fake_dns tool for Android (fixed DEPS).

tools/android/fake_dns/fake_dns.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <netinet/in.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/command_line.h"
+#include "base/eintr_wrapper.h"
+#include "base/logging.h"
+#include "net/base/big_endian.h"
+#include "net/base/net_util.h"
+#include "net/dns/dns_protocol.h"
+#include "tools/android/common/daemon.h"
+#include "tools/android/common/net.h"
+
+namespace {
+
+// Mininum request size: 1 question containing 1 QNAME, 1 TYPE and 1 CLASS.
+const size_t kMinRequestSize = sizeof(net::dns_protocol::Header) + 6;
+
+// The name reference in the answer pointing to the name in the query.
+// Its format is: highest two bits set to 1, then the offset of the name
+// which just follows the header.
+const uint16 kPointerToQueryName =
+    static_cast<uint16>(0xc000 | sizeof(net::dns_protocol::Header));
+
+const uint32 kTTL = 86400;  // One day.
+
+void SendRefusedResponse(int sock, const sockaddr_in& client_addr, uint16 id) {
+  net::dns_protocol::Header response;
+  response.id = htons(id);
+  response.flags = htons(net::dns_protocol::kFlagResponse |
+                         net::dns_protocol::kFlagAA |
+                         net::dns_protocol::kFlagRD |
+                         net::dns_protocol::kFlagRA |
+                         net::dns_protocol::kRcodeREFUSED);
+  response.qdcount = 0;
+  response.ancount = 0;
+  response.nscount = 0;
+  response.arcount = 0;
+  HANDLE_EINTR(sendto(sock, &response, sizeof(response), 0,
+                      reinterpret_cast<const sockaddr*>(&client_addr),
+                      sizeof(client_addr)));
+}
+
+void SendResponse(int sock, const sockaddr_in& client_addr, uint16 id,
+                  uint16 qtype, const char* question, size_t question_length) {
+  net::dns_protocol::Header header;
+  header.id = htons(id);
+  header.flags = htons(net::dns_protocol::kFlagResponse |
+                       net::dns_protocol::kFlagAA |
+                       net::dns_protocol::kFlagRD |
+                       net::dns_protocol::kFlagRA |
+                       net::dns_protocol::kRcodeNOERROR);
+  header.qdcount = htons(1);
+  header.ancount = htons(1);
+  header.nscount = 0;
+  header.arcount = 0;
+
+  // Size of RDATA which is a IPv4 or IPv6 address.
+  size_t rdata_size = qtype == net::dns_protocol::kTypeA ?
+                      net::kIPv4AddressSize : net::kIPv6AddressSize;
+
+  // Size of the whole response which contains the header, the question and
+  // the answer. 12 is the sum of sizes of the compressed name reference, TYPE,
+  // CLASS, TTL and RDLENGTH.
+  size_t response_size = sizeof(header) + question_length + 12 + rdata_size;
+
+  if (response_size > net::dns_protocol::kMaxUDPSize) {
+    LOG(ERROR) << "Response is too large: " << response_size;
+    SendRefusedResponse(sock, client_addr, id);
+    return;
+  }
+
+  char response[net::dns_protocol::kMaxUDPSize];
+  net::BigEndianWriter writer(response, arraysize(response));
+  writer.WriteBytes(&header, sizeof(header));
+
+  // Repeat the question in the response. Some clients (e.g. ping) needs this.
+  writer.WriteBytes(question, question_length);
+
+  // Construct the answer.
