234(sktree, i)) != NULL; i++) {
            p_closesocket(s->s);
        }
        freetree234(sktree);
        sktree = NULL;
    }

    if (p_WSACleanup)
        p_WSACleanup();
    if (winsock_module)
        FreeLibrary(winsock_module);
#ifndef NO_IPV6
    if (wship6_module)
        FreeLibrary(wship6_module);
#endif
}

char *winsock_error_string(int error)
{
    switch (error) {
      case WSAEACCES:
        return "Network error: Permission denied";
      case WSAEADDRINUSE:
        return "Network error: Address already in use";
      case WSAEADDRNOTAVAIL:
        return "Network error: Cannot assign requested address";
      case WSAEAFNOSUPPORT:
        return
            "Network error: Address family not supported by protocol family";
      case WSAEALREADY:
        return "Network error: Operation already in progress";
      case WSAECONNABORTED:
        return "Network error: Software caused connection abort";
      case WSAECONNREFUSED:
        return "Network error: Connection refused";
      case WSAECONNRESET:
        return "Network error: Connection reset by peer";
      case WSAEDESTADDRREQ:
        return "Network error: Destination address required";
      case WSAEFAULT:
        return "Network error: Bad address";
      case WSAEHOSTDOWN:
        return "Network error: Host is down";
      case WSAEHOSTUNREACH:
        return "Network error: No route to host";
      case WSAEINPROGRESS:
        return "Network error: Operation now in progress";
      case WSAEINTR:
        return "Network error: Interrupted function call";
      case WSAEINVAL:
        return "Network error: Invalid argument";
      case WSAEISCONN:
        return "Network error: Socket is already connected";
      case WSAEMFILE:
        return "Network error: Too many open files";
      case WSAEMSGSIZE:
        return "Network error: Message too long";
      case WSAENETDOWN:
        return "Network error: Network is down";
      case WSAENETRESET:
        return "Network error: Network dropped connection on reset";
      case WSAENETUNREACH:
        return "Network error: Network is unreachable";
      case WSAENOBUFS:
        return "Network error: No buffer space available";
      case WSAENOPROTOOPT:
        return "Network error: Bad protocol option";
      case WSAENOTCONN:
        return "Network error: Socket is not connected";
      case WSAENOTSOCK:
        return "Network error: Socket operation on non-socket";
      case WSAEOPNOTSUPP:
        return "Network error: Operation not supported";
      case WSAEPFNOSUPPORT:
        return "Network error: Protocol family not supported";
      case WSAEPROCLIM:
        return "Network error: Too many processes";
      case WSAEPROTONOSUPPORT:
        return "Network error: Protocol not supported";
      case WSAEPROTOTYPE:
        return "Network error: Protocol wrong type for socket";
      case WSAESHUTDOWN:
        return "Network error: Cannot send after socket shutdown";
      case WSAESOCKTNOSUPPORT:
        return "Network error: Socket type not supported";
      case WSAETIMEDOUT:
        return "Network error: Connection timed out";
      case WSAEWOULDBLOCK:
        return "Network error: Resource temporarily unavailable";
      case WSAEDISCON:
        return "Network error: Graceful shutdown in progress";
      default:
        return "Unknown network error";
    }
}

SockAddr sk_namelookup(const char *host, char **canonicalname,
                       int address_family)
{
    SockAddr ret = snew(struct SockAddr_tag);
    unsigned long a;
    char realhost[8192];
    int hint_family;

    /* Default to IPv4. */
    hint_family = (address_family == ADDRTYPE_IPV4 ? AF_INET :
#ifndef NO_IPV6
                   address_family == ADDRTYPE_IPV6 ? AF_INET6 :
#endif
                   AF_UNSPEC);

    /* Clear the structure and default to IPv4. */
    memset(ret, 0, sizeof(struct SockAddr_tag));
#ifndef NO_IPV6
    ret->ais = NULL;
#endif
    ret->addresses = NULL;
    ret->resolved = FALSE;
    ret->refcount = 1;
    *realhost = '\0';

    if ((a = p_inet_addr(host)) == (unsigned long) INADDR_NONE) {
        struct hostent *h = NULL;
        int err;
#ifndef NO_IPV6
        /*
         * Use getaddrinfo when it's available
         */
        if (p_getaddrinfo) {
            struct addrinfo hints;
#ifdef NET_SETUP_DIAGNOSTICS
            logevent(NULL, "Using getaddrinfo() for resolving");
#endif
            memset(&hints, 0, sizeof(hints));
            hints.ai_family = hint_family;
            hints.ai_flags = AI_CANONNAME;
            if ((err = p_getaddrinfo(host, NULL, &hints, &ret->ais)) == 0)
                ret->resolved = TRUE;
        } else
#endif
        {
#ifdef NET_SETUP_DIAGNOSTICS
            logevent(NULL, "Using gethostbyname() for resolving");
#endif
            /*
             * Otherwise use the IPv4-only gethostbyname...
             * (NOTE: we don't use gethostbyname as a fallback!)
             */
            if ( (h = p_gethostbyname(host)) )
                ret->resolved = TRUE;
            else
                err = p_WSAGetLastError();
        }

        if (!ret->resolved) {
            ret->error = (err == WSAENETDOWN ? "Network is down" :
                          err == WSAHOST_NOT_FOUND ? "Host does not exist" :
                          err == WSATRY_AGAIN ? "Host not found" :
#ifndef NO_IPV6
                          p_getaddrinfo&&p_gai_strerror ? p_gai_strerror(err) :
#endif
                          "gethostbyname: unknown error");
        } else {
            ret->error = NULL;

