/*
 Compile server client functions
 Copyright (C) 2010-2018 Red Hat Inc.

 This file is part of systemtap, and is free software.  You can
 redistribute it and/or modify it under the terms of the GNU General
 Public License (GPL); either version 2, or (at your option) any
 later version.
*/

// Completely disable the client if NSS is not available.
#include "config.h"
#if HAVE_NSS
#include "session.h"
#include "cscommon.h"
#include "csclient.h"
#include "client-nss.h"
#include "util.h"
#include "stap-probe.h"

#include <sys/times.h>
#include <vector>
#include <fstream>
#include <sstream>
#include <cassert>
#include <cstdlib>
#include <cstdio>
#include <algorithm>

extern "C" {
#include <unistd.h>
#include <linux/limits.h>
#include <sys/time.h>
#include <glob.h>
#include <limits.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <net/if.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <pwd.h>
}

#if HAVE_AVAHI
extern "C" {
#include <avahi-client/client.h>
#include <avahi-client/lookup.h>

#include <avahi-common/simple-watch.h>
#include <avahi-common/malloc.h>
#include <avahi-common/error.h>
#include <avahi-common/timeval.h>
}
#endif // HAVE_AVAHI

extern "C" {
#include <ssl.h>
#include <nspr.h>
#include <nss.h>
#include <certdb.h>
#include <pk11pub.h>
#include <prerror.h>
#include <secerr.h>
#include <sslerr.h>
}

#include "nsscommon.h"

using namespace std;

static PRIPv6Addr &copyAddress (PRIPv6Addr &PRin6, const in6_addr &in6);
static PRNetAddr &copyNetAddr (PRNetAddr &x, const PRNetAddr &y);
bool operator!= (const PRNetAddr &x, const PRNetAddr &y);
bool operator== (const PRNetAddr &x, const PRNetAddr &y);

// Information about compile servers.
compile_server_info::compile_server_info ()
  : port(0), fully_specified(false)
{
  memset (& address, 0, sizeof (address));
}

bool
compile_server_info::empty () const
{
  return (this->host_name.empty () && ! this->hasAddress ()
	  && certinfo.empty ());
}

bool
compile_server_info::hasAddress () const
{
  return this->address.raw.family != 0;
}

unsigned short
compile_server_info::setAddressPort (unsigned short port)
{
  if (this->address.raw.family == PR_AF_INET)
    return this->address.inet.port = htons (port);
  if (this->address.raw.family == PR_AF_INET6)
    return this->address.ipv6.port = htons (port);
  assert (0);
  return 0;
}

bool
compile_server_info::isComplete () const
{
  return this->hasAddress () && port != 0;
}

string 
compile_server_info::host_specification () const
{
  ostringstream host_spec;
  if (!this->isComplete())
      return host_spec.str();

  if (! this->host_name.empty ())
      host_spec << this->host_name;
  else if (this->hasAddress())
    {
      PRStatus prStatus;
      switch (this->address.raw.family)
	{
	case PR_AF_INET:
	case PR_AF_INET6:
	  {
#define MAX_NETADDR_SIZE 46 // from the NSPR API reference.
	    char buf[MAX_NETADDR_SIZE];
	    prStatus = PR_NetAddrToString(&this->address, buf, sizeof (buf));
	    if (prStatus == PR_SUCCESS) {
	      host_spec << buf;
	      break;
	    }
	  }
	  break;
	default:
	  // Do nothing.
	  break;
	}
    }
  if (! host_spec.str().empty())
      host_spec << ":" << this->port;
  return host_spec.str();
}

bool
compile_server_info::operator== (const compile_server_info &that) const
{
  // If one item or the other has only a name, and possibly a port
  // specified, then allow a match by name and port only. This is so
  // that the user can specify names which are returned by avahi, but
  // are not dns resolvable. Otherwise, we will ignore the host_name.
  if ((! this->hasAddress() && this->version.empty () &&
       this->sysinfo.empty () && this->certinfo.empty ()) ||
      (! that.hasAddress() && that.version.empty () &&
       that.sysinfo.empty () && that.certinfo.empty ()))
  {
    if (this->host_name != that.host_name)
      return false;
  }

  // Compare the other fields only if they have both been set.
  if (this->hasAddress() && that.hasAddress() && this->address != that.address)
    return false;
  if (this->port != 0 && that.port != 0 && this->port != that.port)
    return false;
  if (! this->version.empty () && ! that.version.empty ()
      && this->version != that.version)
    return false;
  if (! this->sysinfo.empty () && ! that.sysinfo.empty ()
      && this->sysinfo != that.sysinfo)
    return false;
  if (! this->certinfo.empty () && ! that.certinfo.empty ()
      && this->certinfo != that.certinfo)
    return false;
  if (! this->mok_fingerprints.empty () && ! that.mok_fingerprints.empty ()
      && this->mok_fingerprints != that.mok_fingerprints)
    return false;

  return true;				// They are equal
}

// Used to sort servers by preference for order of contact. The
// preferred server is "less" than the other one.
bool compile_server_info::operator< (const compile_server_info &that) const
{
  // Prefer servers with a later (higher) version number.
  cs_protocol_version this_version (this->version.c_str ());
  cs_protocol_version that_version (that.version.c_str ());
  return that_version < this_version;
}

ostream &operator<< (ostream &s, const compile_server_info &i);
ostream &operator<< (ostream &s, const vector<compile_server_info> &v);

static void
preferred_order (vector<compile_server_info> &servers)
{
  // Sort the given list of servers into the preferred order for contacting.
  // Don't bother if there are less than 2 servers in the list.
  if (servers.size () < 2)
    return;

  // Sort the list using compile_server_info::operator<
  sort (servers.begin (), servers.end ());
}

struct resolved_host // see also PR16326, PR16342
{
  string host_name;
  PRNetAddr address;
  resolved_host(string chost_name, PRNetAddr caddress):
    host_name(chost_name), address(caddress) {}
};

struct compile_server_cache
{
  vector<compile_server_info> default_servers;
  vector<compile_server_info> specified_servers;
  vector<compile_server_info> trusted_servers;
  vector<compile_server_info> signing_servers;
  vector<compile_server_info> online_servers;
  vector<compile_server_info> all_servers;
  map<string,vector<resolved_host> > resolved_hosts;
};

// For filtering queries.
enum compile_server_properties {
  compile_server_all        = 0x1,
  compile_server_trusted    = 0x2,
  compile_server_online     = 0x4,
  compile_server_compatible = 0x8,
  compile_server_signer     = 0x10,
  compile_server_specified  = 0x20
};

// Static functions.
static compile_server_cache* cscache(systemtap_session& s);
static void
query_server_status (systemtap_session &s, const string &status_string);

static void
get_server_info (systemtap_session &s, int pmask,
		 vector<compile_server_info> &servers);
static void
get_default_server_info (systemtap_session &s,
			 vector<compile_server_info> &servers);

static void
merge_server_info (const compile_server_info &source,
		   compile_server_info &target);

static void
resolve_host (systemtap_session& s, compile_server_info &server,
	      vector<compile_server_info> &servers);

// -----------------------------------------------------
// NSS related code used by the compile server client
// -----------------------------------------------------
static void
add_server_trust (systemtap_session &s, const string &cert_db_path,
		  vector<compile_server_info> &server_list);
static void
revoke_server_trust (systemtap_session &s, const string &cert_db_path,
		     const vector<compile_server_info> &server_list);

void
get_server_info_from_db (systemtap_session &s,
			 vector<compile_server_info> &servers,
			 const string &cert_db_path);

string
global_client_cert_db_path ()
{
  return SYSCONFDIR "/systemtap/ssl/client";
}

static string
private_ssl_cert_db_path ()
{
  return local_client_cert_db_path ();
}

string
global_ssl_cert_db_path ()
{
  return global_client_cert_db_path ();
}

string
signing_cert_db_path ()
{
  return SYSCONFDIR "/systemtap/staprun";
}

/* Connection state.  */
typedef struct connectionState_t
{
  const char *hostName;
  PRNetAddr   addr;
  const char *infileName;
  const char *outfileName;
  const char *trustNewServerMode;
} connectionState_t;

/* Add the server's certificate to our database of trusted servers.  */
SECStatus
nss_trustNewServer (CERTCertificate *serverCert)
{
  SECStatus secStatus;
  CERTCertTrust *trust = NULL;
  PK11SlotInfo *slot = NULL;

  /* Import the certificate.  */
  slot = PK11_GetInternalKeySlot();
  const char *nickname = server_cert_nickname ();
  secStatus = PK11_ImportCert(slot, serverCert, CK_INVALID_HANDLE, nickname, PR_FALSE);
  if (secStatus != SECSuccess)
    goto done;

  if (PK11_NeedUserInit(slot)) {
    PK11_InitPin(slot, (char*)NULL, "");
  }
  
  /* Make it a trusted peer.  */
  trust = (CERTCertTrust *)PORT_ZAlloc(sizeof(CERTCertTrust));
  if (! trust)
    {
      secStatus = SECFailure;
      goto done;
    }

  secStatus = CERT_DecodeTrustString(trust, "P,P,P");
  if (secStatus != SECSuccess)
    goto done;

  secStatus = CERT_ChangeCertTrust(CERT_GetDefaultCertDB(), serverCert, trust);

done:
  if (slot)
    PK11_FreeSlot (slot);
  if (trust)
    PORT_Free(trust);
  return secStatus;
}

static bool
isIPv6LinkLocal (const PRNetAddr &address)
{
  // Link-local addresses are members of the address block fe80::
  if (address.raw.family == PR_AF_INET6 &&
      address.ipv6.ip.pr_s6_addr[0] == 0xfe && address.ipv6.ip.pr_s6_addr[1] == 0x80)
    return true;
  return false;
}

