1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
// Copyright 2013-2015 The rust-url developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

/*!

rust-url is an implementation of the [URL Standard](http://url.spec.whatwg.org/)
for the [Rust](http://rust-lang.org/) programming language.

It builds with [Cargo](http://crates.io/).
To use it in your project, add this to your `Cargo.toml` file:

```Cargo
[dependencies.url]
git = "https://github.com/servo/rust-url"
```

Supporting encodings other than UTF-8 in query strings is an optional feature
that requires [rust-encoding](https://github.com/lifthrasiir/rust-encoding)
and is off by default.
You can enable it with
[Cargo’s *features* mechanism](http://doc.crates.io/manifest.html#the-[features]-section):

```Cargo
[dependencies.url]
git = "https://github.com/servo/rust-url"
features = ["query_encoding"]
```

… or by passing `--cfg 'feature="query_encoding"'` to rustc.


# URL parsing and data structures

First, URL parsing may fail for various reasons and therefore returns a `Result`.

```
use url::{Url, ParseError};

assert!(Url::parse("http://[:::1]") == Err(ParseError::InvalidIpv6Address))
```

Let’s parse a valid URL and look at its components.

```
use url::{Url, Host};

let issue_list_url = Url::parse(
    "https://github.com/rust-lang/rust/issues?labels=E-easy&state=open"
).unwrap();


assert!(issue_list_url.scheme() == "https");
assert!(issue_list_url.username() == "");
assert!(issue_list_url.password() == None);
assert!(issue_list_url.host_str() == Some("github.com"));
assert!(issue_list_url.host() == Some(Host::Domain("github.com")));
assert!(issue_list_url.port() == None);
assert!(issue_list_url.path() == "/rust-lang/rust/issues");
assert!(issue_list_url.path_segments().map(|c| c.collect::<Vec<_>>()) ==
        Some(vec!["rust-lang", "rust", "issues"]));
assert!(issue_list_url.query() == Some("labels=E-easy&state=open"));
assert!(issue_list_url.fragment() == None);
assert!(!issue_list_url.cannot_be_a_base());
```

Some URLs are said to be *cannot-be-a-base*:
they don’t have a username, password, host, or port,
and their "path" is an arbitrary string rather than slash-separated segments:

```
use url::Url;

let data_url = Url::parse("data:text/plain,Hello?World#").unwrap();

assert!(data_url.cannot_be_a_base());
assert!(data_url.scheme() == "data");
assert!(data_url.path() == "text/plain,Hello");
assert!(data_url.path_segments().is_none());
assert!(data_url.query() == Some("World"));
assert!(data_url.fragment() == Some(""));
```


# Base URL

Many contexts allow URL *references* that can be relative to a *base URL*:

```html
<link rel="stylesheet" href="../main.css">
```

Since parsed URL are absolute, giving a base is required for parsing relative URLs:

```
use url::{Url, ParseError};

assert!(Url::parse("../main.css") == Err(ParseError::RelativeUrlWithoutBase))
```

Use the `join` method on an `Url` to use it as a base URL:

```
use url::Url;

let this_document = Url::parse("http://servo.github.io/rust-url/url/index.html").unwrap();
let css_url = this_document.join("../main.css").unwrap();
assert_eq!(css_url.as_str(), "http://servo.github.io/rust-url/main.css")
*/

#[cfg(feature="rustc-serialize")] extern crate rustc_serialize;
#[macro_use] extern crate matches;
#[cfg(feature="serde")] extern crate serde;
#[cfg(feature="heapsize")] #[macro_use] extern crate heapsize;

pub extern crate idna;

use encoding::EncodingOverride;
#[cfg(feature = "heapsize")] use heapsize::HeapSizeOf;
use host::HostInternal;
use parser::{Parser, Context, SchemeType, to_u32};
use percent_encoding::{PATH_SEGMENT_ENCODE_SET, USERINFO_ENCODE_SET,
                       percent_encode, percent_decode, utf8_percent_encode};
use std::cmp;
use std::fmt::{self, Write};
use std::hash;
use std::io;
use std::mem;
use std::net::{ToSocketAddrs, IpAddr};
use std::ops::{Range, RangeFrom, RangeTo};
use std::path::{Path, PathBuf};
use std::str;

pub use origin::{Origin, OpaqueOrigin};
pub use host::{Host, HostAndPort, SocketAddrs};
pub use path_segments::PathSegmentsMut;
pub use parser::ParseError;
pub use slicing::Position;

mod encoding;
mod host;
mod origin;
mod path_segments;
mod parser;
mod slicing;

pub mod form_urlencoded;
pub mod percent_encoding;
pub mod quirks;

/// A parsed URL record.
#[derive(Clone)]
pub struct Url {
    /// Syntax in pseudo-BNF:
    ///
    ///   url = scheme ":" [ hierarchical | non-hierarchical ] [ "?" query ]? [ "#" fragment ]?
    ///   non-hierarchical = non-hierarchical-path
    ///   non-hierarchical-path = /* Does not start with "/" */
    ///   hierarchical = authority? hierarchical-path
    ///   authority = "//" userinfo? host [ ":" port ]?
    ///   userinfo = username [ ":" password ]? "@"
    ///   hierarchical-path = [ "/" path-segment ]+
    serialization: String,

    // Components
    scheme_end: u32,  // Before ':'
    username_end: u32,  // Before ':' (if a password is given) or '@' (if not)
    host_start: u32,
    host_end: u32,
    host: HostInternal,
    port: Option<u16>,
    path_start: u32,  // Before initial '/', if any
    query_start: Option<u32>,  // Before '?', unlike Position::QueryStart
    fragment_start: Option<u32>,  // Before '#', unlike Position::FragmentStart
}

#[cfg(feature = "heapsize")]
impl HeapSizeOf for Url {
    fn heap_size_of_children(&self) -> usize {
        self.serialization.heap_size_of_children()
    }
}

/// Full configuration for the URL parser.
#[derive(Copy, Clone)]
pub struct ParseOptions<'a> {
    base_url: Option<&'a Url>,
    encoding_override: encoding::EncodingOverride,
    log_syntax_violation: Option<&'a Fn(&'static str)>,
}

impl<'a> ParseOptions<'a> {
    /// Change the base URL
    pub fn base_url(mut self, new: Option<&'a Url>) -> Self {
        self.base_url = new;
        self
    }

    /// Override the character encoding of query strings.
