The JSONPointer notation (rfc6901) allows you to denote a location in a JSON document as a string.
I was surprised to see that the specification uses a tilde '~' as the escape character?
Why was this chosen rather than something more conventioal like a backslash ''?
The reason backslash cannot be used is that backslash already has a meaning in JSON and it is desirable to be able to include a JSONPointer in a JSON document without having to double escape it.
If you read the specification carefully you will note:
JSON String Representation
A JSON Pointer can be represented in a JSON string value. Per
[RFC4627], Section 2.5, all instances of quotation mark '"' (%x22),
reverse solidus '\' (%x5C), and control (%x00-1F) characters MUST be
escaped.
Note that before processing a JSON string as a JSON Pointer,
backslash escape sequences must be unescaped.
Another reason is to allow for URI encoding.
According to this discussion it was almost caret '^' instead.
Note also that tilde '~' is allowed in URLs whereas caret '^' is not.
Though see http://jkorpela.fi/tilde.html for a counterpoint to tildes in URLs.
I'm receiving a string from the server and it has the special characters in code. Here's the example:
"El usuario o las contrase\UOOOOfffda no son v\UOOOOfffdlidos"
The first one should be an "ñ" and the second one "á"
I know it's not complicated but I can't find the answer. How can I get the string with the special characters correctly formatted?
Unicode U+FFFD (in your string, displayed as UTF-32 \U0000fffd) is "�", the replacement character. It is often substituted in strings when a system encounters unrecognized characters.
This character really shouldn't appear in string data since its purpose is to indicate an error in displaying or interpreting the string. Since your server is sending you that character for both ñ and á, there is no way to retrieve the correct character.
How are you "receiving" this string? It could be that you are accessing the server incorrectly so it isn't sending you an unmodified string.
Unicode for those characters should look like this:
#"accented-a is \u00f1, and tilda-n is \u00e1"
But it's not clear what you're getting from the server makes any sense. The objective-c literal must have a lowercase leading "u" followed only by valid hex digits (0-9 and a-f). I don't see a transformation that changes the literals you have to the ones you expect.
Once the characters are formatted properly, the built-in classes will just work, for example, assigning the string to a label's text property will show the user a nice glyph.
Hello and thank you for reading my post.
The Apache Commons StringEscapeUtils.escapeHtml3() and StringEscapeUtils.escapeHtml4() functions allow, in particular, to convert characters with an acute (like é, à...) in a string into
character entity references which have the format &name; where name is a case-sensitive alphanumeric string.
How can I get the escaped string of a given string with numeric character references instead (&#nnnn; or &#xhhhh; where nnnn is the code point in decimal form, and hhhh is the code point in hexadecimal form)?
I actually need to escape strings for a XML document which doesn't know about such entities as & eacute;, & agrave; etc.
Best regards.
To solve this problem, I wrote a method which takes a string as an argument and replaces, in this string, character entity references (like é) with their corresponding numeric character references (é in this case).
I used this W3C list of references: http://www.sagehill.net/livedtd/xhtml1-transitional/xhtml-lat1.ent.html
Nota: It would be great to be able to pass another argument to the StringEscapeUtils.escapeHtml4() method to tell it whether we would like character entity references or numeric character references in the output string...
Create your CharacterTranslator:
CharacterTranslator XML_ESCAPE = StringEscapeUtils.ESCAPE_XML11.with(
NumericEntityEscaper.between(0x7f, Integer.MAX_VALUE) );
and use it:
XML_ESCAPE.translate(…)
I am making a program in Delphi 7, that is supposed to encode a unicode string into html entity string.
For example, "ABCģķī" would result in "ABCģķī"
Now 2 basic things:
Delphi 7 is non-Unicode, so I can't just write unicode chars directly in code to encode them.
Codepages consist of 255 entries, each holding a character, specific to that codepage, except first 127, that are same for all the codepages.
So - How do I get a value of a char, that is in 1-255 range?
I tried Ord(Integer), but it also returns values way past 255. Basically, everything is fine (A returns 65 an so on) until my string reaches non-Latin unicode.
Is there any other method for returning char value? Any help appreciated
I suggest you avoid codepages like the plague.
There are two approaches for Unicode that I'd consider: WideString, and UTF-8.
Widestrings have the advantage that it's 'native' to Windows, which helps if you need to use Windows API calls. Disadvantages are storage space, and that they (like UTF-8) can require multiple WideChars to encode the full Unicode space.
UTF-8 is generally preferable. Like WideStrings, this is a multi-byte encoding, so a particular unicode 'code point' may need several bytes in the string to encode it. This is only an issue if you're doing lots of character-by-character processing on your strings.
#DavidHeffernan comments (correctly) that WideStrings may be more compact in certain cases. However, I'd only recommend UTF-16 only if you are absolutely sure that your encoded text will really be more compact (don't forget markup!), and this compactness is highly important to you.