// Issue a status message for when a server's trust is already in place.
static void
trust_already_in_place (
  const compile_server_info &server,
  const vector<compile_server_info> &server_list,
  const string cert_db_path,
  bool revoking
)
{
  // What level of trust?
  string purpose;
  if (cert_db_path == signing_cert_db_path ())
    purpose = _("as a module signer for all users");
  else
    {
      purpose = _("as an SSL peer");
      if (cert_db_path == global_ssl_cert_db_path ())
	purpose += _(" for all users");
      else
	purpose += _(" for the current user");
    }

  // Issue a message for each server in the list with the same certificate.
  unsigned limit = server_list.size ();
  for (unsigned i = 0; i < limit; ++i)
    {
      if (server.certinfo != server_list[i].certinfo)
	continue;
      clog << server_list[i] << _(" is already ");
      if (revoking)
	clog << _("untrusted ") << purpose << endl;
      else
       clog << _("trusted ") << purpose << endl;
    }
}

// Add the given servers to the given database of trusted servers.
static void
add_server_trust (
  systemtap_session &s,
  const string &cert_db_path,
  vector<compile_server_info> &server_list
)
{
  // Get a list of servers already trusted. This opens the database, so do it
  // before we open it for our own purposes.
  vector<compile_server_info> already_trusted;
  get_server_info_from_db (s, already_trusted, cert_db_path);

  // Make sure the given path exists.
  if (create_dir (cert_db_path.c_str (), 0755) != 0)
    {
      clog << _F("Unable to find or create the client certificate database directory %s: ", cert_db_path.c_str());
      perror ("");
      return;
    }

  // Must predeclare this because of jumps to cleanup: below.
  vector<string> processed_certs;

  client_backend *backend = nss_get_client_backend (s);
  if (backend->initialize () != 0)
    return;

  // Make sure NSPR is initialized. Must be done before NSS is initialized
  s.NSPR_init ();

  // Initialize the NSS libraries -- read/write
  SECStatus secStatus = nssInit (cert_db_path.c_str (), 1/*readwrite*/);
  if (secStatus != SECSuccess)
    {
      // Message already issued.
      goto cleanup;
    }

  // Enable all cipher suites.
  // SSL_ClearSessionCache is required for the new settings to take effect.
  /* Some NSS versions don't do this correctly in NSS_SetDomesticPolicy. */
  do {
    const PRUint16 *cipher;
    for (cipher = SSL_GetImplementedCiphers(); *cipher != 0; ++cipher)
      SSL_CipherPolicySet(*cipher, SSL_ALLOWED);
  } while (0);
  SSL_ClearSessionCache ();
  
  // Iterate over the servers to become trusted. Contact each one and
  // add it to the list of trusted servers if it is not already trusted.
  // trust_server_info() will issue any error messages.
  for (vector<compile_server_info>::iterator server = server_list.begin();
       server != server_list.end ();
       ++server)
    {
      // Trust is based on certificates. We need only add trust in the
      // same certificate once.
      //
      // RHBZ 1075685: If the new server to be trusted is selected by address + port,
      // and there is no avahi assistance available, or the server is not known
      // to avahi, then its certificate serial number field will be empty. We
      // therefore have no basis for comparing it to the serial numbers on already-trusted
      // certificates. In this case, unconditionally contact the new server to obtain
      // its certificate.
      if (! server->certinfo.empty ())
	{
	  // We need not contact the server if it has already been processed.
	  if (find (processed_certs.begin (), processed_certs.end (),
		    server->certinfo) != processed_certs.end ())
	    continue;
	  processed_certs.push_back (server->certinfo);

	  // We need not contact the server if it is already trusted.
	  if (find (already_trusted.begin (), already_trusted.end (), *server) !=
	      already_trusted.end ())
	    {
	      if (s.verbose >= 2)
		trust_already_in_place (*server, server_list, cert_db_path, false/*revoking*/);
	      continue;
	    }
	}

      // At a minimum we need an ip_address along with a port
      // number in order to contact an nss server.
      if (s.http_servers.empty ())
        {
          if (! server->hasAddress() || server->port == 0)
            continue;
          // Set the port within the address.
          server->setAddressPort (server->port);
        }

      int rc = backend->trust_server_info (*server);
      if (rc != NSS_SUCCESS)
	{
	  // Notice no space before the '%s'? The compile_server_info
	  // '<<' operator always outputs a space.
	  clog << _F("Unable to connect to%s", lex_cast(*server).c_str()) << endl;
	  nssError ();
	  // Additional information: if the address is IPv6 and is link-local, then it must
	  // have a scope_id.
	  if (isIPv6LinkLocal (server->address) && server->address.ipv6.scope_id == 0)
	    {
	      clog << _("  The address is an IPv6 link-local address with no scope specifier.")
		   << endl;
	    }
	}
    }

 cleanup:
  // Shutdown NSS.
  // SSL_ClearSessionCache is required before shutdown for client applications.
  SSL_ClearSessionCache ();
  nssCleanup (cert_db_path.c_str (), NULL);

  // Make sure the database files are readable.
  glob_t globbuf;
  string filespec = cert_db_path + "/*.db";
  if (s.verbose >= 3)
    clog << _F("Searching \"%s\"\n", filespec.c_str());
  int r = glob (filespec.c_str (), 0, NULL, & globbuf);
  if (r != GLOB_NOSPACE && r != GLOB_ABORTED && r != GLOB_NOMATCH)
    {
      for (unsigned i = 0; i < globbuf.gl_pathc; ++i)
	{
	  string filename = globbuf.gl_pathv[i];
	  if (s.verbose >= 3)
	    clog << _("  found ") << filename << endl;

	  if (chmod (filename.c_str (), 0644) != 0)
	    {
             s.print_warning("Unable to change permissions on " + filename + ": ");
	      perror ("");
	    }
	}
      globfree(& globbuf);
    }
}

// Remove the given servers from the given database of trusted servers.
static void
revoke_server_trust (
  systemtap_session &s,
  const string &cert_db_path,
  const vector<compile_server_info> &server_list
)
{
  // Make sure the given path exists.
  if (! file_exists (cert_db_path))
    {
      if (s.verbose >= 5)
	{
	  clog << _F("Certificate database '%s' does not exist",
		     cert_db_path.c_str()) << endl;
	  for (vector<compile_server_info>::const_iterator server = server_list.begin();
	       server != server_list.end ();
	       ++server)
	    trust_already_in_place (*server, server_list, cert_db_path, true/*revoking*/);
	}
      return;
    }

  // Must predeclare these because of jumps to cleanup: below.
  CERTCertDBHandle *handle;
  PRArenaPool *tmpArena = NULL;
  CERTCertList *certs = NULL;
  CERTCertificate *db_cert;
  vector<string> processed_certs;
  const char *nickname;
  SECStatus secStatus;
  
  // Make sure NSPR is initialized. Must be done before NSS is initialized
  s.NSPR_init ();

  // Initialize the NSS libraries -- read/write
  secStatus = nssInit (cert_db_path.c_str (), 1/*readwrite*/);
  if (secStatus != SECSuccess)
    {
      // Message already issued
      goto cleanup;
    }
  handle = CERT_GetDefaultCertDB();

  // A memory pool to work in
  tmpArena = PORT_NewArena(DER_DEFAULT_CHUNKSIZE);
  if (! tmpArena) 
    {
      clog << _("Out of memory:");
      nssError ();
      goto cleanup;
    }

  // Iterate over the servers to become untrusted.
  nickname = server_cert_nickname ();
  for (vector<compile_server_info>::const_iterator server = server_list.begin();
       server != server_list.end ();
       ++server)
    {
      // If the server's certificate serial number is unknown, then we can't
      // match it with one in the database.
      if (server->certinfo.empty ())
	continue;

      // Trust is based on certificates. We need only revoke trust in the same
      // certificate once.
      if (find (processed_certs.begin (), processed_certs.end (),
		server->certinfo) != processed_certs.end ())
	continue;
      processed_certs.push_back (server->certinfo);

      // Search the client-side database of trusted servers.
      db_cert = PK11_FindCertFromNickname (nickname, NULL);
      if (! db_cert)
	{
	  // No trusted servers. Not an error, but issue a status message.
	  if (s.verbose >= 2)
	    trust_already_in_place (*server, server_list, cert_db_path, true/*revoking*/);
	  continue;
	}