    /// This is a legacy concept only relevant for HTML.
    #[cfg(feature = "query_encoding")]
    pub fn encoding_override(mut self, new: Option<encoding::EncodingRef>) -> Self {
        self.encoding_override = EncodingOverride::from_opt_encoding(new).to_output_encoding();
        self
    }

    /// Call the provided function or closure on non-fatal parse errors.
    pub fn log_syntax_violation(mut self, new: Option<&'a Fn(&'static str)>) -> Self {
        self.log_syntax_violation = new;
        self
    }

    /// Parse an URL string with the configuration so far.
    pub fn parse(self, input: &str) -> Result<Url, ::ParseError> {
        Parser {
            serialization: String::with_capacity(input.len()),
            base_url: self.base_url,
            query_encoding_override: self.encoding_override,
            log_syntax_violation: self.log_syntax_violation,
            context: Context::UrlParser,
        }.parse_url(input)
    }
}

impl Url {
    /// Parse an absolute URL from a string.
    #[inline]
    pub fn parse(input: &str) -> Result<Url, ::ParseError> {
        Url::options().parse(input)
    }

    /// Parse a string as an URL, with this URL as the base URL.
    #[inline]
    pub fn join(&self, input: &str) -> Result<Url, ::ParseError> {
        Url::options().base_url(Some(self)).parse(input)
    }

    /// Return a default `ParseOptions` that can fully configure the URL parser.
    pub fn options<'a>() -> ParseOptions<'a> {
        ParseOptions {
            base_url: None,
            encoding_override: EncodingOverride::utf8(),
            log_syntax_violation: None,
        }
    }

    /// Return the serialization of this URL.
    ///
    /// This is fast since that serialization is already stored in the `Url` struct.
    #[inline]
    pub fn as_str(&self) -> &str {
        &self.serialization
    }

    /// Return the serialization of this URL.
    ///
    /// This consumes the `Url` and takes ownership of the `String` stored in it.
    #[inline]
    pub fn into_string(self) -> String {
        self.serialization
    }

    /// For internal testing, not part of the public API.
    ///
    /// Methods of the `Url` struct assume a number of invariants.
    /// This checks each of these invariants and panic if one is not met.
    /// This is for testing rust-url itself.
    #[doc(hidden)]
    pub fn assert_invariants(&self) {
        macro_rules! assert {
            ($x: expr) => {
                if !$x {
                    panic!("!( {} ) for URL {:?}", stringify!($x), self.serialization)
                }
            }
        }

        macro_rules! assert_eq {
            ($a: expr, $b: expr) => {
                {
                    let a = $a;
                    let b = $b;
                    if a != b {
                        panic!("{:?} != {:?} ({} != {}) for URL {:?}",
                               a, b, stringify!($a), stringify!($b), self.serialization)
                    }
                }
            }
        }

        assert!(self.scheme_end >= 1);
        assert!(matches!(self.byte_at(0), b'a'...b'z' | b'A'...b'Z'));
        assert!(self.slice(1..self.scheme_end).chars()
                .all(|c| matches!(c, 'a'...'z' | 'A'...'Z' | '0'...'9' | '+' | '-' | '.')));
        assert_eq!(self.byte_at(self.scheme_end), b':');

        if self.slice(self.scheme_end + 1 ..).starts_with("//") {
            // URL with authority
            match self.byte_at(self.username_end) {
                b':' => {
                    assert!(self.host_start >= self.username_end + 2);
                    assert_eq!(self.byte_at(self.host_start - 1), b'@');
                }
                b'@' => assert!(self.host_start == self.username_end + 1),
                _ => assert_eq!(self.username_end, self.scheme_end + 3),
            }
            assert!(self.host_start >= self.username_end);
            assert!(self.host_end >= self.host_start);
            let host_str = self.slice(self.host_start..self.host_end);
            match self.host {
                HostInternal::None => assert_eq!(host_str, ""),
                HostInternal::Ipv4(address) => assert_eq!(host_str, address.to_string()),
                HostInternal::Ipv6(address) => assert_eq!(host_str, format!("[{}]", address)),
                HostInternal::Domain => {
                    if SchemeType::from(self.scheme()).is_special() {
                        assert!(!host_str.is_empty())
                    }
                }
            }
            if self.path_start == self.host_end {
                assert_eq!(self.port, None);
            } else {
                assert_eq!(self.byte_at(self.host_end), b':');
                let port_str = self.slice(self.host_end + 1..self.path_start);
                assert_eq!(self.port, Some(port_str.parse::<u16>().expect("Couldn't parse port?")));
            }
            assert_eq!(self.byte_at(self.path_start), b'/');
        } else {
            // Anarchist URL (no authority)
            assert_eq!(self.username_end, self.scheme_end + 1);
            assert_eq!(self.host_start, self.scheme_end + 1);
            assert_eq!(self.host_end, self.scheme_end + 1);
            assert_eq!(self.host, HostInternal::None);
            assert_eq!(self.port, None);
            assert_eq!(self.path_start, self.scheme_end + 1);
        }
        if let Some(start) = self.query_start {
            assert!(start > self.path_start);
            assert_eq!(self.byte_at(start), b'?');
        }
        if let Some(start) = self.fragment_start {
            assert!(start > self.path_start);
            assert_eq!(self.byte_at(start), b'#');
        }
        if let (Some(query_start), Some(fragment_start)) = (self.query_start, self.fragment_start) {
            assert!(fragment_start > query_start);
        }

        let other = Url::parse(self.as_str()).expect("Failed to parse myself?");
        assert_eq!(&self.serialization, &other.serialization);
        assert_eq!(self.scheme_end, other.scheme_end);
        assert_eq!(self.username_end, other.username_end);
        assert_eq!(self.host_start, other.host_start);
        assert_eq!(self.host_end, other.host_end);
        assert!(self.host == other.host ||
                // XXX No host round-trips to empty host.
                // See https://github.com/whatwg/url/issues/79
                (self.host_str(), other.host_str()) == (None, Some("")));
        assert_eq!(self.port, other.port);
        assert_eq!(self.path_start, other.path_start);
        assert_eq!(self.query_start, other.query_start);
        assert_eq!(self.fragment_start, other.fragment_start);
    }

    /// Return the origin of this URL (https://url.spec.whatwg.org/#origin)
    ///
    /// Note: this returns an opaque origin for `file:` URLs, which causes
    /// `url.origin() != url.origin()`.
