github.com/mdempsky/go@v0.0.0-20151201204031-5dd372bd1e70/src/net/url/url.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package url parses URLs and implements query escaping.
     6  // See RFC 3986.
     7  package url
     8  
     9  import (
    10  	"bytes"
    11  	"errors"
    12  	"fmt"
    13  	"sort"
    14  	"strconv"
    15  	"strings"
    16  )
    17  
    18  // Error reports an error and the operation and URL that caused it.
    19  type Error struct {
    20  	Op  string
    21  	URL string
    22  	Err error
    23  }
    24  
    25  func (e *Error) Error() string { return e.Op + " " + e.URL + ": " + e.Err.Error() }
    26  
    27  type timeout interface {
    28  	Timeout() bool
    29  }
    30  
    31  func (e *Error) Timeout() bool {
    32  	t, ok := e.Err.(timeout)
    33  	return ok && t.Timeout()
    34  }
    35  
    36  type temporary interface {
    37  	Temporary() bool
    38  }
    39  
    40  func (e *Error) Temporary() bool {
    41  	t, ok := e.Err.(temporary)
    42  	return ok && t.Temporary()
    43  }
    44  
    45  func ishex(c byte) bool {
    46  	switch {
    47  	case '0' <= c && c <= '9':
    48  		return true
    49  	case 'a' <= c && c <= 'f':
    50  		return true
    51  	case 'A' <= c && c <= 'F':
    52  		return true
    53  	}
    54  	return false
    55  }
    56  
    57  func unhex(c byte) byte {
    58  	switch {
    59  	case '0' <= c && c <= '9':
    60  		return c - '0'
    61  	case 'a' <= c && c <= 'f':
    62  		return c - 'a' + 10
    63  	case 'A' <= c && c <= 'F':
    64  		return c - 'A' + 10
    65  	}
    66  	return 0
    67  }
    68  
    69  type encoding int
    70  
    71  const (
    72  	encodePath encoding = 1 + iota
    73  	encodeHost
    74  	encodeUserPassword
    75  	encodeQueryComponent
    76  	encodeFragment
    77  )
    78  
    79  type EscapeError string
    80  
    81  func (e EscapeError) Error() string {
    82  	return "invalid URL escape " + strconv.Quote(string(e))
    83  }
    84  
    85  // Return true if the specified character should be escaped when
    86  // appearing in a URL string, according to RFC 3986.
    87  //
    88  // Please be informed that for now shouldEscape does not check all
    89  // reserved characters correctly. See golang.org/issue/5684.
    90  func shouldEscape(c byte, mode encoding) bool {
    91  	// §2.3 Unreserved characters (alphanum)
    92  	if 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' {
    93  		return false
    94  	}
    95  
    96  	if mode == encodeHost {
    97  		// §3.2.2 Host allows
    98  		//	sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="
    99  		// as part of reg-name.
   100  		// We add : because we include :port as part of host.
   101  		// We add [ ] because we include [ipv6]:port as part of host
   102  		switch c {
   103  		case '!', '$', '&', '\'', '(', ')', '*', '+', ',', ';', '=', ':', '[', ']':
   104  			return false
   105  		}
   106  	}
   107  
   108  	switch c {
   109  	case '-', '_', '.', '~': // §2.3 Unreserved characters (mark)
   110  		return false
   111  
   112  	case '$', '&', '+', ',', '/', ':', ';', '=', '?', '@': // §2.2 Reserved characters (reserved)
   113  		// Different sections of the URL allow a few of
   114  		// the reserved characters to appear unescaped.
   115  		switch mode {
   116  		case encodePath: // §3.3
   117  			// The RFC allows : @ & = + $ but saves / ; , for assigning
   118  			// meaning to individual path segments. This package
   119  			// only manipulates the path as a whole, so we allow those
   120  			// last two as well. That leaves only ? to escape.
   121  			return c == '?'
   122  
   123  		case encodeUserPassword: // §3.2.1
   124  			// The RFC allows ';', ':', '&', '=', '+', '$', and ',' in
   125  			// userinfo, so we must escape only '@', '/', and '?'.