      // Here, we have one cert with the desired nickname.
      // Now, we will attempt to get a list of ALL certs 
      // with the same subject name as the cert we have.  That list 
      // should contain, at a minimum, the one cert we have already found.
      // If the list of certs is empty (NULL), the libraries have failed.
      certs = CERT_CreateSubjectCertList (NULL, handle, & db_cert->derSubject,
					  PR_Now (), PR_FALSE);
      CERT_DestroyCertificate (db_cert);
      if (! certs)
	{
         clog << _F("Unable to query certificate database %s: ",
                    cert_db_path.c_str()) << endl;
	  PORT_SetError (SEC_ERROR_LIBRARY_FAILURE);
	  nssError ();
	  goto cleanup;
	}

      // Find the certificate matching the one belonging to our server.
      CERTCertListNode *node;
      for (node = CERT_LIST_HEAD (certs);
	   ! CERT_LIST_END (node, certs);
	   node = CERT_LIST_NEXT (node))
	{
	  // The certificate we're working with.
	  db_cert = node->cert;

	  // Get the serial number.
	  string serialNumber = get_cert_serial_number (db_cert);

	  // Does the serial number match that of the current server?
	  if (serialNumber != server->certinfo)
	    continue; // goto next certificate

	  // All is ok! Remove the certificate from the database.
	  break;
	} // Loop over certificates in the database

      // Was a certificate matching the server found?  */
      if (CERT_LIST_END (node, certs))
	{
	  // Not found. Server is already untrusted.
	  if (s.verbose >= 2)
	    trust_already_in_place (*server, server_list, cert_db_path, true/*revoking*/);
	}
      else
	{
	  secStatus = SEC_DeletePermCertificate (db_cert);
	  if (secStatus != SECSuccess)
	    {
             clog << _F("Unable to remove certificate from %s: ",
                        cert_db_path.c_str()) << endl;
	      nssError ();
	    }
	}
      CERT_DestroyCertList (certs);
      certs = NULL;
    } // Loop over servers

 cleanup:
  assert(!certs);
  if (tmpArena)
    PORT_FreeArena (tmpArena, PR_FALSE);

  nssCleanup (cert_db_path.c_str (), NULL);
}

// Obtain information about servers from the certificates in the given database.
void
get_server_info_from_db (
    systemtap_session &s,
    vector<compile_server_info> &servers,
    const string &cert_db_path
  )
{
  NSSInitContext *context;

  // Make sure the given path exists.
  if (! file_exists (cert_db_path))
    {
      if (s.verbose >= 5)
       clog << _F("Certificate database '%s' does not exist.",
                  cert_db_path.c_str()) << endl;
      return;
    }

  // Make sure NSPR is initialized. Must be done before NSS is initialized
  s.NSPR_init ();

  // Initialize the NSS libraries -- readonly
  context = nssInitContext (cert_db_path.c_str (), 0 /* readWrite */, 0 /* issueMessage */);
  if (context == NULL)
    {
      // Message already issued.
      return;
    }

  CERTCertList *certs = get_cert_list_from_db (server_cert_nickname ());
  if (! certs)
    {
      if (s.verbose >= 5)
	clog << _F("No certificate found in database %s", cert_db_path.c_str ()) << endl;
      goto cleanup;
    }

  for (CERTCertListNode *node = CERT_LIST_HEAD (certs);
       ! CERT_LIST_END (node, certs);
       node = CERT_LIST_NEXT (node))
    {
      compile_server_info server_info;

      // The certificate we're working with.
      CERTCertificate *db_cert = node->cert;

      if (get_host_name (db_cert, server_info.host_name) == false)
        continue;

      // Get the serial number.
      server_info.certinfo = get_cert_serial_number (db_cert);

      // Our results will at a minimum contain this server.
      nss_add_server_info (server_info, servers);

      // Augment the list by querying all online servers and keeping the ones
      // with the same cert serial number.
      vector<compile_server_info> online_servers;
      nss_get_or_keep_online_server_info (s, online_servers, false/*keep*/);
      nss_keep_server_info_with_cert_and_port (s, server_info, online_servers);
      nss_add_server_info (online_servers, servers);
    }

 cleanup:
  if (certs)
    CERT_DestroyCertList (certs);

  nssCleanup (cert_db_path.c_str (), context);
}

// Utility Functions.
//-----------------------------------------------------------------------
ostream &operator<< (ostream &s, const compile_server_info &i)
{
  // Don't print empty information
  if (i.empty ())
    return s;

  s << " host=";
  if (! i.host_name.empty ())
    s << i.host_name;
  else
    s << "unknown";
  s << " address=";
  if (i.hasAddress())
    {
      PRStatus prStatus;
      switch (i.address.raw.family)
	{
	case PR_AF_INET:
	case PR_AF_INET6:
	  {
#define MAX_NETADDR_SIZE 46 // from the NSPR API reference.
	    char buf[MAX_NETADDR_SIZE];
	    prStatus = PR_NetAddrToString(& i.address, buf, sizeof (buf));
	    if (prStatus == PR_SUCCESS) {
	      s << buf;
	      break;
	    }
	  }
	  // Fall through
	default:
	  s << "offline";
	  break;
	}
    }
  else
    s << "offline";
  s << " port=";
  if (i.port != 0)
    s << i.port;
  else
    s << "unknown";
  s << " sysinfo=\"";
  if (! i.sysinfo.empty ())
    s << i.sysinfo << '"';
  else
    s << "unknown\"";
  s << " version=";
  if (! i.version.empty ())
    s << i.version;
  else
    s << "unknown";
  s << " certinfo=\"";
  if (! i.certinfo.empty ())
    s << i.certinfo << '"';
  else
    s << "unknown\"";
  if (! i.mok_fingerprints.empty ())
    {
      // FIXME: Yikes, this output is ugly. Perhaps the server output
      // needs a more structured approach.
      s << " mok_fingerprints=\"";
      vector<string>::const_iterator it;
      for (it = i.mok_fingerprints.begin (); it != i.mok_fingerprints.end ();
	   it++)
        {
	  if (it != i.mok_fingerprints.begin ())
	    s << ", ";
	  s << *it;
	}      
      s << "\"";
    }
  return s;
}

ostream &operator<< (ostream &s, const vector<compile_server_info> &v)
{
  // Indicate an empty list.
  if (v.size () == 0 || (v.size () == 1 && v[0].empty()))
    s << "No Servers" << endl;
  else
    {
      for (unsigned i = 0; i < v.size(); ++i)
	{
	  // Don't print empty items.
	  if (! v[i].empty())
	    s << v[i] << endl;
	}
    }
  return s;
}

PRNetAddr &
copyNetAddr (PRNetAddr &x, const PRNetAddr &y)
{
  PRUint32 saveScope = 0;

  // For IPv6 addresses, don't overwrite the scope_id of x unless x is uninitialized or it is 0.
  if (x.raw.family == PR_AF_INET6)
    saveScope = x.ipv6.scope_id;

  x = y;

  if (saveScope != 0)
    x.ipv6.scope_id = saveScope;

  return x;
}

bool
operator== (const PRNetAddr &x, const PRNetAddr &y)
{
  // Same address family?
  if (x.raw.family != y.raw.family)
    return false;

  switch (x.raw.family)
    {
    case PR_AF_INET6:
      // If both scope ids are set, compare them.
      if (x.ipv6.scope_id != 0 && y.ipv6.scope_id != 0 && x.ipv6.scope_id != y.ipv6.scope_id)
	return false; // not equal
      // Scope is not a factor. Compare the address bits
      return memcmp (& x.ipv6.ip, & y.ipv6.ip, sizeof(x.ipv6.ip)) == 0;
    case PR_AF_INET:
      return x.inet.ip == y.inet.ip;
    default:
      break;
    }
  return false;
}

bool
operator!= (const PRNetAddr &x, const PRNetAddr &y)
{
  return !(x == y);
}

static PRIPv6Addr &
copyAddress (PRIPv6Addr &PRin6, const in6_addr &in6)
{
  // The NSPR type is a typedef of struct in6_addr, but C++ won't let us copy it
  assert (sizeof (PRin6) == sizeof (in6));
  memcpy (& PRin6, & in6, sizeof (PRin6));
  return PRin6;
}

