I've been running into a problem that was revealed through our Google adwords-driven marketing campaign. One of the standard parameters used is "region". When a user searches and clicks on a sponsored link, Google generates a long URL to track the click and sends a bunch of stuff along in the referrer. We capture this for our records, and we've noticed that the "Region" parameter is coming through incorrectly. What should be
http://ravercats.com/meow?foo=bar®ion=catnip
is instead coming through as:
http://ravercats.com/meow?foo=bar®ion=catnip
I've verified that this occurs in all browsers. It's my understanding that HTML entity syntax is defined as follows:
&VALUE;
where the leading boundary is the ampersand and the closing boundary is the semicolon. Seems straightforward enough. The problem is that this isn't being respected for the ® entity, and it's wreaking all kinds of havoc throughout our system.
Does anyone know why this is occurring? Is it a bug in the DTD? (I'm looking for the current HTML DTD to see if I can make sense of it) I'm trying to figure out what would be common across browsers to make this happen, thus my looking for the DTD.
Here is a proof you can use. Take this code, make an HTML file out of it and render it in a browser:
<html>
http://foo.com/bar?foo=bar®ion=US®ister=lowpass®_test=fail&trademark=correct
</html>
EDIT: To everyone who's suggesting that I need to escape the entire URL, the example URLs above are exactly that, examples. The real URL is coming directly from Google and I have no control over how it is constructed. These suggestions, while valid, don't answer the question: "Why is this happening".
Although valid character references always have a semicolon at the end, some invalid named character references without a semicolon are, for backward compatibility reasons, recognized by modern browsers' HTML parsers.
Either you know what that entire list is, or you follow the HTML5 rules for when & is valid without being escaped (e.g. when followed by a space) or otherwise always escape & as & whenever in doubt.
For reference, the full list of named character references that are recognized without a semicolon is:
AElig, AMP, Aacute, Acirc, Agrave, Aring, Atilde, Auml, COPY, Ccedil,
ETH, Eacute, Ecirc, Egrave, Euml, GT, Iacute, Icirc, Igrave, Iuml, LT,
Ntilde, Oacute, Ocirc, Ograve, Oslash, Otilde, Ouml, QUOT, REG, THORN,
Uacute, Ucirc, Ugrave, Uuml, Yacute, aacute, acirc, acute, aelig,
agrave, amp, aring, atilde, auml, brvbar, ccedil, cedil, cent, copy,
curren, deg, divide, eacute, ecirc, egrave, eth, euml, frac12, frac14,
frac34, gt, iacute, icirc, iexcl, igrave, iquest, iuml, laquo, lt,
macr, micro, middot, nbsp, not, ntilde, oacute, ocirc, ograve, ordf,
ordm, oslash, otilde, ouml, para, plusmn, pound, quot, raquo, reg,
sect, shy, sup1, sup2, sup3, szlig, thorn, times, uacute, ucirc,
ugrave, uml, uuml, yacute, yen, yuml
However, it should be noted that only when in an attribute value, named character references in the above list are not processed as such by conforming HTML5 parsers if the next character is a = or a alphanumeric ASCII character.
For the full list of named character references with or without ending semicolons, see here.
This is a very messy business and depends on context (text content vs. attribute value).
Formally, by HTML specs up to and including HTML 4.01, an entity reference may appear without trailing semicolon, if the next character is not a name character. So e.g. ®ion= would be syntactically correct but undefined, as entity region has not been defined. XHTML makes the trailing semicolon required.
Browsers have traditionally played by other rules, though. Due to the common syntax of query URLs, they parse e.g. href="http://ravercats.com/meow?foo=bar®ion=catnip" so that ®ion is not treated as an entity reference but as just text data. And authors mostly used such constructs, even though they are formally incorrect.
Contrary to what the question seems to be saying, href="http://ravercats.com/meow?foo=bar®ion=catnip" actually works well. Problems arise when the string is not in an attribute value but inside text content, which is rather uncommon: we don’t normally write URLs in text. In text, ®ion= gets processed so that ® is recognized as an entity reference (for “®”) and the rest is just character data. Such odd behavior is being made official in HTML5 CR, where clause 8.2.4.69 Tokenizing character references describes the “double standard”:
If the character reference is being consumed as part of an attribute,
and the last character matched is not a ";" (U+003B) character, and
the next character is either a "=" (U+003D) character or in the range
ASCII digits, uppercase ASCII letters, or lowercase ASCII letters,
then, for historical reasons, all the characters that were matched
after the U+0026 AMPERSAND character (&) must be unconsumed, and
nothing is returned.
Thus, in an attribute value, even ®= would not be treated as containing a character reference, and still less ®ion=. (But reg_test= is a different case, due to the underscore character.)
