gnupg/dirmngr/ks-engine-hkp.c

/* ks-engine-hkp.c - HKP keyserver engine
 * Copyright (C) 2011, 2012 Free Software Foundation, Inc.
 * Copyright (C) 2011, 2012, 2014 Werner Koch
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <https://www.gnu.org/licenses/>.
 */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#ifdef HAVE_W32_SYSTEM
# ifdef HAVE_WINSOCK2_H
#  include <winsock2.h>
# endif
# include <windows.h>
#else /*!HAVE_W32_SYSTEM*/
# include <sys/types.h>
# include <sys/socket.h>
# include <netdb.h>
#endif /*!HAVE_W32_SYSTEM*/

#include "dirmngr.h"
#include "misc.h"
#include "userids.h"
#include "dns-stuff.h"
#include "ks-engine.h"

/* Substitutes for missing Mingw macro.  The EAI_SYSTEM mechanism
   seems not to be available (probably because there is only one set
   of error codes anyway).  For now we use WSAEINVAL. */
#ifndef EAI_OVERFLOW
# define EAI_OVERFLOW EAI_FAIL
#endif
#ifdef HAVE_W32_SYSTEM
# ifndef EAI_SYSTEM
#  define EAI_SYSTEM WSAEINVAL
# endif
#endif


/* Number of seconds after a host is marked as resurrected.  */
#define RESURRECT_INTERVAL  (3600*3)  /* 3 hours */

/* To match the behaviour of our old gpgkeys helper code we escape
   more characters than actually needed. */
#define EXTRA_ESCAPE_CHARS "@!\"#$%&'()*+,-./:;<=>?[\\]^_{|}~"

/* How many redirections do we allow.  */
#define MAX_REDIRECTS 2

/* Number of retries done for a dead host etc.  */
#define SEND_REQUEST_RETRIES 3

/* Objects used to maintain information about hosts.  */
struct hostinfo_s;
typedef struct hostinfo_s *hostinfo_t;
struct hostinfo_s
{
  time_t lastfail;   /* Time we tried to connect and failed.  */
  time_t lastused;   /* Time of last use.  */
  int *pool;         /* A -1 terminated array with indices into
                        HOSTTABLE or NULL if NAME is not a pool
                        name.  */
  int poolidx;       /* Index into POOL with the used host.  -1 if not set.  */
  unsigned int v4:1; /* Host supports AF_INET.  */
  unsigned int v6:1; /* Host supports AF_INET6.  */
  unsigned int onion:1;/* NAME is an onion (Tor HS) address.  */
  unsigned int dead:1; /* Host is currently unresponsive.  */
  time_t died_at;    /* The time the host was marked dead.  If this is
                        0 the host has been manually marked dead.  */
  char *cname;       /* Canonical name of the host.  Only set if this
                        is a pool.  */
  char *v4addr;      /* A string with the v4 IP address of the host.
                        NULL if NAME has a numeric IP address or no v4
                        address is available.  */
  char *v6addr;      /* A string with the v6 IP address of the host.
                        NULL if NAME has a numeric IP address or no v6
                        address is available.  */
  unsigned short port; /* The port used by the host, 0 if unknown.  */
  char name[1];      /* The hostname.  */
};


/* An array of hostinfo_t for all hosts requested by the caller or
   resolved from a pool name and its allocated size.*/
static hostinfo_t *hosttable;
static int hosttable_size;

/* The number of host slots we initially allocate for HOSTTABLE.  */
#define INITIAL_HOSTTABLE_SIZE 10


/* Create a new hostinfo object, fill in NAME and put it into
   HOSTTABLE.  Return the index into hosttable on success or -1 on
   error. */
static int
create_new_hostinfo (const char *name)
{
  hostinfo_t hi, *newtable;
  int newsize;
  int idx, rc;

  hi = xtrymalloc (sizeof *hi + strlen (name));
  if (!hi)
    return -1;
  strcpy (hi->name, name);
  hi->pool = NULL;
  hi->poolidx = -1;
  hi->lastused = (time_t)(-1);
  hi->lastfail = (time_t)(-1);
  hi->v4 = 0;
  hi->v6 = 0;
  hi->onion = 0;
  hi->dead = 0;
  hi->died_at = 0;
  hi->cname = NULL;
  hi->v4addr = NULL;
  hi->v6addr = NULL;
  hi->port = 0;

  /* Add it to the hosttable. */
  for (idx=0; idx < hosttable_size; idx++)
    if (!hosttable[idx])
      {
        hosttable[idx] = hi;
        return idx;
      }
  /* Need to extend the hosttable.  */
  newsize = hosttable_size + INITIAL_HOSTTABLE_SIZE;
  newtable = xtryrealloc (hosttable, newsize * sizeof *hosttable);
  if (!newtable)
    {
      xfree (hi);
      return -1;
    }
  hosttable = newtable;
  idx = hosttable_size;
  hosttable_size = newsize;
  rc = idx;
  hosttable[idx++] = hi;
  while (idx < hosttable_size)
    hosttable[idx++] = NULL;

  return rc;
}


/* Find the host NAME in our table.  Return the index into the
   hosttable or -1 if not found.  */
static int
find_hostinfo (const char *name)
{
  int idx;

  for (idx=0; idx < hosttable_size; idx++)
    if (hosttable[idx] && !ascii_strcasecmp (hosttable[idx]->name, name))
      return idx;
  return -1;
}


static int
sort_hostpool (const void *xa, const void *xb)
{
  int a = *(int *)xa;
  int b = *(int *)xb;

  assert (a >= 0 && a < hosttable_size);
  assert (b >= 0 && b < hosttable_size);
  assert (hosttable[a]);
  assert (hosttable[b]);

  return ascii_strcasecmp (hosttable[a]->name, hosttable[b]->name);
}


/* Return true if the host with the hosttable index TBLIDX is in POOL.  */
static int
host_in_pool_p (int *pool, int tblidx)
{
  int i, pidx;

  for (i=0; (pidx = pool[i]) != -1; i++)
    if (pidx == tblidx && hosttable[pidx])
      return 1;
  return 0;
}