#ifndef NO_IPV6
            /* If we got an address info use that... */
            if (ret->ais) {
                /* Are we in IPv4 fallback mode? */
                /* We put the IPv4 address into the a variable so we can further-on use the IPv4 code... */
                if (ret->ais->ai_family == AF_INET)
                    memcpy(&a,
                           (char *) &((SOCKADDR_IN *) ret->ais->
                                      ai_addr)->sin_addr, sizeof(a));

                if (ret->ais->ai_canonname)
                    strncpy(realhost, ret->ais->ai_canonname, lenof(realhost));
                else
                    strncpy(realhost, host, lenof(realhost));
            }
            /* We used the IPv4-only gethostbyname()... */
            else
#endif
            {
                int n;
                for (n = 0; h->h_addr_list[n]; n++);
                ret->addresses = snewn(n, unsigned long);
                ret->naddresses = n;
                for (n = 0; n < ret->naddresses; n++) {
                    memcpy(&a, h->h_addr_list[n], sizeof(a));
                    ret->addresses[n] = p_ntohl(a);
                }
                memcpy(&a, h->h_addr, sizeof(a));
                /* This way we are always sure the h->h_name is valid :) */
                strncpy(realhost, h->h_name, sizeof(realhost));
            }
        }
    } else {
        /*
         * This must be a numeric IPv4 address because it caused a
         * success return from inet_addr.
         */
        ret->addresses = snewn(1, unsigned long);
        ret->naddresses = 1;
        ret->addresses[0] = p_ntohl(a);
        ret->resolved = TRUE;
        strncpy(realhost, host, sizeof(realhost));
    }
    realhost[lenof(realhost)-1] = '\0';
    *canonicalname = snewn(1+strlen(realhost), char);
    strcpy(*canonicalname, realhost);
    return ret;
}

SockAddr sk_nonamelookup(const char *host)
{
    SockAddr ret = snew(struct SockAddr_tag);
    ret->error = NULL;
    ret->resolved = FALSE;
#ifndef NO_IPV6
    ret->ais = NULL;
#endif
    ret->addresses = NULL;
    ret->naddresses = 0;
    ret->refcount = 1;
    strncpy(ret->hostname, host, lenof(ret->hostname));
    ret->hostname[lenof(ret->hostname)-1] = '\0';
    return ret;
}

int sk_nextaddr(SockAddr addr, SockAddrStep *step)
{
#ifndef NO_IPV6
    if (step->ai) {
        if (step->ai->ai_next) {
            step->ai = step->ai->ai_next;
            return TRUE;
        } else
            return FALSE;
    }
#endif
    if (step->curraddr+1 < addr->naddresses) {
        step->curraddr++;
        return TRUE;
    } else {
        return FALSE;
    }
}

void sk_getaddr(SockAddr addr, char *buf, int buflen)
{
    SockAddrStep step;
    START_STEP(addr, step);

#ifndef NO_IPV6
    if (step.ai) {
        int err = 0;
        if (p_WSAAddressToStringA) {
            DWORD dwbuflen = buflen;
            err = p_WSAAddressToStringA(step.ai->ai_addr, step.ai->ai_addrlen,
                                        NULL, buf, &dwbuflen);
        } else
            err = -1;
        if (err) {
            strncpy(buf, addr->hostname, buflen);
            if (!buf[0])
                strncpy(buf, "<unknown>", buflen);
            buf[buflen-1] = '\0';
        }
    } else
#endif
    if (SOCKADDR_FAMILY(addr, step) == AF_INET) {
        struct in_addr a;
        assert(addr->addresses && step.curraddr < addr->naddresses);
        a.s_addr = p_htonl(addr->addresses[step.curraddr]);
        strncpy(buf, p_inet_ntoa(a), buflen);
        buf[buflen-1] = '\0';
    } else {
        strncpy(buf, addr->hostname, buflen);
        buf[buflen-1] = '\0';
    }
}

int sk_hostname_is_local(char *name)
{
    return !strcmp(name, "localhost") ||
           !strcmp(name, "::1") ||
           !strncmp(name, "127.", 4);
}

static INTERFACE_INFO local_interfaces[16];
static int n_local_interfaces;       /* 0=not yet, -1=failed, >0=number */

static int ipv4_is_local_addr(struct in_addr addr)
{
    if (ipv4_is_loopback(addr))
        return 1;                      /* loopback addresses are local */
    if (!n_local_interfaces) {
        SOCKET s = p_socket(AF_INET, SOCK_DGRAM, 0);
        DWORD retbytes;

        if (p_WSAIoctl &&
            p_WSAIoctl(s, SIO_GET_INTERFACE_LIST, NULL, 0,
                       local_interfaces, sizeof(local_interfaces),
                       &retbytes, NULL, NULL) == 0)
            n_local_interfaces = retbytes / sizeof(INTERFACE_INFO);
        else
            logevent(NULL, "Unable to get list of local IP addresses");
    }
    if (n_local_interfaces > 0) {
        int i;
        for (i = 0; i < n_local_interfaces; i++) {
            SOCKADDR_IN *address =
                (SOCKADDR_IN *)&local_interfaces[i].iiAddress;
            if (address->sin_addr.s_addr == addr.s_addr)
                return 1;              /* this address is local */
        }
    }
    return 0;                  /* this address is not local */
}

int sk_address_is_local(SockAddr addr)
{
    SockAddrStep step;
    int family;
    START_STEP(addr, step);
    family = SOCKADDR_FAMILY(addr, step);

