net/dns/dns_hosts.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/dns/dns_hosts.h"
   6
   7 #include "base/files/file_util.h"
   8 #include "base/logging.h"
   9 #include "base/metrics/histogram.h"
  10 #include "base/strings/string_util.h"
  11
  12 using base::StringPiece;
  13
  14 namespace net {
  15
  16 namespace {
  17
  18 // Parses the contents of a hosts file.  Returns one token (IP or hostname) at
  19 // a time.  Doesn't copy anything; accepts the file as a StringPiece and
  20 // returns tokens as StringPieces.
  21 class HostsParser {
  22  public:
  23   explicit HostsParser(const StringPiece& text, ParseHostsCommaMode comma_mode)
  24       : text_(text),
  25         data_(text.data()),
  26         end_(text.size()),
  27         pos_(0),
  28         token_is_ip_(false),
  29         comma_mode_(comma_mode) {}
  30
  31   // Advances to the next token (IP or hostname).  Returns whether another
  32   // token was available.  |token_is_ip| and |token| can be used to find out
  33   // the type and text of the token.
  34   bool Advance() {
  35     bool next_is_ip = (pos_ == 0);
  36     while (pos_ < end_ && pos_ != std::string::npos) {
  37       switch (text_[pos_]) {
  38         case ' ':
  39         case '\t':
  40           SkipWhitespace();
  41           break;
  42
  43         case '\r':
  44         case '\n':
  45           next_is_ip = true;
  46           pos_++;
  47           break;
  48
  49         case '#':
  50           SkipRestOfLine();
  51           break;
  52
  53         case ',':
  54           if (comma_mode_ == PARSE_HOSTS_COMMA_IS_WHITESPACE) {
  55             SkipWhitespace();
  56             break;
  57           }
  58
  59           // If comma_mode_ is COMMA_IS_TOKEN, fall through:
  60
  61         default: {
  62           size_t token_start = pos_;
  63           SkipToken();
  64           size_t token_end = (pos_ == std::string::npos) ? end_ : pos_;
  65
  66           token_ = StringPiece(data_ + token_start, token_end - token_start);
  67           token_is_ip_ = next_is_ip;
  68
  69           return true;
  70         }
  71       }
  72     }
  73
  74     return false;
  75   }
  76
  77   // Fast-forwards the parser to the next line.  Should be called if an IP
  78   // address doesn't parse, to avoid wasting time tokenizing hostnames that
  79   // will be ignored.
  80   void SkipRestOfLine() {
  81     pos_ = text_.find("\n", pos_);
  82   }
  83
  84   // Returns whether the last-parsed token is an IP address (true) or a
  85   // hostname (false).
  86   bool token_is_ip() { return token_is_ip_; }
  87
  88   // Returns the text of the last-parsed token as a StringPiece referencing
  89   // the same underlying memory as the StringPiece passed to the constructor.
  90   // Returns an empty StringPiece if no token has been parsed or the end of
  91   // the input string has been reached.