   126  			// The parsing of userinfo treats ':' as special so we must escape
   127  			// that too.
   128  			return c == '@' || c == '/' || c == '?' || c == ':'
   129  
   130  		case encodeQueryComponent: // §3.4
   131  			// The RFC reserves (so we must escape) everything.
   132  			return true
   133  
   134  		case encodeFragment: // §4.1
   135  			// The RFC text is silent but the grammar allows
   136  			// everything, so escape nothing.
   137  			return false
   138  		}
   139  	}
   140  
   141  	// Everything else must be escaped.
   142  	return true
   143  }
   144  
   145  // QueryUnescape does the inverse transformation of QueryEscape, converting
   146  // %AB into the byte 0xAB and '+' into ' ' (space). It returns an error if
   147  // any % is not followed by two hexadecimal digits.
   148  func QueryUnescape(s string) (string, error) {
   149  	return unescape(s, encodeQueryComponent)
   150  }
   151  
   152  // unescape unescapes a string; the mode specifies
   153  // which section of the URL string is being unescaped.
   154  func unescape(s string, mode encoding) (string, error) {
   155  	// Count %, check that they're well-formed.
   156  	n := 0
   157  	hasPlus := false
   158  	for i := 0; i < len(s); {
   159  		switch s[i] {
   160  		case '%':
   161  			n++
   162  			if i+2 >= len(s) || !ishex(s[i+1]) || !ishex(s[i+2]) {
   163  				s = s[i:]
   164  				if len(s) > 3 {
   165  					s = s[:3]
   166  				}
   167  				return "", EscapeError(s)
   168  			}
   169  			i += 3
   170  		case '+':
   171  			hasPlus = mode == encodeQueryComponent
   172  			i++
   173  		default:
   174  			i++
   175  		}
   176  	}
   177  
   178  	if n == 0 && !hasPlus {
   179  		return s, nil
   180  	}
   181  
   182  	t := make([]byte, len(s)-2*n)
   183  	j := 0
   184  	for i := 0; i < len(s); {
   185  		switch s[i] {
   186  		case '%':
   187  			t[j] = unhex(s[i+1])<<4 | unhex(s[i+2])
   188  			j++
   189  			i += 3
   190  		case '+':
   191  			if mode == encodeQueryComponent {
   192  				t[j] = ' '
   193  			} else {
   194  				t[j] = '+'
   195  			}
   196  			j++
   197  			i++
   198  		default:
   199  			t[j] = s[i]
   200  			j++
   201  			i++
   202  		}
   203  	}
   204  	return string(t), nil
   205  }
   206  
   207  // QueryEscape escapes the string so it can be safely placed
   208  // inside a URL query.
   209  func QueryEscape(s string) string {
   210  	return escape(s, encodeQueryComponent)
   211  }
   212  
   213  func escape(s string, mode encoding) string {
   214  	spaceCount, hexCount := 0, 0
   215  	for i := 0; i < len(s); i++ {
   216  		c := s[i]
   217  		if shouldEscape(c, mode) {
   218  			if c == ' ' && mode == encodeQueryComponent {
   219  				spaceCount++
   220  			} else {
   221  				hexCount++
   222  			}
   223  		}
   224  	}
   225  
   226  	if spaceCount == 0 && hexCount == 0 {
   227  		return s
   228  	}
   229  
   230  	t := make([]byte, len(s)+2*hexCount)
   231  	j := 0
   232  	for i := 0; i < len(s); i++ {
   233  		switch c := s[i]; {
   234  		case c == ' ' && mode == encodeQueryComponent:
   235  			t[j] = '+'
   236  			j++
   237  		case shouldEscape(c, mode):
   238  			t[j] = '%'
   239  			t[j+1] = "0123456789ABCDEF"[c>>4]
   240  			t[j+2] = "0123456789ABCDEF"[c&15]
   241  			j += 3
   242  		default:
   243  			t[j] = s[i]
   244  			j++
   245  		}
   246  	}
   247  	return string(t)
   248  }
   249  
   250  // A URL represents a parsed URL (technically, a URI reference).
