text: /***************************************************************************
   *                                  _   _ ____  _
   *  Project                     ___| | | |  _ \| |
   *                             / __| | | | |_) | |
   *                            | (__| |_| |  _ <| |___
   *                             \___|\___/|_| \_\_____|
   *
   * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
   *
   * This software is licensed as described in the file COPYING, which
   * you should have received as part of this distribution. The terms
   * are also available at https://curl.se/docs/copyright.html.
   *
   * You may opt to use, copy, modify, merge, publish, distribute and/or sell
   * copies of the Software, and permit persons to whom the Software is
   * furnished to do so, under the terms of the COPYING file.
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
   * KIND, either express or implied.
   *
   ***************************************************************************/
  
  #include "curl_setup.h"
  #include "socketpair.h"
  
  /***********************************************************************
   * Only for threaded name resolves builds
   **********************************************************************/
  #ifdef CURLRES_THREADED
  
  #ifdef HAVE_NETINET_IN_H
  #include <netinet/in.h>
  #endif
  #ifdef HAVE_NETDB_H
  #include <netdb.h>
  #endif
  #ifdef HAVE_ARPA_INET_H
  #include <arpa/inet.h>
  #endif
  #ifdef __VMS
  #include <in.h>
  #include <inet.h>
  #endif
  
  #if defined(USE_THREADS_POSIX)
  #  ifdef HAVE_PTHREAD_H
  #    include <pthread.h>
  #  endif
  #elif defined(USE_THREADS_WIN32)
  #  ifdef HAVE_PROCESS_H
  #    include <process.h>
  #  endif
  #endif
  
  #if (defined(NETWARE) && defined(__NOVELL_LIBC__))
  #undef in_addr_t
  #define in_addr_t unsigned long
  #endif
  
  #ifdef HAVE_GETADDRINFO
  #  define RESOLVER_ENOMEM  EAI_MEMORY
  #else
  #  define RESOLVER_ENOMEM  ENOMEM
  #endif
  
  #include "urldata.h"
  #include "sendf.h"
  #include "hostip.h"
  #include "hash.h"
  #include "share.h"
  #include "strerror.h"
  #include "url.h"
  #include "multiif.h"
  #include "inet_ntop.h"
  #include "curl_threads.h"
  #include "connect.h"
  #include "socketpair.h"
  /* The last 3 #include files should be in this order */
  #include "curl_printf.h"
  #include "curl_memory.h"
  #include "memdebug.h"
  
  struct resdata {
    struct curltime start;
  };
  
  /*
   * Curl_resolver_global_init()
   * Called from curl_global_init() to initialize global resolver environment.
   * Does nothing here.
   */
  int Curl_resolver_global_init(void)
  {
    return CURLE_OK;
  }
  
  /*
   * Curl_resolver_global_cleanup()
   * Called from curl_global_cleanup() to destroy global resolver environment.
   * Does nothing here.
   */
  void Curl_resolver_global_cleanup(void)
  {
  }
  
  /*
   * Curl_resolver_init()
   * Called from curl_easy_init() -> Curl_open() to initialize resolver
   * URL-state specific environment ('resolver' member of the UrlState
   * structure).
   */
  CURLcode Curl_resolver_init(struct Curl_easy *easy, void **resolver)
  {
    (void)easy;
    *resolver = calloc(1, sizeof(struct resdata));
    if(!*resolver)
      return CURLE_OUT_OF_MEMORY;
    return CURLE_OK;
  }
  
  /*
   * Curl_resolver_cleanup()
   * Called from curl_easy_cleanup() -> Curl_close() to cleanup resolver
   * URL-state specific environment ('resolver' member of the UrlState
   * structure).
   */
  void Curl_resolver_cleanup(void *resolver)
  {
    free(resolver);
  }
  