In text content, other rules apply. The construct ®ion= causes then a parse error (by HTML5 CR rules), but with well-defined error handling: ® is recognized as a character reference.
Maybe try replacing your & as &? Ampersands are characters that must be escaped in HTML as well, because they are reserved to be used as parts of entities.
1: The following markup is invalid in the first place (use the W3C Markup Validation Service to verify):
In the above example, the & character should be encoded as &, like so:
2: Browsers are tolerant; they try to make sense out of broken HTML. In your case, all possibly valid HTML entities are converted to HTML entities.
Here is a simple solution and it may not work in all instances.
So from this:
http://ravercats.com/meow?status=Online®ion=Atlantis
To This:
http://ravercats.com/meow?region=Atlantis&status=Online
Because the ® as we know triggers the special character ®
Caveat: If you have no control over the order of your URL query string parameters then you'll have to change your variable name to something else.
Escape your output!
Simply enough, you need to encode the url format into html format for accurate representation (ideally you would do so with a template engine variable escaping function, but barring that, with htmlspecialchars($url) or htmlentities($url) in php).
See your test case and then the correctly encoded html at this jsfiddle:
http://jsfiddle.net/tchalvakspam/Fp3W6/
Inactive code here:
<div>
Unescaped:
<br>
http://foo.com/bar?foo=bar®ion=US®ister=lowpass®_test=fail&trademark=correct
</div>
<div>
Correctly escaped:
<br>
http://foo.com/bar?foo=bar®ion=US®ister=lowpass®_test=fail&trademark=correct
</div>
It seems to me that what you have received from google is not an actual URL but a variable which refers to a url (query-string). So, thats why it's being parsed as registration mark when rendered.
I would say, you owe to url-encode it and decode it whenever processing it. Like any other variable containing special entities.
To prevent this from happening you should encode urls, which replaces characters like the ampersand with a % and a hexadecimal number behind it in the url.
Is the ampersand the only character that should be encoded in an HTML attribute?
It's well known that this won't pass validation:
Because the ampersand should be &. Here's a direct link to the validation fail.
This guy lists a bunch of characters that should be encoded, but he's wrong. If you encode the first "/" in http:// the href won't work.
In ASP.NET, is there a helper method already built to handle this? Stuff like Server.UrlEncode and HtmlEncode obviously don't work - those are for different purposes.
I can build my own simple extension method (like .ToAttributeView()) which does a simple string replace.
Other than standard URI encoding of the values, & is the only character related to HTML entities that you have to worry about simply because this is the character that begins every HTML entity. Take for example the following URL:
http://query.com/?q=foo<=bar>=baz
Even though there aren't trailing semi-colons, since < is the entity for < and > is the entity for >, some old browsers would translate this URL to:
http://query.com/?q=foo<=bar>=baz
So you need to specify & as & to prevent this from occurring for links within an HTML parsed document.
The purpose of escaping characters is so that they won't be processed as arguments. So you actually don't want to encode the entire url, just the values you are passing via the querystring. For example:
http://example.com/?parameter1=<ENCODED VALUE>¶meter2=<ENCODED VALUE>
The url you showed is actually a perfectly valid url that will pass validation. However, the browser will interpret the & symbols as a break between parameters in the querystring. So your querystring:
?q=whatever&lang=en
Will actually be translated by the recipient as two parameters:
q = "whatever"
lang = "en"
For your url to work you just need to ensure that your values are being encoded:
?q=<ENCODED VALUE>&lang=<ENCODED VALUE>
Edit: The common problems page from the W3C you linked to is talking about edge cases when urls are rendered in html and the & is followed by text that could be interpreted as an entity reference (© for example). Here is a test in jsfiddle showing the url:
http://jsfiddle.net/YjPHA/1/
In Chrome and FireFox the links works correctly, but IE renders © as ©, breaking the link. I have to admit I've never had a problem with this in the wild (it would only affect those entity references which don't require a semicolon, which is a pretty small subset).
To ensure you're safe from this bug you can HTML encode any of your URLS you render to the page and you should be fine. If you're using ASP.NET the HttpUtility.HtmlEncode method should work just fine.
You do not need HTML escapement here:
According to the HTML5 spec:
http://www.w3.org/TR/html5/tokenization.html#character-reference-in-attribute-value-state
&lang= should be parsed as non-recognized character reference and value of the attribute should be used as it is: http://domain.com/search?q=whatever&lang=en
For the reference: added question to HTML5 WG: http://lists.w3.org/Archives/Public/public-html/2011Sep/0163.html
In HTML attribute values, if you want ", '&' and a non-breaking space as a result, you should (as an author who is clear about intent) have ", & and in the markup.