   251  // The general form represented is:
   252  //
   253  //	scheme://[userinfo@]host/path[?query][#fragment]
   254  //
   255  // URLs that do not start with a slash after the scheme are interpreted as:
   256  //
   257  //	scheme:opaque[?query][#fragment]
   258  //
   259  // Note that the Path field is stored in decoded form: /%47%6f%2f becomes /Go/.
   260  // A consequence is that it is impossible to tell which slashes in the Path were
   261  // slashes in the raw URL and which were %2f. This distinction is rarely important,
   262  // but when it is, code must not use Path directly.
   263  //
   264  // Go 1.5 introduced the RawPath field to hold the encoded form of Path.
   265  // The Parse function sets both Path and RawPath in the URL it returns,
   266  // and URL's String method uses RawPath if it is a valid encoding of Path,
   267  // by calling the EscapedPath method.
   268  //
   269  // In earlier versions of Go, the more indirect workarounds were that an
   270  // HTTP server could consult req.RequestURI and an HTTP client could
   271  // construct a URL struct directly and set the Opaque field instead of Path.
   272  // These still work as well.
   273  type URL struct {
   274  	Scheme   string
   275  	Opaque   string    // encoded opaque data
   276  	User     *Userinfo // username and password information
   277  	Host     string    // host or host:port
   278  	Path     string
   279  	RawPath  string // encoded path hint (Go 1.5 and later only; see EscapedPath method)
   280  	RawQuery string // encoded query values, without '?'
   281  	Fragment string // fragment for references, without '#'
   282  }
   283  
   284  // User returns a Userinfo containing the provided username
   285  // and no password set.
   286  func User(username string) *Userinfo {
   287  	return &Userinfo{username, "", false}
   288  }
   289  
   290  // UserPassword returns a Userinfo containing the provided username
   291  // and password.
   292  // This functionality should only be used with legacy web sites.
   293  // RFC 2396 warns that interpreting Userinfo this way
   294  // ``is NOT RECOMMENDED, because the passing of authentication
   295  // information in clear text (such as URI) has proven to be a
   296  // security risk in almost every case where it has been used.''
   297  func UserPassword(username, password string) *Userinfo {
   298  	return &Userinfo{username, password, true}
   299  }
   300  
   301  // The Userinfo type is an immutable encapsulation of username and
   302  // password details for a URL. An existing Userinfo value is guaranteed
   303  // to have a username set (potentially empty, as allowed by RFC 2396),
   304  // and optionally a password.
   305  type Userinfo struct {
   306  	username    string
   307  	password    string
   308  	passwordSet bool
   309  }
   310  
   311  // Username returns the username.
   312  func (u *Userinfo) Username() string {
   313  	return u.username
   314  }
   315  
   316  // Password returns the password in case it is set, and whether it is set.
   317  func (u *Userinfo) Password() (string, bool) {
   318  	if u.passwordSet {
   319  		return u.password, true
   320  	}
   321  	return "", false
   322  }
   323  
   324  // String returns the encoded userinfo information in the standard form
   325  // of "username[:password]".
   326  func (u *Userinfo) String() string {
   327  	s := escape(u.username, encodeUserPassword)
   328  	if u.passwordSet {
   329  		s += ":" + escape(u.password, encodeUserPassword)
   330  	}
   331  	return s
   332  }
   333  
   334  // Maybe rawurl is of the form scheme:path.
   335  // (Scheme must be [a-zA-Z][a-zA-Z0-9+-.]*)
   336  // If so, return scheme, path; else return "", rawurl.