  /*
   * Curl_resolver_duphandle()
   * Called from curl_easy_duphandle() to duplicate resolver URL state-specific
   * environment ('resolver' member of the UrlState structure).
   */
  CURLcode Curl_resolver_duphandle(struct Curl_easy *easy, void **to, void *from)
  {
    (void)from;
    return Curl_resolver_init(easy, to);
  }
  
  static void destroy_async_data(struct Curl_async *);
  
  /*
   * Cancel all possibly still on-going resolves for this connection.
   */
  void Curl_resolver_cancel(struct Curl_easy *data)
  {
    destroy_async_data(&data->state.async);
  }
  
  /* This function is used to init a threaded resolve */
  static bool init_resolve_thread(struct Curl_easy *data,
                                  const char *hostname, int port,
                                  const struct addrinfo *hints);
  
  
  /* Data for synchronization between resolver thread and its parent */
  struct thread_sync_data {
    curl_mutex_t *mtx;
    int done;
    int port;
    char *hostname;        /* hostname to resolve, Curl_async.hostname
                              duplicate */
  #ifndef CURL_DISABLE_SOCKETPAIR
    struct Curl_easy *data;
    curl_socket_t sock_pair[2]; /* socket pair */
  #endif
    int sock_error;
    struct Curl_addrinfo *res;
  #ifdef HAVE_GETADDRINFO
    struct addrinfo hints;
  #endif
    struct thread_data *td; /* for thread-self cleanup */
  };
  
  struct thread_data {
    curl_thread_t thread_hnd;
    unsigned int poll_interval;
    timediff_t interval_end;
    struct thread_sync_data tsd;
  };
  
  static struct thread_sync_data *conn_thread_sync_data(struct Curl_easy *data)
  {
    return &(data->state.async.tdata->tsd);
  }
  
  /* Destroy resolver thread synchronization data */
  static
  void destroy_thread_sync_data(struct thread_sync_data *tsd)
  {
    if(tsd->mtx) {
      Curl_mutex_destroy(tsd->mtx);
      free(tsd->mtx);
    }
  
    free(tsd->hostname);
  
    if(tsd->res)
      Curl_freeaddrinfo(tsd->res);
  
  #ifndef CURL_DISABLE_SOCKETPAIR
    /*
     * close one end of the socket pair (may be done in resolver thread);
     * the other end (for reading) is always closed in the parent thread.
     */
    if(tsd->sock_pair[1] != CURL_SOCKET_BAD) {
      sclose(tsd->sock_pair[1]);
    }
  #endif
    memset(tsd, 0, sizeof(*tsd));
  }
  
  /* Initialize resolver thread synchronization data */
  static
  int init_thread_sync_data(struct thread_data *td,
                             const char *hostname,
                             int port,
                             const struct addrinfo *hints)
  {
    struct thread_sync_data *tsd = &td->tsd;
  
    memset(tsd, 0, sizeof(*tsd));
  
    tsd->td = td;
    tsd->port = port;
    /* Treat the request as done until the thread actually starts so any early
     * cleanup gets done properly.
     */
    tsd->done = 1;
  #ifdef HAVE_GETADDRINFO
    DEBUGASSERT(hints);
    tsd->hints = *hints;
  #else
    (void) hints;
  #endif
  
    tsd->mtx = malloc(sizeof(curl_mutex_t));
    if(!tsd->mtx)
      goto err_exit;
  
    Curl_mutex_init(tsd->mtx);
  
  #ifndef CURL_DISABLE_SOCKETPAIR
    /* create socket pair, avoid AF_LOCAL since it doesn't build on Solaris */
    if(Curl_socketpair(AF_UNIX, SOCK_STREAM, 0, &tsd->sock_pair[0]) < 0) {
      tsd->sock_pair[0] = CURL_SOCKET_BAD;
      tsd->sock_pair[1] = CURL_SOCKET_BAD;
      goto err_exit;
    }
  #endif
    tsd->sock_error = CURL_ASYNC_SUCCESS;
  