For " though, you don't have to use " if you use single quotes to encase your attribute values.
For HTML text nodes, in addition to the above, if you want < and > as a result, you should use < and >. (I'd even use these in attribute values too.)
For hfnames and hfvalues (and directory names in the path) for URIs, I'd used Javascript's encodeURIComponent() (on a utf-8 page when encoding for use on a utf-8 page).
If I understand the question correctly, I believe this is what you want.
I have a PHP script that will generate <input>s dynamically, so I was wondering if I needed to filter any characters in the name attribute.
I know that the name has to start with a letter, but I don't know any other rules. I figure square brackets must be allowed, since PHP uses these to create arrays from form data. How about parentheses? Spaces?
Note, that not all characters are submitted for name attributes of form fields (even when using POST)!
White-space characters are trimmed and inner white-space characters as well the character . are replaced by _.
(Tested in Chrome 23, Firefox 13 and Internet Explorer 9, all Win7.)
Any character you can include in an [X]HTML file is fine to put in an <input name>. As Allain's comment says, <input name> is defined as containing CDATA, so the only things you can't put in there are the control codes and invalid codepoints that the underlying standard (SGML or XML) disallows.
Allain quoted W3 from the HTML4 spec:
Note. The "get" method restricts form data set values to ASCII characters. Only the "post" method (with enctype="multipart/form-data") is specified to cover the entire ISO10646 character set.
However this isn't really true in practice.
The theory is that application/x-www-form-urlencoded data doesn't have a mechanism to specify an encoding for the form's names or values, so using non-ASCII characters in either is “not specified” as working and you should use POSTed multipart/form-data instead.
Unfortunately, in the real world, no browser specifies an encoding for fields even when it theoretically could, in the subpart headers of a multipart/form-data POST request body. (I believe Mozilla tried to implement it once, but backed out as it broke servers.)
And no browser implements the astonishingly complex and ugly RFC2231 standard that would be necessary to insert encoded non-ASCII field names into the multipart's subpart headers. In any case, the HTML spec that defines multipart/form-data doesn't directly say that RFC2231 should be used, and, again, it would break servers if you tried.
So the reality of the situation is there is no way to know what encoding is being used for the names and values in a form submission, no matter what type of form it is. What browsers will do with field names and values that contain non-ASCII characters is the same for GET and both types of POST form: it encodes them using the encoding the page containing the form used. Non-ASCII GET form names are no more broken than everything else.
DLH:
So name has a different data type for than it does for other elements?
Actually the only element whose name attribute is not CDATA is <meta>. See the HTML4 spec's attribute list for all the different uses of name; it's an overloaded attribute name, having many different meanings on the different elements. This is generally considered a bad thing.
However, typically these days you would avoid name except on form fields (where it's a control name) and param (where it's a plugin-specific parameter identifier). That's only two meanings to grapple with. The old-school use of name for identifying elements like <form> or <a> on the page should be avoided (use id instead).
The only real restriction on what characters can appear in form control names is when a form is submitted with GET
"The "get" method restricts form data set values to ASCII characters." reference
There's a good thread on it here.
While Allain's comment did answer OP's direct question and bobince provided some brilliant in-depth information, I believe many people come here seeking answer to more specific question: "Can I use a dot character in form's input name attribute?"
As this thread came up as first result when I searched for this knowledge I guessed I may as well share what I found.
Firstly, Matthias' claimed that:
character . are replaced by _
This is untrue. I don't know if browser's actually did this kind of operation back in 2013 - though, I doubt that. Browsers send dot characters as they are(talking about POST data)! You can check it in developer tools of any decent browser.
Please, notice that tiny little comment by abluejelly, that probably is missed by many:
I'd like to note that this is a server-specific thing, not a browser thing. Tested on Win7 FF3/3.5/31, IE5/7/8/9/10/Edge, Chrome39, and Safari Windows 5, and all of them sent " test this.stuff" (four leading spaces) as the name in POST to the ASP.NET dev server bundled with VS2012.
I checked it with Apache HTTP server(v2.4.25) and indeed input name like "foo.bar" is changed to "foo_bar". But in a name like "foo[foo.bar]" that dot is not replaced by _!
My conclusion: You can use dots but I wouldn't use it as this may lead to some unexpected behaviours depending on HTTP server used.
Do you mean the id and name attributes of the HTML input tag?
If so, I'd be very tempted to restrict (or convert) allowed "input" name characters into only a-z (A-Z), 0-9 and a limited range of punctuation (".", ",", etc.), if only to limit the potential for XSS exploits, etc.
Additionally, why let the user control any aspect of the input tag? (Might it not ultimately be easier from a validation perspective to keep the input tag names are 'custom_1', 'custom_2', etc. and then map these as required.)