   337  func getscheme(rawurl string) (scheme, path string, err error) {
   338  	for i := 0; i < len(rawurl); i++ {
   339  		c := rawurl[i]
   340  		switch {
   341  		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
   342  		// do nothing
   343  		case '0' <= c && c <= '9' || c == '+' || c == '-' || c == '.':
   344  			if i == 0 {
   345  				return "", rawurl, nil
   346  			}
   347  		case c == ':':
   348  			if i == 0 {
   349  				return "", "", errors.New("missing protocol scheme")
   350  			}
   351  			return rawurl[:i], rawurl[i+1:], nil
   352  		default:
   353  			// we have encountered an invalid character,
   354  			// so there is no valid scheme
   355  			return "", rawurl, nil
   356  		}
   357  	}
   358  	return "", rawurl, nil
   359  }
   360  
   361  // Maybe s is of the form t c u.
   362  // If so, return t, c u (or t, u if cutc == true).
   363  // If not, return s, "".
   364  func split(s string, c string, cutc bool) (string, string) {
   365  	i := strings.Index(s, c)
   366  	if i < 0 {
   367  		return s, ""
   368  	}
   369  	if cutc {
   370  		return s[:i], s[i+len(c):]
   371  	}
   372  	return s[:i], s[i:]
   373  }
   374  
   375  // Parse parses rawurl into a URL structure.
   376  // The rawurl may be relative or absolute.
   377  func Parse(rawurl string) (url *URL, err error) {
   378  	// Cut off #frag
   379  	u, frag := split(rawurl, "#", true)
   380  	if url, err = parse(u, false); err != nil {
   381  		return nil, err
   382  	}
   383  	if frag == "" {
   384  		return url, nil
   385  	}
   386  	if url.Fragment, err = unescape(frag, encodeFragment); err != nil {
   387  		return nil, &Error{"parse", rawurl, err}
   388  	}
   389  	return url, nil
   390  }
   391  
   392  // ParseRequestURI parses rawurl into a URL structure.  It assumes that
   393  // rawurl was received in an HTTP request, so the rawurl is interpreted
   394  // only as an absolute URI or an absolute path.
   395  // The string rawurl is assumed not to have a #fragment suffix.
   396  // (Web browsers strip #fragment before sending the URL to a web server.)
   397  func ParseRequestURI(rawurl string) (url *URL, err error) {
   398  	return parse(rawurl, true)
   399  }
   400  
   401  // parse parses a URL from a string in one of two contexts.  If
   402  // viaRequest is true, the URL is assumed to have arrived via an HTTP request,
   403  // in which case only absolute URLs or path-absolute relative URLs are allowed.
   404  // If viaRequest is false, all forms of relative URLs are allowed.
   405  func parse(rawurl string, viaRequest bool) (url *URL, err error) {
   406  	var rest string
   407  
   408  	if rawurl == "" && viaRequest {
   409  		err = errors.New("empty url")
   410  		goto Error
   411  	}
   412  	url = new(URL)
   413  
   414  	if rawurl == "*" {
   415  		url.Path = "*"
   416  		return
   417  	}
   418  
   419  	// Split off possible leading "http:", "mailto:", etc.
   420  	// Cannot contain escaped characters.
   421  	if url.Scheme, rest, err = getscheme(rawurl); err != nil {
   422  		goto Error
   423  	}
   424  	url.Scheme = strings.ToLower(url.Scheme)
   425  
   426  	rest, url.RawQuery = split(rest, "?", true)
   427  
   428  	if !strings.HasPrefix(rest, "/") {
   429  		if url.Scheme != "" {
   430  			// We consider rootless paths per RFC 3986 as opaque.
   431  			url.Opaque = rest
   432  			return url, nil
   433  		}
   434  		if viaRequest {
   435  			err = errors.New("invalid URI for request")
   436  			goto Error
   437  		}
   438  	}
   439  
   440  	if (url.Scheme != "" || !viaRequest && !strings.HasPrefix(rest, "///")) && strings.HasPrefix(rest, "//") {
   441  		var authority string
   442  		authority, rest = split(rest[2:], "/", false)
   443  		url.User, url.Host, err = parseAuthority(authority)
   444  		if err != nil {
   445  			goto Error
   446  		}
   447  	}
   448  	if url.Path, err = unescape(rest, encodePath); err != nil {
   449  		goto Error
   450  	}
   451  	// RawPath is a hint as to the encoding of Path to use
   452  	// in url.EscapedPath. If that method already gets the
   453  	// right answer without RawPath, leave it empty.