    /* Copying hostname string because original can be destroyed by parent
     * thread during gethostbyname execution.
     */
    tsd->hostname = strdup(hostname);
    if(!tsd->hostname)
      goto err_exit;
  
    return 1;
  
   err_exit:
    /* Memory allocation failed */
    destroy_thread_sync_data(tsd);
    return 0;
  }
  
  static int getaddrinfo_complete(struct Curl_easy *data)
  {
    struct thread_sync_data *tsd = conn_thread_sync_data(data);
    int rc;
  
    rc = Curl_addrinfo_callback(data, tsd->sock_error, tsd->res);
    /* The tsd->res structure has been copied to async.dns and perhaps the DNS
       cache.  Set our copy to NULL so destroy_thread_sync_data doesn't free it.
    */
    tsd->res = NULL;
  
    return rc;
  }
  
  
  #ifdef HAVE_GETADDRINFO
  
  /*
   * getaddrinfo_thread() resolves a name and then exits.
   *
   * For builds without ARES, but with ENABLE_IPV6, create a resolver thread
   * and wait on it.
   */
  static unsigned int CURL_STDCALL getaddrinfo_thread(void *arg)
  {
    struct thread_sync_data *tsd = (struct thread_sync_data *)arg;
    struct thread_data *td = tsd->td;
    char service[12];
    int rc;
  #ifndef CURL_DISABLE_SOCKETPAIR
    char buf[1];
  #endif
  
    msnprintf(service, sizeof(service), "%d", tsd->port);
  
    rc = Curl_getaddrinfo_ex(tsd->hostname, service, &tsd->hints, &tsd->res);
  
    if(rc) {
      tsd->sock_error = SOCKERRNO?SOCKERRNO:rc;
      if(tsd->sock_error == 0)
        tsd->sock_error = RESOLVER_ENOMEM;
    }
    else {
      Curl_addrinfo_set_port(tsd->res, tsd->port);
    }
  
    Curl_mutex_acquire(tsd->mtx);
    if(tsd->done) {
      /* too late, gotta clean up the mess */
      Curl_mutex_release(tsd->mtx);
      destroy_thread_sync_data(tsd);
      free(td);
    }
    else {
  #ifndef CURL_DISABLE_SOCKETPAIR
      if(tsd->sock_pair[1] != CURL_SOCKET_BAD) {
        /* DNS has been resolved, signal client task */
        buf[0] = 1;
        if(swrite(tsd->sock_pair[1],  buf, sizeof(buf)) < 0) {
          /* update sock_erro to errno */
          tsd->sock_error = SOCKERRNO;
        }
      }
  #endif
      tsd->done = 1;
      Curl_mutex_release(tsd->mtx);
    }
  
    return 0;
  }
  
  #else /* HAVE_GETADDRINFO */
  
  /*
   * gethostbyname_thread() resolves a name and then exits.
   */
  static unsigned int CURL_STDCALL gethostbyname_thread(void *arg)
  {
    struct thread_sync_data *tsd = (struct thread_sync_data *)arg;
    struct thread_data *td = tsd->td;
  
    tsd->res = Curl_ipv4_resolve_r(tsd->hostname, tsd->port);
  
    if(!tsd->res) {
      tsd->sock_error = SOCKERRNO;
      if(tsd->sock_error == 0)
        tsd->sock_error = RESOLVER_ENOMEM;
    }
  
    Curl_mutex_acquire(tsd->mtx);
    if(tsd->done) {
      /* too late, gotta clean up the mess */
      Curl_mutex_release(tsd->mtx);
      destroy_thread_sync_data(tsd);
      free(td);
    }
    else {
      tsd->done = 1;
      Curl_mutex_release(tsd->mtx);
    }
  
    return 0;
  }
  
  #endif /* HAVE_GETADDRINFO */
  
  /*
   * destroy_async_data() cleans up async resolver data and thread handle.
   */
  static void destroy_async_data(struct Curl_async *async)
  {
    if(async->tdata) {
      struct thread_data *td = async->tdata;
      int done;
  #ifndef CURL_DISABLE_SOCKETPAIR
      curl_socket_t sock_rd = td->tsd.sock_pair[0];
      struct Curl_easy *data = td->tsd.data;
  #endif
  
