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✏️ Editing: udp.c

/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "uv.h"
#include "internal.h"

#include <assert.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>

#if defined(IPV6_JOIN_GROUP) && !defined(IPV6_ADD_MEMBERSHIP)
# define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP
#endif

#if defined(IPV6_LEAVE_GROUP) && !defined(IPV6_DROP_MEMBERSHIP)
# define IPV6_DROP_MEMBERSHIP IPV6_LEAVE_GROUP
#endif

static void uv__udp_run_completed(uv_udp_t* handle);
static void uv__udp_io(uv_loop_t* loop, uv__io_t* w, unsigned int revents);
static void uv__udp_recvmsg(uv_udp_t* handle);
static void uv__udp_sendmsg(uv_udp_t* handle);
static int uv__udp_maybe_deferred_bind(uv_udp_t* handle,
                                       int domain,
                                       unsigned int flags);

void uv__udp_close(uv_udp_t* handle) {
  uv__io_close(handle->loop, &handle->io_watcher);
  uv__handle_stop(handle);

if (handle->io_watcher.fd != -1) {
    uv__close(handle->io_watcher.fd);
    handle->io_watcher.fd = -1;
  }
}

void uv__udp_finish_close(uv_udp_t* handle) {
  uv_udp_send_t* req;
  QUEUE* q;

assert(!uv__io_active(&handle->io_watcher, UV__POLLIN | UV__POLLOUT));
  assert(handle->io_watcher.fd == -1);

while (!QUEUE_EMPTY(&handle->write_queue)) {
    q = QUEUE_HEAD(&handle->write_queue);
    QUEUE_REMOVE(q);

req = QUEUE_DATA(q, uv_udp_send_t, queue);
    req->status = -ECANCELED;
    QUEUE_INSERT_TAIL(&handle->write_completed_queue, &req->queue);
  }

uv__udp_run_completed(handle);

assert(handle->send_queue_size == 0);
  assert(handle->send_queue_count == 0);

/* Now tear down the handle. */
  handle->recv_cb = NULL;
  handle->alloc_cb = NULL;
  /* but _do not_ touch close_cb */
}

static void uv__udp_run_completed(uv_udp_t* handle) {
  uv_udp_send_t* req;
  QUEUE* q;

assert(!(handle->flags & UV_UDP_PROCESSING));
  handle->flags |= UV_UDP_PROCESSING;

while (!QUEUE_EMPTY(&handle->write_completed_queue)) {
    q = QUEUE_HEAD(&handle->write_completed_queue);
    QUEUE_REMOVE(q);

req = QUEUE_DATA(q, uv_udp_send_t, queue);
    uv__req_unregister(handle->loop, req);

handle->send_queue_size -= uv__count_bufs(req->bufs, req->nbufs);
    handle->send_queue_count--;

if (req->bufs != req->bufsml)
      uv__free(req->bufs);
    req->bufs = NULL;

if (req->send_cb == NULL)
      continue;

/* req->status >= 0 == bytes written
     * req->status <  0 == errno
     */
    if (req->status >= 0)
      req->send_cb(req, 0);
    else
      req->send_cb(req, req->status);
  }

if (QUEUE_EMPTY(&handle->write_queue)) {
    /* Pending queue and completion queue empty, stop watcher. */
    uv__io_stop(handle->loop, &handle->io_watcher, UV__POLLOUT);
    if (!uv__io_active(&handle->io_watcher, UV__POLLIN))
      uv__handle_stop(handle);
  }

handle->flags &= ~UV_UDP_PROCESSING;
}

static void uv__udp_io(uv_loop_t* loop, uv__io_t* w, unsigned int revents) {
  uv_udp_t* handle;

handle = container_of(w, uv_udp_t, io_watcher);
  assert(handle->type == UV_UDP);

if (revents & UV__POLLIN)
    uv__udp_recvmsg(handle);

if (revents & UV__POLLOUT) {
    uv__udp_sendmsg(handle);
    uv__udp_run_completed(handle);
  }
}

static void uv__udp_recvmsg(uv_udp_t* handle) {
  struct sockaddr_storage peer;
  struct msghdr h;
  ssize_t nread;
  uv_buf_t buf;
  int flags;
  int count;

assert(handle->recv_cb != NULL);
  assert(handle->alloc_cb != NULL);