   454  	// This will help make sure that people don't rely on it in general.
   455  	if url.EscapedPath() != rest && validEncodedPath(rest) {
   456  		url.RawPath = rest
   457  	}
   458  	return url, nil
   459  
   460  Error:
   461  	return nil, &Error{"parse", rawurl, err}
   462  }
   463  
   464  func parseAuthority(authority string) (user *Userinfo, host string, err error) {
   465  	i := strings.LastIndex(authority, "@")
   466  	if i < 0 {
   467  		host, err = parseHost(authority)
   468  	} else {
   469  		host, err = parseHost(authority[i+1:])
   470  	}
   471  	if err != nil {
   472  		return nil, "", err
   473  	}
   474  	if i < 0 {
   475  		return nil, host, nil
   476  	}
   477  	userinfo := authority[:i]
   478  	if strings.Index(userinfo, ":") < 0 {
   479  		if userinfo, err = unescape(userinfo, encodeUserPassword); err != nil {
   480  			return nil, "", err
   481  		}
   482  		user = User(userinfo)
   483  	} else {
   484  		username, password := split(userinfo, ":", true)
   485  		if username, err = unescape(username, encodeUserPassword); err != nil {
   486  			return nil, "", err
   487  		}
   488  		if password, err = unescape(password, encodeUserPassword); err != nil {
   489  			return nil, "", err
   490  		}
   491  		user = UserPassword(username, password)
   492  	}
   493  	return user, host, nil
   494  }
   495  
   496  // parseHost parses host as an authority without user
   497  // information. That is, as host[:port].
   498  func parseHost(host string) (string, error) {
   499  	litOrName := host
   500  	if strings.HasPrefix(host, "[") {
   501  		// Parse an IP-Literal in RFC 3986 and RFC 6874.
   502  		// E.g., "[fe80::1], "[fe80::1%25en0]"
   503  		//
   504  		// RFC 4007 defines "%" as a delimiter character in
   505  		// the textual representation of IPv6 addresses.
   506  		// Per RFC 6874, in URIs that "%" is encoded as "%25".
   507  		i := strings.LastIndex(host, "]")
   508  		if i < 0 {
   509  			return "", errors.New("missing ']' in host")
   510  		}
   511  		colonPort := host[i+1:]
   512  		if !validOptionalPort(colonPort) {
   513  			return "", fmt.Errorf("invalid port %q after host", colonPort)
   514  		}
   515  		// Parse a host subcomponent without a ZoneID in RFC
   516  		// 6874 because the ZoneID is allowed to use the
   517  		// percent encoded form.
   518  		j := strings.Index(host[:i], "%25")
   519  		if j < 0 {
   520  			litOrName = host[1:i]
   521  		} else {
   522  			litOrName = host[1:j]
   523  		}
   524  	}
   525  
   526  	// A URI containing an IP-Literal without a ZoneID or
   527  	// IPv4address in RFC 3986 and RFC 6847 must not be
   528  	// percent-encoded.
   529  	//
   530  	// A URI containing a DNS registered name in RFC 3986 is
   531  	// allowed to be percent-encoded, though we don't use it for
   532  	// now to avoid messing up with the gap between allowed
   533  	// characters in URI and allowed characters in DNS.
   534  	// See golang.org/issue/7991.
   535  	if strings.Contains(litOrName, "%") {
   536  		return "", errors.New("percent-encoded characters in host")
   537  	}
   538  	var err error
   539  	if host, err = unescape(host, encodeHost); err != nil {
   540  		return "", err
   541  	}
   542  	return host, nil
   543  }
   544  
   545  // EscapedPath returns the escaped form of u.Path.
   546  // In general there are multiple possible escaped forms of any path.
   547  // EscapedPath returns u.RawPath when it is a valid escaping of u.Path.
   548  // Otherwise EscapedPath ignores u.RawPath and computes an escaped
   549  // form on its own.