    ///
    /// # Examples
    ///
    /// URL with `ftp` scheme:
    ///
    /// ```rust
    /// use url::{Host, Origin, Url};
    ///
    /// let url = Url::parse("ftp://example.com/foo").unwrap();
    /// assert_eq!(url.origin(),
    ///            Origin::Tuple("ftp".into(),
    ///                          Host::Domain("example.com".into()),
    ///                          21));
    /// ```
    ///
    /// URL with `blob` scheme:
    ///
    /// ```rust
    /// use url::{Host, Origin, Url};
    ///
    /// let url = Url::parse("blob:https://example.com/foo").unwrap();
    /// assert_eq!(url.origin(),
    ///            Origin::Tuple("https".into(),
    ///                          Host::Domain("example.com".into()),
    ///                          443));
    /// ```
    ///
    /// URL with `file` scheme:
    ///
    /// ```rust
    /// use url::{Host, Origin, Url};
    ///
    /// let url = Url::parse("file:///tmp/foo").unwrap();
    /// assert!(!url.origin().is_tuple());
    ///
    /// let other_url = Url::parse("file:///tmp/foo").unwrap();
    /// assert!(url.origin() != other_url.origin());
    /// ```
    ///
    /// URL with other scheme:
    ///
    /// ```rust
    /// use url::{Host, Origin, Url};
    ///
    /// let url = Url::parse("foo:bar").unwrap();
    /// assert!(!url.origin().is_tuple());
    /// ```
    #[inline]
    pub fn origin(&self) -> Origin {
        origin::url_origin(self)
    }

    /// Return the scheme of this URL, lower-cased, as an ASCII string without the ':' delimiter.
    ///
    /// # Examples
    ///
    /// ```
    /// use url::Url;
    ///
    /// let url = Url::parse("file:///tmp/foo").unwrap();
    /// assert_eq!(url.scheme(), "file");
    /// ```
    #[inline]
    pub fn scheme(&self) -> &str {
        self.slice(..self.scheme_end)
    }

    /// Return whether the URL has an 'authority',
    /// which can contain a username, password, host, and port number.
    ///
    /// URLs that do *not* are either path-only like `unix:/run/foo.socket`
    /// or cannot-be-a-base like `data:text/plain,Stuff`.
    #[inline]
    pub fn has_authority(&self) -> bool {
        debug_assert!(self.byte_at(self.scheme_end) == b':');
        self.slice(self.scheme_end..).starts_with("://")
    }

    /// Return whether this URL is a cannot-be-a-base URL,
    /// meaning that parsing a relative URL string with this URL as the base will return an error.
    ///
    /// This is the case if the scheme and `:` delimiter are not followed by a `/` slash,
    /// as is typically the case of `data:` and `mailto:` URLs.
    #[inline]
    pub fn cannot_be_a_base(&self) -> bool {
        self.byte_at(self.path_start) != b'/'
    }

    /// Return the username for this URL (typically the empty string)
    /// as a percent-encoded ASCII string.
    ///
    /// # Examples
    ///
    /// ```
    /// use url::Url;
    ///
    /// let url = Url::parse("ftp://rms@example.com").unwrap();
    /// assert_eq!(url.username(), "rms");
    ///
    /// let url = Url::parse("ftp://:secret123@example.com").unwrap();
    /// assert_eq!(url.username(), "");
    ///
    /// let url = Url::parse("https://example.com").unwrap();
    /// assert_eq!(url.username(), "");
    /// ```
    pub fn username(&self) -> &str {
        if self.has_authority() {
            self.slice(self.scheme_end + ("://".len() as u32)..self.username_end)
        } else {
            ""
        }
    }

    /// Return the password for this URL, if any, as a percent-encoded ASCII string.
    ///
    /// # Examples
    ///
    /// ```
    /// use url::Url;
    ///
    /// let url = Url::parse("ftp://rms:secret123@example.com").unwrap();
    /// assert_eq!(url.password(), Some("secret123"));
    ///
    /// let url = Url::parse("ftp://:secret123@example.com").unwrap();
    /// assert_eq!(url.password(), Some("secret123"));
    ///
    /// let url = Url::parse("ftp://rms@example.com").unwrap();
    /// assert_eq!(url.password(), None);
    ///
    /// let url = Url::parse("https://example.com").unwrap();
    /// assert_eq!(url.password(), None);
    /// ```
    pub fn password(&self) -> Option<&str> {
        // This ':' is not the one marking a port number since a host can not be empty.
        // (Except for file: URLs, which do not have port numbers.)
        if self.has_authority() && self.byte_at(self.username_end) == b':' {
            debug_assert!(self.byte_at(self.host_start - 1) == b'@');
            Some(self.slice(self.username_end + 1..self.host_start - 1))
        } else {
            None
        }
    }

    /// Equivalent to `url.host().is_some()`.
    pub fn has_host(&self) -> bool {
        !matches!(self.host, HostInternal::None)
    }

    /// Return the string representation of the host (domain or IP address) for this URL, if any.
    ///
    /// Non-ASCII domains are punycode-encoded per IDNA.
    /// IPv6 addresses are given between `[` and `]` brackets.
    ///
    /// Cannot-be-a-base URLs (typical of `data:` and `mailto:`) and some `file:` URLs
    /// don’t have a host.
    ///
    /// See also the `host` method.
    pub fn host_str(&self) -> Option<&str> {
        if self.has_host() {
            Some(self.slice(self.host_start..self.host_end))
        } else {
            None
        }
    }

    /// Return the parsed representation of the host for this URL.
    /// Non-ASCII domain labels are punycode-encoded per IDNA.
    ///
    /// Cannot-be-a-base URLs (typical of `data:` and `mailto:`) and some `file:` URLs
    /// don’t have a host.
    ///
    /// See also the `host_str` method.
    pub fn host(&self) -> Option<Host<&str>> {
        match self.host {
            HostInternal::None => None,
            HostInternal::Domain => Some(Host::Domain(self.slice(self.host_start..self.host_end))),
            HostInternal::Ipv4(address) => Some(Host::Ipv4(address)),
            HostInternal::Ipv6(address) => Some(Host::Ipv6(address)),
        }
    }

    /// If this URL has a host and it is a domain name (not an IP address), return it.
    pub fn domain(&self) -> Option<&str> {
        match self.host {
            HostInternal::Domain => Some(self.slice(self.host_start..self.host_end)),
            _ => None,
        }
    }

    /// Return the port number for this URL, if any.