In HTML 4, numeric character references are relative to the charset used by the HTML. Whether that charset is specified in the HTML itself via a <meta> tag, or out-of-band via an HTTP/MIME Content-Type header or other means, it does not matter. As such, "ABCģķī" would be an accurate representation of "ABCģķī" only if the HTML were using UTF-16. If the HTML were using UTF-8, the correct representation would be either "ABCģķī" or "ABCģķī" instead. Most other charsets do no support those particular Unicode characters.
In HTML 5, numeric character references contain original Unicode codepoint values regardless of the charset used by the HTML. As such, "ABCģķī" would be represented as either "ABC#291;ķī" or "ABCģķī".
So, to answer your question, the first thing you have to do is decide whether you need to use HTML 4 or HTML 5 semantics for numeric character references. Then, you need to assign your Unicode data to a WideString (which is the only Unicode string type that Delphi 7 natively supports), which uses UTF-16, then:
if you need HTML 4:
A. if the HTML charset is not UTF-16, then use WideCharToMultiByte() (or equivalent) to convert the WideString to that charset, then loop through the resulting values outputting unreserved characters as-is and character references for reserved values, using IntToStr() for decimal notation or IntToHex() for hex notation.
B. if the HTML charset is UTF-16, then simply loop through each WideChar in the WideString, outputting unreserved characters as-is and character references for reserved values, using IntToStr() for decimal notation or IntToHex() for hex notation.
If you need HTML 5:
A. if the WideString does not contain any surrogate pairs, then simply loop through each WideChar in the WideString, outputting unreserved characters as-is and character references for reserved values, using IntToStr() for decimal notation or IntToHex() for hex notation.
B. otherwise, convert the WideString to UTF-32 using WideStringToUCS4String(), then loop through the resulting values outputting unreserved codepoints as-is and character references for reserved codepoints, using IntToStr() for decimal notation or IntToHex() for hex notation.
In case I understood the OP correctly, I'll just leave this here.
function Entitties(const S: WideString): string;
var
I: Integer;
begin
Result := '';
for I := 1 to Length(S) do
begin
if Word(S[I]) > Word(High(AnsiChar)) then
Result := Result + '#' + IntToStr(Word(S[I])) + ';'
else
Result := Result + S[I];
end;
end;
Background (question further down)
I've been Googling this back and forth reading RFCs and SO questions trying to crack this, but I still don't got jack.
So I guess we just vote for the "best" answer and that's it, or?
Basically it boils down to this.
3.4. Query Component
The query component is a string of information to be interpreted by the resource.
query = *uric
Within a query component, the characters ";", "/", "?", ":", "#", "&", "=", "+", ",", and "$" are reserved.
The first thing that boggles me is that *uric is defined like this
uric = reserved | unreserved | escaped
reserved = ";" | "/" | "?" | ":" | "#" | "&" | "=" | "+" | "$" | ","
This is however somewhat clarified by paragraphs such as
The "reserved" syntax class above refers to those characters that are allowed within a URI, but which may not be allowed within a particular component of the generic URI syntax; they are used as delimiters of the components described in Section 3.
Characters in the "reserved" set are not reserved in all contexts. The set of characters actually reserved within any given URI component is defined by that component. In general, a character is reserved if the semantics of the URI changes if the character is replaced with its escaped US-ASCII encoding.
This last excerpt feels somewhat backwards, but it clearly states that the reserved character set depends on context. Yet 3.4 states that all the reserved characters are reserved within a query component, however, the only things that would change the semantics here is escaping the question mark (?) as URIs do not define the concept of a query string.
At this point I've given up on the RFCs entirely but found RFC 1738 particularly interesting.
An HTTP URL takes the form:
http://<host>:<port>/<path>?<searchpart>
Within the <path> and <searchpart> components, "/", ";", "?" are reserved. The "/" character may be used within HTTP to designate a hierarchical structure.
I interpret this at least with regards to HTTP URLs that RFC 1738 supersedes RFC 2396. Because the URI query has no notion of a query string also the interpretation of reserved doesn't really let allow me to define query strings as I'm used to doing by now.
Question
This all started when I wanted to pass a list of numbers together with the request of another resource. I didn't think much of it, and just passed it as a comma separated values. To my surprise though the comma was escaped. The query page.html?q=1,2,3 encoded turned into page.html?q=1%2C2%2C3 it works, but it's ugly and didn't expect it. That's when I started going through RFCs.
My first question is simply, is encoding commas really necessary?
My answer, according to RFC 2396: yes, according to RFC 1738: no
Later I found related posts regarding the passing of lists between requests. Where the csv approach was poised as bad. This showed up instead, (haven't seen this before).
page.html?q=1;q=2;q=3
My second question, is this a valid URL?