/* Select a random host.  Consult TABLE which indices into the global
   hosttable.  Returns index into TABLE or -1 if no host could be
   selected.  */
static int
select_random_host (int *table)
{
  int *tbl;
  size_t tblsize;
  int pidx, idx;

  /* We create a new table so that we randomly select only from
     currently alive hosts.  */
  for (idx=0, tblsize=0; (pidx = table[idx]) != -1; idx++)
    if (hosttable[pidx] && !hosttable[pidx]->dead)
      tblsize++;
  if (!tblsize)
    return -1; /* No hosts.  */

  tbl = xtrymalloc (tblsize * sizeof *tbl);
  if (!tbl)
    return -1;
  for (idx=0, tblsize=0; (pidx = table[idx]) != -1; idx++)
    if (hosttable[pidx] && !hosttable[pidx]->dead)
      tbl[tblsize++] = pidx;

  if (tblsize == 1)  /* Save a get_uint_nonce.  */
    pidx = tbl[0];
  else
    pidx = tbl[get_uint_nonce () % tblsize];

  xfree (tbl);
  return pidx;
}


/* Figure out if a set of DNS records looks like a pool.  */
static int
arecords_is_pool (dns_addrinfo_t aibuf)
{
  dns_addrinfo_t ai;
  int n_v6, n_v4;

  n_v6 = n_v4 = 0;
  for (ai = aibuf; ai; ai = ai->next)
    {
      if (ai->family == AF_INET6)
        n_v6++;
      else if (ai->family == AF_INET)
        n_v4++;
    }

  return n_v6 > 1 || n_v4 > 1;
}


/* Add the host AI under the NAME into the HOSTTABLE.  If PORT is not
   zero, it specifies which port to use to talk to the host.  If NAME
   specifies a pool (as indicated by IS_POOL), update the given
   reference table accordingly.  */
static void
add_host (const char *name, int is_pool,
          const dns_addrinfo_t ai, unsigned short port,
          int *reftbl, size_t reftblsize, int *refidx)
{
  gpg_error_t tmperr;
  char *tmphost;
  int idx, tmpidx;
  int is_numeric = 0;
  int i;

  idx = find_hostinfo (name);

  if (!is_pool && !is_ip_address (name))
    {
      /* This is a hostname but not a pool.  Use the name
         as given without going through resolve_dns_addr.  */
      tmphost = xtrystrdup (name);
      if (!tmphost)
        tmperr = gpg_error_from_syserror ();
      else
        tmperr = 0;
    }
  else
    {
      tmperr = resolve_dns_addr (ai->addr, ai->addrlen,
                                 DNS_WITHBRACKET, &tmphost);
      if (tmphost && is_ip_address (tmphost))
        is_numeric = 1;
    }

  if (tmperr)
    {
      log_info ("resolve_dns_addr failed while checking '%s': %s\n",
                name, gpg_strerror (tmperr));
    }
  else if ((*refidx) + 1 >= reftblsize)
    {
      log_error ("resolve_dns_addr for '%s': '%s'"
                 " [index table full - ignored]\n", name, tmphost);
    }
  else
    {
      if (!is_pool && is_ip_address (name))
        /* Update the original entry.  */
        tmpidx = idx;
      else
        tmpidx = find_hostinfo (tmphost);
      log_info ("resolve_dns_addr for '%s': '%s'%s\n",
                name, tmphost,
                tmpidx == -1? "" : " [already known]");

      if (tmpidx == -1) /* Create a new entry.  */
        tmpidx = create_new_hostinfo (tmphost);

      if (tmpidx == -1)
        {
          log_error ("map_host for '%s' problem: %s - '%s'"
                     " [ignored]\n",
                     name, strerror (errno), tmphost);
        }
      else  /* Set or update the entry. */
        {
          char *ipaddr = NULL;

          if (port)
            hosttable[tmpidx]->port = port;

          if (!is_numeric)
            {
              xfree (tmphost);
              tmperr = resolve_dns_addr (ai->addr, ai->addrlen,
                                         (DNS_NUMERICHOST
                                          | DNS_WITHBRACKET),
                                         &tmphost);
              if (tmperr)
                log_info ("resolve_dns_addr failed: %s\n",
                          gpg_strerror (tmperr));
              else
                {
                  ipaddr = tmphost;
                  tmphost = NULL;
                }
            }

          if (ai->family == AF_INET6)
            {
              hosttable[tmpidx]->v6 = 1;
              xfree (hosttable[tmpidx]->v6addr);
              hosttable[tmpidx]->v6addr = ipaddr;
            }
          else if (ai->family == AF_INET)
            {
              hosttable[tmpidx]->v4 = 1;
              xfree (hosttable[tmpidx]->v4addr);
              hosttable[tmpidx]->v4addr = ipaddr;
            }
          else
            BUG ();

          for (i=0; i < *refidx; i++)
            if (reftbl[i] == tmpidx)
              break;
          if (!(i < *refidx) && tmpidx != idx)
            reftbl[(*refidx)++] = tmpidx;
        }
    }
  xfree (tmphost);
}