      /*
       * if the thread is still blocking in the resolve syscall, detach it and
       * let the thread do the cleanup...
       */
      Curl_mutex_acquire(td->tsd.mtx);
      done = td->tsd.done;
      td->tsd.done = 1;
      Curl_mutex_release(td->tsd.mtx);
  
      if(!done) {
        Curl_thread_destroy(td->thread_hnd);
      }
      else {
        if(td->thread_hnd != curl_thread_t_null)
          Curl_thread_join(&td->thread_hnd);
  
        destroy_thread_sync_data(&td->tsd);
  
        free(async->tdata);
      }
  #ifndef CURL_DISABLE_SOCKETPAIR
      /*
       * ensure CURLMOPT_SOCKETFUNCTION fires CURL_POLL_REMOVE
       * before the FD is invalidated to avoid EBADF on EPOLL_CTL_DEL
       */
      Curl_multi_closed(data, sock_rd);
      sclose(sock_rd);
  #endif
    }
    async->tdata = NULL;
  
    free(async->hostname);
    async->hostname = NULL;
  }
  
  /*
   * init_resolve_thread() starts a new thread that performs the actual
   * resolve. This function returns before the resolve is done.
   *
   * Returns FALSE in case of failure, otherwise TRUE.
   */
  static bool init_resolve_thread(struct Curl_easy *data,
                                  const char *hostname, int port,
                                  const struct addrinfo *hints)
  {
    struct thread_data *td = calloc(1, sizeof(struct thread_data));
    int err = ENOMEM;
    struct Curl_async *asp = &data->state.async;
  
    data->state.async.tdata = td;
    if(!td)
      goto errno_exit;
  
    asp->port = port;
    asp->done = FALSE;
    asp->status = 0;
    asp->dns = NULL;
    td->thread_hnd = curl_thread_t_null;
  
    if(!init_thread_sync_data(td, hostname, port, hints)) {
      asp->tdata = NULL;
      free(td);
      goto errno_exit;
    }
  
    free(asp->hostname);
    asp->hostname = strdup(hostname);
    if(!asp->hostname)
      goto err_exit;
  
    /* The thread will set this to 1 when complete. */
    td->tsd.done = 0;
  
  #ifdef HAVE_GETADDRINFO
    td->thread_hnd = Curl_thread_create(getaddrinfo_thread, &td->tsd);
  #else
    td->thread_hnd = Curl_thread_create(gethostbyname_thread, &td->tsd);
  #endif
  
    if(!td->thread_hnd) {
      /* The thread never started, so mark it as done here for proper cleanup. */
      td->tsd.done = 1;
      err = errno;
      goto err_exit;
    }
  
    return TRUE;
  
   err_exit:
    destroy_async_data(asp);
  
   errno_exit:
    errno = err;
    return FALSE;
  }
  
  /*
   * 'entry' may be NULL and then no data is returned
   */
  static CURLcode thread_wait_resolv(struct Curl_easy *data,
                                     struct Curl_dns_entry **entry,
                                     bool report)
  {
    struct thread_data *td;
    CURLcode result = CURLE_OK;
  
    DEBUGASSERT(data);
    td = data->state.async.tdata;
    DEBUGASSERT(td);
    DEBUGASSERT(td->thread_hnd != curl_thread_t_null);
  
    /* wait for the thread to resolve the name */
    if(Curl_thread_join(&td->thread_hnd)) {
      if(entry)
        result = getaddrinfo_complete(data);
    }
    else
      DEBUGASSERT(0);
  
    data->state.async.done = TRUE;
  
    if(entry)
      *entry = data->state.async.dns;
  
    if(!data->state.async.dns && report)
      /* a name was not resolved, report error */
      result = Curl_resolver_error(data);
  
    destroy_async_data(&data->state.async);
  
    if(!data->state.async.dns && report)
      connclose(data->conn, "asynch resolve failed");
  
    return result;
  }
  
  
  /*
   * Until we gain a way to signal the resolver threads to stop early, we must
   * simply wait for them and ignore their results.
   */
  void Curl_resolver_kill(struct Curl_easy *data)
  {
    struct thread_data *td = data->state.async.tdata;
  