// Return the default server specification, used when none is given on the
// command line.
static string
default_server_spec (const systemtap_session &s)
{
  // If --privilege=X has been used, where X is not stapdev,
  //   the default is online,trusted,compatible,signer
  // otherwise
  //   the default is online,trusted,compatible
  //
  // Having said that,
  //   'online' and 'compatible' will only succeed if we have avahi
  //   'trusted' and 'signer' will only succeed if we have NSS
  //
  string working_string = "online,trusted,compatible";
  if (! pr_contains (s.privilege, pr_stapdev))
    working_string += ",signer";
  return working_string;
}

static int
server_spec_to_pmask (const string &server_spec)
{
  // Construct a mask of the server properties that have been requested.
  // The available properties are:
  //     trusted    - servers which are trusted SSL peers.
  //	 online     - online servers.
  //     compatible - servers which compile for the current kernel release
  //	 	      and architecture.
  //     signer     - servers which are trusted module signers.
  //	 specified  - servers which have been specified using --use-server=XXX.
  //	 	      If no servers have been specified, then this is
  //		      equivalent to --list-servers=trusted,online,compatible.
  //     all        - all trusted servers, trusted module signers,
  //                  servers currently online and specified servers.
  string working_spec = server_spec;
  vector<string> properties;
  tokenize (working_spec, properties, ",");
  int pmask = 0;
  unsigned limit = properties.size ();
  for (unsigned i = 0; i < limit; ++i)
    {
      const string &property = properties[i];
      // Tolerate (and ignore) empty properties.
      if (property.empty ())
	continue;
      if (property == "all")
	{
	  pmask |= compile_server_all;
	}
      else if (property == "specified")
	{
	  pmask |= compile_server_specified;
	}
      else if (property == "trusted")
	{
	  pmask |= compile_server_trusted;
	}
      else if (property == "online")
	{
	  pmask |= compile_server_online;
	}
      else if (property == "compatible")
	{
	  pmask |= compile_server_compatible;
	}
      else if (property == "signer")
	{
	  pmask |= compile_server_signer;
	}
      else
	{
          // XXX PR13274 needs-session to use print_warning()
	  clog << _F("WARNING: unsupported compile server property: %s", property.c_str())
	       << endl;
	}
    }
  return pmask;
}

void
nss_client_query_server_status (systemtap_session &s)
{
  unsigned limit = s.server_status_strings.size ();
  for (unsigned i = 0; i < limit; ++i)
    query_server_status (s, s.server_status_strings[i]);
}

static void
query_server_status (systemtap_session &s, const string &status_string)
{
  // If this string is empty, then the default is "specified"
  string working_string = status_string;
  if (working_string.empty ())
    working_string = "specified";

  // If the query is "specified" and no servers have been specified
  // (i.e. '--use-server' and/or '--use-http-server' not used or used
  // with no argument), then use the default query.
  //
  // TODO: This may not be necessary. The underlying queries should handle
  //       "specified" properly.
  if (working_string == "specified"
      && (s.specified_servers.empty ()
	  || (s.specified_servers.size () == 1
	      && s.specified_servers[0].empty ()))
      && (s.http_servers.empty()
	  || (s.http_servers.size () == 1
	      && s.http_servers[0].empty ())))
    working_string = default_server_spec (s);

  int pmask = server_spec_to_pmask (working_string);

  // Now obtain a list of the servers which match the criteria.
  vector<compile_server_info> raw_servers;
  get_server_info (s, pmask, raw_servers);

  // Augment the listing with as much information as possible by adding
  // information from known servers.
  vector<compile_server_info> servers;
  nss_get_all_server_info (s, servers);
  nss_keep_common_server_info (raw_servers, servers);

  // Sort the list of servers into a preferred order.
  preferred_order (servers);

  // Print the server information. Skip the empty entry at the head of the list.
  clog << _F("Systemtap Compile Server Status for '%s'", working_string.c_str()) << endl;
  bool found = false;
  unsigned limit = servers.size ();
  for (unsigned i = 0; i < limit; ++i)
    {
      assert (! servers[i].empty ());
      // Don't list servers with no cert information. They may not actually
      // exist.
      // TODO: Could try contacting the server and obtaining its cert
      if (servers[i].certinfo.empty ())
	continue;
      clog << servers[i] << endl;
      found = true;
    }
  if (! found)
    clog << _("No servers found") << endl;
}

// Add or remove trust of the servers specified on the command line.
void
nss_client_manage_server_trust (systemtap_session &s)
{
  // This function should do nothing if we don't have NSS.
  // Nothing to do if --trust-servers was not specified.
  if (s.server_trust_spec.empty ())
    return;

  // Break up and analyze the trust specification. Recognized components are:
  //   ssl       - trust the specified servers as ssl peers
  //   signer    - trust the specified servers as module signers
  //   revoke    - revoke the requested trust
  //   all-users - apply/revoke the requested trust for all users
  //   no-prompt - don't prompt the user for confirmation
  vector<string>components;
  tokenize (s.server_trust_spec, components, ",");
  bool ssl = false;
  bool signer = false;
  bool revoke = false;
  bool all_users = false;
  bool no_prompt = false;
  bool error = false;
  for (vector<string>::const_iterator i = components.begin ();
       i != components.end ();
       ++i)
    {
      if (*i == "ssl")
	ssl = true;
      else if (*i == "signer")
	{
	  if (geteuid () != 0)
	    {
	      clog << _("Only root can specify 'signer' on --trust-servers") << endl;
	      error = true;
	    }
	  else
	    signer = true;
	}
      else if (*i == "revoke")
	revoke = true;
      else if (*i == "all-users")
	{
	  if (geteuid () != 0)
	    {
	      clog << _("Only root can specify 'all-users' on --trust-servers") << endl;
	      error = true;
	    }
	  else
	    all_users = true;
	}
      else if (*i == "no-prompt")
	no_prompt = true;
      else
	s.print_warning("Unrecognized server trust specification: " + *i);
    }
  if (error)
    return;

  // Make sure NSPR is initialized
  s.NSPR_init ();

  // Now obtain the list of specified servers.
  vector<compile_server_info> server_list;
  nss_get_specified_server_info (s, server_list, true/*no_default*/);

  // Did we identify any potential servers?
  unsigned limit = server_list.size ();
  if (limit == 0)
    {
      clog << _("No servers identified for trust") << endl;
      return;
    }

  // Create a string representing the request in English.
  // If neither 'ssl' or 'signer' was specified, the default is 'ssl'.
  if (! ssl && ! signer)
    ssl = true;
  ostringstream trustString;
  if (ssl)
    {
      trustString << _("as an SSL peer");
      if (all_users)
	trustString << _(" for all users");
      else
	trustString << _(" for the current user");
    }
  if (signer)
    {
      if (ssl)
	trustString << _(" and ");
      trustString << _("as a module signer for all users");
    }

  // Prompt the user to confirm what's about to happen.
  if (no_prompt)
    {
      if (revoke)
	clog << _("Revoking trust ");
      else
	clog << _("Adding trust ");
    }
  else
    {
      if (revoke)
	clog << _("Revoke trust ");
      else
	clog << _("Add trust ");
    }
  clog << _F("in the following servers %s", trustString.str().c_str());
  if (! no_prompt)
    clog << '?';
  clog << endl;
  for (unsigned i = 0; i < limit; ++i)
    clog << "  " << server_list[i] << endl;
  if (! no_prompt)
    {
      clog << "[y/N] " << flush;

      // Only carry out the operation if the response is "yes"
      string response;
      cin >> response;
      if (response[0] != 'y' && response [0] != 'Y')
	{
	  clog << _("Server trust unchanged") << endl;
	  return;
	}
    }

  // Now add/revoke the requested trust.
  string cert_db_path;
  if (ssl)
    {
      if (all_users)
	cert_db_path = global_ssl_cert_db_path ();
      else
	cert_db_path = private_ssl_cert_db_path ();
      if (revoke)
	revoke_server_trust (s, cert_db_path, server_list);
      else
	add_server_trust (s, cert_db_path, server_list);
    }
  if (signer)
    {
      cert_db_path = signing_cert_db_path ();
      if (revoke)
	revoke_server_trust (s, cert_db_path, server_list);
      else
	add_server_trust (s, cert_db_path, server_list);
    }
}

static compile_server_cache*
cscache(systemtap_session& s)
{
  if (!s.server_cache)
    s.server_cache = new compile_server_cache();
  return s.server_cache;
}

static void
get_server_info (
  systemtap_session &s,
  int pmask,
  vector<compile_server_info> &servers
)
{
  // Get information on compile servers matching the requested criteria.
  // The order of queries is significant. Accumulating queries must go first
  // followed by accumulating/filtering queries.
  bool keep = false;
  if (((pmask & compile_server_all)))
    {
      nss_get_all_server_info (s, servers);
      keep = true;
    }
  // Add the specified servers, if requested
  if ((pmask & compile_server_specified))
    {
      nss_get_specified_server_info (s, servers);
      keep = true;
    }
  // Now filter or accumulate the list depending on whether a query has
  // already been made.
  if ((pmask & compile_server_online))
    {
      nss_get_or_keep_online_server_info (s, servers, keep);
      keep = true;
    }
  if ((pmask & compile_server_trusted))
    {
      nss_get_or_keep_trusted_server_info (s, servers, keep);
      keep = true;
    }
  if ((pmask & compile_server_signer))
    {
      nss_get_or_keep_signing_server_info (s, servers, keep);
      keep = true;
    }
  if ((pmask & compile_server_compatible))
    {
      nss_get_or_keep_compatible_server_info (s, servers, keep);
      keep = true;
    }
}

// Get information about all online servers as well as servers trusted
// as SSL peers and servers trusted as signers.
void
nss_get_all_server_info (
  systemtap_session &s,
  vector<compile_server_info> &servers
)
{
  // We only need to obtain this once per session. This is a good thing(tm)
  // since obtaining this information is expensive.
  vector<compile_server_info>& all_servers = cscache(s)->all_servers;
  if (all_servers.empty ())
    {
      nss_get_or_keep_online_server_info (s, all_servers, false/*keep*/);
      nss_get_or_keep_trusted_server_info (s, all_servers, false/*keep*/);
      nss_get_or_keep_signing_server_info (s, all_servers, false/*keep*/);

      if (s.verbose >= 4)
	{
	  clog << _("All known servers:") << endl;
	  clog << all_servers;
	}
    }