    #[inline]
    pub fn port(&self) -> Option<u16> {
        self.port
    }

    /// Return the port number for this URL, or the default port number if it is known.
    ///
    /// This method only knows the default port number
    /// of the `http`, `https`, `ws`, `wss`, `ftp`, and `gopher` schemes.
    ///
    /// For URLs in these schemes, this method always returns `Some(_)`.
    /// For other schemes, it is the same as `Url::port()`.
    #[inline]
    pub fn port_or_known_default(&self) -> Option<u16> {
        self.port.or_else(|| parser::default_port(self.scheme()))
    }

    /// If the URL has a host, return something that implements `ToSocketAddrs`.
    ///
    /// If the URL has no port number and the scheme’s default port number is not known
    /// (see `Url::port_or_known_default`),
    /// the closure is called to obtain a port number.
    /// Typically, this closure can match on the result `Url::scheme`
    /// to have per-scheme default port numbers,
    /// and panic for schemes it’s not prepared to handle.
    /// For example:
    ///
    /// ```rust
    /// # use url::Url;
    /// # use std::net::TcpStream;
    /// # use std::io;
    ///
    /// fn connect(url: &Url) -> io::Result<TcpStream> {
    ///     TcpStream::connect(try!(url.with_default_port(default_port)))
    /// }
    ///
    /// fn default_port(url: &Url) -> Result<u16, ()> {
    ///     match url.scheme() {
    ///         "git" => Ok(9418),
    ///         "git+ssh" => Ok(22),
    ///         "git+https" => Ok(443),
    ///         "git+http" => Ok(80),
    ///         _ => Err(()),
    ///     }
    /// }
    /// ```
    pub fn with_default_port<F>(&self, f: F) -> io::Result<HostAndPort<&str>>
    where F: FnOnce(&Url) -> Result<u16, ()> {
        Ok(HostAndPort {
            host: try!(self.host()
                           .ok_or(())
                           .or_else(|()| io_error("URL has no host"))),
            port: try!(self.port_or_known_default()
                           .ok_or(())
                           .or_else(|()| f(self))
                           .or_else(|()| io_error("URL has no port number")))
        })
    }

    /// Return the path for this URL, as a percent-encoded ASCII string.
    /// For cannot-be-a-base URLs, this is an arbitrary string that doesn’t start with '/'.
    /// For other URLs, this starts with a '/' slash
    /// and continues with slash-separated path segments.
    pub fn path(&self) -> &str {
        match (self.query_start, self.fragment_start) {
            (None, None) => self.slice(self.path_start..),
            (Some(next_component_start), _) |
            (None, Some(next_component_start)) => {
                self.slice(self.path_start..next_component_start)
            }
        }
    }

    /// Unless this URL is cannot-be-a-base,
    /// return an iterator of '/' slash-separated path segments,
    /// each as a percent-encoded ASCII string.
    ///
    /// Return `None` for cannot-be-a-base URLs.
    ///
    /// When `Some` is returned, the iterator always contains at least one string
    /// (which may be empty).
    pub fn path_segments(&self) -> Option<str::Split<char>> {
        let path = self.path();
        if path.starts_with('/') {
            Some(path[1..].split('/'))
        } else {
            None
        }
    }

    /// Return this URL’s query string, if any, as a percent-encoded ASCII string.
    pub fn query(&self) -> Option<&str> {
        match (self.query_start, self.fragment_start) {
            (None, _) => None,
            (Some(query_start), None) => {
                debug_assert!(self.byte_at(query_start) == b'?');
                Some(self.slice(query_start + 1..))
            }
            (Some(query_start), Some(fragment_start)) => {
                debug_assert!(self.byte_at(query_start) == b'?');
                Some(self.slice(query_start + 1..fragment_start))
            }
        }
    }

    /// Parse the URL’s query string, if any, as `application/x-www-form-urlencoded`
    /// and return an iterator of (key, value) pairs.
    #[inline]
    pub fn query_pairs(&self) -> form_urlencoded::Parse {
        form_urlencoded::parse(self.query().unwrap_or("").as_bytes())
    }

    /// Return this URL’s fragment identifier, if any.
    ///
    /// **Note:** the parser did *not* percent-encode this component,
    /// but the input may have been percent-encoded already.
    pub fn fragment(&self) -> Option<&str> {
        self.fragment_start.map(|start| {
            debug_assert!(self.byte_at(start) == b'#');
            self.slice(start + 1..)
        })
    }

    fn mutate<F: FnOnce(&mut Parser) -> R, R>(&mut self, f: F) -> R {
        let mut parser = Parser::for_setter(mem::replace(&mut self.serialization, String::new()));
        let result = f(&mut parser);
        self.serialization = parser.serialization;
        result
    }

    /// Change this URL’s fragment identifier.
    pub fn set_fragment(&mut self, fragment: Option<&str>) {
        // Remove any previous fragment
        if let Some(start) = self.fragment_start {
            debug_assert!(self.byte_at(start) == b'#');
            self.serialization.truncate(start as usize);
        }
        // Write the new one
        if let Some(input) = fragment {
            self.fragment_start = Some(to_u32(self.serialization.len()).unwrap());
            self.serialization.push('#');
            self.mutate(|parser| parser.parse_fragment(parser::Input::new(input)))
        } else {
            self.fragment_start = None
        }
    }

    fn take_fragment(&mut self) -> Option<String> {
        self.fragment_start.take().map(|start| {
            debug_assert!(self.byte_at(start) == b'#');
            let fragment = self.slice(start + 1..).to_owned();
            self.serialization.truncate(start as usize);
            fragment
        })
    }

    fn restore_already_parsed_fragment(&mut self, fragment: Option<String>) {
        if let Some(ref fragment) = fragment {
            assert!(self.fragment_start.is_none());
            self.fragment_start = Some(to_u32(self.serialization.len()).unwrap());
            self.serialization.push('#');
            self.serialization.push_str(fragment);
        }
    }

    /// Change this URL’s query string.
    pub fn set_query(&mut self, query: Option<&str>) {
        let fragment = self.take_fragment();

        // Remove any previous query
        if let Some(start) = self.query_start.take() {
            debug_assert!(self.byte_at(start) == b'?');
            self.serialization.truncate(start as usize);
        }
        // Write the new query, if any
        if let Some(input) = query {
            self.query_start = Some(to_u32(self.serialization.len()).unwrap());
            self.serialization.push('?');
            let scheme_end = self.scheme_end;
            self.mutate(|parser| parser.parse_query(scheme_end, parser::Input::new(input)));
        }

        self.restore_already_parsed_fragment(fragment);
    }

    /// Manipulate this URL’s query string, viewed as a sequence of name/value pairs
    /// in `application/x-www-form-urlencoded` syntax.