   550  // The String and RequestURI methods use EscapedPath to construct
   551  // their results.
   552  // In general, code should call EscapedPath instead of
   553  // reading u.RawPath directly.
   554  func (u *URL) EscapedPath() string {
   555  	if u.RawPath != "" && validEncodedPath(u.RawPath) {
   556  		p, err := unescape(u.RawPath, encodePath)
   557  		if err == nil && p == u.Path {
   558  			return u.RawPath
   559  		}
   560  	}
   561  	if u.Path == "*" {
   562  		return "*" // don't escape (Issue 11202)
   563  	}
   564  	return escape(u.Path, encodePath)
   565  }
   566  
   567  // validEncodedPath reports whether s is a valid encoded path.
   568  // It must not contain any bytes that require escaping during path encoding.
   569  func validEncodedPath(s string) bool {
   570  	for i := 0; i < len(s); i++ {
   571  		// RFC 3986, Appendix A.
   572  		// pchar = unreserved / pct-encoded / sub-delims / ":" / "@".
   573  		// shouldEscape is not quite compliant with the RFC,
   574  		// so we check the sub-delims ourselves and let
   575  		// shouldEscape handle the others.
   576  		switch s[i] {
   577  		case '!', '$', '&', '\'', '(', ')', '*', '+', ',', ';', '=', ':', '@':
   578  			// ok
   579  		case '[', ']':
   580  			// ok - not specified in RFC 3986 but left alone by modern browsers
   581  		case '%':
   582  			// ok - percent encoded, will decode
   583  		default:
   584  			if shouldEscape(s[i], encodePath) {
   585  				return false
   586  			}
   587  		}
   588  	}
   589  	return true
   590  }
   591  
   592  // validOptionalPort reports whether port is either an empty string
   593  // or matches /^:\d+$/
   594  func validOptionalPort(port string) bool {
   595  	if port == "" {
   596  		return true
   597  	}
   598  	if port[0] != ':' || len(port) == 1 {
   599  		return false
   600  	}
   601  	for _, b := range port[1:] {
   602  		if b < '0' || b > '9' {
   603  			return false
   604  		}
   605  	}
   606  	return true
   607  }
   608  
   609  // String reassembles the URL into a valid URL string.
   610  // The general form of the result is one of:
   611  //
   612  //	scheme:opaque?query#fragment
   613  //	scheme://userinfo@host/path?query#fragment
   614  //
   615  // If u.Opaque is non-empty, String uses the first form;
   616  // otherwise it uses the second form.
   617  // To obtain the path, String uses u.EscapedPath().
   618  //
   619  // In the second form, the following rules apply:
   620  //	- if u.Scheme is empty, scheme: is omitted.
   621  //	- if u.User is nil, userinfo@ is omitted.
   622  //	- if u.Host is empty, host/ is omitted.
   623  //	- if u.Scheme and u.Host are empty and u.User is nil,
   624  //	   the entire scheme://userinfo@host/ is omitted.
   625  //	- if u.Host is non-empty and u.Path begins with a /,
   626  //	   the form host/path does not add its own /.
   627  //	- if u.RawQuery is empty, ?query is omitted.
   628  //	- if u.Fragment is empty, #fragment is omitted.
   629  func (u *URL) String() string {
   630  	var buf bytes.Buffer
   631  	if u.Scheme != "" {
   632  		buf.WriteString(u.Scheme)
   633  		buf.WriteByte(':')
   634  	}
   635  	if u.Opaque != "" {
   636  		buf.WriteString(u.Opaque)
   637  	} else {
   638  		if u.Scheme != "" || u.Host != "" || u.User != nil {
   639  			buf.WriteString("//")
   640  			if ui := u.User; ui != nil {
   641  				buf.WriteString(ui.String())
   642  				buf.WriteByte('@')
   643  			}
   644  			if h := u.Host; h != "" {
   645  				buf.WriteString(escape(h, encodeHost))
   646  			}
   647  		}
   648  		path := u.EscapedPath()
   649  		if path != "" && path[0] != '/' && u.Host != "" {
   650  			buf.WriteByte('/')
   651  		}
   652  		buf.WriteString(path)
   653  	}
   654  	if u.RawQuery != "" {
   655  		buf.WriteByte('?')