  // Add the information, but not duplicates.
  nss_add_server_info (all_servers, servers);
}

static void
get_default_server_info (
  systemtap_session &s,
  vector<compile_server_info> &servers
)
{
  if (s.verbose >= 3)
    clog << _("Using the default servers") << endl;

  // We only need to obtain this once per session. This is a good thing(tm)
  // since obtaining this information is expensive.
  vector<compile_server_info>& default_servers = cscache(s)->default_servers;
  if (default_servers.empty ())
    {
      // Get the required information.
      // get_server_info will add an empty entry at the beginning to indicate
      // that the search has been performed, in case the search comes up empty.
      int pmask = server_spec_to_pmask (default_server_spec (s));
      get_server_info (s, pmask, default_servers);

      if (s.verbose >= 3)
	{
	  clog << _("Default servers are:") << endl;
	  clog << default_servers;
	}
    }

  // Add the information, but not duplicates.
  nss_add_server_info (default_servers, servers);
}

static bool
isPort (const char *pstr, compile_server_info &server_info)
{
  errno = 0;
  char *estr;
  unsigned long p = strtoul (pstr, & estr, 10);
  if (errno != 0 || *estr != '\0' || p > USHRT_MAX)
    {
      clog << _F("Invalid port number specified: %s", pstr) << endl;
      return false;
    }
  server_info.port = p;
  server_info.fully_specified = true;
  return true;
}

static bool
isIPv6 (const string &server, compile_server_info &server_info)
{
  // An IPv6 address is 8 hex components separated by colons.
  // One contiguous block of zero segments in the address may be elided using ::.
  // An interface may be specified by appending %IF_NAME to the address (e.g. %eth0).
  // A port may be specified by enclosing the ip address in [] and adding :<port>.
  // Allow a bracketed address without a port.
  assert (! server.empty());
  string ip;
  string::size_type portIx;
  if (server[0] == '[')
    {
      string::size_type endBracket = server.find (']');
      if (endBracket == string::npos)
	return false; // Not a valid IPv6 address
      // Extract the address.
      ip = server.substr (1, endBracket - 1);
      portIx = endBracket + 1;
    }
  else
    {
      ip = server;
      portIx = string::npos;
    }

  // Find out how many components there are. The maximum is 8
  unsigned empty = 0;
  vector<string> components;
  tokenize_full (ip, components, ":");
  if (components.size() > 8)
    return false; // Not a valid IPv6 address

  // The components must be either hex values between 0 and 0xffff, or must be empty.
  // There can be only one empty component.
  string interface;
  for (unsigned i = 0; i < components.size(); ++i)
    {
      if (components[i].empty())
	{
	  if (++empty > 1)
	    return false; // Not a valid IPv6 address
	}
      // If it's the final component, see if it specifies the interface. If so, strip it from the
      // component in order to simplify parsing. It still remains as part of the original ip address
      // string.
      if (i == components.size() - 1)
	{
	  size_t ix = components[i].find ('%');
	  if (ix != string::npos)
	    {
	      interface = components[i].substr(ix);
	      components[i] = components[i].substr(0, ix);
	    }
	}
      // Skip leading zeroes.
      unsigned j;
      for (j = 0; j < components[i].size(); ++j)
	{
	  if (components[i][j] != '0')
	    break;
	}
      // Max of 4 hex digits
      if (components[i].size() - j > 4)
	return false; // Not a valid IPv6 address
      for (/**/; j < components[i].size(); ++j)
	{
	  if (! isxdigit (components[i][j]))
	    return false; // Not a valid IPv6 address
	}
    }
  // If there is no empty component, then there must be exactly 8 components.
  if (! empty && components.size() != 8)
    return false; // Not a valid IPv6 address

  // Try to convert the string to an address.
  PRStatus prStatus = PR_StringToNetAddr (ip.c_str(), & server_info.address);
  if (prStatus != PR_SUCCESS)
    return false;

  // Examine the optional port
  if (portIx != string::npos)
    {
      string port = server.substr (portIx);
      if (port.size() != 0)
	{
	  if (port.size() < 2 || port[0] != ':')
	    return false; // Not a valid Port

	  port = port.substr (1);
	  if (! isPort (port.c_str(), server_info))
	    return false; // not a valid port
	}
    }
  else
    server_info.port = 0;

  return true; // valid IPv6 address.
}

static bool
isIPv4 (const string &server, compile_server_info &server_info)
{
  // An IPv4 address is 4 decimal components separated by periods with an
  // additional optional decimal port separated from the address by a colon.
  assert (! server.empty());

  // Find out how many components there are. The maximum is 8
  vector<string> components;
  tokenize (server, components, ":");
  if (components.size() > 2)
    return false; // Not a valid IPv4 address

  // Separate the address from the port (if any).
  string addr;
  string port;
  if (components.size() <= 1)
    addr = server;
  else {
    addr = components[0];
    port = components[1];
  }

  // Separate the address components.
  // There must be exactly 4 components.
  components.clear ();
  tokenize (addr, components, ".");
  if (components.size() != 4)
    return false; // Not a valid IPv4 address
  
  // The components must be decimal values between 0 and 255.
  for (unsigned i = 0; i < components.size(); ++i)
    {
      if (components[i].empty())
	return false; // Not a valid IPv4 address
      errno = 0;
      char *estr;
      long p = strtol (components[i].c_str(), & estr, 10);
      if (errno != 0 || *estr != '\0' || p < 0 || p > 255)
	return false; // Not a valid IPv4 address
    }

  // Try to convert the string to an address.
  PRStatus prStatus = PR_StringToNetAddr (addr.c_str(), & server_info.address);
  if (prStatus != PR_SUCCESS)
    return false;

  // Examine the optional port
  if (! port.empty ()) {
    if (! isPort (port.c_str(), server_info))
      return false; // not a valid port
  }
  else
    server_info.port = 0;

  return true; // valid IPv4 address.
}

static bool
isCertSerialNumber (const string &server, compile_server_info &server_info)
{
  // This function assumes that we have already ruled out the server spec being an IPv6 address.
  // Certificate serial numbers are 5 fields separated by colons plus an optional 6th decimal
  // field specifying a port.
  assert (! server.empty());
  string host = server;
  vector<string> components;
  tokenize (host, components, ":");
  switch (components.size ())
    {
    case 6:
      if (! isPort (components.back().c_str(), server_info))
	return false; // not a valid port
      host = host.substr (0, host.find_last_of (':'));
      // fall through
    case 5:
      server_info.certinfo = host;
      break;
    default:
      return false; // not a cert serial number
    }

  return true; // valid cert serial number and optional port
}

static bool
isDomain (const string &server, compile_server_info &server_info)
{
  // Accept one or two components separated by a colon. The first will be the domain name and
  // the second must a port number.
  assert (! server.empty());
  string host = server;
  vector<string> components;
  unsigned scheme_offset = 0;
  if (host.substr (0, 6) == "https:")
    scheme_offset = 1;
  tokenize (host, components, ":");
  switch (components.size ())
    {
    case 3:
    case 2:
      if (! isPort (components.back().c_str(), server_info))
	return false; // not a valid port
      host = components[(0 + scheme_offset)].substr (scheme_offset * 2);
      // fall through
    case 1:
      server_info.host_name = host;
      break;
    default:
      return false; // not a valid domain name
    }

  return true;
}

void
nss_get_specified_server_info (
  systemtap_session &s,
  vector<compile_server_info> &servers,
  bool no_default
)
{
  // We only need to obtain this once per session. This is a good thing(tm)
  // since obtaining this information is expensive.
  vector<compile_server_info>& specified_servers = cscache(s)->specified_servers;
  if (specified_servers.empty ())
    {
      // Maintain an empty entry to indicate that this search has been
      // performed, in case the search comes up empty.
      specified_servers.push_back (compile_server_info ());

      // If --use-server was not specified at all, then return info for the
      // default server list.
      if (s.specified_servers.empty () && s.http_servers.empty ())
	{
	  if (s.verbose >= 3)
	    clog << _("No servers specified") << endl;
	  if (! no_default)
	    get_default_server_info (s, specified_servers);
	}
      else
	{
	  // Iterate over the specified servers. For each
	  // specification, add to the list of servers.
	  vector<string> &server_list = (! s.http_servers.empty ()
					 ? s.http_servers
					 : s.specified_servers);
	  client_backend *backend = nss_get_client_backend (s);
	  if (backend->initialize () != 0)
	    return;

	  for (auto it = server_list.begin (); it != server_list.end (); ++it)
	    {
	      string &server = *it;

	      // If no specific server(s) specified, then use the
	      // default servers.
	      if (server.empty ())
		{
		  if (s.verbose >= 3)
		    clog << _("No servers specified") << endl;
		  if (! no_default)
		    get_default_server_info (s, specified_servers);
		  continue;
		}