/* Map the host name NAME to the actual to be used host name.  This
 * allows us to manage round robin DNS names.  We use our own strategy
 * to choose one of the hosts.  For example we skip those hosts which
 * failed for some time and we stick to one host for a time
 * independent of DNS retry times.  If FORCE_RESELECT is true a new
 * host is always selected.  If NO_SRV is set no service record lookup
 * will be done.  The selected host is stored as a malloced string at
 * R_HOST; on error NULL is stored.  If we know the port used by the
 * selected host from a service record, a string representation is
 * written to R_PORTSTR, otherwise it is left untouched.  If
 * R_HTTPFLAGS is not NULL it will receive flags which are to be
 * passed to http_open.  If R_POOLNAME is not NULL a malloced name of
 * the pool is stored or NULL if it is not a pool. */
static gpg_error_t
map_host (ctrl_t ctrl, const char *name, int force_reselect, int no_srv,
          char **r_host, char *r_portstr,
          unsigned int *r_httpflags, char **r_poolname)
{
  gpg_error_t err = 0;
  hostinfo_t hi;
  int idx;

  *r_host = NULL;
  if (r_httpflags)
    *r_httpflags = 0;
  if (r_poolname)
    *r_poolname = NULL;

  /* No hostname means localhost.  */
  if (!name || !*name)
    {
      *r_host = xtrystrdup ("localhost");
      return *r_host? 0 : gpg_error_from_syserror ();
    }

  /* See whether the host is in our table.  */
  idx = find_hostinfo (name);
  if (idx == -1 && is_onion_address (name))
    {
      idx = create_new_hostinfo (name);
      if (idx == -1)
        return gpg_error_from_syserror ();
      hi = hosttable[idx];
      hi->onion = 1;
    }
  else if (idx == -1)
    {
      /* We never saw this host.  Allocate a new entry.  */
      dns_addrinfo_t aibuf, ai;
      int *reftbl;
      size_t reftblsize;
      int refidx;
      int is_pool = 0;
      char *cname;
      struct srventry *srvs;
      unsigned int srvscount;

      reftblsize = 100;
      reftbl = xtrymalloc (reftblsize * sizeof *reftbl);
      if (!reftbl)
        return gpg_error_from_syserror ();
      refidx = 0;

      idx = create_new_hostinfo (name);
      if (idx == -1)
        {
          err = gpg_error_from_syserror ();
          xfree (reftbl);
          return err;
        }
      hi = hosttable[idx];

      if (!no_srv && !is_ip_address (name))
        {
          /* Check for SRV records.  */
          err = get_dns_srv (name, "hkp", NULL, &srvs, &srvscount);
          if (err)
            {
              xfree (reftbl);
              return err;
            }

          if (srvscount > 0)
            {
              int i;
              is_pool = srvscount > 1;

              for (i = 0; i < srvscount; i++)
                {
                  err = resolve_dns_name (srvs[i].target, 0,
                                          AF_UNSPEC, SOCK_STREAM,
                                          &ai, &cname);
                  if (err)
                    continue;
                  dirmngr_tick (ctrl);
                  add_host (name, is_pool, ai, srvs[i].port,
                            reftbl, reftblsize, &refidx);
                }

              xfree (srvs);
            }
        }

      /* Find all A records for this entry and put them into the pool
         list - if any.  */
      err = resolve_dns_name (name, 0, 0, SOCK_STREAM, &aibuf, &cname);
      if (err)
        {
          log_error ("resolving '%s' failed: %s\n", name, gpg_strerror (err));
          err = 0;
        }
      else
        {
          /* First figure out whether this is a pool.  For a pool we
             use a different strategy than for a plain server: We use
             the canonical name of the pool as the virtual host along
             with the IP addresses.  If it is not a pool, we use the
             specified name. */
          if (! is_pool)
            is_pool = arecords_is_pool (aibuf);
          if (is_pool && cname)
            {
              hi->cname = cname;
              cname = NULL;
            }

          for (ai = aibuf; ai; ai = ai->next)
            {
              if (ai->family != AF_INET && ai->family != AF_INET6)
                continue;
              dirmngr_tick (ctrl);

              add_host (name, is_pool, ai, 0, reftbl, reftblsize, &refidx);
            }
        }
      reftbl[refidx] = -1;
      xfree (cname);
      free_dns_addrinfo (aibuf);

      if (refidx && is_pool)
        {
          assert (!hi->pool);
          hi->pool = xtryrealloc (reftbl, (refidx+1) * sizeof *reftbl);
          if (!hi->pool)
            {
              err = gpg_error_from_syserror ();
              log_error ("shrinking index table in map_host failed: %s\n",
                         gpg_strerror (err));
              xfree (reftbl);
              return err;
            }
          qsort (hi->pool, refidx, sizeof *reftbl, sort_hostpool);
        }
      else
        xfree (reftbl);
    }

  hi = hosttable[idx];
  if (hi->pool)
    {
      /* Deal with the pool name before selecting a host. */
      if (r_poolname)
        {
          *r_poolname = xtrystrdup (hi->cname? hi->cname : hi->name);
          if (!*r_poolname)
            return gpg_error_from_syserror ();
        }

      /* If the currently selected host is now marked dead, force a
         re-selection .  */
      if (force_reselect)
        hi->poolidx = -1;
      else if (hi->poolidx >= 0 && hi->poolidx < hosttable_size
               && hosttable[hi->poolidx] && hosttable[hi->poolidx]->dead)
        hi->poolidx = -1;

