Find URI in text
Write a function to search plain text for URIs or IRIs.
The function should return a list of URIs or IRIs found in the text.
The definition of a URI is given in RFC 3986. IRI is defined in RFC 3987.
For searching URIs in particular "Appendix C. Delimiting a URI in Context" is noteworthy.
Consider the following issues:
. , ; ' ? ( )are legal characters in a URI, but they are often used in plain text as a delimiter.- IRIs allow most (but not all) unicode characters.
- URIs can be something else besides http:// or https://
sample text:
this URI contains an illegal character, parentheses and a misplaced full stop: http://en.wikipedia.org/wiki/Erich_Kästner_(camera_designer). (which is handled by http://mediawiki.org/). and another one just to confuse the parser: http://en.wikipedia.org/wiki/-) ")" is handled the wrong way by the mediawiki parser. ftp://domain.name/path(balanced_brackets)/foo.html ftp://domain.name/path(balanced_brackets)/ending.in.dot. ftp://domain.name/path(unbalanced_brackets/ending.in.dot. leading junk ftp://domain.name/path/embedded?punct/uation. leading junk ftp://domain.name/dangling_close_paren) if you have other interesting URIs for testing, please add them here:
Regular expressions to solve the task are fine, but alternative approaches are welcome too. (otherwise, this task would degrade into 'finding and applying the best regular expression')
Extra Credit: implement the parser to match the IRI specification in RFC 3987.
Icon and Unicon
This example follows RFC 3986 very closely (see Talk page for discussion). For better IP parsing see Parse_an_IP_Address. This solution doesn't handle IRIs per RFC 3987. Neither Icon nor Unicon natively support Unicode although ObjectIcon does. This solution doesn't currently handle delimitation explicitly. Examples of the form <URI> or "URI" aren't needed as they will correctly parse in any event. Ambiguous examples like (URI) which use valid URI characters will currently parse as URI) and not URI. URIs are returned per the RFC. For example URIs ending in dots are currently returned with the dot. Once the information is lost the user must guess and reconstruct; however, it's far easier to make remove a character if the URI doesn't work.
Filtering of URIs for disambiguation and delineation would be best handled in the 'findURItext' procedure. It might also be a good idea to return both unfiltered and filtered URIs here.
<lang Icon>procedure main()
every write(findURItext("this URI contains an illegal character, parentheses_
and a misplaced full stop:\n_
http://en.wikipedia.org/wiki/Erich_Kästner_(camera_designer). _
which is handled by http://mediawiki.org/).\n_
and another one just to confuse the parser: _
http://en.wikipedia.org/wiki/-)\n_
\")\" is handled the wrong way by the mediawiki parser.\n_
ftp://domain.name/path(balanced_brackets)/foo.html\n_
ftp://domain.name/path(balanced_brackets)/ending.in.dot.\n_
ftp://domain.name/path(unbalanced_brackets/ending.in.dot.\n_
leading junk ftp://domain.name/path/embedded?punct/uation.\n_
leading junk ftp://domain.name/dangling_close_paren)\n_
if you have other interesting URIs for testing, please add them here:"))
end
$define GENDELIM ':/?#[]@' $define SUBDELIM '!$&()*+,;=\ $define UNRESERVED &letters ++ &digits ++ '-._~' $define RESERVED GENDELIM++SUBDELIM $define HEXDIGITS '0123456789aAbBcCdDeEfF'
procedure findURItext(s) #: generate all syntatically valid URI's from s
local u
s ? while tab(upto(&letters)) || (u := URI()) do
suspend u # suspend result as parsed
end
procedure URI() #: match longest URI at cursor
static sc2
initial sc2 := &letters ++ &digits ++ '+-.' # scheme
suspend (
( tab(any(&letters)) || (tab(many(sc2)) |="") || =":" ) || # scheme
( (="//" || authority() || arbsp("/",segment)) | # heir ...