/* Prevent loop starvation when the data comes in as fast as (or faster than)
   * we can read it. XXX Need to rearm fd if we switch to edge-triggered I/O.
   */
  count = 32;

memset(&h, 0, sizeof(h));
  h.msg_name = &peer;

do {
    handle->alloc_cb((uv_handle_t*) handle, 64 * 1024, &buf);
    if (buf.len == 0) {
      handle->recv_cb(handle, UV_ENOBUFS, &buf, NULL, 0);
      return;
    }
    assert(buf.base != NULL);

h.msg_namelen = sizeof(peer);
    h.msg_iov = (void*) &buf;
    h.msg_iovlen = 1;

do {
      nread = recvmsg(handle->io_watcher.fd, &h, 0);
    }
    while (nread == -1 && errno == EINTR);

if (nread == -1) {
      if (errno == EAGAIN || errno == EWOULDBLOCK)
        handle->recv_cb(handle, 0, &buf, NULL, 0);
      else
        handle->recv_cb(handle, -errno, &buf, NULL, 0);
    }
    else {
      const struct sockaddr *addr;
      if (h.msg_namelen == 0)
        addr = NULL;
      else
        addr = (const struct sockaddr*) &peer;

flags = 0;
      if (h.msg_flags & MSG_TRUNC)
        flags |= UV_UDP_PARTIAL;

handle->recv_cb(handle, nread, &buf, addr, flags);
    }
  }
  /* recv_cb callback may decide to pause or close the handle */
  while (nread != -1
      && count-- > 0
      && handle->io_watcher.fd != -1
      && handle->recv_cb != NULL);
}

static void uv__udp_sendmsg(uv_udp_t* handle) {
  uv_udp_send_t* req;
  QUEUE* q;
  struct msghdr h;
  ssize_t size;

while (!QUEUE_EMPTY(&handle->write_queue)) {
    q = QUEUE_HEAD(&handle->write_queue);
    assert(q != NULL);

req = QUEUE_DATA(q, uv_udp_send_t, queue);
    assert(req != NULL);

memset(&h, 0, sizeof h);
    h.msg_name = &req->addr;
    h.msg_namelen = (req->addr.ss_family == AF_INET6 ?
      sizeof(struct sockaddr_in6) : sizeof(struct sockaddr_in));
    h.msg_iov = (struct iovec*) req->bufs;
    h.msg_iovlen = req->nbufs;

do {
      size = sendmsg(handle->io_watcher.fd, &h, 0);
    } while (size == -1 && errno == EINTR);

if (size == -1 && (errno == EAGAIN || errno == EWOULDBLOCK))
      break;

req->status = (size == -1 ? -errno : size);

/* Sending a datagram is an atomic operation: either all data
     * is written or nothing is (and EMSGSIZE is raised). That is
     * why we don't handle partial writes. Just pop the request
     * off the write queue and onto the completed queue, done.
     */
    QUEUE_REMOVE(&req->queue);
    QUEUE_INSERT_TAIL(&handle->write_completed_queue, &req->queue);
    uv__io_feed(handle->loop, &handle->io_watcher);
  }
}

/* On the BSDs, SO_REUSEPORT implies SO_REUSEADDR but with some additional
 * refinements for programs that use multicast.
 *
 * Linux as of 3.9 has a SO_REUSEPORT socket option but with semantics that
 * are different from the BSDs: it _shares_ the port rather than steal it
 * from the current listener.  While useful, it's not something we can emulate
 * on other platforms so we don't enable it.
 */
static int uv__set_reuse(int fd) {
  int yes;

#if defined(SO_REUSEPORT) && !defined(__linux__)
  yes = 1;
  if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &yes, sizeof(yes)))
    return -errno;
#else
  yes = 1;
  if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)))
    return -errno;
#endif

return 0;
}

int uv__udp_bind(uv_udp_t* handle,
                 const struct sockaddr* addr,
                 unsigned int addrlen,
                 unsigned int flags) {
  int err;
  int yes;
  int fd;

/* Check for bad flags. */
  if (flags & ~(UV_UDP_IPV6ONLY | UV_UDP_REUSEADDR))
    return -EINVAL;