      /* Select a host if needed.  */
      if (hi->poolidx == -1)
        {
          hi->poolidx = select_random_host (hi->pool);
          if (hi->poolidx == -1)
            {
              log_error ("no alive host found in pool '%s'\n", name);
              if (r_poolname)
                {
                  xfree (*r_poolname);
                  *r_poolname = NULL;
                }
              return gpg_error (GPG_ERR_NO_KEYSERVER);
            }
        }

      assert (hi->poolidx >= 0 && hi->poolidx < hosttable_size);
      hi = hosttable[hi->poolidx];
      assert (hi);
    }

  if (hi->dead)
    {
      log_error ("host '%s' marked as dead\n", hi->name);
      if (r_poolname)
        {
          xfree (*r_poolname);
          *r_poolname = NULL;
        }
      return gpg_error (GPG_ERR_NO_KEYSERVER);
    }

  if (r_httpflags)
    {
      /* If the hosttable does not indicate that a certain host
         supports IPv<N>, we explicit set the corresponding http
         flags.  The reason for this is that a host might be listed in
         a pool as not v6 only but actually support v6 when later
         the name is resolved by our http layer.  */
      if (!hi->v4)
        *r_httpflags |= HTTP_FLAG_IGNORE_IPv4;
      if (!hi->v6)
        *r_httpflags |= HTTP_FLAG_IGNORE_IPv6;

      /* Note that we do not set the HTTP_FLAG_FORCE_TOR for onion
         addresses because the http module detects this itself.  This
         also allows us to use an onion address without Tor mode being
         enabled.  */
    }

  *r_host = xtrystrdup (hi->name);
  if (!*r_host)
    {
      err = gpg_error_from_syserror ();
      if (r_poolname)
        {
          xfree (*r_poolname);
          *r_poolname = NULL;
        }
      return err;
    }
  if (hi->port)
    snprintf (r_portstr, 6 /* five digits and the sentinel */,
              "%hu", hi->port);
  return 0;
}


/* Mark the host NAME as dead.  NAME may be given as an URL.  Returns
   true if a host was really marked as dead or was already marked dead
   (e.g. by a concurrent session).  */
static int
mark_host_dead (const char *name)
{
  const char *host;
  char *host_buffer = NULL;
  parsed_uri_t parsed_uri = NULL;
  int done = 0;

  if (name && *name && !http_parse_uri (&parsed_uri, name, 1))
    {
      if (parsed_uri->v6lit)
        {
          host_buffer = strconcat ("[", parsed_uri->host, "]", NULL);
          if (!host_buffer)
            log_error ("out of core in mark_host_dead");
          host = host_buffer;
        }
      else
        host = parsed_uri->host;
    }
  else
    host = name;

  if (host && *host && strcmp (host, "localhost"))
    {
      hostinfo_t hi;
      int idx;

      idx = find_hostinfo (host);
      if (idx != -1)
        {
          hi = hosttable[idx];
          log_info ("marking host '%s' as dead%s\n",
                    hi->name, hi->dead? " (again)":"");
          hi->dead = 1;
          hi->died_at = gnupg_get_time ();
          if (!hi->died_at)
            hi->died_at = 1;
          done = 1;
        }
    }

  http_release_parsed_uri (parsed_uri);
  xfree (host_buffer);
  return done;
}


/* Mark a host in the hosttable as dead or - if ALIVE is true - as
   alive.  */
gpg_error_t
ks_hkp_mark_host (ctrl_t ctrl, const char *name, int alive)
{
  gpg_error_t err = 0;
  hostinfo_t hi, hi2;
  int idx, idx2, idx3, n;

  if (!name || !*name || !strcmp (name, "localhost"))
    return 0;

  idx = find_hostinfo (name);
  if (idx == -1)
    return gpg_error (GPG_ERR_NOT_FOUND);

  hi = hosttable[idx];
  if (alive && hi->dead)
    {
      hi->dead = 0;
      err = ks_printf_help (ctrl, "marking '%s' as alive", name);
    }
  else if (!alive && !hi->dead)
    {
      hi->dead = 1;
      hi->died_at = 0; /* Manually set dead.  */
      err = ks_printf_help (ctrl, "marking '%s' as dead", name);
    }

  /* If the host is a pool mark all member hosts. */
  if (!err && hi->pool)
    {
      for (idx2=0; !err && (n=hi->pool[idx2]) != -1; idx2++)
        {
          assert (n >= 0 && n < hosttable_size);

          if (!alive)
            {
              /* Do not mark a host from a pool dead if it is also a
                 member in another pool.  */
              for (idx3=0; idx3 < hosttable_size; idx3++)
                {
                  if (hosttable[idx3]
                      && hosttable[idx3]->pool
                      && idx3 != idx
                      && host_in_pool_p (hosttable[idx3]->pool, n))
                    break;
                }
              if (idx3 < hosttable_size)
                continue;  /* Host is also a member of another pool.  */
            }

          hi2 = hosttable[n];
          if (!hi2)
            ;
          else if (alive && hi2->dead)
            {
              hi2->dead = 0;
              err = ks_printf_help (ctrl, "marking '%s' as alive",
                                    hi2->name);
            }
          else if (!alive && !hi2->dead)
            {
              hi2->dead = 1;
              hi2->died_at = 0; /* Manually set dead. */
              err = ks_printf_help (ctrl, "marking '%s' as dead",
                                    hi2->name);
            }
        }
    }

  return err;
}


/* Debug function to print the entire hosttable.  */
gpg_error_t
ks_hkp_print_hosttable (ctrl_t ctrl)
{
  gpg_error_t err;
  int idx, idx2;
  hostinfo_t hi;
  membuf_t mb;
  time_t curtime;
  char *p, *died;
  const char *diedstr;

  err = ks_print_help (ctrl, "hosttable (idx, ipv6, ipv4, dead, name, time):");
  if (err)
    return err;