(="/" || ( path_rootless() |="")) |
path_rootless() |
=""
) ||
( ( ="?" || queryfrag() ) |="" ) || # query
( ( ="#" || queryfrag() ) |="" ) # fragment
)
end
procedure queryfrag() #: match a query or fragment
static pc initial pc := UNRESERVED ++ SUBDELIM ++ ':@/?' suspend arbcp(pc,pctencode)
end
procedure segment(n) #: match a pchar segment
static sc initial sc := UNRESERVED ++ SUBDELIM ++ ':@' suspend arbcp(sc,pctencode,n)
end
procedure segmentnc(n) #: match a pchar--':' segment
static sc initial sc := UNRESERVED ++ SUBDELIM ++ '@' suspend arbcp(sc,pctencode,n)
end
procedure path_rootless() #: match a rootless path
suspend segment(1) || arbsp("/",segment)
end
procedure authority() #: match authority
static uic,rnc
initial {
rnc := UNRESERVED ++ SUBDELIM # regular name
uic := rnc ++ ':' # userinfo
}
suspend ( (arbcp(uic,pctencode) || ="@") |="") || # userinfo
( IPsimple() | arbcp(rnc,pctencode) ) || # host
( (=":" || tab(many(&digits))) |="")
end
procedure IPsimple() #: match ip address (trickable )
static i4c,i6c,ifc
initial {
i4c := &digits ++ '.'
i6c := HEXDIGITS ++ '.:'
ifc := UNRESERVED ++ SUBDELIM ++ ':'
}
suspend (
="[" ||
( tab(many(i6c)) |
( ="v"||tab(any(HEXDIGITS))||="."||tab(any(ifc))||tab(many(ifc)) )
) || ="]" ) | tab(many(i4c))
end
procedure arbcp(cs,pr,n) #: match arbitrary numbers of (cset|proc,n)
local p,i /n := 0 # for 0* / 1* runerr(0 > n,205) p := &pos i := 0 while tab(many(cs)) | pr() do i +:= 1 if i >= n then suspend &subject[p:&pos] &pos := p # restore &pos
end
procedure arbsp(st,pr,n) #: match arbitrary numbers of (string || proc,n)
local p,i /n := 0 # for 0* / 1* runerr(0 > n,205) p := &pos i := 0 while =st || pr() do i +:= 1 if i >= n then suspend &subject[p:&pos] &pos := p # restore &pos
end
procedure pctencode() #: match 1 % encoded single byte character
suspend ="%" || tab(any(HEXDIGITS)) || tab(any(HEXDIGITS))
end</lang>
Output:
stop: http://en.wikipedia.org/wiki/Erich_K http://mediawiki.org/). parser: http://en.wikipedia.org/wiki/-) ftp://domain.name/path(balanced_brackets)/foo.html ftp://domain.name/path(balanced_brackets)/ending.in.dot. ftp://domain.name/path(unbalanced_brackets/ending.in.dot. ftp://domain.name/path/embedded?punct/uation. ftp://domain.name/dangling_close_paren) here:
Pike
<lang Pike>string uritext = #"this URI contains an illegal character, parentheses and a misplaced full stop: http://en.wikipedia.org/wiki/Erich_Kästner_(camera_designer). which is handled by http://mediawiki.org/). and another one just to confuse the parser: http://en.wikipedia.org/wiki/-) \")\" is handled the wrong way by the mediawiki parser. ftp://domain.name/path(balanced_brackets)/foo.html ftp://domain.name/path(balanced_brackets)/ending.in.dot. ftp://domain.name/path(unbalanced_brackets/ending.in.dot. leading junk ftp://domain.name/path/embedded?punct/uation. leading junk ftp://domain.name/dangling_close_paren) if you have other interesting URIs for testing, please add them here:";