#ifndef NO_IPV6
    if (family == AF_INET6) {
        return IN6_IS_ADDR_LOOPBACK((const struct in6_addr *)step.ai->ai_addr);
    } else
#endif
    if (family == AF_INET) {
#ifndef NO_IPV6
        if (step.ai) {
            return ipv4_is_local_addr(((struct sockaddr_in *)step.ai->ai_addr)
                                      ->sin_addr);
        } else
#endif
        {
            struct in_addr a;
            assert(addr->addresses && step.curraddr < addr->naddresses);
            a.s_addr = p_htonl(addr->addresses[step.curraddr]);
            return ipv4_is_local_addr(a);
        }
    } else {
        assert(family == AF_UNSPEC);
        return 0;                      /* we don't know; assume not */
    }
}

int sk_addrtype(SockAddr addr)
{
    SockAddrStep step;
    int family;
    START_STEP(addr, step);
    family = SOCKADDR_FAMILY(addr, step);

    return (family == AF_INET ? ADDRTYPE_IPV4 :
#ifndef NO_IPV6
            family == AF_INET6 ? ADDRTYPE_IPV6 :
#endif
            ADDRTYPE_NAME);
}

void sk_addrcopy(SockAddr addr, char *buf)
{
    SockAddrStep step;
    int family;
    START_STEP(addr, step);
    family = SOCKADDR_FAMILY(addr, step);

    assert(family != AF_UNSPEC);
#ifndef NO_IPV6
    if (step.ai) {
        if (family == AF_INET)
            memcpy(buf, &((struct sockaddr_in *)step.ai->ai_addr)->sin_addr,
                   sizeof(struct in_addr));
        else if (family == AF_INET6)
            memcpy(buf, &((struct sockaddr_in6 *)step.ai->ai_addr)->sin6_addr,
                   sizeof(struct in6_addr));
        else
            assert(FALSE);
    } else
#endif
    if (family == AF_INET) {
        struct in_addr a;
        assert(addr->addresses && step.curraddr < addr->naddresses);
        a.s_addr = p_htonl(addr->addresses[step.curraddr]);
        memcpy(buf, (char*) &a.s_addr, 4);
    }
}

void sk_addr_free(SockAddr addr)
{
    if (--addr->refcount > 0)
        return;
#ifndef NO_IPV6
    if (addr->ais && p_freeaddrinfo)
        p_freeaddrinfo(addr->ais);
#endif
    if (addr->addresses)
        sfree(addr->addresses);
    sfree(addr);
}

SockAddr sk_addr_dup(SockAddr addr)
{
    addr->refcount++;
    return addr;
}

static Plug sk_tcp_plug(Socket sock, Plug p)
{
    Actual_Socket s = (Actual_Socket) sock;
    Plug ret = s->plug;
    if (p)
        s->plug = p;
    return ret;
}

static void sk_tcp_flush(Socket s)
{
    /*
     * We send data to the socket as soon as we can anyway,
     * so we don't need to do anything here.  :-)
     */
}

static void sk_tcp_close(Socket s);
static int sk_tcp_write(Socket s, const char *data, int len);
static int sk_tcp_write_oob(Socket s, const char *data, int len);
static void sk_tcp_write_eof(Socket s);
static void sk_tcp_set_private_ptr(Socket s, void *ptr);
static void *sk_tcp_get_private_ptr(Socket s);
static void sk_tcp_set_frozen(Socket s, int is_frozen);
static const char *sk_tcp_socket_error(Socket s);

extern char *do_select(SOCKET skt, int startup);

Socket sk_register(void *sock, Plug plug)
{
    static const struct socket_function_table fn_table = {
        sk_tcp_plug,
        sk_tcp_close,
        sk_tcp_write,
        sk_tcp_write_oob,
        sk_tcp_write_eof,
        sk_tcp_flush,
        sk_tcp_set_private_ptr,
        sk_tcp_get_private_ptr,
        sk_tcp_set_frozen,
        sk_tcp_socket_error
    };

    DWORD err;
    char *errstr;
    Actual_Socket ret;

    /*
     * Create Socket structure.
     */
    ret = snew(struct Socket_tag);
    ret->fn = &fn_table;
    ret->error = NULL;
    ret->plug = plug;
    bufchain_init(&ret->output_data);
    ret->writable = 1;                 /* to start with */
    ret->sending_oob = 0;
    ret->outgoingeof = EOF_NO;
    ret->frozen = 1;
    ret->frozen_readable = 0;
    ret->localhost_only = 0;           /* unused, but best init anyway */
    ret->pending_error = 0;
    ret->parent = ret->child = NULL;
    ret->addr = NULL;

    ret->s = (SOCKET)sock;

    if (ret->s == INVALID_SOCKET) {
        err = p_WSAGetLastError();
        ret->error = winsock_error_string(err);
        return (Socket) ret;
    }

    ret->oobinline = 0;