  curtime = gnupg_get_time ();
  for (idx=0; idx < hosttable_size; idx++)
    if ((hi=hosttable[idx]))
      {
        if (hi->dead && hi->died_at)
          {
            died = elapsed_time_string (hi->died_at, curtime);
            diedstr = died? died : "error";
          }
        else
          diedstr = died = NULL;
        err = ks_printf_help (ctrl, "%3d %s %s %s %s%s%s%s%s%s%s%s\n",
                              idx,
                              hi->onion? "O" : hi->v6? "6":" ",
                              hi->v4? "4":" ",
                              hi->dead? "d":" ",
                              hi->name,
                              hi->v6addr? " v6=":"",
                              hi->v6addr? hi->v6addr:"",
                              hi->v4addr? " v4=":"",
                              hi->v4addr? hi->v4addr:"",
                              diedstr? "  (":"",
                              diedstr? diedstr:"",
                              diedstr? ")":""   );
        xfree (died);
        if (err)
          return err;

        if (hi->cname)
          err = ks_printf_help (ctrl, "  .       %s", hi->cname);
        if (err)
          return err;

        if (hi->pool)
          {
            init_membuf (&mb, 256);
            put_membuf_printf (&mb, "  .   -->");
            for (idx2=0; hi->pool[idx2] != -1; idx2++)
              {
                put_membuf_printf (&mb, " %d", hi->pool[idx2]);
                if (hi->poolidx == hi->pool[idx2])
                  put_membuf_printf (&mb, "*");
              }
            put_membuf( &mb, "", 1);
            p = get_membuf (&mb, NULL);
            if (!p)
              return gpg_error_from_syserror ();
            err = ks_print_help (ctrl, p);
            xfree (p);
            if (err)
              return err;
          }
      }
  return 0;
}



/* Print a help output for the schemata supported by this module. */
gpg_error_t
ks_hkp_help (ctrl_t ctrl, parsed_uri_t uri)
{
  const char const data[] =
    "Handler for HKP URLs:\n"
    "  hkp://\n"
#if  HTTP_USE_GNUTLS || HTTP_USE_NTBTLS
    "  hkps://\n"
#endif
    "Supported methods: search, get, put\n";
  gpg_error_t err;

#if  HTTP_USE_GNUTLS || HTTP_USE_NTBTLS
  const char data2[] = "  hkp\n  hkps";
#else
  const char data2[] = "  hkp";
#endif

  if (!uri)
    err = ks_print_help (ctrl, data2);
  else if (uri->is_http && (!strcmp (uri->scheme, "hkp")
                            || !strcmp (uri->scheme, "hkps")))
    err = ks_print_help (ctrl, data);
  else
    err = 0;

  return err;
}


/* Build the remote part of the URL from SCHEME, HOST and an optional
 * PORT.  If NO_SRV is set no SRV record lookup will be done.  Returns
 * an allocated string at R_HOSTPORT or NULL on failure If R_POOLNAME
 * is not NULL it receives a malloced string with the poolname.  */
static gpg_error_t
make_host_part (ctrl_t ctrl,
                const char *scheme, const char *host, unsigned short port,
                int force_reselect, int no_srv,
                char **r_hostport, unsigned int *r_httpflags, char **r_poolname)
{
  gpg_error_t err;
  char portstr[10];
  char *hostname;

  *r_hostport = NULL;

  portstr[0] = 0;
  err = map_host (ctrl, host, force_reselect, no_srv,
                  &hostname, portstr, r_httpflags, r_poolname);
  if (err)
    return err;

  /* If map_host did not return a port (from a SRV record) but a port
   * has been specified (implicitly or explicitly) then use that port.
   * Only in the case that a port was not specified (which might be a
   * bug in https.c) we will later make sure that it has been set.  */
  if (!*portstr && port)
    snprintf (portstr, sizeof portstr, "%hu", port);

  /* Map scheme and port.  */
  if (!strcmp (scheme, "hkps") || !strcmp (scheme,"https"))
    {
      scheme = "https";
      if (! *portstr)
        strcpy (portstr, "443");
    }
  else /* HKP or HTTP.  */
    {
      scheme = "http";
      if (! *portstr)
        strcpy (portstr, "11371");
    }

  *r_hostport = strconcat (scheme, "://", hostname, ":", portstr, NULL);
  xfree (hostname);
  if (!*r_hostport)
    {
      if (r_poolname)
        {
          xfree (*r_poolname);
          *r_poolname = NULL;
        }
      return gpg_error_from_syserror ();
    }
  return 0;
}


/* Resolve all known keyserver names and update the hosttable.  This
   is mainly useful for debugging because the resolving is anyway done
   on demand.  */
gpg_error_t
ks_hkp_resolve (ctrl_t ctrl, parsed_uri_t uri)
{
  gpg_error_t err;
  char *hostport = NULL;

  /* NB: With an explicitly given port we do not want to consult a
   * service record because that might be in conflict with the port
   * from such a service record.  */
  err = make_host_part (ctrl, uri->scheme, uri->host, uri->port,
                        1, uri->explicit_port,
                        &hostport, NULL, NULL);
  if (err)
    {
      err = ks_printf_help (ctrl, "%s://%s:%hu: resolve failed: %s",
                            uri->scheme, uri->host, uri->port,
                            gpg_strerror (err));
    }
  else
    {
      err = ks_printf_help (ctrl, "%s", hostport);
      xfree (hostport);
    }
  return err;
}