/* Cannot set IPv6-only mode on non-IPv6 socket. */
  if ((flags & UV_UDP_IPV6ONLY) && addr->sa_family != AF_INET6)
    return -EINVAL;

fd = handle->io_watcher.fd;
  if (fd == -1) {
    err = uv__socket(addr->sa_family, SOCK_DGRAM, 0);
    if (err < 0)
      return err;
    fd = err;
    handle->io_watcher.fd = fd;
  }

if (flags & UV_UDP_REUSEADDR) {
    err = uv__set_reuse(fd);
    if (err)
      goto out;
  }

if (flags & UV_UDP_IPV6ONLY) {
#ifdef IPV6_V6ONLY
    yes = 1;
    if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &yes, sizeof yes) == -1) {
      err = -errno;
      goto out;
    }
#else
    err = -ENOTSUP;
    goto out;
#endif
  }

if (bind(fd, addr, addrlen)) {
    err = -errno;
    if (errno == EAFNOSUPPORT)
      /* OSX, other BSDs and SunoS fail with EAFNOSUPPORT when binding a
       * socket created with AF_INET to an AF_INET6 address or vice versa. */
      err = -EINVAL;
    goto out;
  }

if (addr->sa_family == AF_INET6)
    handle->flags |= UV_HANDLE_IPV6;

return 0;

out:
  uv__close(handle->io_watcher.fd);
  handle->io_watcher.fd = -1;
  return err;
}

static int uv__udp_maybe_deferred_bind(uv_udp_t* handle,
                                       int domain,
                                       unsigned int flags) {
  unsigned char taddr[sizeof(struct sockaddr_in6)];
  socklen_t addrlen;

if (handle->io_watcher.fd != -1)
    return 0;

switch (domain) {
  case AF_INET:
  {
    struct sockaddr_in* addr = (void*)&taddr;
    memset(addr, 0, sizeof *addr);
    addr->sin_family = AF_INET;
    addr->sin_addr.s_addr = INADDR_ANY;
    addrlen = sizeof *addr;
    break;
  }
  case AF_INET6:
  {
    struct sockaddr_in6* addr = (void*)&taddr;
    memset(addr, 0, sizeof *addr);
    addr->sin6_family = AF_INET6;
    addr->sin6_addr = in6addr_any;
    addrlen = sizeof *addr;
    break;
  }
  default:
    assert(0 && "unsupported address family");
    abort();
  }

return uv__udp_bind(handle, (const struct sockaddr*) &taddr, addrlen, flags);
}

int uv__udp_send(uv_udp_send_t* req,
                 uv_udp_t* handle,
                 const uv_buf_t bufs[],
                 unsigned int nbufs,
                 const struct sockaddr* addr,
                 unsigned int addrlen,
                 uv_udp_send_cb send_cb) {
  int err;
  int empty_queue;

assert(nbufs > 0);

err = uv__udp_maybe_deferred_bind(handle, addr->sa_family, 0);
  if (err)
    return err;

/* It's legal for send_queue_count > 0 even when the write_queue is empty;
   * it means there are error-state requests in the write_completed_queue that
   * will touch up send_queue_size/count later.
   */
  empty_queue = (handle->send_queue_count == 0);

uv__req_init(handle->loop, req, UV_UDP_SEND);
  assert(addrlen <= sizeof(req->addr));
  memcpy(&req->addr, addr, addrlen);
  req->send_cb = send_cb;
  req->handle = handle;
  req->nbufs = nbufs;

req->bufs = req->bufsml;
  if (nbufs > ARRAY_SIZE(req->bufsml))
    req->bufs = uv__malloc(nbufs * sizeof(bufs[0]));

if (req->bufs == NULL) {
    uv__req_unregister(handle->loop, req);
    return -ENOMEM;
  }

memcpy(req->bufs, bufs, nbufs * sizeof(bufs[0]));
  handle->send_queue_size += uv__count_bufs(req->bufs, req->nbufs);
  handle->send_queue_count++;
  QUEUE_INSERT_TAIL(&handle->write_queue, &req->queue);
  uv__handle_start(handle);

if (empty_queue && !(handle->flags & UV_UDP_PROCESSING)) {
    uv__udp_sendmsg(handle);
  } else {
    uv__io_start(handle->loop, &handle->io_watcher, UV__POLLOUT);
  }

return 0;
}

int uv__udp_try_send(uv_udp_t* handle,
                     const uv_buf_t bufs[],
                     unsigned int nbufs,
                     const struct sockaddr* addr,
                     unsigned int addrlen) {
  int err;
  struct msghdr h;
  ssize_t size;

assert(nbufs > 0);