   656  		buf.WriteString(u.RawQuery)
   657  	}
   658  	if u.Fragment != "" {
   659  		buf.WriteByte('#')
   660  		buf.WriteString(escape(u.Fragment, encodeFragment))
   661  	}
   662  	return buf.String()
   663  }
   664  
   665  // Values maps a string key to a list of values.
   666  // It is typically used for query parameters and form values.
   667  // Unlike in the http.Header map, the keys in a Values map
   668  // are case-sensitive.
   669  type Values map[string][]string
   670  
   671  // Get gets the first value associated with the given key.
   672  // If there are no values associated with the key, Get returns
   673  // the empty string. To access multiple values, use the map
   674  // directly.
   675  func (v Values) Get(key string) string {
   676  	if v == nil {
   677  		return ""
   678  	}
   679  	vs, ok := v[key]
   680  	if !ok || len(vs) == 0 {
   681  		return ""
   682  	}
   683  	return vs[0]
   684  }
   685  
   686  // Set sets the key to value. It replaces any existing
   687  // values.
   688  func (v Values) Set(key, value string) {
   689  	v[key] = []string{value}
   690  }
   691  
   692  // Add adds the value to key. It appends to any existing
   693  // values associated with key.
   694  func (v Values) Add(key, value string) {
   695  	v[key] = append(v[key], value)
   696  }
   697  
   698  // Del deletes the values associated with key.
   699  func (v Values) Del(key string) {
   700  	delete(v, key)
   701  }
   702  
   703  // ParseQuery parses the URL-encoded query string and returns
   704  // a map listing the values specified for each key.
   705  // ParseQuery always returns a non-nil map containing all the
   706  // valid query parameters found; err describes the first decoding error
   707  // encountered, if any.
   708  func ParseQuery(query string) (m Values, err error) {
   709  	m = make(Values)
   710  	err = parseQuery(m, query)
   711  	return
   712  }
   713  
   714  func parseQuery(m Values, query string) (err error) {
   715  	for query != "" {
   716  		key := query
   717  		if i := strings.IndexAny(key, "&;"); i >= 0 {
   718  			key, query = key[:i], key[i+1:]
   719  		} else {
   720  			query = ""
   721  		}
   722  		if key == "" {
   723  			continue
   724  		}
   725  		value := ""
   726  		if i := strings.Index(key, "="); i >= 0 {
   727  			key, value = key[:i], key[i+1:]
   728  		}
   729  		key, err1 := QueryUnescape(key)
   730  		if err1 != nil {
   731  			if err == nil {
   732  				err = err1
   733  			}
   734  			continue
   735  		}
   736  		value, err1 = QueryUnescape(value)
   737  		if err1 != nil {
   738  			if err == nil {
   739  				err = err1
   740  			}
   741  			continue
   742  		}
   743  		m[key] = append(m[key], value)
   744  	}
   745  	return err
   746  }
   747  
   748  // Encode encodes the values into ``URL encoded'' form
   749  // ("bar=baz&foo=quux") sorted by key.
   750  func (v Values) Encode() string {
   751  	if v == nil {
   752  		return ""
   753  	}
   754  	var buf bytes.Buffer
   755  	keys := make([]string, 0, len(v))
   756  	for k := range v {
   757  		keys = append(keys, k)
   758  	}
   759  	sort.Strings(keys)
   760  	for _, k := range keys {
   761  		vs := v[k]
   762  		prefix := QueryEscape(k) + "="
   763  		for _, v := range vs {
   764  			if buf.Len() > 0 {
   765  				buf.WriteByte('&')
   766  			}
   767  			buf.WriteString(prefix)
   768  			buf.WriteString(QueryEscape(v))
   769  		}
   770  	}
   771  	return buf.String()
   772  }
   773  
   774  // resolvePath applies special path segments from refs and applies
   775  // them to base, per RFC 3986.