    ///
    /// The return value has a method-chaining API:
    ///
    /// ```rust
    /// # use url::Url;
    /// let mut url = Url::parse("https://example.net?lang=fr#nav").unwrap();
    /// assert_eq!(url.query(), Some("lang=fr"));
    ///
    /// url.query_pairs_mut().append_pair("foo", "bar");
    /// assert_eq!(url.query(), Some("lang=fr&foo=bar"));
    /// assert_eq!(url.as_str(), "https://example.net/?lang=fr&foo=bar#nav");
    ///
    /// url.query_pairs_mut()
    ///     .clear()
    ///     .append_pair("foo", "bar & baz")
    ///     .append_pair("saisons", "Été+hiver");
    /// assert_eq!(url.query(), Some("foo=bar+%26+baz&saisons=%C3%89t%C3%A9%2Bhiver"));
    /// assert_eq!(url.as_str(),
    ///            "https://example.net/?foo=bar+%26+baz&saisons=%C3%89t%C3%A9%2Bhiver#nav");
    /// ```
    ///
    /// Note: `url.query_pairs_mut().clear();` is equivalent to `url.set_query(Some(""))`,
    /// not `url.set_query(None)`.
    ///
    /// The state of `Url` is unspecified if this return value is leaked without being dropped.
    pub fn query_pairs_mut(&mut self) -> form_urlencoded::Serializer<UrlQuery> {
        let fragment = self.take_fragment();

        let query_start;
        if let Some(start) = self.query_start {
            debug_assert!(self.byte_at(start) == b'?');
            query_start = start as usize;
        } else {
            query_start = self.serialization.len();
            self.query_start = Some(to_u32(query_start).unwrap());
            self.serialization.push('?');
        }

        let query = UrlQuery { url: self, fragment: fragment };
        form_urlencoded::Serializer::for_suffix(query, query_start + "?".len())
    }

    fn take_after_path(&mut self) -> String {
        match (self.query_start, self.fragment_start) {
            (Some(i), _) | (None, Some(i)) => {
                let after_path = self.slice(i..).to_owned();
                self.serialization.truncate(i as usize);
                after_path
            },
            (None, None) => String::new(),
        }
    }

    /// Change this URL’s path.
    pub fn set_path(&mut self, mut path: &str) {
        let after_path = self.take_after_path();
        let old_after_path_pos = to_u32(self.serialization.len()).unwrap();
        let cannot_be_a_base = self.cannot_be_a_base();
        let scheme_type = SchemeType::from(self.scheme());
        self.serialization.truncate(self.path_start as usize);
        self.mutate(|parser| {
            if cannot_be_a_base {
                if path.starts_with('/') {
                    parser.serialization.push_str("%2F");
                    path = &path[1..];
                }
                parser.parse_cannot_be_a_base_path(parser::Input::new(path));
            } else {
                let mut has_host = true;  // FIXME
                parser.parse_path_start(scheme_type, &mut has_host, parser::Input::new(path));
            }
        });
        self.restore_after_path(old_after_path_pos, &after_path);
    }

    /// Return an object with methods to manipulate this URL’s path segments.
    ///
    /// Return `Err(())` if this URl is cannot-be-a-base.
    pub fn path_segments_mut(&mut self) -> Result<PathSegmentsMut, ()> {
        if self.cannot_be_a_base() {
            Err(())
        } else {
            Ok(path_segments::new(self))
        }
    }

    fn restore_after_path(&mut self, old_after_path_position: u32, after_path: &str) {
        let new_after_path_position = to_u32(self.serialization.len()).unwrap();
        let adjust = |index: &mut u32| {
            *index -= old_after_path_position;
            *index += new_after_path_position;
        };
        if let Some(ref mut index) = self.query_start { adjust(index) }
        if let Some(ref mut index) = self.fragment_start { adjust(index) }
        self.serialization.push_str(after_path)
    }

    /// Change this URL’s port number.
    ///
    /// If this URL is cannot-be-a-base, does not have a host, or has the `file` scheme;
    /// do nothing and return `Err`.
    pub fn set_port(&mut self, mut port: Option<u16>) -> Result<(), ()> {
        if !self.has_host() || self.scheme() == "file" {
            return Err(())
        }
        if port.is_some() && port == parser::default_port(self.scheme()) {
            port = None
        }
        self.set_port_internal(port);
        Ok(())
    }

    fn set_port_internal(&mut self, port: Option<u16>) {
        match (self.port, port) {
            (None, None) => {}
            (Some(_), None) => {
                self.serialization.drain(self.host_end as usize .. self.path_start as usize);
                let offset = self.path_start - self.host_end;
                self.path_start = self.host_end;
                if let Some(ref mut index) = self.query_start { *index -= offset }
                if let Some(ref mut index) = self.fragment_start { *index -= offset }
            }
            (Some(old), Some(new)) if old == new => {}
            (_, Some(new)) => {
                let path_and_after = self.slice(self.path_start..).to_owned();
                self.serialization.truncate(self.host_end as usize);
                write!(&mut self.serialization, ":{}", new).unwrap();
                let old_path_start = self.path_start;
                let new_path_start = to_u32(self.serialization.len()).unwrap();
                self.path_start = new_path_start;
                let adjust = |index: &mut u32| {
                    *index -= old_path_start;
                    *index += new_path_start;
                };
                if let Some(ref mut index) = self.query_start { adjust(index) }
                if let Some(ref mut index) = self.fragment_start { adjust(index) }
                self.serialization.push_str(&path_and_after);
            }
        }
        self.port = port;
    }

    /// Change this URL’s host.
    ///
    /// If this URL is cannot-be-a-base or there is an error parsing the given `host`,
    /// do nothing and return `Err`.