/* already sending a message */
  if (handle->send_queue_count != 0)
    return -EAGAIN;

err = uv__udp_maybe_deferred_bind(handle, addr->sa_family, 0);
  if (err)
    return err;

memset(&h, 0, sizeof h);
  h.msg_name = (struct sockaddr*) addr;
  h.msg_namelen = addrlen;
  h.msg_iov = (struct iovec*) bufs;
  h.msg_iovlen = nbufs;

do {
    size = sendmsg(handle->io_watcher.fd, &h, 0);
  } while (size == -1 && errno == EINTR);

if (size == -1) {
    if (errno == EAGAIN || errno == EWOULDBLOCK)
      return -EAGAIN;
    else
      return -errno;
  }

return size;
}

static int uv__udp_set_membership4(uv_udp_t* handle,
                                   const struct sockaddr_in* multicast_addr,
                                   const char* interface_addr,
                                   uv_membership membership) {
  struct ip_mreq mreq;
  int optname;
  int err;

memset(&mreq, 0, sizeof mreq);

if (interface_addr) {
    err = uv_inet_pton(AF_INET, interface_addr, &mreq.imr_interface.s_addr);
    if (err)
      return err;
  } else {
    mreq.imr_interface.s_addr = htonl(INADDR_ANY);
  }

mreq.imr_multiaddr.s_addr = multicast_addr->sin_addr.s_addr;

switch (membership) {
  case UV_JOIN_GROUP:
    optname = IP_ADD_MEMBERSHIP;
    break;
  case UV_LEAVE_GROUP:
    optname = IP_DROP_MEMBERSHIP;
    break;
  default:
    return -EINVAL;
  }

if (setsockopt(handle->io_watcher.fd,
                 IPPROTO_IP,
                 optname,
                 &mreq,
                 sizeof(mreq))) {
    return -errno;
  }

return 0;
}

static int uv__udp_set_membership6(uv_udp_t* handle,
                                   const struct sockaddr_in6* multicast_addr,
                                   const char* interface_addr,
                                   uv_membership membership) {
  int optname;
  struct ipv6_mreq mreq;
  struct sockaddr_in6 addr6;

memset(&mreq, 0, sizeof mreq);

if (interface_addr) {
    if (uv_ip6_addr(interface_addr, 0, &addr6))
      return -EINVAL;
    mreq.ipv6mr_interface = addr6.sin6_scope_id;
  } else {
    mreq.ipv6mr_interface = 0;
  }

mreq.ipv6mr_multiaddr = multicast_addr->sin6_addr;

switch (membership) {
  case UV_JOIN_GROUP:
    optname = IPV6_ADD_MEMBERSHIP;
    break;
  case UV_LEAVE_GROUP:
    optname = IPV6_DROP_MEMBERSHIP;
    break;
  default:
    return -EINVAL;
  }

if (setsockopt(handle->io_watcher.fd,
                 IPPROTO_IPV6,
                 optname,
                 &mreq,
                 sizeof(mreq))) {
    return -errno;
  }

return 0;
}

int uv_udp_init_ex(uv_loop_t* loop, uv_udp_t* handle, unsigned int flags) {
  int domain;
  int err;
  int fd;

/* Use the lower 8 bits for the domain */
  domain = flags & 0xFF;
  if (domain != AF_INET && domain != AF_INET6 && domain != AF_UNSPEC)
    return -EINVAL;

if (flags & ~0xFF)
    return -EINVAL;

if (domain != AF_UNSPEC) {
    err = uv__socket(domain, SOCK_DGRAM, 0);
    if (err < 0)
      return err;
    fd = err;
  } else {
    fd = -1;
  }

uv__handle_init(loop, (uv_handle_t*)handle, UV_UDP);
  handle->alloc_cb = NULL;
  handle->recv_cb = NULL;
  handle->send_queue_size = 0;
  handle->send_queue_count = 0;
  uv__io_init(&handle->io_watcher, uv__udp_io, fd);
  QUEUE_INIT(&handle->write_queue);
  QUEUE_INIT(&handle->write_completed_queue);
  return 0;
}

int uv_udp_init(uv_loop_t* loop, uv_udp_t* handle) {
  return uv_udp_init_ex(loop, handle, AF_UNSPEC);
}

int uv_udp_open(uv_udp_t* handle, uv_os_sock_t sock) {
  int err;