  92   const StringPiece& token() { return token_; }
  93
  94  private:
  95   void SkipToken() {
  96     switch (comma_mode_) {
  97       case PARSE_HOSTS_COMMA_IS_TOKEN:
  98         pos_ = text_.find_first_of(" \t\n\r#", pos_);
  99         break;
 100       case PARSE_HOSTS_COMMA_IS_WHITESPACE:
 101         pos_ = text_.find_first_of(" ,\t\n\r#", pos_);
 102         break;
 103     }
 104   }
 105
 106   void SkipWhitespace() {
 107     switch (comma_mode_) {
 108       case PARSE_HOSTS_COMMA_IS_TOKEN:
 109         pos_ = text_.find_first_not_of(" \t", pos_);
 110         break;
 111       case PARSE_HOSTS_COMMA_IS_WHITESPACE:
 112         pos_ = text_.find_first_not_of(" ,\t", pos_);
 113         break;
 114     }
 115   }
 116
 117   const StringPiece text_;
 118   const char* data_;
 119   const size_t end_;
 120
 121   size_t pos_;
 122   StringPiece token_;
 123   bool token_is_ip_;
 124
 125   const ParseHostsCommaMode comma_mode_;
 126
 127   DISALLOW_COPY_AND_ASSIGN(HostsParser);
 128 };
 129
 130 void ParseHostsWithCommaMode(const std::string& contents,
 131                              DnsHosts* dns_hosts,
 132                              ParseHostsCommaMode comma_mode) {
 133   CHECK(dns_hosts);
 134   DnsHosts& hosts = *dns_hosts;
 135
 136   StringPiece ip_text;
 137   IPAddressNumber ip;
 138   AddressFamily family = ADDRESS_FAMILY_IPV4;
 139   HostsParser parser(contents, comma_mode);
 140   while (parser.Advance()) {
 141     if (parser.token_is_ip()) {
 142       StringPiece new_ip_text = parser.token();
 143       // Some ad-blocking hosts files contain thousands of entries pointing to
 144       // the same IP address (usually 127.0.0.1).  Don't bother parsing the IP
 145       // again if it's the same as the one above it.
 146       if (new_ip_text != ip_text) {
 147         IPAddressNumber new_ip;
 148         if (ParseIPLiteralToNumber(parser.token().as_string(), &new_ip)) {
 149           ip_text = new_ip_text;
 150           ip.swap(new_ip);
 151           family = (ip.size() == 4) ? ADDRESS_FAMILY_IPV4 : ADDRESS_FAMILY_IPV6;
 152         } else {
 153           parser.SkipRestOfLine();
 154         }
 155       }
 156     } else {
 157       DnsHostsKey key(parser.token().as_string(), family);
 158       base::StringToLowerASCII(&key.first);
 159       IPAddressNumber& mapped_ip = hosts[key];
 160       if (mapped_ip.empty())
 161         mapped_ip = ip;
 162       // else ignore this entry (first hit counts)
 163     }
 164   }
 165 }
 166
 167 }  // namespace
 168
 169 void ParseHostsWithCommaModeForTesting(const std::string& contents,
 170                                        DnsHosts* dns_hosts,
 171                                        ParseHostsCommaMode comma_mode) {
 172   ParseHostsWithCommaMode(contents, dns_hosts, comma_mode);
 173 }
 174
 175 void ParseHosts(const std::string& contents, DnsHosts* dns_hosts) {
 176   ParseHostsCommaMode comma_mode;
 177 #if defined(OS_MACOSX)
 178   // Mac OS X allows commas to separate hostnames.
 179   comma_mode = PARSE_HOSTS_COMMA_IS_WHITESPACE;
 180 #else
 181   // Linux allows commas in hostnames.
 182   comma_mode = PARSE_HOSTS_COMMA_IS_TOKEN;
 183 #endif
 184
 185   ParseHostsWithCommaMode(contents, dns_hosts, comma_mode);
 186 }
 187
 188 bool ParseHostsFile(const base::FilePath& path, DnsHosts* dns_hosts) {
 189   dns_hosts->clear();
 190   // Missing file indicates empty HOSTS.
 191   if (!base::PathExists(path))
 192     return true;
 193
 194   int64 size;
 195   if (!base::GetFileSize(path, &size))
 196     return false;
 197
 198   UMA_HISTOGRAM_COUNTS("AsyncDNS.HostsSize", size);
 199
 200   // Reject HOSTS files larger than |kMaxHostsSize| bytes.
 201   const int64 kMaxHostsSize = 1 << 25;  // 32MB
 202   if (size > kMaxHostsSize)
 203     return false;
 204
 205   std::string contents;
 206   if (!base::ReadFileToString(path, &contents))
 207     return false;
 208
 209   ParseHosts(contents, dns_hosts);
 210   return true;
 211 }
 212
 213 }  // namespace net
 214