    ///
    /// Removing the host (calling this with `None`)
    /// will also remove any username, password, and port number.
    pub fn set_host(&mut self, host: Option<&str>) -> Result<(), ParseError> {
        if self.cannot_be_a_base() {
            return Err(ParseError::SetHostOnCannotBeABaseUrl)
        }

        if let Some(host) = host {
            self.set_host_internal(try!(Host::parse(host)), None)
        } else if self.has_host() {
            debug_assert!(self.byte_at(self.scheme_end) == b':');
            debug_assert!(self.byte_at(self.path_start) == b'/');
            let new_path_start = self.scheme_end + 1;
            self.serialization.drain(self.path_start as usize..new_path_start as usize);
            let offset = self.path_start - new_path_start;
            self.path_start = new_path_start;
            self.username_end = new_path_start;
            self.host_start = new_path_start;
            self.host_end = new_path_start;
            self.port = None;
            if let Some(ref mut index) = self.query_start { *index -= offset }
            if let Some(ref mut index) = self.fragment_start { *index -= offset }
        }
        Ok(())
    }

    /// opt_new_port: None means leave unchanged, Some(None) means remove any port number.
    fn set_host_internal(&mut self, host: Host<String>, opt_new_port: Option<Option<u16>>) {
        let old_suffix_pos = if opt_new_port.is_some() { self.path_start } else { self.host_end };
        let suffix = self.slice(old_suffix_pos..).to_owned();
        self.serialization.truncate(self.host_start as usize);
        if !self.has_authority() {
            debug_assert!(self.slice(self.scheme_end..self.host_start) == ":");
            debug_assert!(self.username_end == self.host_start);
            self.serialization.push('/');
            self.serialization.push('/');
            self.username_end += 2;
            self.host_start += 2;
        }
        write!(&mut self.serialization, "{}", host).unwrap();
        self.host_end = to_u32(self.serialization.len()).unwrap();
        self.host = host.into();

        if let Some(new_port) = opt_new_port {
            self.port = new_port;
            if let Some(port) = new_port {
                write!(&mut self.serialization, ":{}", port).unwrap();
            }
        }
        let new_suffix_pos = to_u32(self.serialization.len()).unwrap();
        self.serialization.push_str(&suffix);

        let adjust = |index: &mut u32| {
            *index -= old_suffix_pos;
            *index += new_suffix_pos;
        };
        adjust(&mut self.path_start);
        if let Some(ref mut index) = self.query_start { adjust(index) }
        if let Some(ref mut index) = self.fragment_start { adjust(index) }
    }

    /// Change this URL’s host to the given IP address.
    ///
    /// If this URL is cannot-be-a-base, do nothing and return `Err`.
    ///
    /// Compared to `Url::set_host`, this skips the host parser.
    pub fn set_ip_host(&mut self, address: IpAddr) -> Result<(), ()> {
        if self.cannot_be_a_base() {
            return Err(())
        }

        let address = match address {
            IpAddr::V4(address) => Host::Ipv4(address),
            IpAddr::V6(address) => Host::Ipv6(address),
        };
        self.set_host_internal(address, None);
        Ok(())
    }

    /// Change this URL’s password.
    ///
    /// If this URL is cannot-be-a-base or does not have a host, do nothing and return `Err`.
    pub fn set_password(&mut self, password: Option<&str>) -> Result<(), ()> {
        if !self.has_host() {
            return Err(())
        }
        if let Some(password) = password {
            let host_and_after = self.slice(self.host_start..).to_owned();
            self.serialization.truncate(self.username_end as usize);
            self.serialization.push(':');
            self.serialization.extend(utf8_percent_encode(password, USERINFO_ENCODE_SET));
            self.serialization.push('@');

            let old_host_start = self.host_start;
            let new_host_start = to_u32(self.serialization.len()).unwrap();
            let adjust = |index: &mut u32| {
                *index -= old_host_start;
                *index += new_host_start;
            };
            self.host_start = new_host_start;
            adjust(&mut self.host_end);
            adjust(&mut self.path_start);
            if let Some(ref mut index) = self.query_start { adjust(index) }
            if let Some(ref mut index) = self.fragment_start { adjust(index) }

            self.serialization.push_str(&host_and_after);
        } else if self.byte_at(self.username_end) == b':' {  // If there is a password to remove
            let has_username_or_password = self.byte_at(self.host_start - 1) == b'@';
            debug_assert!(has_username_or_password);
            let username_start = self.scheme_end + 3;
            let empty_username = username_start == self.username_end;
            let start = self.username_end;  // Remove the ':'
            let end = if empty_username {
                self.host_start // Remove the '@' as well
            } else {
                self.host_start - 1  // Keep the '@' to separate the username from the host
            };
            self.serialization.drain(start as usize .. end as usize);
            let offset = end - start;
            self.host_start -= offset;
            self.host_end -= offset;
            self.path_start -= offset;
            if let Some(ref mut index) = self.query_start { *index -= offset }
            if let Some(ref mut index) = self.fragment_start { *index -= offset }
        }
        Ok(())
    }

    /// Change this URL’s username.
    ///
    /// If this URL is cannot-be-a-base or does not have a host, do nothing and return `Err`.
    pub fn set_username(&mut self, username: &str) -> Result<(), ()> {
        if !self.has_host() {
            return Err(())
        }
        let username_start = self.scheme_end + 3;
        debug_assert!(self.slice(self.scheme_end..username_start) == "://");
        if self.slice(username_start..self.username_end) == username {
            return Ok(())
        }
        let after_username = self.slice(self.username_end..).to_owned();
        self.serialization.truncate(username_start as usize);
        self.serialization.extend(utf8_percent_encode(username, USERINFO_ENCODE_SET));

        let mut removed_bytes = self.username_end;
        self.username_end = to_u32(self.serialization.len()).unwrap();
        let mut added_bytes = self.username_end;

        let new_username_is_empty = self.username_end == username_start;
        match (new_username_is_empty, after_username.chars().next()) {
            (true, Some('@')) => {
                removed_bytes += 1;
                self.serialization.push_str(&after_username[1..]);
            }
            (false, Some('@')) | (_, Some(':')) | (true, _) => {
                self.serialization.push_str(&after_username);
            }
            (false, _) => {
                added_bytes += 1;
                self.serialization.push('@');
                self.serialization.push_str(&after_username);
            }
        }

        let adjust = |index: &mut u32| {
            *index -= removed_bytes;
            *index += added_bytes;
        };
        adjust(&mut self.host_start);
        adjust(&mut self.host_end);
        adjust(&mut self.path_start);
        if let Some(ref mut index) = self.query_start { adjust(index) }
        if let Some(ref mut index) = self.fragment_start { adjust(index) }
        Ok(())
    }

    /// Change this URL’s scheme.