/* Check for already active socket. */
  if (handle->io_watcher.fd != -1)
    return -EBUSY;

err = uv__nonblock(sock, 1);
  if (err)
    return err;

err = uv__set_reuse(sock);
  if (err)
    return err;

handle->io_watcher.fd = sock;
  return 0;
}

int uv_udp_set_membership(uv_udp_t* handle,
                          const char* multicast_addr,
                          const char* interface_addr,
                          uv_membership membership) {
  int err;
  struct sockaddr_in addr4;
  struct sockaddr_in6 addr6;

if (uv_ip4_addr(multicast_addr, 0, &addr4) == 0) {
    err = uv__udp_maybe_deferred_bind(handle, AF_INET, UV_UDP_REUSEADDR);
    if (err)
      return err;
    return uv__udp_set_membership4(handle, &addr4, interface_addr, membership);
  } else if (uv_ip6_addr(multicast_addr, 0, &addr6) == 0) {
    err = uv__udp_maybe_deferred_bind(handle, AF_INET6, UV_UDP_REUSEADDR);
    if (err)
      return err;
    return uv__udp_set_membership6(handle, &addr6, interface_addr, membership);
  } else {
    return -EINVAL;
  }
}

static int uv__setsockopt(uv_udp_t* handle,
                         int option4,
                         int option6,
                         const void* val,
                         size_t size) {
  int r;

if (handle->flags & UV_HANDLE_IPV6)
    r = setsockopt(handle->io_watcher.fd,
                   IPPROTO_IPV6,
                   option6,
                   val,
                   size);
  else
    r = setsockopt(handle->io_watcher.fd,
                   IPPROTO_IP,
                   option4,
                   val,
                   size);
  if (r)
    return -errno;

return 0;
}

static int uv__setsockopt_maybe_char(uv_udp_t* handle,
                                     int option4,
                                     int option6,
                                     int val) {
#if defined(__sun) || defined(_AIX)
  char arg = val;
#elif defined(__OpenBSD__)
  unsigned char arg = val;
#else
  int arg = val;
#endif

if (val < 0 || val > 255)
    return -EINVAL;

return uv__setsockopt(handle, option4, option6, &arg, sizeof(arg));
}

int uv_udp_set_broadcast(uv_udp_t* handle, int on) {
  if (setsockopt(handle->io_watcher.fd,
                 SOL_SOCKET,
                 SO_BROADCAST,
                 &on,
                 sizeof(on))) {
    return -errno;
  }

return 0;
}

int uv_udp_set_ttl(uv_udp_t* handle, int ttl) {
  if (ttl < 1 || ttl > 255)
    return -EINVAL;

/*
 * On Solaris and derivatives such as SmartOS, the length of socket options
 * is sizeof(int) for IP_TTL and IPV6_UNICAST_HOPS,
 * so hardcode the size of these options on this platform,
 * and use the general uv__setsockopt_maybe_char call on other platforms.
 */
#if defined(__sun) || defined(_AIX) || defined(__OpenBSD__)
  return uv__setsockopt(handle,
                        IP_TTL,
                        IPV6_UNICAST_HOPS,
                        &ttl,
                        sizeof(ttl));
#endif /* defined(__sun) || defined(_AIX) || defined (__OpenBSD__) */

return uv__setsockopt_maybe_char(handle,
                                   IP_TTL,
                                   IPV6_UNICAST_HOPS,
                                   ttl);
}

int uv_udp_set_multicast_ttl(uv_udp_t* handle, int ttl) {
/*
 * On Solaris and derivatives such as SmartOS, the length of socket options
 * is sizeof(int) for IPV6_MULTICAST_HOPS and sizeof(char) for
 * IP_MULTICAST_TTL, so hardcode the size of the option in the IPv6 case,
 * and use the general uv__setsockopt_maybe_char call otherwise.
 */
#if defined(__sun) || defined(_AIX)
  if (handle->flags & UV_HANDLE_IPV6)
    return uv__setsockopt(handle,
                          IP_MULTICAST_TTL,
                          IPV6_MULTICAST_HOPS,
                          &ttl,
                          sizeof(ttl));
#endif /* defined(__sun) || defined(_AIX) */

return uv__setsockopt_maybe_char(handle,
                                   IP_MULTICAST_TTL,
                                   IPV6_MULTICAST_HOPS,
                                   ttl);
}

