android clat service

This software provides the nat 4->6 translation needed for the "clat" part of
the 464xlat standard.  It is needed for better IPv4 application support while
on an IPv6-only mobile network connection using 464xlat's nat64 (such as
T-Mobile's IPv6 trial).

A general diagram of how 464xlat works:
http://dan.drown.org/android/clat/Clat-Plat.png

Depends-on: I2392f8127dcd90d16b0f20ff31bcc5aa096db464
Change-Id: If2bc6916fc66fd4bca7cc241c83cfae839b82e15
Signed-off-by: Daniel Drown <dan-android@drown.org>

1 files changed, 91 insertions, 0 deletions

diff --git a/dns64.c b/dns64.c
new file mode 100644
index 0000000..ab662c7
--- /dev/null
+++ b/dns64.c
@@ -0,0 +1,91 @@
+/*
+ * Copyright 2011 Daniel Drown
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * dns64.c - find the nat64 prefix with a dns64 lookup
+ */
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <strings.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "dns64.h"
+#include "logging.h"
+
+/* function: plat_prefix
+ * looks up an ipv4-only hostname and looks for a nat64 /96 prefix, returns 1 on success, 0 on temporary failure, -1 on permanent failure
+ * ipv4_name - name to lookup
+ * prefix    - the plat /96 prefix
+ */
+int plat_prefix(const char *ipv4_name, struct in6_addr *prefix) {
+  struct addrinfo hints, *result, *p;
+  int status, plat_addr_set, ipv4_records, ipv6_records;
+  struct in6_addr plat_addr, this_plat_addr;
+  struct sockaddr_in6 *this_addr;
+
+  result = NULL;
+  plat_addr_set = 0;
+  ipv4_records = ipv6_records = 0;
+
+  bzero(&hints, sizeof(hints));
+  hints.ai_family = AF_UNSPEC;
+  status = getaddrinfo(ipv4_name, NULL, &hints, &result);
+  if(status != 0) {
+    logmsg(ANDROID_LOG_ERROR,"plat_prefix/dns(%s) status = %d/%s\n", ipv4_name, status, gai_strerror(status));
+    return 0;
+  }
+
+  for(p = result; p; p = p->ai_next) {
+    if(p->ai_family == AF_INET) {
+      ipv4_records++;
+      continue;
+    }
+    if(p->ai_family != AF_INET6) {
+      logmsg(ANDROID_LOG_WARN,"plat_prefix/unexpected address family: %d\n", p->ai_family);
+      continue;
+    }
+    ipv6_records++;
+    this_addr = (struct sockaddr_in6 *)p->ai_addr;
+    this_plat_addr = this_addr->sin6_addr;
+    this_plat_addr.s6_addr32[3] = 0;
+
+    if(!plat_addr_set) {
+      plat_addr = this_plat_addr;
+      plat_addr_set = 1;
+      continue;
+    }
+
+    if(!IN6_ARE_ADDR_EQUAL(&plat_addr, &this_plat_addr)) {
+      char plat_addr_str[INET6_ADDRSTRLEN], this_plat_addr_str[INET6_ADDRSTRLEN];
+      logmsg(ANDROID_LOG_ERROR,"plat_prefix/two different plat addrs = %s,%s",
+          inet_ntop(AF_INET6, &plat_addr, plat_addr_str, sizeof(plat_addr_str)),
+          inet_ntop(AF_INET6, &this_plat_addr, this_plat_addr_str, sizeof(this_plat_addr_str))
+          );
+    }
+  }
+  if(result != NULL) {
+    freeaddrinfo(result);
+  }
+  if(ipv4_records > 0 && ipv6_records == 0) {
+    logmsg(ANDROID_LOG_WARN,"plat_prefix/no dns64 detected\n");
+    return -1;
+  }
+  *prefix = plat_addr;
+  return 1;
+}