    /* Set up a select mechanism. This could be an AsyncSelect on a
     * window, or an EventSelect on an event object. */
    errstr = do_select(ret->s, 1);
    if (errstr) {
        ret->error = errstr;
        return (Socket) ret;
    }

    add234(sktree, ret);

    return (Socket) ret;
}

static DWORD try_connect(Actual_Socket sock)
{
    SOCKET s;
#ifndef NO_IPV6
    SOCKADDR_IN6 a6;
#endif
    SOCKADDR_IN a;
    DWORD err;
    char *errstr;
    short localport;
    int family;

    if (sock->s != INVALID_SOCKET) {
        do_select(sock->s, 0);
        p_closesocket(sock->s);
    }

    plug_log(sock->plug, 0, sock->addr, sock->port, NULL, 0);

    /*
     * Open socket.
     */
    family = SOCKADDR_FAMILY(sock->addr, sock->step);

    /*
     * Remove the socket from the tree before we overwrite its
     * internal socket id, because that forms part of the tree's
     * sorting criterion. We'll add it back before exiting this
     * function, whether we changed anything or not.
     */
    del234(sktree, sock);

    s = p_socket(family, SOCK_STREAM, 0);
    sock->s = s;

    if (s == INVALID_SOCKET) {
        err = p_WSAGetLastError();
        sock->error = winsock_error_string(err);
        goto ret;
    }

    if (sock->oobinline) {
        BOOL b = TRUE;
        p_setsockopt(s, SOL_SOCKET, SO_OOBINLINE, (void *) &b, sizeof(b));
    }

    if (sock->nodelay) {
        BOOL b = TRUE;
        p_setsockopt(s, IPPROTO_TCP, TCP_NODELAY, (void *) &b, sizeof(b));
    }

    if (sock->keepalive) {
        BOOL b = TRUE;
        p_setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, (void *) &b, sizeof(b));
    }

    /*
     * Bind to local address.
     */
    if (sock->privport)
        localport = 1023;              /* count from 1023 downwards */
    else
        localport = 0;                 /* just use port 0 (ie winsock picks) */

    /* Loop round trying to bind */
    while (1) {
        int sockcode;

#ifndef NO_IPV6
        if (family == AF_INET6) {
            memset(&a6, 0, sizeof(a6));
            a6.sin6_family = AF_INET6;
          /*a6.sin6_addr = in6addr_any; */ /* == 0 done by memset() */
            a6.sin6_port = p_htons(localport);
        } else
#endif
        {
            a.sin_family = AF_INET;
            a.sin_addr.s_addr = p_htonl(INADDR_ANY);
            a.sin_port = p_htons(localport);
        }
#ifndef NO_IPV6
        sockcode = p_bind(s, (family == AF_INET6 ?
                              (struct sockaddr *) &a6 :
                              (struct sockaddr *) &a),
                          (family == AF_INET6 ? sizeof(a6) : sizeof(a)));
#else
        sockcode = p_bind(s, (struct sockaddr *) &a, sizeof(a));
#endif
        if (sockcode != SOCKET_ERROR) {
            err = 0;
            break;                     /* done */
        } else {
            err = p_WSAGetLastError();
            if (err != WSAEADDRINUSE)  /* failed, for a bad reason */
                break;
        }

        if (localport == 0)
            break;                     /* we're only looping once */
        localport--;
        if (localport == 0)
            break;                     /* we might have got to the end */
    }

    if (err) {
        sock->error = winsock_error_string(err);
        goto ret;
    }

    /*
     * Connect to remote address.
     */
#ifndef NO_IPV6
    if (sock->step.ai) {
        if (family == AF_INET6) {
            a6.sin6_family = AF_INET6;
            a6.sin6_port = p_htons((short) sock->port);
            a6.sin6_addr =
                ((struct sockaddr_in6 *) sock->step.ai->ai_addr)->sin6_addr;
            a6.sin6_flowinfo = ((struct sockaddr_in6 *) sock->step.ai->ai_addr)->sin6_flowinfo;
            a6.sin6_scope_id = ((struct sockaddr_in6 *) sock->step.ai->ai_addr)->sin6_scope_id;
        } else {
            a.sin_family = AF_INET;
            a.sin_addr =
                ((struct sockaddr_in *) sock->step.ai->ai_addr)->sin_addr;
            a.sin_port = p_htons((short) sock->port);
        }
    } else
#endif
    {
        assert(sock->addr->addresses && sock->step.curraddr < sock->addr->naddresses);
        a.sin_family = AF_INET;
        a.sin_addr.s_addr = p_htonl(sock->addr->addresses[sock->step.curraddr]);
        a.sin_port = p_htons((short) sock->port);
    }

    /* Set up a select mechanism. This could be an AsyncSelect on a
     * window, or an EventSelect on an event object. */
    errstr = do_select(s, 1);
    if (errstr) {
        sock->error = errstr;
        err = 1;
        goto ret;
    }

    if ((
#ifndef NO_IPV6
            p_connect(s,
                      ((family == AF_INET6) ? (struct sockaddr *) &a6 :
                       (struct sockaddr *) &a),
                      (family == AF_INET6) ? sizeof(a6) : sizeof(a))
#else
            p_connect(s, (struct sockaddr *) &a, sizeof(a))
#endif
        ) == SOCKET_ERROR) {
        err = p_WSAGetLastError();
        /*
         * We expect a potential EWOULDBLOCK here, because the
         * chances are the front end has done a select for
         * FD_CONNECT, so that connect() will complete
         * asynchronously.
         */
        if ( err != WSAEWOULDBLOCK ) {
            sock->error = winsock_error_string(err);
            goto ret;
        }
    } else {
        /*
         * If we _don't_ get EWOULDBLOCK, the connect has completed
         * and we should set the socket as writable.
         */
        sock->writable = 1;
    }

    err = 0;

    ret:

    /*
     * No matter what happened, put the socket back in the tree.
     */
    add234(sktree, sock);

    if (err)
        plug_log(sock->plug, 1, sock->addr, sock->port, sock->error, err);
    return err;
}

Socket sk_new(SockAddr addr, int port, int privport, int oobinline,
              int nodelay, int keepalive, Plug plug)
{
    static const struct socket_function_table fn_table = {
        sk_tcp_plug,
        sk_tcp_close,
        sk_tcp_write,
        sk_tcp_write_oob,
        sk_tcp_write_eof,
        sk_tcp_flush,
        sk_tcp_set_private_ptr,
        sk_tcp_get_private_ptr,
        sk_tcp_set_frozen,
        sk_tcp_socket_error
    };

    Actual_Socket ret;
    DWORD err;

    /*
     * Create Socket structure.
     */
    ret = snew(struct Socket_tag);
    ret->fn = &fn_table;
    ret->error = NULL;
    ret->plug = plug;
    bufchain_init(&ret->output_data);
    ret->connected = 0;                /* to start with */
    ret->writable = 0;                 /* to start with */
    ret->sending_oob = 0;
    ret->outgoingeof = EOF_NO;
    ret->frozen = 0;
    ret->frozen_readable = 0;
    ret->localhost_only = 0;           /* unused, but best init anyway */
    ret->pending_error = 0;
    ret->parent = ret->child = NULL;
    ret->oobinline = oobinline;
    ret->nodelay = nodelay;
    ret->keepalive = keepalive;
    ret->privport = privport;
    ret->port = port;
    ret->addr = addr;
    START_STEP(ret->addr, ret->step);
    ret->s = INVALID_SOCKET;

    err = 0;
    do {
        err = try_connect(ret);
    } while (err && sk_nextaddr(ret->addr, &ret->step));

    return (Socket) ret;
}

Socket sk_newlistener(char *srcaddr, int port, Plug plug, int local_host_only,
                      int orig_address_family)
{
    static const struct socket_function_table fn_table = {
        sk_tcp_plug,
        sk_tcp_close,
        sk_tcp_write,
        sk_tcp_write_oob,
        sk_tcp_write_eof,
        sk_tcp_flush,
        sk_tcp_set_private_ptr,
        sk_tcp_get_private_ptr,
        sk_tcp_set_frozen,
        sk_tcp_socket_error
    };

    SOCKET s;
#ifndef NO_IPV6
    SOCKADDR_IN6 a6;
#endif
    SOCKADDR_IN a;

    DWORD err;
    char *errstr;
    Actual_Socket ret;
    int retcode;
    int on = 1;

    int address_family;

    /*
     * Create Socket structure.
     */
    ret = snew(struct Socket_tag);
    ret->fn = &fn_table;
    ret->error = NULL;
    ret->plug = plug;
    bufchain_init(&ret->output_data);
    ret->writable = 0;                 /* to start with */
    ret->sending_oob = 0;
    ret->outgoingeof = EOF_NO;
    ret->frozen = 0;
    ret->frozen_readable = 0;
    ret->localhost_only = local_host_only;
    ret->pending_error = 0;
    ret->parent = ret->child = NULL;
    ret->addr = NULL;

    /*
     * Translate address_family from platform-independent constants
     * into local reality.
     */
    address_family = (orig_address_family == ADDRTYPE_IPV4 ? AF_INET :
#ifndef NO_IPV6
                      orig_address_family == ADDRTYPE_IPV6 ? AF_INET6 :
#endif
                      AF_UNSPEC);

    /*
     * Our default, if passed the `don't care' value
     * ADDRTYPE_UNSPEC, is to listen on IPv4. If IPv6 is supported,
     * we will also set up a second socket listening on IPv6, but
     * the v4 one is primary since that ought to work even on
     * non-v6-supporting systems.
     */
    if (address_family == AF_UNSPEC) address_family = AF_INET;

    /*
     * Open socket.
     */
    s = p_socket(address_family, SOCK_STREAM, 0);
    ret->s = s;

    if (s == INVALID_SOCKET) {
        err = p_WSAGetLastError();
        ret->error = winsock_error_string(err);
        return (Socket) ret;
    }

    ret->oobinline = 0;

    p_setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (const char *)&on, sizeof(on));

#ifndef NO_IPV6
        if (address_family == AF_INET6) {
            memset(&a6, 0, sizeof(a6));
            a6.sin6_family = AF_INET6;
            /* FIXME: srcaddr is ignored for IPv6, because I (SGT) don't
             * know how to do it. :-)
             * (jeroen:) saddr is specified as an address.. eg 2001:db8::1
             * Thus we need either a parser that understands [2001:db8::1]:80
             * style addresses and/or enhance this to understand hostnames too. */
            if (local_host_only)
                a6.sin6_addr = in6addr_loopback;
            else
                a6.sin6_addr = in6addr_any;
            a6.sin6_port = p_htons(port);
        } else
#endif
        {
            int got_addr = 0;
            a.sin_family = AF_INET;

            /*
             * Bind to source address. First try an explicitly
             * specified one...
             */
            if (srcaddr) {
                a.sin_addr.s_addr = p_inet_addr(srcaddr);
                if (a.sin_addr.s_addr != INADDR_NONE) {
                    /* Override localhost_only with specified listen addr. */
                    ret->localhost_only = ipv4_is_loopback(a.sin_addr);
                    got_addr = 1;
                }
            }