int uv_udp_set_multicast_loop(uv_udp_t* handle, int on) {
/*
 * On Solaris and derivatives such as SmartOS, the length of socket options
 * is sizeof(int) for IPV6_MULTICAST_LOOP and sizeof(char) for
 * IP_MULTICAST_LOOP, so hardcode the size of the option in the IPv6 case,
 * and use the general uv__setsockopt_maybe_char call otherwise.
 */
#if defined(__sun) || defined(_AIX)
  if (handle->flags & UV_HANDLE_IPV6)
    return uv__setsockopt(handle,
                          IP_MULTICAST_LOOP,
                          IPV6_MULTICAST_LOOP,
                          &on,
                          sizeof(on));
#endif /* defined(__sun) || defined(_AIX) */

return uv__setsockopt_maybe_char(handle,
                                   IP_MULTICAST_LOOP,
                                   IPV6_MULTICAST_LOOP,
                                   on);
}

int uv_udp_set_multicast_interface(uv_udp_t* handle, const char* interface_addr) {
  struct sockaddr_storage addr_st;
  struct sockaddr_in* addr4;
  struct sockaddr_in6* addr6;

addr4 = (struct sockaddr_in*) &addr_st;
  addr6 = (struct sockaddr_in6*) &addr_st;

if (!interface_addr) {
    memset(&addr_st, 0, sizeof addr_st);
    if (handle->flags & UV_HANDLE_IPV6) {
      addr_st.ss_family = AF_INET6;
      addr6->sin6_scope_id = 0;
    } else {
      addr_st.ss_family = AF_INET;
      addr4->sin_addr.s_addr = htonl(INADDR_ANY);
    }
  } else if (uv_ip4_addr(interface_addr, 0, addr4) == 0) {
    /* nothing, address was parsed */
  } else if (uv_ip6_addr(interface_addr, 0, addr6) == 0) {
    /* nothing, address was parsed */
  } else {
    return -EINVAL;
  }

if (addr_st.ss_family == AF_INET) {
    if (setsockopt(handle->io_watcher.fd,
                   IPPROTO_IP,
                   IP_MULTICAST_IF,
                   (void*) &addr4->sin_addr,
                   sizeof(addr4->sin_addr)) == -1) {
      return -errno;
    }
  } else if (addr_st.ss_family == AF_INET6) {
    if (setsockopt(handle->io_watcher.fd,
                   IPPROTO_IPV6,
                   IPV6_MULTICAST_IF,
                   &addr6->sin6_scope_id,
                   sizeof(addr6->sin6_scope_id)) == -1) {
      return -errno;
    }
  } else {
    assert(0 && "unexpected address family");
    abort();
  }

return 0;
}

int uv_udp_getsockname(const uv_udp_t* handle,
                       struct sockaddr* name,
                       int* namelen) {
  socklen_t socklen;

if (handle->io_watcher.fd == -1)
    return -EINVAL;  /* FIXME(bnoordhuis) -EBADF */

/* sizeof(socklen_t) != sizeof(int) on some systems. */
  socklen = (socklen_t) *namelen;

if (getsockname(handle->io_watcher.fd, name, &socklen))
    return -errno;

*namelen = (int) socklen;
  return 0;
}

int uv__udp_recv_start(uv_udp_t* handle,
                       uv_alloc_cb alloc_cb,
                       uv_udp_recv_cb recv_cb) {
  int err;

if (alloc_cb == NULL || recv_cb == NULL)
    return -EINVAL;

if (uv__io_active(&handle->io_watcher, UV__POLLIN))
    return -EALREADY;  /* FIXME(bnoordhuis) Should be -EBUSY. */

err = uv__udp_maybe_deferred_bind(handle, AF_INET, 0);
  if (err)
    return err;

handle->alloc_cb = alloc_cb;
  handle->recv_cb = recv_cb;

uv__io_start(handle->loop, &handle->io_watcher, UV__POLLIN);
  uv__handle_start(handle);

return 0;
}

int uv__udp_recv_stop(uv_udp_t* handle) {
  uv__io_stop(handle->loop, &handle->io_watcher, UV__POLLIN);

if (!uv__io_active(&handle->io_watcher, UV__POLLOUT))
    uv__handle_stop(handle);

handle->alloc_cb = NULL;
  handle->recv_cb = NULL;

return 0;
}

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