1 ============================== 2 The Google URL Parsing Library 3 ============================== 4 5 This is the Google URL Parsing Library which parses and canonicalizes URLs. 6 Please see the LICENSE.txt file for licensing information. 7 8 Features 9 ======== 10 11 * Easily embeddable: This library was written for a variety of client and 12 server programs in mind, so unlike most implementations of URL parsing 13 and canonicalization, it can be easily emdedded. 14 15 * Fast: hundreds of thousands of typical URLs can be parsed and 16 canonicalized per second on a modern CPU. It is much faster than, for 17 example, calling WinInet's corresponding functions. 18 19 * Compatible: When possible, this library has strived for IE7 compatability 20 for both general web compatability, and so IE addons or other applications 21 that communicate with or embed IE will work properly. 22 23 It supports Unix-style file URLs, as well as the more complex rules for 24 Window file URLs. Note that total compatability is not possible (for 25 example, IE6 and IE7 disagree about how to parse certain IP addresses), 26 and that this is more strict about certain illegal, rarely used, and 27 potentially dangerous constructs such as escaped control characters in 28 host names that IE will allow. It is typically a little less strict than 29 Firefox. 30 31 32 Example 33 ======= 34 35 An example implementation of a URL object that uses this library is provided 36 in src/gurl.*. This implementation uses the "application integration" layer 37 discussed below to interface with the low-level parsing and canonicalization 38 functions. 39 40 41 Building 42 ======== 43 44 The canonicalization files require ICU for some UTF-8 and UTF-16 conversion 45 macros. If your project does not use ICU, it should be straightforward to 46 factor out the macros and functions used in ICU, there are only a few well- 47 isolated things that are used. 48 49 TODO(brettw) ADD INSTRUCTIONS FOR GETTING ICU HERE! 50 51 logging.h and logging.cc are Windows-only because the corresponding Unix 52 logging system has many dependencies. This library uses few of the logging 53 macros, and a dummy header can easily be written that defines the 54 appropriate things for Unix. 55 56 57 Definitions 58 =========== 59 60 "Standard URL": A URL with an "authority", which is a hostname and optionally 61 a port, username, and password. Most URLs are standard such as HTTP and FTP. 62 63 "File URL": A URL that references a file on disk. There are special rules for 64 this type of URL. Note that it may have a hostname! "localhost" is allowed, 65 for example "file://localhost/foo" is the same as "file:///foo". 66 67 "Path URL": This is everything else. There is no standard on how to treat these 68 URLs, or even what they are called. This library decomposes them into a 69 scheme and a path. The path is everything following the scheme. This type of 70 URL includes "javascript", "data", and even "mailto" (although "mailto" 71 might look like a standard scheme in some respects, it is not). 72 73 74 Design 75 ====== 76 77 The library is divided into four layers. They are listed here from the lowest 78 to the highest; you can use any portion of the library as long as you embed the 79 layers below it. 80 81 1. Parsing 82 ---------- 83 At the lowest level is the parsing code. The files encompasing this are 84 url_parse.* and the main include file is src/url_parse.h. This code will, given 85 an input string, parse it into the most likely form of a URL. 86 87 Parsing can not fail and does no validation. The exception is the port number, 88 which it currently validates, but this is a bug. Given crazy input, the parser 89 will do its best to find the various URL components according to its rules (see 90 url_parse_unittest.cc for some examples). 91 92 To use this, an application will typically use ExtractScheme to determine the 93 type of a given input URL, and then call one of the initialization functions: 94 "ParseStandardURL", "ParsePathURL", or "ParseFileURL". This will result in 95 a "Parsed" structure which identifies the substrings of each identified 96 component. 97 98 2. Canonicalization 99 ------------------- 100 At the next highest level is canonicalization. The files encompasing this are 101 url_canon.* and the main include file is src/url_canon.h. This code will 102 validate an already-parsed URL, and will convert it to a canonical form. For 103 example, this will convert host names to lowercase, convert IP addresses 104 into dotted-decimal notation, handle encoding issues, etc. 105 106 This layer will always do its best to produce a reasonable output string, but 107 it may return that the string is invalid. For example, if there are invalid 108 characters in the host name, it will escape them or replace them with the 109 Unicode "invalid character" character, but will fail. This way, the program can 110 display error messages to the user with the output, log it, etc. and the 111 string will have some meaning. 112 113 Canonicalized output is written to a CanonOutput object which is a simple 114 wrapper around an expanding buffer. An implementation called RawCanonOutput is 115 proivided that writes to a raw buffer with a fixed amount statically allocated 116 (for performance). Applications using STL can use StdStringCanonOutput defined 117 in url_canon_stdstring.h which writes into a std::string. 118 119 A normal application would call one of the three high-level functions 120 "CanonicalizeStandardURL", "CanonicalizeFileURL", and CanonicalizePathURL" 121 depending on the type of URL in question. Lower-level functions are also 122 provided which will canonicalize individual parts of a URL (for example, 123 "CanonicalizeHost"). 124 125 Part of this layer is the integration with the host system for IDN and encoding 126 conversion. An implementation that provides integration with the ICU 127 (http://www-306.ibm.com/software/globalization/icu/index.jsp) is provided in 128 src/url_canon_icu.cc. The embedder may wish to replace this file with 129 implementations of the functions for their own IDN library if they do not use 130 ICU. 131 132 3. Application integration 133 -------------------------- 134 The canonicalization and parsing layers do not know anything about the URI 135 schemes supported by your application. The parsing and canonicalization 136 functions are very low-level, and you must call the correct function to do the 137 work (for example, "CanonicalizeFileURL"). 138 139 The application integration in url_util.* provides wrappers around the 140 low-level parsing and canonicalization to call the correct versions for 141 different identified schemes. Embedders will want to modify this file if 142 necessary to suit the needs of their application. 143 144 4. URL object 145 ------------- 146 The highest level is the "URL" object that a C++ application would use to 147 to encapsulate a URL. Embedders will typically want to provide their own URL 148 object that meets the requirements of their system. A reasonably complete 149 example implemnetation is provided in src/gurl.*. You may wish to use this 150 object, extend or modify it, or write your own. 151 152 Whitespace 153 ---------- 154 Sometimes, you may want to remove linefeeds and tabs from the content of a URL. 155 Some web pages, for example, expect that a URL spanning two lines should be 156 treated as one with the newline removed. Depending on the source of the URLs 157 you are canonicalizing, these newlines may or may not be trimmed off. 158 159 If you want this behavior, call RemoveURLWhitespace before parsing. This will 160 remove CR, LF and TAB from the input. Note that it preserves spaces. On typical 161 URLs, this function produces a 10-15% speed reduction, so it is optional and 162 not done automatically. The example GURL object and the url_util wrapper does 163 this for you. 164 165 Tests 166 ===== 167 168 There are a number of *_unittest.cc and *_perftest.cc files. These files are 169 not currently compilable as they rely on a not-included unit testing framework 170 Tests are declared like this: 171 TEST(TestCaseName, TestName) { 172 ASSERT_TRUE(a); 173 EXPECT_EQ(a, b); 174 } 175 If you would like to compile them, it should be straightforward to define 176 the TEST macro (which would declare a function by combining the two arguments) 177 and the other macros whose behavior should be self-explanatory (EXPECT is like 178 an ASSERT, but does not stop the test, if you are doing this, you probably 179 don't care about this difference). Then you would define a .cc file that 180 calls all of these functions. 181