/* Housekeeping function called from the housekeeping thread.  It is
   used to mark dead hosts alive so that they may be tried again after
   some time.  */
void
ks_hkp_housekeeping (time_t curtime)
{
  int idx;
  hostinfo_t hi;

  for (idx=0; idx < hosttable_size; idx++)
    {
      hi = hosttable[idx];
      if (!hi)
        continue;
      if (!hi->dead)
        continue;
      if (!hi->died_at)
        continue; /* Do not resurrect manually shot hosts.  */
      if (hi->died_at + RESURRECT_INTERVAL <= curtime
          || hi->died_at > curtime)
        {
          hi->dead = 0;
          log_info ("resurrected host '%s'", hi->name);
        }
    }
}


/* Send an HTTP request.  On success returns an estream object at
   R_FP.  HOSTPORTSTR is only used for diagnostics.  If HTTPHOST is
   not NULL it will be used as HTTP "Host" header.  If POST_CB is not
   NULL a post request is used and that callback is called to allow
   writing the post data.  If R_HTTP_STATUS is not NULL, the http
   status code will be stored there.  */
static gpg_error_t
send_request (ctrl_t ctrl, const char *request, const char *hostportstr,
              const char *httphost, unsigned int httpflags,
              gpg_error_t (*post_cb)(void *, http_t), void *post_cb_value,
              estream_t *r_fp, unsigned int *r_http_status)
{
  gpg_error_t err;
  http_session_t session = NULL;
  http_t http = NULL;
  int redirects_left = MAX_REDIRECTS;
  estream_t fp = NULL;
  char *request_buffer = NULL;

  *r_fp = NULL;

  err = http_session_new (&session, NULL, httphost, HTTP_FLAG_TRUST_DEF);
  if (err)
    goto leave;
  http_session_set_log_cb (session, cert_log_cb);

 once_more:
  err = http_open (&http,
                   post_cb? HTTP_REQ_POST : HTTP_REQ_GET,
                   request,
                   httphost,
                   /* fixme: AUTH */ NULL,
                   (httpflags
                    |(opt.honor_http_proxy? HTTP_FLAG_TRY_PROXY:0)
                    |(opt.use_tor? HTTP_FLAG_FORCE_TOR:0)),
                   ctrl->http_proxy,
                   session,
                   NULL,
                   /*FIXME curl->srvtag*/NULL);
  if (!err)
    {
      fp = http_get_write_ptr (http);
      /* Avoid caches to get the most recent copy of the key.  We set
         both the Pragma and Cache-Control versions of the header, so
         we're good with both HTTP 1.0 and 1.1.  */
      es_fputs ("Pragma: no-cache\r\n"
                "Cache-Control: no-cache\r\n", fp);
      if (post_cb)
        err = post_cb (post_cb_value, http);
      if (!err)
        {
          http_start_data (http);
          if (es_ferror (fp))
            err = gpg_error_from_syserror ();
        }
    }
  if (err)
    {
      /* Fixme: After a redirection we show the old host name.  */
      log_error (_("error connecting to '%s': %s\n"),
                 hostportstr, gpg_strerror (err));
      goto leave;
    }

  /* Wait for the response.  */
  dirmngr_tick (ctrl);
  err = http_wait_response (http);
  if (err)
    {
      log_error (_("error reading HTTP response for '%s': %s\n"),
                 hostportstr, gpg_strerror (err));
      goto leave;
    }

  if (http_get_tls_info (http, NULL))
    {
      /* Update the httpflags so that a redirect won't fallback to an
         unencrypted connection.  */
      httpflags |= HTTP_FLAG_FORCE_TLS;
    }

  if (r_http_status)
    *r_http_status = http_get_status_code (http);

  switch (http_get_status_code (http))
    {
    case 200:
      err = 0;
      break; /* Success.  */

    case 301:
    case 302:
    case 307:
      {
        const char *s = http_get_header (http, "Location");

        log_info (_("URL '%s' redirected to '%s' (%u)\n"),
                  request, s?s:"[none]", http_get_status_code (http));
        if (s && *s && redirects_left-- )
          {
            xfree (request_buffer);
            request_buffer = xtrystrdup (s);
            if (request_buffer)
              {
                request = request_buffer;
                http_close (http, 0);
                http = NULL;
                goto once_more;
              }
            err = gpg_error_from_syserror ();
          }
        else
          err = gpg_error (GPG_ERR_NO_DATA);
        log_error (_("too many redirections\n"));
      }
      goto leave;

    case 501:
      err = gpg_error (GPG_ERR_NOT_IMPLEMENTED);
      goto leave;

    default:
      log_error (_("error accessing '%s': http status %u\n"),
                 request, http_get_status_code (http));
      err = gpg_error (GPG_ERR_NO_DATA);
      goto leave;
    }

  /* FIXME: We should register a permanent redirection and whether a
     host has ever used TLS so that future calls will always use
     TLS. */

  fp = http_get_read_ptr (http);
  if (!fp)
    {
      err = gpg_error (GPG_ERR_BUG);
      goto leave;
    }

  /* Return the read stream and close the HTTP context.  */
  *r_fp = fp;
  http_close (http, 1);
  http = NULL;

 leave:
  http_close (http, 0);
  http_session_release (session);
  xfree (request_buffer);
  return err;
}


