refactoring dns service to take stub code into separate library for use in gns2dns proxy

1 files changed, 520 insertions, 0 deletions

diff --git a/src/dns/dnsstub.c b/src/dns/dnsstub.c
new file mode 100644
index 000000000..383b1d699
--- /dev/null
+++ b/src/dns/dnsstub.c
@@ -0,0 +1,520 @@
+/*
+     This file is part of GNUnet.
+     (C) 2012 Christian Grothoff (and other contributing authors)
+
+     GNUnet 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, or (at your
+     option) any later version.
+
+     GNUnet 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 GNUnet; see the file COPYING.  If not, write to the
+     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+     Boston, MA 02111-1307, USA.
+*/
+/**
+ * @file dns/dnsstub.c
+ * @brief DNS stub resolver which sends DNS requests to an actual resolver
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include "gnunet_util_lib.h"
+#include "gnunet_dnsstub_lib.h"
+
+/**
+ * Timeout for an external (Internet-DNS) DNS resolution
+ */
+#define REQUEST_TIMEOUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 5)
+
+/**
+ * How many DNS sockets do we open at most at the same time?
+ * (technical socket maximum is this number x2 for IPv4+IPv6)
+ */
+#define DNS_SOCKET_MAX 128
+
+
+/**
+ * UDP socket we are using for sending DNS requests to the Internet.
+ */
+struct GNUNET_DNSSTUB_RequestSocket
+{
+  
+  /**
+   * UDP socket we use for this request for IPv4
+   */
+  struct GNUNET_NETWORK_Handle *dnsout4;
+
+  /**
+   * UDP socket we use for this request for IPv6
+   */
+  struct GNUNET_NETWORK_Handle *dnsout6;
+
+  /**
+   * Function to call with result.
+   */
+  GNUNET_DNSSTUB_ResultCallback rc;
+
+  /**
+   * Closure for 'rc'.
+   */
+  void *rc_cls;
+
+  /**
+   * Task for reading from dnsout4 and dnsout6.
+   */
+  GNUNET_SCHEDULER_TaskIdentifier read_task;
+
+  /**
+   * When should this request time out?
+   */
+  struct GNUNET_TIME_Absolute timeout;
+
+  /**
+   * Address we sent the DNS request to.
+   */
+  struct sockaddr_storage addr;
+
+  /**
+   * Number of bytes in 'addr'.
+   */
+  socklen_t addrlen;
+
+};
+
+
+struct GNUNET_DNSSTUB_Context
+{
+
+  /**
+   * Array of all open sockets for DNS requests. 
+   */
+  struct GNUNET_DNSSTUB_RequestSocket sockets[DNS_SOCKET_MAX];
+
+  /**
+   * IP address to use for the DNS server if we are a DNS exit service
+   * (for VPN via mesh); otherwise NULL.
+   */
+  char *dns_exit;
+};
+
+
+
+/**
+ * We're done with a GNUNET_DNSSTUB_RequestSocket, close it for now.
+ *
+ * @param rs request socket to clean up
+ */
+static void
+cleanup_rs (struct GNUNET_DNSSTUB_RequestSocket *rs)
+{
+  if (NULL != rs->dnsout4)
+  {
+    GNUNET_NETWORK_socket_close (rs->dnsout4);
+    rs->dnsout4 = NULL;
+  }
+  if (NULL != rs->dnsout6)
+  {
+    GNUNET_NETWORK_socket_close (rs->dnsout6);
+    rs->dnsout6 = NULL;
+  }
+  if (GNUNET_SCHEDULER_NO_TASK != rs->read_task)
+  {
+    GNUNET_SCHEDULER_cancel (rs->read_task);
+    rs->read_task = GNUNET_SCHEDULER_NO_TASK;
+  }
+}
+
+
+/**
+ * Open source port for sending DNS requests
+ *
+ * @param af AF_INET or AF_INET6
+ * @return GNUNET_OK on success
+ */ 
+static struct GNUNET_NETWORK_Handle *
+open_socket (int af)
+{
+  struct sockaddr_in a4;
+  struct sockaddr_in6 a6;
+  struct sockaddr *sa;
+  socklen_t alen;
+  struct GNUNET_NETWORK_Handle *ret;
+
+  ret = GNUNET_NETWORK_socket_create (af, SOCK_DGRAM, 0);
+  if (NULL == ret)
+    return NULL;
+  switch (af)
+  {
+  case AF_INET:
+    memset (&a4, 0, alen = sizeof (struct sockaddr_in));
+    sa = (struct sockaddr *) &a4;
+    break;
+  case AF_INET6:
+    memset (&a6, 0, alen = sizeof (struct sockaddr_in6));
+    sa = (struct sockaddr *) &a6;
+    break;
+  default:
+    GNUNET_break (0);
+    GNUNET_NETWORK_socket_close (ret);