            /*
             * ... and failing that, go with one of the standard ones.
             */
            if (!got_addr) {
                if (local_host_only)
                    a.sin_addr.s_addr = p_htonl(INADDR_LOOPBACK);
                else
                    a.sin_addr.s_addr = p_htonl(INADDR_ANY);
            }

            a.sin_port = p_htons((short)port);
        }
#ifndef NO_IPV6
        retcode = p_bind(s, (address_family == AF_INET6 ?
                           (struct sockaddr *) &a6 :
                           (struct sockaddr *) &a),
                       (address_family ==
                        AF_INET6 ? sizeof(a6) : sizeof(a)));
#else
        retcode = p_bind(s, (struct sockaddr *) &a, sizeof(a));
#endif
        if (retcode != SOCKET_ERROR) {
            err = 0;
        } else {
            err = p_WSAGetLastError();
        }

    if (err) {
        p_closesocket(s);
        ret->error = winsock_error_string(err);
        return (Socket) ret;
    }


    if (p_listen(s, SOMAXCONN) == SOCKET_ERROR) {
        p_closesocket(s);
        ret->error = winsock_error_string(err);
        return (Socket) ret;
    }

    /* Set up a select mechanism. This could be an AsyncSelect on a
     * window, or an EventSelect on an event object. */
    errstr = do_select(s, 1);
    if (errstr) {
        p_closesocket(s);
        ret->error = errstr;
        return (Socket) ret;
    }

    add234(sktree, ret);

#ifndef NO_IPV6
    /*
     * If we were given ADDRTYPE_UNSPEC, we must also create an
     * IPv6 listening socket and link it to this one.
     */
    if (address_family == AF_INET && orig_address_family == ADDRTYPE_UNSPEC) {
        Actual_Socket other;

        other = (Actual_Socket) sk_newlistener(srcaddr, port, plug,
                                               local_host_only, ADDRTYPE_IPV6);

        if (other) {
            if (!other->error) {
                other->parent = ret;
                ret->child = other;
            } else {
                sfree(other);
            }
        }
    }
#endif

    return (Socket) ret;
}

static void sk_tcp_close(Socket sock)
{
    extern char *do_select(SOCKET skt, int startup);
    Actual_Socket s = (Actual_Socket) sock;

    if (s->child)
        sk_tcp_close((Socket)s->child);

    del234(sktree, s);
    do_select(s->s, 0);
    p_closesocket(s->s);
    if (s->addr)
        sk_addr_free(s->addr);
    sfree(s);
}

/*
 * The function which tries to send on a socket once it's deemed
 * writable.
 */
void try_send(Actual_Socket s)
{
    while (s->sending_oob || bufchain_size(&s->output_data) > 0) {
        int nsent;
        DWORD err;
        void *data;
        int len, urgentflag;

        if (s->sending_oob) {
            urgentflag = MSG_OOB;
            len = s->sending_oob;
            data = &s->oobdata;
        } else {
            urgentflag = 0;
            bufchain_prefix(&s->output_data, &data, &len);
        }
        nsent = p_send(s->s, data, len, urgentflag);
        noise_ultralight(nsent);
        if (nsent <= 0) {
            err = (nsent < 0 ? p_WSAGetLastError() : 0);
            if ((err < WSABASEERR && nsent < 0) || err == WSAEWOULDBLOCK) {
                /*
                 * Perfectly normal: we've sent all we can for the moment.
                 * 
                 * (Some WinSock send() implementations can return
                 * <0 but leave no sensible error indication -
                 * WSAGetLastError() is called but returns zero or
                 * a small number - so we check that case and treat
                 * it just like WSAEWOULDBLOCK.)
                 */
                s->writable = FALSE;
                return;
            } else if (nsent == 0 ||
                       err == WSAECONNABORTED || err == WSAECONNRESET) {
                /*
                 * If send() returns CONNABORTED or CONNRESET, we
                 * unfortunately can't just call plug_closing(),
                 * because it's quite likely that we're currently
                 * _in_ a call from the code we'd be calling back
                 * to, so we'd have to make half the SSH code
                 * reentrant. Instead we flag a pending error on
                 * the socket, to be dealt with (by calling
                 * plug_closing()) at some suitable future moment.
                 */
                s->pending_error = err;
                return;
            } else {
                /* We're inside the Windows frontend here, so we know
                 * that the frontend handle is unnecessary. */
                logevent(NULL, winsock_error_string(err));
                fatalbox("%s", winsock_error_string(err));
            }
        } else {
            if (s->sending_oob) {
                if (nsent < len) {
                    memmove(s->oobdata, s->oobdata+nsent, len-nsent);
                    s->sending_oob = len - nsent;
                } else {
                    s->sending_oob = 0;
                }
            } else {
                bufchain_consume(&s->output_data, nsent);
            }
        }
    }

    /*
     * If we reach here, we've finished sending everything we might
     * have needed to send. Send EOF, if we need to.
     */
    if (s->outgoingeof == EOF_PENDING) {
        p_shutdown(s->s, SD_SEND);
        s->outgoingeof = EOF_SENT;
    }
}

static int sk_tcp_write(Socket sock, const char *buf, int len)
{
    Actual_Socket s = (Actual_Socket) sock;

    assert(s->outgoingeof == EOF_NO);