	      // Determine what has been specified. Servers may be
	      // specified by:
	      // - domain{:port}
	      // - certificate-serial-number{:port}
              // - IPv4-address{:port}
              // - IPv6-address{:port}
	      // where items within {} are optional.
	      //
	      // Check for IPv6 addresses first. It reduces the amount
	      // of checking necessary for certificate serial numbers.
	      compile_server_info server_info;
	      vector<compile_server_info> resolved_servers;
	      if (isIPv6 (server, server_info)
		  || isIPv4 (server, server_info)
		  || isCertSerialNumber (server, server_info))
		{
		  // An address or cert serial number has been specified.
		  // No resolution is needed.
		  resolved_servers.push_back (server_info);
		}		  
	      else if (isDomain (server, server_info))
		{
		  // Try to resolve the given name.
		  resolve_host (s, server_info, resolved_servers);
		}
	      else
		{
		  clog << _F("Invalid server specification: %s", server.c_str())
		       << endl;
		  continue;
		}

	      // Now examine the server(s) identified and add them to
	      // the list of specified servers.
	      vector<compile_server_info> known_servers;
	      vector<compile_server_info> new_servers;
	      for (auto i = resolved_servers.begin();
		   i != resolved_servers.end();
		   ++i)
		{
		  // If this item was fully specified, then just add it.
		  if (i->fully_specified || ! s.http_servers.empty ()) {
		    // In this instance, "fully specified" means
		    // address and port. At this point we haven't
		    // tried to contact the server to get online
		    // information, certificate information,
		    // etc. Certain server types need us to connect to
		    // the server directly to get this information.
		    // Assume http servers are fully specified
		    if (backend)
		      backend->fill_in_server_info (*i);
		    nss_add_server_info (*i, new_servers);
		  }
		  else {
		    // It was not fully specified, so we need additional info. Try
		    // to get it by matching what we have against other known servers.
		    if (known_servers.empty ())
		      nss_get_all_server_info (s, known_servers);

		    // See if this server spec matches that of a known server
		    vector<compile_server_info> matched_servers = known_servers;
		    nss_keep_common_server_info (*i, matched_servers);

		    // If this server spec matches one or more known servers, then add the
		    // augmented info to the specified_servers. Otherwise, if this server
		    // spec is complete, then add it directly. Otherwise this server spec
		    // is incomplete.
		    if (! matched_servers.empty())
		      nss_add_server_info (matched_servers, new_servers);
		    else if (i->isComplete ())
		      nss_add_server_info (*i, new_servers);
		    else if (s.verbose >= 3)
		      clog << _("Incomplete server spec: ") << *i << endl;
		  }
		}

	      if (s.verbose >= 3)
		{
		  clog << _F("Servers matching %s: ", server.c_str()) << endl;
		  clog << new_servers;
		}

	      // Add the newly identified servers to the list.
	      if (! new_servers.empty())
		nss_add_server_info (new_servers, specified_servers);
	    } // Loop over --use-server options
	} // -- use-server specified

      if (s.verbose >= 2)
	{
	  clog << _("All specified servers:") << endl;
	  clog << specified_servers;
	}
    } // Server information is not cached

  // Add the information, but not duplicates.
  nss_add_server_info (specified_servers, servers);
}

void
nss_get_or_keep_trusted_server_info (
  systemtap_session &s,
  vector<compile_server_info> &servers,
  bool keep
)
{
  // If we're filtering the list and it's already empty, then
  // there's nothing to do.
  if (keep && servers.empty ())
    return;

  // We only need to obtain this once per session. This is a good thing(tm)
  // since obtaining this information is expensive.
  vector<compile_server_info>& trusted_servers = cscache(s)->trusted_servers;
  if (trusted_servers.empty ())
    {
      // Maintain an empty entry to indicate that this search has been
      // performed, in case the search comes up empty.
      trusted_servers.push_back (compile_server_info ());

      // Check the private database first.
      string cert_db_path = private_ssl_cert_db_path ();
      get_server_info_from_db (s, trusted_servers, cert_db_path);

      // Now check the global database.
      cert_db_path = global_ssl_cert_db_path ();
      get_server_info_from_db (s, trusted_servers, cert_db_path);

      if (s.verbose >= 5)
	{
	  clog << _("All servers trusted as ssl peers:") << endl;
	  clog << trusted_servers;
	}
    } // Server information is not cached

  if (keep)
    {
      // Filter the existing vector by keeping the information in common with
      // the trusted_server vector.
      nss_keep_common_server_info (trusted_servers, servers);
    }
  else
    {
      // Add the information, but not duplicates.
      nss_add_server_info (trusted_servers, servers);
    }
}

void
nss_get_or_keep_signing_server_info (
  systemtap_session &s,
  vector<compile_server_info> &servers,
  bool keep
)
{
  // If we're filtering the list and it's already empty, then
  // there's nothing to do.
  if (keep && servers.empty ())
    return;

  // We only need to obtain this once per session. This is a good thing(tm)
  // since obtaining this information is expensive.
  vector<compile_server_info>& signing_servers = cscache(s)->signing_servers;
  if (signing_servers.empty ())
    {
      // Maintain an empty entry to indicate that this search has been
      // performed, in case the search comes up empty.
      signing_servers.push_back (compile_server_info ());

      // For all users, check the global database.
      string cert_db_path = signing_cert_db_path ();
      get_server_info_from_db (s, signing_servers, cert_db_path);

      if (s.verbose >= 5)
	{
	  clog << _("All servers trusted as module signers:") << endl;
	  clog << signing_servers;
	}
    } // Server information is not cached

  if (keep)
    {
      // Filter the existing vector by keeping the information in common with
      // the signing_server vector.
      nss_keep_common_server_info (signing_servers, servers);
    }
  else
    {
      // Add the information, but not duplicates.
      nss_add_server_info (signing_servers, servers);
    }
}

void
nss_get_or_keep_compatible_server_info (
  systemtap_session &s,
  vector<compile_server_info> &servers,
  bool keep
)
{
#if HAVE_AVAHI
  // If we're filtering the list and it's already empty, then
  // there's nothing to do.
  if (keep && servers.empty ())
    return;

  // Remove entries for servers incompatible with the host environment
  // from the given list of servers.
  // A compatible server compiles for the kernel release and architecture
  // of the host environment.
  //
  // Compatibility can only be determined for online servers. So, augment
  // and filter the information we have with information for online servers.
  vector<compile_server_info> online_servers;
  nss_get_or_keep_online_server_info (s, online_servers, false/*keep*/);
  if (keep)
    nss_keep_common_server_info (online_servers, servers);
  else
    nss_add_server_info (online_servers, servers);

  // Now look to see which ones are compatible.
  // The vector can change size as we go, so be careful!!
  for (unsigned i = 0; i < servers.size (); /**/)
    {
      // Retain empty entries.
      assert (! servers[i].empty ());

      // Check the target of the server.
      if (servers[i].sysinfo != s.kernel_release + " " + s.architecture
	  && servers[i].sysinfo != s.architecture)
	{
	  // Target platform mismatch.
	  if (s.verbose > 3)
	    clog << "Rejected server (platform): " << servers[i] << endl;
	  servers.erase (servers.begin () + i);
	  continue;
	}
  
      // If the client requires secure boot signing, make sure the
      // server has the right MOK.
      if (! s.mok_fingerprints.empty ())
        {
	  // Make sure the server has at least one MOK in common with
	  // the client.
	  vector<string>::const_iterator it;
	  bool mok_found = false;
	  for (it = s.mok_fingerprints.begin(); it != s.mok_fingerprints.end(); it++)
	    {
	      if ((*it == "missing") || // PR26665: see also session.cxx check_options()
		  find(servers[i].mok_fingerprints.begin(),
		       servers[i].mok_fingerprints.end(), *it)
		  != servers[i].mok_fingerprints.end ())
	        {
		  mok_found = true;
		  break;
		}
	    }
	  
	  // This server has no MOK in common with the client.
	  if (! mok_found)
	    {
	      if (s.verbose > 3)
		clog << "Rejected server (common mok): " << servers[i] << endl;
	      servers.erase (servers.begin () + i);
	      continue;
	    }
	}

      // The server is compatible. Leave it in the list.
      if (s.verbose > 3)
	clog << "Accepted server: " << servers[i] << endl;
      ++i;
    }
#else // ! HAVE_AVAHI
  // Without Avahi, we can't obtain the target platform of the server.
  // Issue a warning.
  if (s.verbose >= 2)
    clog << _("Unable to detect server compatibility without avahi") << endl;
  if (keep)
    servers.clear ();
#endif
}

void
nss_keep_server_info_with_cert_and_port (
  systemtap_session &,
  const compile_server_info &server,
  vector<compile_server_info> &servers
)
{
  assert (! server.certinfo.empty ());

  // Search the list of servers for ones matching the
  // serial number specified.
  // The vector can change size as we go, so be careful!!
  for (unsigned i = 0; i < servers.size (); /**/)
    {
      // Retain empty entries.
      if (servers[i].empty ())
	{
	  ++i;
	  continue;
	}
      if (servers[i].certinfo == server.certinfo &&
	  (servers[i].port == 0 || server.port == 0 ||
	   servers[i].port == server.port))
	{
	  // If the server is not online, then use the specified
	  // port, if any.
	  if (servers[i].port == 0)
	    {
	      servers[i].port = server.port;
	      servers[i].fully_specified = server.fully_specified;
	    }
	  ++i;
	  continue;
	}
      // The item does not match. Delete it.
      servers.erase (servers.begin () + i);
    }
}