/* Helper to evaluate the error code ERR form a send_request() call
   with REQUEST.  The function returns true if the caller shall try
   again.  TRIES_LEFT points to a variable to track the number of
   retries; this function decrements it and won't return true if it is
   down to zero. */
static int
handle_send_request_error (gpg_error_t err, const char *request,
                           unsigned int *tries_left)
{
  int retry = 0;

  switch (gpg_err_code (err))
    {
    case GPG_ERR_ECONNREFUSED:
    case GPG_ERR_ENETUNREACH:
    case GPG_ERR_UNKNOWN_HOST:
    case GPG_ERR_NETWORK:
      if (mark_host_dead (request) && *tries_left)
        retry = 1;
      break;

    case GPG_ERR_ETIMEDOUT:
      if (*tries_left)
        {
          log_info ("selecting a different host due to a timeout\n");
          retry = 1;
        }

    default:
      break;
    }

  if (*tries_left)
    --*tries_left;

  return retry;
}


/* Search the keyserver identified by URI for keys matching PATTERN.
   On success R_FP has an open stream to read the data.  If
   R_HTTP_STATUS is not NULL, the http status code will be stored
   there.  */
gpg_error_t
ks_hkp_search (ctrl_t ctrl, parsed_uri_t uri, const char *pattern,
               estream_t *r_fp, unsigned int *r_http_status)
{
  gpg_error_t err;
  KEYDB_SEARCH_DESC desc;
  char fprbuf[2+40+1];
  char *hostport = NULL;
  char *request = NULL;
  estream_t fp = NULL;
  int reselect;
  unsigned int httpflags;
  char *httphost = NULL;
  unsigned int tries = SEND_REQUEST_RETRIES;

  *r_fp = NULL;

  /* Remove search type indicator and adjust PATTERN accordingly.
     Note that HKP keyservers like the 0x to be present when searching
     by keyid.  We need to re-format the fingerprint and keyids so to
     remove the gpg specific force-use-of-this-key flag ("!").  */
  err = classify_user_id (pattern, &desc, 1);
  if (err)
    return err;
  switch (desc.mode)
    {
    case KEYDB_SEARCH_MODE_EXACT:
    case KEYDB_SEARCH_MODE_SUBSTR:
    case KEYDB_SEARCH_MODE_MAIL:
    case KEYDB_SEARCH_MODE_MAILSUB:
      pattern = desc.u.name;
      break;
    case KEYDB_SEARCH_MODE_SHORT_KID:
      snprintf (fprbuf, sizeof fprbuf, "0x%08lX", (ulong)desc.u.kid[1]);
      pattern = fprbuf;
      break;
    case KEYDB_SEARCH_MODE_LONG_KID:
      snprintf (fprbuf, sizeof fprbuf, "0x%08lX%08lX",
                (ulong)desc.u.kid[0], (ulong)desc.u.kid[1]);
      pattern = fprbuf;
      break;
    case KEYDB_SEARCH_MODE_FPR16:
      fprbuf[0] = '0';
      fprbuf[1] = 'x';
      bin2hex (desc.u.fpr, 16, fprbuf+2);
      pattern = fprbuf;
      break;
    case KEYDB_SEARCH_MODE_FPR20:
    case KEYDB_SEARCH_MODE_FPR:
      fprbuf[0] = '0';
      fprbuf[1] = 'x';
      bin2hex (desc.u.fpr, 20, fprbuf+2);
      pattern = fprbuf;
      break;
    default:
      return gpg_error (GPG_ERR_INV_USER_ID);
    }

  /* Build the request string.  */
  reselect = 0;
 again:
  {
    char *searchkey;

    xfree (hostport); hostport = NULL;
    xfree (httphost); httphost = NULL;
    err = make_host_part (ctrl, uri->scheme, uri->host, uri->port,
                          reselect, uri->explicit_port,
                          &hostport, &httpflags, &httphost);
    if (err)
      goto leave;

    searchkey = http_escape_string (pattern, EXTRA_ESCAPE_CHARS);
    if (!searchkey)
      {
        err = gpg_error_from_syserror ();
        goto leave;
      }

    xfree (request);
    request = strconcat (hostport,
                         "/pks/lookup?op=index&options=mr&search=",
                         searchkey,
                         NULL);
    xfree (searchkey);
    if (!request)
      {
        err = gpg_error_from_syserror ();
        goto leave;
      }
  }

  /* Send the request.  */
  err = send_request (ctrl, request, hostport, httphost, httpflags,
                      NULL, NULL, &fp, r_http_status);
  if (handle_send_request_error (err, request, &tries))
    {
      reselect = 1;
      goto again;
    }
  if (err)
    goto leave;

  err = dirmngr_status (ctrl, "SOURCE", hostport, NULL);
  if (err)
    goto leave;

  /* Peek at the response.  */
  {
    int c = es_getc (fp);
    if (c == -1)
      {
        err = es_ferror (fp)?gpg_error_from_syserror ():gpg_error (GPG_ERR_EOF);
        log_error ("error reading response: %s\n", gpg_strerror (err));
        goto leave;
      }
    if (c == '<')
      {
        /* The document begins with a '<': Assume a HTML response,
           which we don't support.  */
        err = gpg_error (GPG_ERR_UNSUPPORTED_ENCODING);
        goto leave;
      }
    es_ungetc (c, fp);
  }

  /* Return the read stream.  */
  *r_fp = fp;
  fp = NULL;

 leave:
  es_fclose (fp);
  xfree (request);
  xfree (hostport);
  xfree (httphost);
  return err;
}


/* Get the key described key the KEYSPEC string from the keyserver
   identified by URI.  On success R_FP has an open stream to read the
   data.  The data will be provided in a format GnuPG can import
   (either a binary OpenPGP message or an armored one).  */
gpg_error_t
ks_hkp_get (ctrl_t ctrl, parsed_uri_t uri, const char *keyspec, estream_t *r_fp)
{
  gpg_error_t err;
  KEYDB_SEARCH_DESC desc;
  char kidbuf[2+40+1];
  const char *exactname = NULL;
  char *searchkey = NULL;
  char *hostport = NULL;
  char *request = NULL;
  estream_t fp = NULL;
  int reselect;
  char *httphost = NULL;
  unsigned int httpflags;
  unsigned int tries = SEND_REQUEST_RETRIES;

  *r_fp = NULL;