    /*
     * Add the data to the buffer list on the socket.
     */
    bufchain_add(&s->output_data, buf, len);

    /*
     * Now try sending from the start of the buffer list.
     */
    if (s->writable)
        try_send(s);

    return bufchain_size(&s->output_data);
}

static int sk_tcp_write_oob(Socket sock, const char *buf, int len)
{
    Actual_Socket s = (Actual_Socket) sock;

    assert(s->outgoingeof == EOF_NO);

    /*
     * Replace the buffer list on the socket with the data.
     */
    bufchain_clear(&s->output_data);
    assert(len <= sizeof(s->oobdata));
    memcpy(s->oobdata, buf, len);
    s->sending_oob = len;

    /*
     * Now try sending from the start of the buffer list.
     */
    if (s->writable)
        try_send(s);

    return s->sending_oob;
}

static void sk_tcp_write_eof(Socket sock)
{
    Actual_Socket s = (Actual_Socket) sock;

    assert(s->outgoingeof == EOF_NO);

    /*
     * Mark the socket as pending outgoing EOF.
     */
    s->outgoingeof = EOF_PENDING;

    /*
     * Now try sending from the start of the buffer list.
     */
    if (s->writable)
        try_send(s);
}

int select_result(WPARAM wParam, LPARAM lParam)
{
    int ret, open;
    DWORD err;
    char buf[20480];                   /* nice big buffer for plenty of speed */
    Actual_Socket s;
    u_long atmark;

    /* wParam is the socket itself */

    if (wParam == 0)
        return 1;                      /* boggle */

    s = find234(sktree, (void *) wParam, cmpforsearch);
    if (!s)
        return 1;                      /* boggle */

    if ((err = WSAGETSELECTERROR(lParam)) != 0) {
        /*
         * An error has occurred on this socket. Pass it to the
         * plug.
         */
        if (s->addr) {
            plug_log(s->plug, 1, s->addr, s->port,
                     winsock_error_string(err), err);
            while (s->addr && sk_nextaddr(s->addr, &s->step)) {
                err = try_connect(s);
            }
        }
        if (err != 0)
            return plug_closing(s->plug, winsock_error_string(err), err, 0);
        else
            return 1;
    }

    noise_ultralight(lParam);

    switch (WSAGETSELECTEVENT(lParam)) {
      case FD_CONNECT:
        s->connected = s->writable = 1;
        /*
         * Once a socket is connected, we can stop falling
         * back through the candidate addresses to connect
         * to.
         */
        if (s->addr) {
            sk_addr_free(s->addr);
            s->addr = NULL;
        }
        break;
      case FD_READ:
        /* In the case the socket is still frozen, we don't even bother */
        if (s->frozen) {
            s->frozen_readable = 1;
            break;
        }

        /*
         * We have received data on the socket. For an oobinline
         * socket, this might be data _before_ an urgent pointer,
         * in which case we send it to the back end with type==1
         * (data prior to urgent).
         */
        if (s->oobinline) {
            atmark = 1;
            p_ioctlsocket(s->s, SIOCATMARK, &atmark);
            /*
             * Avoid checking the return value from ioctlsocket(),
             * on the grounds that some WinSock wrappers don't
             * support it. If it does nothing, we get atmark==1,
             * which is equivalent to `no OOB pending', so the
             * effect will be to non-OOB-ify any OOB data.
             */
        } else
            atmark = 1;

        ret = p_recv(s->s, buf, sizeof(buf), 0);
        noise_ultralight(ret);
        if (ret < 0) {
            err = p_WSAGetLastError();
            if (err == WSAEWOULDBLOCK) {
                break;
            }
        }
        if (ret < 0) {
            return plug_closing(s->plug, winsock_error_string(err), err,
                                0);
        } else if (0 == ret) {
            return plug_closing(s->plug, NULL, 0, 0);
        } else {
            return plug_receive(s->plug, atmark ? 0 : 1, buf, ret);
        }
        break;
      case FD_OOB:
        /*
         * This will only happen on a non-oobinline socket. It
         * indicates that we can immediately perform an OOB read
         * and get back OOB data, which we will send to the back
         * end with type==2 (urgent data).
         */
        ret = p_recv(s->s, buf, sizeof(buf), MSG_OOB);
        noise_ultralight(ret);
        if (ret <= 0) {
            char *str = (ret == 0 ? "Internal networking trouble" :
                         winsock_error_string(p_WSAGetLastError()));
            /* We're inside the Windows frontend here, so we know
             * that the frontend handle is unnecessary. */
            logevent(NULL, str);
            fatalbox("%s", str);
        } else {
            return plug_receive(s->plug, 2, buf, ret);
        }
        break;
      case FD_WRITE:
        {
            int bufsize_before, bufsize_after;
            s->writable = 1;
            bufsize_before = s->sending_oob + bufchain_size(&s->output_data);
            try_send(s);
            bufsize_after = s->sending_oob + bufchain_size(&s->output_data);
            if (bufsize_after < bufsize_before)
                plug_sent(s->plug, bufsize_after);
        }
        break;
      case FD_CLOSE:
        /* Signal a close on the socket. First read any outstanding data. */
        open = 1;
        do {
            ret = p_recv(s->s, buf, sizeof(buf), 0);
            if (ret < 0) {
                err = p_WSAGetLastError();
                if (err == WSAEWOULDBLOCK)
                    break;
                return plug_closing(s->plug, winsock_error_string(err),
                                    err, 0);
            } else {
                if (ret)
                    open &= plug_receive(s->plug, 0, buf, ret);
                else
                    open &= plug_closing(s->plug, NULL, 0, 0);
            }
        } while (ret > 0);
        return open;
       case FD_ACCEPT:
        {
#ifdef NO_IPV6
            struct sockaddr_in isa;
#else
            struct sockaddr_storage isa;
#endif
            int addrlen = sizeof(isa);
            SOCKET t;  /* socket of connection */