+    return NULL;
+  }
+  sa->sa_family = af;
+  if (GNUNET_OK != GNUNET_NETWORK_socket_bind (ret,
+                                               sa, 
+                                               alen))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR, 
+                _("Could not bind to any port: %s\n"),
+                STRERROR (errno));
+    GNUNET_NETWORK_socket_close (ret);
+    return NULL;
+  }
+  return ret;
+}
+
+
+/**
+ * Read a DNS response from the (unhindered) UDP-Socket
+ *
+ * @param cls socket to read from
+ * @param tc scheduler context (must be shutdown or read ready)
+ */
+static void
+read_response (void *cls,
+               const struct GNUNET_SCHEDULER_TaskContext *tc);
+
+
+/**
+ * Get a socket of the specified address family to send out a
+ * UDP DNS request to the Internet.  
+ *
+ * @param af desired address family
+ * @return NULL on error (given AF not "supported")
+ */
+static struct GNUNET_DNSSTUB_RequestSocket *
+get_request_socket (struct GNUNET_DNSSTUB_Context *ctx,
+                    int af)
+{
+  struct GNUNET_DNSSTUB_RequestSocket *rs;
+  struct GNUNET_NETWORK_FDSet *rset;
+
+  rs = &ctx->sockets[GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_NONCE, 
+                                               DNS_SOCKET_MAX)];
+  rs->timeout = GNUNET_TIME_relative_to_absolute (REQUEST_TIMEOUT);
+  switch (af)
+  {
+  case AF_INET:
+    if (NULL == rs->dnsout4)
+      rs->dnsout4 = open_socket (AF_INET);
+    break;
+  case AF_INET6:
+    if (NULL == rs->dnsout6)
+      rs->dnsout6 = open_socket (AF_INET6);
+    break;
+  default:
+    return NULL;
+  }  
+  if (GNUNET_SCHEDULER_NO_TASK != rs->read_task)
+  {
+    GNUNET_SCHEDULER_cancel (rs->read_task);
+    rs->read_task = GNUNET_SCHEDULER_NO_TASK;
+  }
+  if ( (NULL == rs->dnsout4) &&
+       (NULL == rs->dnsout6) )
+    return NULL;
+  rset = GNUNET_NETWORK_fdset_create ();
+  if (NULL != rs->dnsout4)
+    GNUNET_NETWORK_fdset_set (rset, rs->dnsout4);
+  if (NULL != rs->dnsout6)
+    GNUNET_NETWORK_fdset_set (rset, rs->dnsout6);
+  rs->read_task = GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
+                                               REQUEST_TIMEOUT,
+                                               rset,
+                                               NULL,
+                                               &read_response, rs);
+  GNUNET_NETWORK_fdset_destroy (rset);
+  return rs;
+}
+
+
+/**
+ * Perform DNS resolution.
+ *
+ * @param ctx stub resolver to use
+ * @param af address family to use
+ * @param request DNS request to transmit
+ * @param request_len number of bytes in msg
+ * @param rc function to call with result
+ * @param rc_cls closure for 'rc'
+ * @return socket used for the request, NULL on error
+ */
+struct GNUNET_DNSSTUB_RequestSocket *
+GNUNET_DNSSTUB_resolve (struct GNUNET_DNSSTUB_Context *ctx,
+                        const struct sockaddr *sa,
+                        socklen_t sa_len,
+                        const void *request,
+                        size_t request_len,
+                        GNUNET_DNSSTUB_ResultCallback rc,
+                        void *rc_cls)
+{
+  struct GNUNET_DNSSTUB_RequestSocket *rs;
+  struct GNUNET_NETWORK_Handle *ret;
+  int af;
+
+  af = sa->sa_family;
+  if (NULL == (rs = get_request_socket (ctx, af)))
+    return NULL;
+  if (NULL != rs->dnsout4)
+    ret = rs->dnsout4;
+  else
+    ret = rs->dnsout6;
+  GNUNET_assert (NULL != ret);
+  rs->rc = rc;
+  rs->rc_cls = rc_cls;
+  GNUNET_NETWORK_socket_sendto (ret,
+                                request,
+                                request_len,
+                                sa,
+                                sa_len);
+  return rs;
+}
+
+
+/**
+ * Perform DNS resolution using our default IP from init.