+  writer.WriteU16(kPointerToQueryName);
+  writer.WriteU16(qtype);
+  writer.WriteU16(net::dns_protocol::kClassIN);
+  writer.WriteU32(kTTL);
+  writer.WriteU16(rdata_size);
+  if (qtype == net::dns_protocol::kTypeA)
+    writer.WriteU32(INADDR_LOOPBACK);
+  else
+    writer.WriteBytes(&in6addr_loopback, sizeof(in6_addr));
+  DCHECK(writer.ptr() - response == response_size);
+
+  HANDLE_EINTR(sendto(sock, response, response_size, 0,
+                      reinterpret_cast<const sockaddr*>(&client_addr),
+                      sizeof(client_addr)));
+}
+
+void HandleRequest(int sock, const char* request, size_t size,
+                   const sockaddr_in& client_addr) {
+  if (size < kMinRequestSize) {
+    LOG(ERROR) << "Request is too small " << size
+               << "\n" << tools::DumpBinary(request, size);
+    return;
+  }
+
+  net::BigEndianReader reader(request, size);
+  net::dns_protocol::Header header;
+  reader.ReadBytes(&header, sizeof(header));
+  uint16 id = ntohs(header.id);
+  uint16 flags = ntohs(header.flags);
+  uint16 qdcount = ntohs(header.qdcount);
+  uint16 ancount = ntohs(header.ancount);
+  uint16 nscount = ntohs(header.nscount);
+  uint16 arcount = ntohs(header.arcount);
+
+  const uint16 kAllowedFlags = 0x07ff;
+  if ((flags & ~kAllowedFlags) ||
+      qdcount != 1 || ancount || nscount || arcount) {
+    LOG(ERROR) << "Unsupported request: FLAGS=" << flags
+               << " QDCOUNT=" << qdcount
+               << " ANCOUNT=" << ancount
+               << " NSCOUNT=" << nscount
+               << " ARCOUNT=" << arcount
+               << "\n" << tools::DumpBinary(request, size);
+    SendRefusedResponse(sock, client_addr, id);
+    return;
+  }
+
+  // request[size - 5] should be the end of the QNAME (a zero byte).
+  // We don't care about the validity of QNAME because we don't parse it.
+  const char* qname_end = &request[size - 5];
+  if (*qname_end) {
+    LOG(ERROR) << "Error parsing QNAME\n" << tools::DumpBinary(request, size);
+    SendRefusedResponse(sock, client_addr, id);
+    return;
+  }
+
+  reader.Skip(qname_end - reader.ptr() + 1);
+
+  uint16 qtype;
+  uint16 qclass;
+  reader.ReadU16(&qtype);
+  reader.ReadU16(&qclass);
+  if ((qtype != net::dns_protocol::kTypeA &&
+       qtype != net::dns_protocol::kTypeAAAA) ||
+      qclass != net::dns_protocol::kClassIN) {
+    LOG(ERROR) << "Unsupported query: QTYPE=" << qtype << " QCLASS=" << qclass
+               << "\n" << tools::DumpBinary(request, size);
+    SendRefusedResponse(sock, client_addr, id);
+    return;
+  }
+
+  SendResponse(sock, client_addr, id, qtype,
+               request + sizeof(header), size - sizeof(header));
+}
+
+}  // namespace
+
+int main(int argc, char** argv) {
+  printf("Fake DNS server\n");
+
+  CommandLine command_line(argc, argv);
+  if (tools::HasHelpSwitch(command_line) || command_line.GetArgs().size()) {
+    tools::ShowHelp(argv[0], "", "");
+    return 0;
+  }
+
+  int sock = socket(AF_INET, SOCK_DGRAM, 0);
+  if (sock < 0) {
+    perror("create socket");
+    return 1;
+  }
+
+  sockaddr_in addr;
+  memset(&addr, 0, sizeof(addr));
+  addr.sin_family = AF_INET;
+  addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+  addr.sin_port = htons(53);
+  int reuse_addr = 1;
+  if (HANDLE_EINTR(bind(sock, reinterpret_cast<sockaddr*>(&addr),
+                        sizeof(addr))) < 0) {
+    perror("server bind");
+    HANDLE_EINTR(close(sock));
+    return 1;
+  }
+
+  if (!tools::HasNoSpawnDaemonSwitch(command_line))
+    tools::SpawnDaemon(0);
+
+  while (true) {
+    sockaddr_in client_addr;
+    socklen_t client_addr_len = sizeof(client_addr);
+    char request[net::dns_protocol::kMaxUDPSize];
+    int size = HANDLE_EINTR(recvfrom(sock, request, sizeof(request),
+                                     MSG_WAITALL,
+                                     reinterpret_cast<sockaddr*>(&client_addr),
+                                     &client_addr_len));
+    if (size < 0) {
+      // Unrecoverable error, can only exit.
+      LOG(ERROR) << "Failed to receive a request: " << strerror(errno);
+      HANDLE_EINTR(close(sock));
+      return 1;
+    }
+
+    if (size > 0)
+      HandleRequest(sock, request, size, client_addr);
+  }
+}
+