            memset(&isa, 0, sizeof(isa));
            err = 0;
            t = p_accept(s->s,(struct sockaddr *)&isa,&addrlen);
            if (t == INVALID_SOCKET)
            {
                err = p_WSAGetLastError();
                if (err == WSATRY_AGAIN)
                    break;
            }
#ifndef NO_IPV6
            if (isa.ss_family == AF_INET &&
                s->localhost_only &&
                !ipv4_is_local_addr(((struct sockaddr_in *)&isa)->sin_addr))
#else
            if (s->localhost_only && !ipv4_is_local_addr(isa.sin_addr))
#endif
            {
                p_closesocket(t);      /* dodgy WinSock let nonlocal through */
            } else if (plug_accepting(s->plug, (void*)t)) {
                p_closesocket(t);      /* denied or error */
            }
        }
    }

    return 1;
}

/*
 * Deal with socket errors detected in try_send().
 */
void net_pending_errors(void)
{
    int i;
    Actual_Socket s;

    /*
     * This might be a fiddly business, because it's just possible
     * that handling a pending error on one socket might cause
     * others to be closed. (I can't think of any reason this might
     * happen in current SSH implementation, but to maintain
     * generality of this network layer I'll assume the worst.)
     * 
     * So what we'll do is search the socket list for _one_ socket
     * with a pending error, and then handle it, and then search
     * the list again _from the beginning_. Repeat until we make a
     * pass with no socket errors present. That way we are
     * protected against the socket list changing under our feet.
     */

    do {
        for (i = 0; (s = index234(sktree, i)) != NULL; i++) {
            if (s->pending_error) {
                /*
                 * An error has occurred on this socket. Pass it to the
                 * plug.
                 */
                plug_closing(s->plug,
                             winsock_error_string(s->pending_error),
                             s->pending_error, 0);
                break;
            }
        }
    } while (s);
}

/*
 * Each socket abstraction contains a `void *' private field in
 * which the client can keep state.
 */
static void sk_tcp_set_private_ptr(Socket sock, void *ptr)
{
    Actual_Socket s = (Actual_Socket) sock;
    s->private_ptr = ptr;
}

static void *sk_tcp_get_private_ptr(Socket sock)
{
    Actual_Socket s = (Actual_Socket) sock;
    return s->private_ptr;
}

/*
 * Special error values are returned from sk_namelookup and sk_new
 * if there's a problem. These functions extract an error message,
 * or return NULL if there's no problem.
 */
const char *sk_addr_error(SockAddr addr)
{
    return addr->error;
}
static const char *sk_tcp_socket_error(Socket sock)
{
    Actual_Socket s = (Actual_Socket) sock;
    return s->error;
}

static void sk_tcp_set_frozen(Socket sock, int is_frozen)
{
    Actual_Socket s = (Actual_Socket) sock;
    if (s->frozen == is_frozen)
        return;
    s->frozen = is_frozen;
    if (!is_frozen) {
        do_select(s->s, 1);
        if (s->frozen_readable) {
            char c;
            p_recv(s->s, &c, 1, MSG_PEEK);
        }
    }
    s->frozen_readable = 0;
}

void socket_reselect_all(void)
{
    Actual_Socket s;
    int i;

    for (i = 0; (s = index234(sktree, i)) != NULL; i++) {
        if (!s->frozen)
            do_select(s->s, 1);
    }
}

/*
 * For Plink: enumerate all sockets currently active.
 */
SOCKET first_socket(int *state)
{
    Actual_Socket s;
    *state = 0;
    s = index234(sktree, (*state)++);
    return s ? s->s : INVALID_SOCKET;
}

SOCKET next_socket(int *state)
{
    Actual_Socket s = index234(sktree, (*state)++);
    return s ? s->s : INVALID_SOCKET;
}

extern int socket_writable(SOCKET skt)
{
    Actual_Socket s = find234(sktree, (void *)skt, cmpforsearch);

    if (s)
        return bufchain_size(&s->output_data) > 0;
    else
        return 0;
}

int net_service_lookup(char *service)
{
    struct servent *se;
    se = p_getservbyname(service, NULL);
    if (se != NULL)
        return p_ntohs(se->s_port);
    else
        return 0;
}

char *get_hostname(void)
{
    int len = 128;
    char *hostname = NULL;
    do {
        len *= 2;
        hostname = sresize(hostname, len, char);
        if (p_gethostname(hostname, len) < 0) {
            sfree(hostname);
            hostname = NULL;
            break;
        }
    } while (strlen(hostname) >= (size_t)(len-1));
    return hostname;
}

SockAddr platform_get_x11_unix_address(const char *display, int displaynum,
                                       char **canonicalname)
{
    SockAddr ret = snew(struct SockAddr_tag);
    memset(ret, 0, sizeof(struct SockAddr_tag));
    ret->error = "unix sockets not supported on this platform";
    ret->refcount = 1;
    return ret;
}