    /* If we're still resolving, we must wait for the threads to fully clean up,
       unfortunately.  Otherwise, we can simply cancel to clean up any resolver
       data. */
    if(td && td->thread_hnd != curl_thread_t_null)
      (void)thread_wait_resolv(data, NULL, FALSE);
    else
      Curl_resolver_cancel(data);
  }
  
  /*
   * Curl_resolver_wait_resolv()
   *
   * Waits for a resolve to finish. This function should be avoided since using
   * this risk getting the multi interface to "hang".
   *
   * If 'entry' is non-NULL, make it point to the resolved dns entry
   *
   * Returns CURLE_COULDNT_RESOLVE_HOST if the host was not resolved,
   * CURLE_OPERATION_TIMEDOUT if a time-out occurred, or other errors.
   *
   * This is the version for resolves-in-a-thread.
   */
  CURLcode Curl_resolver_wait_resolv(struct Curl_easy *data,
                                     struct Curl_dns_entry **entry)
  {
    return thread_wait_resolv(data, entry, TRUE);
  }
  
  /*
   * Curl_resolver_is_resolved() is called repeatedly to check if a previous
   * name resolve request has completed. It should also make sure to time-out if
   * the operation seems to take too long.
   */
  CURLcode Curl_resolver_is_resolved(struct Curl_easy *data,
                                     struct Curl_dns_entry **entry)
  {
    struct thread_data *td = data->state.async.tdata;
    int done = 0;
  
    DEBUGASSERT(entry);
    *entry = NULL;
  
    if(!td) {
      DEBUGASSERT(td);
      return CURLE_COULDNT_RESOLVE_HOST;
    }
  
    Curl_mutex_acquire(td->tsd.mtx);
    done = td->tsd.done;
    Curl_mutex_release(td->tsd.mtx);
  
    if(done) {
      getaddrinfo_complete(data);
  
      if(!data->state.async.dns) {
        CURLcode result = Curl_resolver_error(data);
        destroy_async_data(&data->state.async);
        return result;
      }
      destroy_async_data(&data->state.async);
      *entry = data->state.async.dns;
    }
    else {
      /* poll for name lookup done with exponential backoff up to 250ms */
      /* should be fine even if this converts to 32 bit */
      timediff_t elapsed = Curl_timediff(Curl_now(),
                                         data->progress.t_startsingle);
      if(elapsed < 0)
        elapsed = 0;
  
      if(td->poll_interval == 0)
        /* Start at 1ms poll interval */
        td->poll_interval = 1;
      else if(elapsed >= td->interval_end)
        /* Back-off exponentially if last interval expired  */
        td->poll_interval *= 2;
  
      if(td->poll_interval > 250)
        td->poll_interval = 250;
  
      td->interval_end = elapsed + td->poll_interval;
      Curl_expire(data, td->poll_interval, EXPIRE_ASYNC_NAME);
    }
  
    return CURLE_OK;
  }
  
  int Curl_resolver_getsock(struct Curl_easy *data, curl_socket_t *socks)
  {
    int ret_val = 0;
    timediff_t milli;
    timediff_t ms;
    struct resdata *reslv = (struct resdata *)data->state.async.resolver;
  #ifndef CURL_DISABLE_SOCKETPAIR
    struct thread_data *td = data->state.async.tdata;
  #else
    (void)socks;
  #endif
  