+ *
+ * @param ctx stub resolver to use
+ * @param request DNS request to transmit
+ * @param request_len number of bytes in msg
+ * @param rc function to call with result
+ * @param rc_cls closure for 'rc'
+ * @return socket used for the request, NULL on error
+ */
+struct GNUNET_DNSSTUB_RequestSocket *
+GNUNET_DNSSTUB_resolve2 (struct GNUNET_DNSSTUB_Context *ctx,
+                         const void *request,
+                         size_t request_len,
+                         GNUNET_DNSSTUB_ResultCallback rc,
+                         void *rc_cls)
+{
+  int af;
+  struct sockaddr_in v4;
+  struct sockaddr_in6 v6;
+  struct sockaddr *so;
+  socklen_t salen;
+  struct GNUNET_NETWORK_Handle *dnsout;
+  struct GNUNET_DNSSTUB_RequestSocket *rs;
+
+  memset (&v4, 0, sizeof (v4));
+  memset (&v6, 0, sizeof (v6));
+  if (1 == inet_pton (AF_INET, ctx->dns_exit, &v4.sin_addr))
+  {
+    salen = sizeof (v4);
+    v4.sin_family = AF_INET;
+    v4.sin_port = htons (53);
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    v4.sin_len = (u_char) salen;
+#endif
+    so = (struct sockaddr *) &v4;
+    af = AF_INET;
+  }
+  else if (1 == inet_pton (AF_INET6, ctx->dns_exit, &v6.sin6_addr))
+  {
+    salen = sizeof (v6);
+    v6.sin6_family = AF_INET6;
+    v6.sin6_port = htons (53);
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    v6.sin6_len = (u_char) salen;
+#endif
+    so = (struct sockaddr *) &v6;
+    af = AF_INET6;
+  }  
+  else
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  if (NULL == (rs = get_request_socket (ctx, af)))
+    return NULL;
+  if (NULL != rs->dnsout4)
+    dnsout = rs->dnsout4;
+  else
+    dnsout = rs->dnsout6;
+  if (NULL == dnsout)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                _("Configured DNS exit `%s' is not working / valid.\n"),
+                ctx->dns_exit);
+    return NULL;
+  }
+  memcpy (&rs->addr,
+          so,
+          salen);
+  rs->addrlen = salen;
+  GNUNET_NETWORK_socket_sendto (dnsout,
+                                request,
+                                request_len, so, salen); 
+  rs->timeout = GNUNET_TIME_relative_to_absolute (REQUEST_TIMEOUT);
+  
+  return rs;
+
+}
+
+
+/**
+ * Actually do the reading of a DNS packet from our UDP socket and see
+ * if we have a valid, matching, pending request.