// Obtain missing host name or ip address, if any. Return 0 on success.
static void
resolve_host (
  systemtap_session& s,
  compile_server_info &server,
  vector<compile_server_info> &resolved_servers
)
{
  vector<resolved_host>& cached_hosts = cscache(s)->resolved_hosts[server.host_name];
  if (cached_hosts.empty ())
    {
      // The server's host_name member is a string containing either a host name or an ip address.
      // Either is acceptable for lookup.
      const char *lookup_name = server.host_name.c_str();
      if (s.verbose >= 6)
	clog << _F("Looking up %s", lookup_name) << endl;

      struct addrinfo hints;
      memset(& hints, 0, sizeof (hints));
      hints.ai_family = AF_UNSPEC; // AF_INET or AF_INET6 to force version
      struct addrinfo *addr_info = 0;
      int rc = getaddrinfo (lookup_name, NULL, & hints, & addr_info);

      // Failure to resolve will result in an appropriate message later, if other methods fail.
      if (rc != 0)
	{
	  if (s.verbose >= 6)
	    clog << _F("%s not found: %s", lookup_name, gai_strerror (rc)) << endl;
	}
      else
	{
	  // Loop over the results collecting information.
	  assert (addr_info);
	  for (const struct addrinfo *ai = addr_info; ai != NULL; ai = ai->ai_next)
	    {
	      PRNetAddr new_address;

	      // We support IPv4 and IPv6, Ignore other protocols,
	      if (ai->ai_family == AF_INET)
		{
		  // IPv4 Address
		  struct sockaddr_in *ip = (struct sockaddr_in *)ai->ai_addr;
		  new_address.inet.family = PR_AF_INET;
		  new_address.inet.ip = ip->sin_addr.s_addr;
		}
	      else if (ai->ai_family == AF_INET6)
		{
		  // IPv6 Address
		  struct sockaddr_in6 *ip = (struct sockaddr_in6 *)ai->ai_addr;
		  new_address.ipv6.family = PR_AF_INET6;
		  new_address.ipv6.scope_id = ip->sin6_scope_id;
		  copyAddress (new_address.ipv6.ip, ip->sin6_addr);
		}
	      else
		continue;

	      // Try to obtain a host name. Otherwise, leave it empty.
	      char hbuf[NI_MAXHOST];
	      int status = getnameinfo (ai->ai_addr, ai->ai_addrlen, hbuf, sizeof (hbuf), NULL, 0,
					NI_NAMEREQD | NI_IDN);
	      if (status != 0)
		hbuf[0] = '\0';

	      cached_hosts.push_back(resolved_host(hbuf, new_address));
	    }
	}
      if (addr_info)
	freeaddrinfo (addr_info); // free the linked list
    }

  // If no addresses were resolved, then return the info we were given.
  if (cached_hosts.empty())
    nss_add_server_info (server, resolved_servers);
  else {
    // We will add a new server for each address resolved
    vector<compile_server_info> new_servers;
    for (vector<resolved_host>::const_iterator it = cached_hosts.begin();
	 it != cached_hosts.end(); ++it)
      {
	// Start with the info we were given
	compile_server_info new_server = server;

	// NB: do not overwrite port info
	if (it->address.raw.family == AF_INET)
	  {
	    new_server.address.inet.family = PR_AF_INET;
	    new_server.address.inet.ip = it->address.inet.ip;
	  }
	else // AF_INET6
	  {
	    new_server.address.ipv6.family = PR_AF_INET6;
	    new_server.address.ipv6.scope_id = it->address.ipv6.scope_id;
	    new_server.address.ipv6.ip = it->address.ipv6.ip;
	  }
	if (!it->host_name.empty())
	  {
	    new_server.unresolved_host_name = new_server.host_name;
	    new_server.host_name = it->host_name;
	  }
	nss_add_server_info (new_server, new_servers);
      }

    if (s.verbose >= 6)
      {
	clog << _F("%s resolves to:", server.host_name.c_str()) << endl;
	clog << new_servers;
      }

    nss_add_server_info (new_servers, resolved_servers);
  }
}

#if HAVE_AVAHI
// Avahi API Callbacks.
//-----------------------------------------------------------------------
struct browsing_context {
  AvahiSimplePoll *simple_poll;
  AvahiClient *client;
  vector<compile_server_info> *servers;
};

// Get the value of the requested key from the Avahi string list.
static string
get_value_from_avahi_string_list (AvahiStringList *strlst, const string &key)
{
  AvahiStringList *p = avahi_string_list_find (strlst, key.c_str ());
  if (p == NULL)
    {
      // Key not found.
      return "";
    }
  
  char *k, *v;
  int rc = avahi_string_list_get_pair(p, &k, &v, NULL);
  if (rc < 0 || v == NULL)
    {
      avahi_free (k);
      return "";
    }

  string value = v;
  avahi_free (k);
  avahi_free (v);
  return value;
}

// Get a vector of values of the requested key from the Avahi string
// list. This is for multiple values having the same key.
static void
get_values_from_avahi_string_list (AvahiStringList *strlst, const string &key,
				   vector<string> &value_vector)
{
  AvahiStringList *p;

  value_vector.clear();
  p = avahi_string_list_find (strlst, key.c_str ());
  for (; p != NULL; p = avahi_string_list_get_next(p))
    {
      char *k, *v;
      int rc = avahi_string_list_get_pair(p, &k, &v, NULL);
      if (rc < 0 || v == NULL)
        {
	  avahi_free (k);
	  break;
	}

      value_vector.push_back(v);
      avahi_free (k);
      avahi_free (v);
    }
  return;
}

extern "C"
void resolve_callback(
    AvahiServiceResolver *r,
    AvahiIfIndex interface,
    AvahiProtocol protocol,
    AvahiResolverEvent event,
    const char *name,
    const char *type,
    const char *domain,
    const char *host_name,
    const AvahiAddress *address,
    uint16_t port,
    AvahiStringList *txt,
    AvahiLookupResultFlags /*flags*/,
    AVAHI_GCC_UNUSED void* userdata)
 {
   PRStatus prStatus;

    assert(r);
    const browsing_context *context = (browsing_context *)userdata;
    vector<compile_server_info> *servers = context->servers;

    // Called whenever a service has been resolved successfully or timed out.

    switch (event) {
        case AVAHI_RESOLVER_FAILURE:
	  clog << _F("Failed to resolve service '%s' of type '%s' in domain '%s': %s",
		     name, type, domain,
		     avahi_strerror(avahi_client_errno(avahi_service_resolver_get_client(r)))) << endl;
	  break;

        case AVAHI_RESOLVER_FOUND: {
	    compile_server_info info;

	    // Decode the address.
            char a[AVAHI_ADDRESS_STR_MAX];
            avahi_address_snprint(a, sizeof(a), address);
	    prStatus = PR_StringToNetAddr (a, & info.address);
	    if (prStatus != PR_SUCCESS) {
	      clog << _F("Invalid address '%s' from avahi", a) << endl;
	      break;
	    }
  
	    // We support both IPv4 and IPv6. Ignore other protocols.
	    if (protocol == AVAHI_PROTO_INET6) {
	      info.address.ipv6.family = PR_AF_INET6;
	      info.address.ipv6.scope_id = interface;
	      info.port = port;
	    }
	    else if (protocol == AVAHI_PROTO_INET) {
	      info.address.inet.family = PR_AF_INET;
	      info.port = port;
	    }
	    else
	      break;

	    // Save the host name.
	    info.host_name = host_name;

	    // Save the text tags.
	    info.sysinfo = get_value_from_avahi_string_list (txt, "sysinfo");
	    info.certinfo = get_value_from_avahi_string_list (txt, "certinfo");
	    info.version = get_value_from_avahi_string_list (txt, "version");
	    if (info.version.empty ())
	      info.version = "1.0"; // default version is 1.0

	    // The server might provide one or more MOK certificate's
	    // info.
	    get_values_from_avahi_string_list(txt, "mok_info",
					      info.mok_fingerprints);

	    // Add this server to the list of discovered servers.
	    nss_add_server_info (info, *servers);
	    break;
          }
        default:
          break;
    }

    avahi_service_resolver_free(r);
}

extern "C"
void browse_callback(
    AvahiServiceBrowser *b,
    AvahiIfIndex interface,
    AvahiProtocol protocol,
    AvahiBrowserEvent event,
    const char *name,
    const char *type,
    const char *domain,
    AVAHI_GCC_UNUSED AvahiLookupResultFlags flags,
    void* userdata) {
    
    browsing_context *context = (browsing_context *)userdata;
    AvahiClient *c = context->client;
    AvahiSimplePoll *simple_poll = context->simple_poll;
    assert(b);

    // Called whenever a new services becomes available on the LAN or is removed from the LAN.