array find_uris(string uritext) {
array uris=({});
int pos=0;
while((pos = search(uritext, ":", pos+1))>0)
{
int prepos = sizeof(array_sscanf(reverse(uritext[pos-20..pos-1]), "%[a-zA-Z0-9+.-]%s")[0]);
int postpos = sizeof(array_sscanf(uritext[pos+1..], "%[^\n\r\t <>\"]%s")[0]);
if ((<'.',',','?','!',';'>)[uritext[pos+postpos]])
postpos--;
if (uritext[pos-prepos-1]=='(' && uritext[pos+postpos]==')')
postpos--;
if (uritext[pos-prepos-1]=='\ && uritext[pos+postpos]=='\)
postpos--;
uris+= ({ uritext[pos-prepos..pos+postpos] });
}
return uris;
}
find_uris(uritext); Result: ({ /* 11 elements */
"stop:",
"http://en.wikipedia.org/wiki/Erich_K\303\244stner_(camera_designer)",
"http://mediawiki.org/)",
"parser:",
"http://en.wikipedia.org/wiki/-)",
"ftp://domain.name/path(balanced_brackets)/foo.html",
"ftp://domain.name/path(balanced_brackets)/ending.in.dot",
"ftp://domain.name/path(unbalanced_brackets/ending.in.dot",
"ftp://domain.name/path/embedded?punct/uation",
"ftp://domain.name/dangling_close_paren)",
"here:"
})</lang>
TXR
<lang txr>@(define path (path))@\
@(local x y)@\
@(cases)@\
(@(path x))@(path y)@(bind path `(@x)@y`)@\
@(or)@\
@{x /[.,;'!?][^ \t\f\v]/}@(path y)@(bind path `@x@y`)@\
@(or)@\
@{x /[^ .,;'!?()\t\f\v]/}@(path y)@(bind path `@x@y`)@\
@(or)@\
@(bind path "")@\
@(end)@\
@(end) @(define url (url))@\
@(local proto domain path)@\
@{proto /[A-Za-z]+/}://@{domain /[^ \/\t\f\v]+/}@\
@(cases)/@(path path)@\
@(bind url `@proto://@domain/@path`)@\
@(or)@\
@(bind url `@proto://@domain`)@\
@(end)@\
@(end) @(collect) @ (all) @line @ (and) @ (coll)@(url url)@(end)@(flatten url) @ (end) @(end) @(output) LINE
URLS
@ (repeat) @line @ (repeat)
@url
@ (end) @ (end) @(end)</lang>
Test file:
$ cat url-data Blah blah http://en.wikipedia.org/wiki/Erich_Kästner_(camera_designer). (Handled by http://mediawiki.org/). Confuse the parser: http://en.wikipedia.org/wiki/-) ftp://domain.name/path(balanced_brackets)/foo.html ftp://domain.name/path(balanced_brackets)/ending.in.dot. ftp://domain.name/path(unbalanced_brackets/ending.in.dot. leading junk ftp://domain.name/path/embedded?punct/uation. leading junk ftp://domain.name/dangling_close_paren)
Run:
$ txr url.txr url-data
LINE
URLS
----------------------
Blah blah http://en.wikipedia.org/wiki/Erich_Kästner_(camera_designer). (Handled by http://mediawiki.org/).
http://en.wikipedia.org/wiki/Erich_Kästner_(camera_designer)
http://mediawiki.org/
Confuse the parser: http://en.wikipedia.org/wiki/-)
http://en.wikipedia.org/wiki/-
ftp://domain.name/path(balanced_brackets)/foo.html
ftp://domain.name/path(balanced_brackets)/foo.html
ftp://domain.name/path(balanced_brackets)/ending.in.dot.
ftp://domain.name/path(balanced_brackets)/ending.in.dot
ftp://domain.name/path(unbalanced_brackets/ending.in.dot.
ftp://domain.name/path
leading junk ftp://domain.name/path/embedded?punct/uation.
ftp://domain.name/path/embedded?punct/uation
leading junk ftp://domain.name/dangling_close_paren)
ftp://domain.name/dangling_close_paren