My answer, according to RFC 2396: no, according to RFC 1738: no (; is reserved)
I don't have any issues with passing csv as long as it's numbers, but yes you do run into the risk of having to encode and decode values back and forth if the comma suddenly is needed for something else. Anyway I tried the semi-colon query string thing with ASP.NET and the result was not what I expected.
Default.aspx?a=1;a=2&b=1&a=3
Request.QueryString["a"] = "1;a=2,3"
Request.QueryString["b"] = "1"
I fail to see how this greatly differs from a csv approach as when I ask for "a" I get a string with commas in it. ASP.NET certainly is not a reference implementation but it hasn't let me down yet.
But most importantly -- my third question -- where is specification for this? and what would you do or for that matter not do?
That a character is reserved within a generic URL component doesn't mean it must be escaped when it appears within the component or within data in the component. The character must also be defined as a delimiter within the generic or scheme-specific syntax and the appearance of the character must be within data.
The current standard for generic URIs is RFC 3986, which has this to say:
2.2. Reserved Characters
URIs include components and subcomponents that are delimited by characters in the "reserved" set. These characters are called "reserved" because they may (or may not) be defined as delimiters by the generic syntax, by each scheme-specific syntax, or by the implementation-specific syntax of a URI's dereferencing algorithm. If data for a URI component would conflict with a reserved character's purpose as a delimiter [emphasis added], then the conflicting data must be percent-encoded before the URI is formed.
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "#"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
3.3. Path Component
[...]
pchar = unreserved / pct-encoded / sub-delims / ":" / "#"
[...]
3.4 Query Component
[...]
query = *( pchar / "/" / "?" )
Thus commas are explicitly allowed within query strings and only need to be escaped in data if specific schemes define it as a delimiter. The HTTP scheme doesn't use the comma or semi-colon as a delimiter in query strings, so they don't need to be escaped. Whether browsers follow this standard is another matter.
Using CSV should work fine for string data, you just have to follow standard CSV conventions and either quote data or escape the commas with backslashes.
As for RFC 2396, it also allows for unescaped commas in HTTP query strings:
2.2. Reserved Characters
Many URI include components consisting of or delimited by, certain
special characters. These characters are called "reserved", since
their usage within the URI component is limited to their reserved
purpose. If the data for a URI component would conflict with the
reserved purpose, then the conflicting data must be escaped before
forming the URI.
Since commas don't have a reserved purpose under the HTTP scheme, they don't have to be escaped in data. The note from § 2.3 about reserved characters being those that change semantics when percent-encoded applies only generally; characters may be percent-encoded without changing semantics for specific schemes and yet still be reserved.
I think the real question is: "What characters should be encoded in a query string?" And that depends mainly on two things: The validity and the meaning of a character.
Validity according to the RFC standard
In RFC3986 we can find which special characters are valid and which are not inside a query string:
// Valid:
! $ & ' ( ) * + , - . / : ; = ? # _ ~
% (should be followed by two hex chars to be completely valid (e.g. %7C))
// Invalid:
" < > [ \ ] ^ ` { | }
space
# (marks the end of the query string, so it can't be a part of it)
extended ASCII characters (e.g. °)
Deviations from the standard
Browsers and web frameworks do not always strictly follow the RFC standard. Below are some examples:
[, ] are not valid, but Chrome and Firefox do not encode these characters inside a query string. The reasoning given by Chrome devs is simply: "If other browsers and an RFC disagree, we will generally match other browsers." QueryHelpers.AddQueryString from ASP.NET Core on the other hand will encode these characters.
Other invalid characters that are not encoded by Chrome and Firefox are:
\ ^ ` { | }
' is a valid character inside a query string but will be encoded by Chrome, Firefox and QueryHelpers nevertheless. The explanation given by Firefox devs is that they knew that they don't have to encode it according to the RFC standard, but did it to reduce vulnerabilities.
Special meaning
Some characters are valid and also don't get encoded by browsers, but should still be encoded in certain cases.
+: Spaces are normally encoded as %20 but alternatively they can be encoded as +. So + inside a query string means it's an encoded space. If you want to include a character that's actually supposed to literally mean plus, then you have to use the encoded version of + which is %2B.
~: Some old Unix systems interpreted URI parts that started with ~ as a path to a home directory. So it's a good idea to encode ~ if it's not meant to denote the start of a Unix home directory path for an old system (so nowadays probably always encode).
=, &: Usually (although RFC doesn't specify that this is required) query strings contain parameters in the format "key1=value1&key2=value2". If that's the case and =s or &s should be part of the parameter key or the parameter value instead of giving them the role of separating the key and value or separating the parameters, then you have to encode those =s and &s. So if a parameter value should for some reason consist of the string "=&" then it has to be encoded as %3D%26 which then can be used for the full key and value: "weirdparam=%3D%26".