  /* Remove search type indicator and adjust PATTERN accordingly.
     Note that HKP keyservers like the 0x to be present when searching
     by keyid.  We need to re-format the fingerprint and keyids so to
     remove the gpg specific force-use-of-this-key flag ("!").  */
  err = classify_user_id (keyspec, &desc, 1);
  if (err)
    return err;
  switch (desc.mode)
    {
    case KEYDB_SEARCH_MODE_SHORT_KID:
      snprintf (kidbuf, sizeof kidbuf, "0x%08lX", (ulong)desc.u.kid[1]);
      break;
    case KEYDB_SEARCH_MODE_LONG_KID:
      snprintf (kidbuf, sizeof kidbuf, "0x%08lX%08lX",
		(ulong)desc.u.kid[0], (ulong)desc.u.kid[1]);
      break;
    case KEYDB_SEARCH_MODE_FPR20:
    case KEYDB_SEARCH_MODE_FPR:
      /* This is a v4 fingerprint. */
      kidbuf[0] = '0';
      kidbuf[1] = 'x';
      bin2hex (desc.u.fpr, 20, kidbuf+2);
      break;

    case KEYDB_SEARCH_MODE_EXACT:
      exactname = desc.u.name;
      break;

    case KEYDB_SEARCH_MODE_FPR16:
      log_error ("HKP keyservers do not support v3 fingerprints\n");
    default:
      return gpg_error (GPG_ERR_INV_USER_ID);
    }

  searchkey = http_escape_string (exactname? exactname : kidbuf,
                                  EXTRA_ESCAPE_CHARS);
  if (!searchkey)
    {
      err = gpg_error_from_syserror ();
      goto leave;
    }

  reselect = 0;
 again:
  /* Build the request string.  */
  xfree (hostport); hostport = NULL;
  xfree (httphost); httphost = NULL;
  err = make_host_part (ctrl, uri->scheme, uri->host, uri->port,
                        reselect, uri->explicit_port,
                        &hostport, &httpflags, &httphost);
  if (err)
    goto leave;

  xfree (request);
  request = strconcat (hostport,
                       "/pks/lookup?op=get&options=mr&search=",
                       searchkey,
                       exactname? "&exact=on":"",
                       NULL);
  if (!request)
    {
      err = gpg_error_from_syserror ();
      goto leave;
    }

  /* Send the request.  */
  err = send_request (ctrl, request, hostport, httphost, httpflags,
                      NULL, NULL, &fp, NULL);
  if (handle_send_request_error (err, request, &tries))
    {
      reselect = 1;
      goto again;
    }
  if (err)
    goto leave;

  err = dirmngr_status (ctrl, "SOURCE", hostport, NULL);
  if (err)
    goto leave;

  /* Return the read stream and close the HTTP context.  */
  *r_fp = fp;
  fp = NULL;

 leave:
  es_fclose (fp);
  xfree (request);
  xfree (hostport);
  xfree (httphost);
  xfree (searchkey);
  return err;
}




/* Callback parameters for put_post_cb.  */
struct put_post_parm_s
{
  char *datastring;
};


/* Helper for ks_hkp_put.  */
static gpg_error_t
put_post_cb (void *opaque, http_t http)
{
  struct put_post_parm_s *parm = opaque;
  gpg_error_t err = 0;
  estream_t fp;
  size_t len;

  fp = http_get_write_ptr (http);
  len = strlen (parm->datastring);

  es_fprintf (fp,
              "Content-Type: application/x-www-form-urlencoded\r\n"
              "Content-Length: %zu\r\n", len+8 /* 8 is for "keytext" */);
  http_start_data (http);
  if (es_fputs ("keytext=", fp) || es_write (fp, parm->datastring, len, NULL))
    err = gpg_error_from_syserror ();
  return err;
}


/* Send the key in {DATA,DATALEN} to the keyserver identified by URI.  */
gpg_error_t
ks_hkp_put (ctrl_t ctrl, parsed_uri_t uri, const void *data, size_t datalen)
{
  gpg_error_t err;
  char *hostport = NULL;
  char *request = NULL;
  estream_t fp = NULL;
  struct put_post_parm_s parm;
  char *armored = NULL;
  int reselect;
  char *httphost = NULL;
  unsigned int httpflags;
  unsigned int tries = SEND_REQUEST_RETRIES;

  parm.datastring = NULL;

  err = armor_data (&armored, data, datalen);
  if (err)
    goto leave;

  parm.datastring = http_escape_string (armored, EXTRA_ESCAPE_CHARS);
  if (!parm.datastring)
    {
      err = gpg_error_from_syserror ();
      goto leave;
    }
  xfree (armored);
  armored = NULL;

  /* Build the request string.  */
  reselect = 0;
 again:
  xfree (hostport); hostport = NULL;
  xfree (httphost); httphost = NULL;
  err = make_host_part (ctrl, uri->scheme, uri->host, uri->port,
                        reselect, uri->explicit_port,
                        &hostport, &httpflags, &httphost);
  if (err)
    goto leave;

  xfree (request);
  request = strconcat (hostport, "/pks/add", NULL);
  if (!request)
    {
      err = gpg_error_from_syserror ();
      goto leave;
    }

  /* Send the request.  */
  err = send_request (ctrl, request, hostport, httphost, 0,
                      put_post_cb, &parm, &fp, NULL);
  if (handle_send_request_error (err, request, &tries))
    {
      reselect = 1;
      goto again;
    }
  if (err)
    goto leave;

 leave:
  es_fclose (fp);
  xfree (parm.datastring);
  xfree (armored);
  xfree (request);
  xfree (hostport);
  xfree (httphost);
  return err;
}