[摘录]URL规范

简写:
URL: Uniform Resource Locators
URI: Uniform Resource Identicators

全格式:
protocol://user:password@host:port/directory/file.extension?query=value#hash

一、格式说明
“|” 表示隔开的两部分只能出现其中一个，方括号[]括起来的表示可选，文字由双引号””括起来，以n*开头表示至少n个或更多的，n的缺省值为0。

二、总体格式
genericurl     = scheme “:” schemepart

scheme         = 1*[ lowalpha | digit | “+” | “-” | “.” ]
schemepart     = *xchar | ip-schemepart

ip-schemepart  = “//” login [ “/” urlpath ]
login          = [ user [ “:” password ] “@” ] hostport
hostport       = host [ “:” port ]
host           = hostname | hostnumber
hostname       = *[ domainlabel “.” ] toplabel
domainlabel    = alphadigit | alphadigit *[ alphadigit | “-” ] alphadigit
toplabel       = alpha | alpha *[ alphadigit | “-” ] alphadigit
alphadigit     = alpha | digit
hostnumber     = digits “.” digits “.” digits “.” digits
port           = digits
user           = *[ uchar | “;” | “?” | “&” | “=” ]
password       = *[ uchar | “;” | “?” | “&” | “=” ]
urlpath        = *xchar    ; depends on protocol see section 3.1三、常见scheme
; FTP (参见RFC959)
ftpurl         = “ftp://” login [ “/” fpath [ “;type=” ftptype ]]
fpath          = fsegment *[ “/” fsegment ]
fsegment       = *[ uchar | “?” | “:” | “@” | “&” | “=” ]
ftptype        = “A” | “I” | “D” | “a” | “i” | “d”

; FILE
fileurl        = “file://” [ host | “localhost” ] “/” fpath

; HTTP
httpurl        = “http://” hostport [ “/” hpath [ “?” search ]]
hpath          = hsegment *[ “/” hsegment ]
hsegment       = *[ uchar | “;” | “:” | “@” | “&” | “=” ]
search         = *[ uchar | “;” | “:” | “@” | “&” | “=” ]

; GOPHER (参见RFC1436)
gopherurl      = “gopher://” hostport [ / [ gtype [ selector
                 [ “%09″ search [ “%09″ gopher+_string ] ] ] ] ]
gtype          = xchar
selector       = *xchar
gopher+_string = *xchar

; MAILTO (参见 RFC822)

mailtourl      = “mailto:” encoded822addr
encoded822addr = 1*xchar               ; further defined in RFC822

; NEWS (参见 RFC1036)
newsurl        = “news:” grouppart
grouppart      = “*” | group | article
group          = alpha *[ alpha | digit | “-” | “.” | “+” | “_” ]
article        = 1*[ uchar | “;” | “/” | “?” | “:” | “&” | “=” ] “@” host

; NNTP (参见RFC977)
nntpurl        = “nntp://” hostport “/” group [ “/” digits ]

; TELNET
telneturl      = “telnet://” login [ “/” ]

; WAIS (参见 RFC1625)
waisurl        = waisdatabase | waisindex | waisdoc
waisdatabase   = “wais://” hostport “/” database
waisindex      = “wais://” hostport “/” database “?” search
waisdoc        = “wais://” hostport “/” database “/” wtype “/” wpath
database       = *uchar
wtype          = *uchar
wpath          = *uchar

; PROSPERO
prosperourl    = “prospero://” hostport “/” ppath *[ fieldspec ]
ppath          = psegment *[ “/” psegment ]
psegment       = *[ uchar | “?” | “:” | “@” | “&” | “=” ]
fieldspec      = “;” fieldname “=” fieldvalue
fieldname      = *[ uchar | “?” | “:” | “@” | “&” ]
fieldvalue     = *[ uchar | “?” | “:” | “@” | “&” ]四、杂类
lowalpha       = “a” | “b” | “c” | “d” | “e” | “f” | “g” | “h” |
                 “i” | “j” | “k” | “l” | “m” | “n” | “o” | “p” |
                 “q” | “r” | “s” | “t” | “u” | “v” | “w” | “x” |
                 “y” | “z”
hialpha        = “A” | “B” | “C” | “D” | “E” | “F” | “G” | “H” | “I” |
                 “J” | “K” | “L” | “M” | “N” | “O” | “P” | “Q” | “R” |
                 “S” | “T” | “U” | “V” | “W” | “X” | “Y” | “Z”

alpha          = lowalpha | hialpha
digit          = “0″ | “1″ | “2″ | “3″ | “4″ | “5″ | “6″ | “7″ |
                 “8″ | “9″
safe           = “$” | “-” | “_” | “.” | “+”
extra          = “!” | “*” | “‘” | “(” | “)” | “,”
national       = “{” | “}” | “|” | “\” | “^” | “~” | “[” | “]” | “`”
punctuation    = “<” | “>” | “#” | “%” | <”>

reserved       = “;” | “/” | “?” | “:” | “@” | “&” | “=”
hex            = digit | “A” | “B” | “C” | “D” | “E” | “F” |
                 “a” | “b” | “c” | “d” | “e” | “f”
escape         = “%” hex hex

unreserved     = alpha | digit | safe | extra
uchar          = unreserved | escape
xchar          = unreserved | reserved | escape
digits         = 1*digit