%: Usually web frameworks figure out that %s that are not followed by two hex characters simply mean the % itself, but it's still a good idea to always encode % when it's supposed to only mean % and not indicate the start of an encoded character (e.g. %7C) because RFC3986 specifies that % is only valid when followed by two hex characters. So don't use "percentageparam=%" use "percentageparam=%25" instead.
Encoding guidelines
Encode every character that is otherwise invalid* according to RFC3986 and every character that can have special meaning but should only be interpreted in a literal way without giving it a special meaning. You can also encode things that aren't required to be encoded, like '. Why? Because it doesn't hurt to encode more than necessary. Servers and web frameworks when parsing a query string will decode every encoded character, no matter if it was really necessary to previously encode that character or not.
The only characters of a query string that shouldn't be encoded are those that can have a special meaning and shouldn't lose that special meaning, e.g. don't encode the = of "key1=value1". For that to achieve don't apply an encoding method to the whole query string (and also not to the whole URI) but apply it only and separately to the query parameter keys and values. For example, with JS:
var url = "http://example.com?" + encodeURIComponent(myKey1) + "=" + encodeURIComponent(myValue1) + "&" + encodeURIComponent(myKey2)...;
Note that encodeURIComponent encodes a lot more characters than necessary meaning characters that are valid in a query string and don't have special meaning there e.g. /, ?, ...
The reason is that encodeURIComponent wasn't created for query strings alone but instead encodes characters that have special meaning outside of the query string as well, e.g. / for the path URI component. QueryHelpers.AddQueryString works in a similar manner. Under the hood it uses System.Text.Encodings.Web.DefaultUrlEncoder which is not just meant for query strings but also for isegment, ipath-noscheme and ifragment.
* You could probably get away with only regarding those characters as invalid that are both not allowed by the RFC and that are also always encoded by Chrome for instance. This would be Space " < >. But it's probably better to be on the safer side and encode at least everything that RFC3986 considers invalid.
OP's questions
My first question is simply, is encoding commas really necessary -> No it's not necessary, but it doesn't hurt (except ugliness) and will happen with default encoding methods e.g. encodeURIComponent and decoding and query string parsing should work nevertheless.
My second question, is this a valid URL (page.html?q=1;q=2;q=3)? -> It's RFC valid, but your server / web framework might have a hard time parsing the query string when it might expect the typical "key1=value1&key2=value2" format for query strings.
Where is specification for this? -> There isn't a single specification that covers everything because some things are implementation specific. For instance there are different ways of specifying arrays inside of query strings.
Just use ?q=1+2+3
I am answering here a fourth question :) that did not ask but all started with: how do i pass list of numbers a-la comma-separated values? Seems to me the best approach is just to pass them space-separated, where spaces will get url-form-encoded to +. Works great, as longs as you know the values in the list contain no spaces (something numbers tend not to).
page.html?q=1;q=2;q=3
is this a valid URL?
Yes. The ; is reserved, but not by an RFC. The context that defines this component is the definition of the application/x-www-form-urlencoded media type, which is part of the HTML standard (section 17.13.4.1). In particular the sneaky note hidden away in section B.2.2:
We recommend that HTTP server implementors, and in particular, CGI implementors support the use of ";" in place of "&" to save authors the trouble of escaping "&" characters in this manner.
Unfortunately many popular server-side scripting frameworks including ASP.NET do not support this usage.
I would like to note that page.html?q=1&q=2&q=3 is a valid url as well. This is a completely legitimate way of expressing an array in a query string. Your server technology will determine how exactly that is presented.
In Classic ASP, you check Response.QueryString("q").Count and then use Response.QueryString("q")(0) (and (1) and (2)).
Note that you saw this in your ASP.NET, too (I think it was not intended, but look):
Default.aspx?a=1;a=2&b=1&a=3
Request.QueryString["a"] = "1;a=2,3"
Request.QueryString["b"] = "1"
Notice that the semicolon is ignored, so you have a defined twice, and you got its value twice, separated by a comma. Using all ampersands Default.aspx?a=1&a=2&b=1&a=3 will yield a as "1,2,3". But I am sure there is a method to get each individual element, in case the elements themselves contain commas. It is simply the default property of the non-indexed QueryString that concatenates the sub-values together with comma separators.
I had the same issue. The URL that was hyperlinked was a third party URL and was expecting a list of parameters in format page.html?q=1,2,3 ONLY and the URL page.html?q=1%2C2%2C3 did not work. I was able to get it working using javascript. May not be the best approach but can check out the solution here if it helps anyone.
If you are sending the ENCODED characters to FLASH/SWF file, then you should ENCODE the character twice!! (because of Flash parser)