  #ifndef CURL_DISABLE_SOCKETPAIR
    if(td) {
      /* return read fd to client for polling the DNS resolution status */
      socks[0] = td->tsd.sock_pair[0];
      td->tsd.data = data;
      ret_val = GETSOCK_READSOCK(0);
    }
    else {
  #endif
      ms = Curl_timediff(Curl_now(), reslv->start);
      if(ms < 3)
        milli = 0;
      else if(ms <= 50)
        milli = ms/3;
      else if(ms <= 250)
        milli = 50;
      else
        milli = 200;
      Curl_expire(data, milli, EXPIRE_ASYNC_NAME);
  #ifndef CURL_DISABLE_SOCKETPAIR
    }
  #endif
  
  
    return ret_val;
  }
  
  #ifndef HAVE_GETADDRINFO
  /*
   * Curl_getaddrinfo() - for platforms without getaddrinfo
   */
  struct Curl_addrinfo *Curl_resolver_getaddrinfo(struct Curl_easy *data,
                                                  const char *hostname,
                                                  int port,
                                                  int *waitp)
  {
    struct resdata *reslv = (struct resdata *)data->state.async.resolver;
  
    *waitp = 0; /* default to synchronous response */
  
    reslv->start = Curl_now();
  
    /* fire up a new resolver thread! */
    if(init_resolve_thread(data, hostname, port, NULL)) {
      *waitp = 1; /* expect asynchronous response */
      return NULL;
    }
  
    failf(data, "getaddrinfo() thread failed");
  
    return NULL;
  }
  
  #else /* !HAVE_GETADDRINFO */
  
  /*
   * Curl_resolver_getaddrinfo() - for getaddrinfo
   */
  struct Curl_addrinfo *Curl_resolver_getaddrinfo(struct Curl_easy *data,
                                                  const char *hostname,
                                                  int port,
                                                  int *waitp)
  {
    struct addrinfo hints;
    int pf = PF_INET;
    struct resdata *reslv = (struct resdata *)data->state.async.resolver;
  
    *waitp = 0; /* default to synchronous response */
  
  #ifdef CURLRES_IPV6
    /*
     * Check if a limited name resolve has been requested.
     */
    switch(data->set.ipver) {
    case CURL_IPRESOLVE_V4:
      pf = PF_INET;
      break;
    case CURL_IPRESOLVE_V6:
      pf = PF_INET6;
      break;
    default:
      pf = PF_UNSPEC;
      break;
    }
  
    if((pf != PF_INET) && !Curl_ipv6works(data))
      /* The stack seems to be a non-IPv6 one */
      pf = PF_INET;
  #endif /* CURLRES_IPV6 */
  
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = pf;
    hints.ai_socktype = (data->conn->transport == TRNSPRT_TCP)?
      SOCK_STREAM : SOCK_DGRAM;
  
    reslv->start = Curl_now();
    /* fire up a new resolver thread! */
    if(init_resolve_thread(data, hostname, port, &hints)) {
      *waitp = 1; /* expect asynchronous response */
      return NULL;
    }
  
    failf(data, "getaddrinfo() thread failed to start");
    return NULL;
  
  }
  
  #endif /* !HAVE_GETADDRINFO */
  
  CURLcode Curl_set_dns_servers(struct Curl_easy *data,
                                char *servers)
  {
    (void)data;
    (void)servers;
    return CURLE_NOT_BUILT_IN;
  
  }
  
  CURLcode Curl_set_dns_interface(struct Curl_easy *data,
                                  const char *interf)
  {
    (void)data;
    (void)interf;
    return CURLE_NOT_BUILT_IN;
  }
  
  CURLcode Curl_set_dns_local_ip4(struct Curl_easy *data,
                                  const char *local_ip4)
  {
    (void)data;
    (void)local_ip4;
    return CURLE_NOT_BUILT_IN;
  }
  
  CURLcode Curl_set_dns_local_ip6(struct Curl_easy *data,
                                  const char *local_ip6)
  {
    (void)data;
    (void)local_ip6;
    return CURLE_NOT_BUILT_IN;
  }
  
  #endif /* CURLRES_THREADED */
  