    ///
    /// Do nothing and return `Err` if:
    /// * The new scheme is not in `[a-zA-Z][a-zA-Z0-9+.-]+`
    /// * This URL is cannot-be-a-base and the new scheme is one of
    ///   `http`, `https`, `ws`, `wss`, `ftp`, or `gopher`
    pub fn set_scheme(&mut self, scheme: &str) -> Result<(), ()> {
        let mut parser = Parser::for_setter(String::new());
        let remaining = try!(parser.parse_scheme(parser::Input::new(scheme)));
        if !remaining.is_empty() ||
                (!self.has_host() && SchemeType::from(&parser.serialization).is_special()) {
            return Err(())
        }
        let old_scheme_end = self.scheme_end;
        let new_scheme_end = to_u32(parser.serialization.len()).unwrap();
        let adjust = |index: &mut u32| {
            *index -= old_scheme_end;
            *index += new_scheme_end;
        };

        self.scheme_end = new_scheme_end;
        adjust(&mut self.username_end);
        adjust(&mut self.host_start);
        adjust(&mut self.host_end);
        adjust(&mut self.path_start);
        if let Some(ref mut index) = self.query_start { adjust(index) }
        if let Some(ref mut index) = self.fragment_start { adjust(index) }

        parser.serialization.push_str(self.slice(old_scheme_end..));
        self.serialization = parser.serialization;
        Ok(())
    }

    /// Convert a file name as `std::path::Path` into an URL in the `file` scheme.
    ///
    /// This returns `Err` if the given path is not absolute or,
    /// on Windows, if the prefix is not a disk prefix (e.g. `C:`).
    pub fn from_file_path<P: AsRef<Path>>(path: P) -> Result<Url, ()> {
        let mut serialization = "file://".to_owned();
        let path_start = serialization.len() as u32;
        try!(path_to_file_url_segments(path.as_ref(), &mut serialization));
        Ok(Url {
            serialization: serialization,
            scheme_end: "file".len() as u32,
            username_end: path_start,
            host_start: path_start,
            host_end: path_start,
            host: HostInternal::None,
            port: None,
            path_start: path_start,
            query_start: None,
            fragment_start: None,
        })
    }

    /// Convert a directory name as `std::path::Path` into an URL in the `file` scheme.
    ///
    /// This returns `Err` if the given path is not absolute or,
    /// on Windows, if the prefix is not a disk prefix (e.g. `C:`).
    ///
    /// Compared to `from_file_path`, this ensure that URL’s the path has a trailing slash
    /// so that the entire path is considered when using this URL as a base URL.
    ///
    /// For example:
    ///
    /// * `"index.html"` parsed with `Url::from_directory_path(Path::new("/var/www"))`
    ///   as the base URL is `file:///var/www/index.html`
    /// * `"index.html"` parsed with `Url::from_file_path(Path::new("/var/www"))`
    ///   as the base URL is `file:///var/index.html`, which might not be what was intended.
    ///
    /// Note that `std::path` does not consider trailing slashes significant
    /// and usually does not include them (e.g. in `Path::parent()`).
    pub fn from_directory_path<P: AsRef<Path>>(path: P) -> Result<Url, ()> {
        let mut url = try!(Url::from_file_path(path));
        if !url.serialization.ends_with('/') {
            url.serialization.push('/')
        }
        Ok(url)
    }

    /// Assuming the URL is in the `file` scheme or similar,
    /// convert its path to an absolute `std::path::Path`.
    ///
    /// **Note:** This does not actually check the URL’s `scheme`,
    /// and may give nonsensical results for other schemes.
    /// It is the user’s responsibility to check the URL’s scheme before calling this.
    ///
    /// ```
    /// # use url::Url;
    /// # let url = Url::parse("file:///etc/passwd").unwrap();
    /// let path = url.to_file_path();
    /// ```
    ///
    /// Returns `Err` if the host is neither empty nor `"localhost"`,
    /// or if `Path::new_opt()` returns `None`.
    /// (That is, if the percent-decoded path contains a NUL byte or,
    /// for a Windows path, is not UTF-8.)
    #[inline]
    pub fn to_file_path(&self) -> Result<PathBuf, ()> {
        // FIXME: Figure out what to do w.r.t host.
        if matches!(self.host(), None | Some(Host::Domain("localhost"))) {
            if let Some(segments) = self.path_segments() {
                return file_url_segments_to_pathbuf(segments)
            }
        }
        Err(())
    }

    // Private helper methods:

    #[inline]
    fn slice<R>(&self, range: R) -> &str where R: RangeArg {
        range.slice_of(&self.serialization)
    }

    #[inline]
    fn byte_at(&self, i: u32) -> u8 {
        self.serialization.as_bytes()[i as usize]
    }
}

/// Return an error if `Url::host` or `Url::port_or_known_default` return `None`.
impl ToSocketAddrs for Url {
    type Iter = SocketAddrs;

    fn to_socket_addrs(&self) -> io::Result<Self::Iter> {
        try!(self.with_default_port(|_| Err(()))).to_socket_addrs()
    }
}

/// Parse a string as an URL, without a base URL or encoding override.
impl str::FromStr for Url {
    type Err = ParseError;

    #[inline]
    fn from_str(input: &str) -> Result<Url, ::ParseError> {
        Url::parse(input)
    }
}

/// Display the serialization of this URL.
impl fmt::Display for Url {
    #[inline]
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.serialization, formatter)
    }
}

/// Debug the serialization of this URL.
impl fmt::Debug for Url {
    #[inline]
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        fmt::Debug::fmt(&self.serialization, formatter)
    }
}

/// URLs compare like their serialization.
impl Eq for Url {}

/// URLs compare like their serialization.
impl PartialEq for Url {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        self.serialization == other.serialization
    }
}

/// URLs compare like their serialization.
impl Ord for Url {
    #[inline]
    fn cmp(&self, other: &Self) -> cmp::Ordering {
        self.serialization.cmp(&other.serialization)
    }
}

/// URLs compare like their serialization.
impl PartialOrd for Url {
    #[inline]
    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
        self.serialization.partial_cmp(&other.serialization)
    }
}

/// URLs hash like their serialization.
impl hash::Hash for Url {
    #[inline]
    fn hash<H>(&self, state: &mut H) where H: hash::Hasher {
        hash::Hash::hash(&self.serialization, state)
    }
}

/// Return the serialization of this URL.
impl AsRef<str> for Url {
    #[inline]
    fn as_ref(&self) -> &str {
        &self.serialization
    }
}

trait RangeArg {
    fn slice_of<'a>(&self, s: &'a str) -> &'a str;
}

impl RangeArg for Range<u32> {
    #[inline]
    fn slice_of<'a>(&self, s: &'a str) -> &'a str {
        &s[self.start as usize .. self.end as usize]
    }
}

impl RangeArg for RangeFrom<u32> {
    #[inline]
    fn slice_of<'a>(&self, s: &'a str) -> &'a str {
        &s[self.start as usize ..]