+ *
+ * @param rs request socket with callback details
+ * @param dnsout socket to read from
+ * @return GNUNET_OK on success, GNUNET_NO on drop, GNUNET_SYSERR on IO-errors (closed socket)
+ */
+static int
+do_dns_read (struct GNUNET_DNSSTUB_RequestSocket *rs,
+             struct GNUNET_NETWORK_Handle *dnsout)
+{
+  struct sockaddr_storage addr;
+  socklen_t addrlen;
+  struct GNUNET_TUN_DnsHeader *dns;
+  ssize_t r;
+  int len;
+
+#ifndef MINGW
+  if (0 != ioctl (GNUNET_NETWORK_get_fd (dnsout), FIONREAD, &len))
+  {
+    /* conservative choice: */
+    len = UINT16_MAX;
+  }
+#else
+  /* port the code above? */
+  len = UINT16_MAX;
+#endif
+
+  {
+    unsigned char buf[len] GNUNET_ALIGN;
+
+    addrlen = sizeof (addr);
+    memset (&addr, 0, sizeof (addr));  
+    r = GNUNET_NETWORK_socket_recvfrom (dnsout, 
+                                        buf, sizeof (buf),
+                                        (struct sockaddr*) &addr, &addrlen);
+    if (-1 == r)
+    {
+      GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR, "recvfrom");
+      GNUNET_NETWORK_socket_close (dnsout);
+      return GNUNET_SYSERR;
+    }
+    if (sizeof (struct GNUNET_TUN_DnsHeader) > r)
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR, 
+                  _("Received DNS response that is too small (%u bytes)"),
+                  r);
+      return GNUNET_NO;
+    }
+    dns = (struct GNUNET_TUN_DnsHeader *) buf;
+    if ( (addrlen != rs->addrlen) ||
+         (0 != memcmp (&rs->addr,
+                       &addr,
+                       addrlen)) ||      
+       (0 == GNUNET_TIME_absolute_get_remaining (rs->timeout).rel_value) )
+      return GNUNET_NO;
+    rs->rc (rs->rc_cls,
+            rs,
+            dns,
+            r);
+  }  
+  return GNUNET_OK;
+}
+
+
+/**
+ * Read a DNS response from the (unhindered) UDP-Socket
+ *
+ * @param cls socket to read from
+ * @param tc scheduler context (must be shutdown or read ready)
+ */
+static void
+read_response (void *cls,
+               const struct GNUNET_SCHEDULER_TaskContext *tc)
+{
+  struct GNUNET_DNSSTUB_RequestSocket *rs = cls;
+  struct GNUNET_NETWORK_FDSet *rset;
+
+  rs->read_task = GNUNET_SCHEDULER_NO_TASK;
+  if (0 == (tc->reason & GNUNET_SCHEDULER_REASON_READ_READY))
+  {
+    /* timeout or shutdown */
+    cleanup_rs (rs);
+    return;
+  }
+  /* read and process ready sockets */
+  if ((NULL != rs->dnsout4) &&
+      (GNUNET_NETWORK_fdset_isset (tc->read_ready, rs->dnsout4)) &&
+      (GNUNET_SYSERR == do_dns_read (rs, rs->dnsout4)))
+    rs->dnsout4 = NULL;
+  if ((NULL != rs->dnsout6) &&
+      (GNUNET_NETWORK_fdset_isset (tc->read_ready, rs->dnsout6)) &&
+      (GNUNET_SYSERR == do_dns_read (rs, rs->dnsout6)))
+    rs->dnsout6 = NULL;
+
+  /* re-schedule read task */
+  rset = GNUNET_NETWORK_fdset_create ();
+  if (NULL != rs->dnsout4)
+    GNUNET_NETWORK_fdset_set (rset, rs->dnsout4);
+  if (NULL != rs->dnsout6)
+    GNUNET_NETWORK_fdset_set (rset, rs->dnsout6);
+  rs->read_task = GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
+                                               GNUNET_TIME_absolute_get_remaining (rs->timeout),
+                                               rset,
+                                               NULL,
+                                               &read_response, rs);
+  GNUNET_NETWORK_fdset_destroy (rset);
+}
+
+
+
+/**
+ * Start a DNS stub resolver.
+ *
+ * @param dns_ip target IP address to use
+ * @return NULL on error
+ */
+struct GNUNET_DNSSTUB_Context *
+GNUNET_DNSSTUB_start (const char *dns_ip)
+{
+  struct GNUNET_DNSSTUB_Context *ctx;
+  
+  ctx = GNUNET_malloc (sizeof (struct GNUNET_DNSSTUB_Context));
+  if (NULL != dns_ip)
+    ctx->dns_exit = GNUNET_strdup (dns_ip);
+  return ctx;
+}
+
+
+/**
+ * Cleanup DNSSTUB resolver.
+ *
+ * @param ctx stub resolver to clean up
+ */
+void
+GNUNET_DNSSTUB_stop (struct GNUNET_DNSSTUB_Context *ctx)
+{
+  unsigned int i;
+
+  for (i=0;i<=UINT16_MAX;i++)
+    cleanup_rs (&ctx->sockets[i]);
+  if (NULL != ctx->dns_exit)
+  {
+    GNUNET_free (ctx->dns_exit);
+    ctx->dns_exit = NULL;
+  }
+  GNUNET_free (ctx);
+}
+
+
+/* end of dnsstub.c */