    switch (event) {
        case AVAHI_BROWSER_FAILURE:
	    clog << _F("Avahi browse failed: %s",
	          avahi_strerror(avahi_client_errno(avahi_service_browser_get_client(b))))
                 << endl;
	    avahi_simple_poll_quit(simple_poll);
	    break;

        case AVAHI_BROWSER_NEW:
	    // We ignore the returned resolver object. In the callback
	    // function we free it. If the server is terminated before
	    // the callback function is called the server will free
	    // the resolver for us.
            if (!(avahi_service_resolver_new(c, interface, protocol, name, type, domain,
					     AVAHI_PROTO_UNSPEC, (AvahiLookupFlags)0, resolve_callback, context))) {
             clog << _F("Failed to resolve service '%s': %s",
                     name, avahi_strerror(avahi_client_errno(c))) << endl;
	    }
            break;

        case AVAHI_BROWSER_REMOVE:
        case AVAHI_BROWSER_ALL_FOR_NOW:
        case AVAHI_BROWSER_CACHE_EXHAUSTED:
            break;
    }
}

extern "C"
void client_callback(AvahiClient *c, AvahiClientState state, AVAHI_GCC_UNUSED void * userdata) {
    assert(c);
    browsing_context *context = (browsing_context *)userdata;
    AvahiSimplePoll *simple_poll = context->simple_poll;

    // Called whenever the client or server state changes.

    if (state == AVAHI_CLIENT_FAILURE) {
        clog << _F("Avahi Server connection failure: %s", avahi_strerror(avahi_client_errno(c))) << endl;
        avahi_simple_poll_quit(simple_poll);
    }
}

extern "C"
void timeout_callback(AVAHI_GCC_UNUSED AvahiTimeout *e, AVAHI_GCC_UNUSED void *userdata) {
  browsing_context *context = (browsing_context *)userdata;
  AvahiSimplePoll *simple_poll = context->simple_poll;
  avahi_simple_poll_quit(simple_poll);
}
#endif // HAVE_AVAHI

void
nss_get_or_keep_online_server_info (
  systemtap_session &s,
  vector<compile_server_info> &servers,
  bool keep
)
{
  // If we're filtering the list and it's already empty, then
  // there's nothing to do.
  if (keep && servers.empty ())
    return;

  // We only need to obtain this once per session. This is a good thing(tm)
  // since obtaining this information is expensive.
  vector<compile_server_info>& online_servers = cscache(s)->online_servers;
  if (online_servers.empty () && s.http_servers.empty ())
    {
      // Maintain an empty entry to indicate that this search has been
      // performed, in case the search comes up empty.
      online_servers.push_back (compile_server_info ());
#if HAVE_AVAHI
      // Must predeclare these due to jumping on error to fail:
      vector<compile_server_info> avahi_servers;

      // Initialize.
      AvahiClient *client = NULL;
      AvahiServiceBrowser *sb = NULL;
 
      // Allocate main loop object.
      AvahiSimplePoll *simple_poll;
      if (!(simple_poll = avahi_simple_poll_new()))
	{
	  clog << _("Failed to create Avahi simple poll object") << endl;
	  goto fail;
	}
      browsing_context context;
      context.simple_poll = simple_poll;
      context.servers = & avahi_servers;

      // Allocate a new Avahi client
      int error;
      client = avahi_client_new (avahi_simple_poll_get (simple_poll),
				 (AvahiClientFlags)0,
				 client_callback, & context, & error);

      // Check whether creating the client object succeeded.
      if (! client)
	{
         clog << _F("Failed to create Avahi client: %s",
                    avahi_strerror(error)) << endl;
	  goto fail;
	}
      context.client = client;
    
      // Create the service browser.
      if (!(sb = avahi_service_browser_new (client, AVAHI_IF_UNSPEC,
					    AVAHI_PROTO_UNSPEC, "_stap._tcp",
					    NULL, (AvahiLookupFlags)0,
					    browse_callback, & context)))
	{
         clog << _F("Failed to create Avahi service browser: %s",
                     avahi_strerror(avahi_client_errno(client))) << endl;
	  goto fail;
	}

      // Timeout after 0.5 seconds.
      struct timeval tv;
      avahi_simple_poll_get(simple_poll)->timeout_new(
        avahi_simple_poll_get(simple_poll),
	avahi_elapse_time(&tv, 1000/2, 0),
	timeout_callback,
	& context);

      // Run the main loop.
      avahi_simple_poll_loop(simple_poll);

      if (s.verbose >= 6)
	{
	  clog << _("Avahi reports the following servers online:") << endl;
	  clog << avahi_servers;
	}

      // Merge with the list of servers, as obtained by avahi.
      nss_add_server_info (avahi_servers, online_servers);

    fail:
      // Cleanup.
      if (client) {
	// Also frees the service browser
        avahi_client_free(client);
      }
      if (simple_poll)
        avahi_simple_poll_free(simple_poll);
#else // ! HAVE_AVAHI
      // Without Avahi, we can't detect online servers. Issue a warning.
      if (s.verbose >= 2)
	clog << _("Unable to detect online servers without avahi") << endl;
#endif // ! HAVE_AVAHI

      if (s.verbose >= 5)
	{
	  clog << _("All online servers:") << endl;
	  clog << online_servers;
	}
    } // Server information is not cached.

  if (!s.http_servers.empty ())
    {
      // http server does not depend on avahi, so discover which servers are online by
      // getting a list of potential servers and trying to connect to them
      vector<compile_server_info>& specified_servers = cscache(s)->specified_servers;

      nss_get_specified_server_info (s, specified_servers);

      for (vector<compile_server_info>::const_iterator i = specified_servers.begin ();
           i != specified_servers.end ();
           ++i)
        {
	  client_backend *backend = nss_get_client_backend (s);
	  if (backend)
	    backend->fill_in_server_info ((compile_server_info&)*i);
        }
    }

  if (keep)
    {
      // Filter the existing vector by keeping the information in common with
      // the online_server vector.
      nss_keep_common_server_info (online_servers, servers);
    }
  else
    {
      // Add the information, but not duplicates.
      nss_add_server_info (online_servers, servers);
    }
}

// Add server info to a list, avoiding duplicates. Merge information from
// two duplicate items.
void
nss_add_server_info (
  const compile_server_info &info, vector<compile_server_info>& target
)
{
  if (info.empty ())
    return;

  bool found = false;
  for (vector<compile_server_info>::iterator i = target.begin ();
       i != target.end ();
       ++i)
    {
      if (info == *i)
	{
	  // Duplicate. Merge the two items.
	  merge_server_info (info, *i);
	  found = true;
	}
    }
  if (! found)
    target.push_back (info);
}

// Add server info from one vector to another.
void
nss_add_server_info (
  const vector<compile_server_info> &source,
  vector<compile_server_info> &target
)
{
  for (vector<compile_server_info>::const_iterator i = source.begin ();
       i != source.end ();
       ++i)
    {
      nss_add_server_info (*i, target);
    }
}

// Filter the vector by keeping information in common with the item.
void
nss_keep_common_server_info (
  const	compile_server_info &info_to_keep,
  vector<compile_server_info> &filtered_info
)
{
  assert (! info_to_keep.empty ());

  // The vector may change size as we go. Be careful!!
  for (unsigned i = 0; i < filtered_info.size (); /**/)
    {
      // Retain empty entries.
      if (filtered_info[i].empty ())
	{
	  ++i;
	  continue;
	}
      if (info_to_keep == filtered_info[i])
	{
	  merge_server_info (info_to_keep, filtered_info[i]);
	  ++i;
	  continue;
	}
      // The item does not match. Delete it.
      filtered_info.erase (filtered_info.begin () + i);
      continue;
    }
}

// Filter the second vector by keeping information in common with the first
// vector.
void
nss_keep_common_server_info (
  const	vector<compile_server_info> &info_to_keep,
  vector<compile_server_info> &filtered_info
)
{
  // The vector may change size as we go. Be careful!!
  for (unsigned i = 0; i < filtered_info.size (); /**/)
    {
      // Retain empty entries.
      if (filtered_info[i].empty ())
	{
	  ++i;
	  continue;
	}
      bool found = false;
      for (unsigned j = 0; j < info_to_keep.size (); ++j)
	{
	  if (filtered_info[i] == info_to_keep[j])
	    {
	      merge_server_info (info_to_keep[j], filtered_info[i]);
	      found = true;
	    }
	}

      // If the item was not found. Delete it. Otherwise, advance to the next
      // item.
      if (found)
	++i;
      else
	filtered_info.erase (filtered_info.begin () + i);
    }
}

// Merge two compile server info items.
static void
merge_server_info (
  const compile_server_info &source,
  compile_server_info &target
)
{
  // Copy the host name if the source has one.
  if (! source.host_name.empty())
    target.host_name = source.host_name;
  // Copy the address unconditionally, if the source has an address, even if they are already
  // equal. The source address may be an IPv6 address with a scope_id that the target is missing.
  assert (! target.hasAddress () || ! source.hasAddress () || source.address == target.address);
  if (source.hasAddress ())
    copyNetAddr (target.address, source.address);
  if (target.port == 0)
    {
      target.port = source.port;
      target.fully_specified = source.fully_specified;
    }
  if (target.sysinfo.empty ())
    target.sysinfo = source.sysinfo;
  if (target.version.empty ())
    target.version = source.version;
  if (target.certinfo.empty ())
    target.certinfo = source.certinfo;
}

void
nss_add_online_server_info (systemtap_session &s,
			    const compile_server_info &info)
{
  nss_add_server_info (info, cscache(s)->online_servers);
}
#endif // HAVE_NSS

/* vim: set sw=2 ts=8 cino=>4,n-2,{2,^-2,t0,(0,u0,w1,M1 : */