    }
}

impl RangeArg for RangeTo<u32> {
    #[inline]
    fn slice_of<'a>(&self, s: &'a str) -> &'a str {
        &s[.. self.end as usize]
    }
}

#[cfg(feature="rustc-serialize")]
impl rustc_serialize::Encodable for Url {
    fn encode<S: rustc_serialize::Encoder>(&self, encoder: &mut S) -> Result<(), S::Error> {
        encoder.emit_str(self.as_str())
    }
}


#[cfg(feature="rustc-serialize")]
impl rustc_serialize::Decodable for Url {
    fn decode<D: rustc_serialize::Decoder>(decoder: &mut D) -> Result<Url, D::Error> {
        Url::parse(&*try!(decoder.read_str())).map_err(|error| {
            decoder.error(&format!("URL parsing error: {}", error))
        })
    }
}

/// Serializes this URL into a `serde` stream.
///
/// This implementation is only available if the `serde` Cargo feature is enabled.
#[cfg(feature="serde")]
impl serde::Serialize for Url {
    fn serialize<S>(&self, serializer: &mut S) -> Result<(), S::Error> where S: serde::Serializer {
        format!("{}", self).serialize(serializer)
    }
}

/// Deserializes this URL from a `serde` stream.
///
/// This implementation is only available if the `serde` Cargo feature is enabled.
#[cfg(feature="serde")]
impl serde::Deserialize for Url {
    fn deserialize<D>(deserializer: &mut D) -> Result<Url, D::Error> where D: serde::Deserializer {
        let string_representation: String = try!(serde::Deserialize::deserialize(deserializer));
        Ok(Url::parse(&string_representation).unwrap())
    }
}

#[cfg(unix)]
fn path_to_file_url_segments(path: &Path, serialization: &mut String) -> Result<(), ()> {
    use std::os::unix::prelude::OsStrExt;
    if !path.is_absolute() {
        return Err(())
    }
    let mut empty = true;
    // skip the root component
    for component in path.components().skip(1) {
        empty = false;
        serialization.push('/');
        serialization.extend(percent_encode(
            component.as_os_str().as_bytes(), PATH_SEGMENT_ENCODE_SET));
    }
    if empty {
        // An URL’s path must not be empty.
        serialization.push('/');
    }
    Ok(())
}

#[cfg(windows)]
fn path_to_file_url_segments(path: &Path, serialization: &mut String) -> Result<(), ()> {
    path_to_file_url_segments_windows(path, serialization)
}

// Build this unconditionally to alleviate https://github.com/servo/rust-url/issues/102
#[cfg_attr(not(windows), allow(dead_code))]
fn path_to_file_url_segments_windows(path: &Path, serialization: &mut String) -> Result<(), ()> {
    use std::path::{Prefix, Component};
    if !path.is_absolute() {
        return Err(())
    }
    let mut components = path.components();
    let disk = match components.next() {
        Some(Component::Prefix(ref p)) => match p.kind() {
            Prefix::Disk(byte) => byte,
            Prefix::VerbatimDisk(byte) => byte,
            _ => return Err(()),
        },

        // FIXME: do something with UNC and other prefixes?
        _ => return Err(())
    };

    // Start with the prefix, e.g. "C:"
    serialization.push('/');
    serialization.push(disk as char);
    serialization.push(':');

    for component in components {
        if component == Component::RootDir { continue }
        // FIXME: somehow work with non-unicode?
        let component = try!(component.as_os_str().to_str().ok_or(()));
        serialization.push('/');
        serialization.extend(percent_encode(component.as_bytes(), PATH_SEGMENT_ENCODE_SET));
    }
    Ok(())
}

#[cfg(unix)]
fn file_url_segments_to_pathbuf(segments: str::Split<char>) -> Result<PathBuf, ()> {
    use std::ffi::OsStr;
    use std::os::unix::prelude::OsStrExt;
    use std::path::PathBuf;

    let mut bytes = Vec::new();
    for segment in segments {
        bytes.push(b'/');
        bytes.extend(percent_decode(segment.as_bytes()));
    }
    let os_str = OsStr::from_bytes(&bytes);
    let path = PathBuf::from(os_str);
    debug_assert!(path.is_absolute(),
                  "to_file_path() failed to produce an absolute Path");
    Ok(path)
}

#[cfg(windows)]
fn file_url_segments_to_pathbuf(segments: str::Split<char>) -> Result<PathBuf, ()> {
    file_url_segments_to_pathbuf_windows(segments)
}

// Build this unconditionally to alleviate https://github.com/servo/rust-url/issues/102
#[cfg_attr(not(windows), allow(dead_code))]
fn file_url_segments_to_pathbuf_windows(mut segments: str::Split<char>) -> Result<PathBuf, ()> {
    let first = try!(segments.next().ok_or(()));
    if first.len() != 2 || !first.starts_with(parser::ascii_alpha)
            || first.as_bytes()[1] != b':' {
        return Err(())
    }
    let mut string = first.to_owned();
    for segment in segments {
        string.push('\\');

        // Currently non-unicode windows paths cannot be represented
        match String::from_utf8(percent_decode(segment.as_bytes()).collect()) {
            Ok(s) => string.push_str(&s),
            Err(..) => return Err(()),
        }
    }
    let path = PathBuf::from(string);
    debug_assert!(path.is_absolute(),
                  "to_file_path() failed to produce an absolute Path");
    Ok(path)
}

fn io_error<T>(reason: &str) -> io::Result<T> {
    Err(io::Error::new(io::ErrorKind::InvalidData, reason))
}

/// Implementation detail of `Url::query_pairs_mut`. Typically not used directly.
pub struct UrlQuery<'a> {
    url: &'a mut Url,
    fragment: Option<String>,
}

impl<'a> Drop for UrlQuery<'a> {
    fn drop(&mut self) {
        self.url.restore_already_parsed_fragment(self.fragment.take())
    }
}