   776  func resolvePath(base, ref string) string {
   777  	var full string
   778  	if ref == "" {
   779  		full = base
   780  	} else if ref[0] != '/' {
   781  		i := strings.LastIndex(base, "/")
   782  		full = base[:i+1] + ref
   783  	} else {
   784  		full = ref
   785  	}
   786  	if full == "" {
   787  		return ""
   788  	}
   789  	var dst []string
   790  	src := strings.Split(full, "/")
   791  	for _, elem := range src {
   792  		switch elem {
   793  		case ".":
   794  			// drop
   795  		case "..":
   796  			if len(dst) > 0 {
   797  				dst = dst[:len(dst)-1]
   798  			}
   799  		default:
   800  			dst = append(dst, elem)
   801  		}
   802  	}
   803  	if last := src[len(src)-1]; last == "." || last == ".." {
   804  		// Add final slash to the joined path.
   805  		dst = append(dst, "")
   806  	}
   807  	return "/" + strings.TrimLeft(strings.Join(dst, "/"), "/")
   808  }
   809  
   810  // IsAbs reports whether the URL is absolute.
   811  func (u *URL) IsAbs() bool {
   812  	return u.Scheme != ""
   813  }
   814  
   815  // Parse parses a URL in the context of the receiver.  The provided URL
   816  // may be relative or absolute.  Parse returns nil, err on parse
   817  // failure, otherwise its return value is the same as ResolveReference.
   818  func (u *URL) Parse(ref string) (*URL, error) {
   819  	refurl, err := Parse(ref)
   820  	if err != nil {
   821  		return nil, err
   822  	}
   823  	return u.ResolveReference(refurl), nil
   824  }
   825  
   826  // ResolveReference resolves a URI reference to an absolute URI from
   827  // an absolute base URI, per RFC 3986 Section 5.2.  The URI reference
   828  // may be relative or absolute.  ResolveReference always returns a new
   829  // URL instance, even if the returned URL is identical to either the
   830  // base or reference. If ref is an absolute URL, then ResolveReference
   831  // ignores base and returns a copy of ref.
   832  func (u *URL) ResolveReference(ref *URL) *URL {
   833  	url := *ref
   834  	if ref.Scheme == "" {
   835  		url.Scheme = u.Scheme
   836  	}
   837  	if ref.Scheme != "" || ref.Host != "" || ref.User != nil {
   838  		// The "absoluteURI" or "net_path" cases.
   839  		url.Path = resolvePath(ref.Path, "")
   840  		return &url
   841  	}
   842  	if ref.Opaque != "" {
   843  		url.User = nil
   844  		url.Host = ""
   845  		url.Path = ""
   846  		return &url
   847  	}
   848  	if ref.Path == "" {
   849  		if ref.RawQuery == "" {
   850  			url.RawQuery = u.RawQuery
   851  			if ref.Fragment == "" {
   852  				url.Fragment = u.Fragment
   853  			}
   854  		}
   855  	}
   856  	// The "abs_path" or "rel_path" cases.
   857  	url.Host = u.Host
   858  	url.User = u.User
   859  	url.Path = resolvePath(u.Path, ref.Path)
   860  	return &url
   861  }
   862  
   863  // Query parses RawQuery and returns the corresponding values.
   864  func (u *URL) Query() Values {
   865  	v, _ := ParseQuery(u.RawQuery)
   866  	return v
   867  }
   868  
   869  // RequestURI returns the encoded path?query or opaque?query
   870  // string that would be used in an HTTP request for u.
   871  func (u *URL) RequestURI() string {
   872  	result := u.Opaque
   873  	if result == "" {
   874  		result = u.EscapedPath()
   875  		if result == "" {
   876  			result = "/"
   877  		}
   878  	} else {
   879  		if strings.HasPrefix(result, "//") {
   880  			result = u.Scheme + ":" + result
   881  		}
   882  	}
   883  	if u.RawQuery != "" {
   884  		result += "?" + u.RawQuery
   885  	}
   886  	return result
   887  }