I know of the non-standard %uxxxx scheme but that doesn't seem like a wise choice since the scheme has been rejected by the W3C.
Some interesting examples:
The heart character.
If I type this into my browser:
http://www.google.com/search?q=♥
Then copy and paste it, I see this URL
http://www.google.com/search?q=%E2%99%A5
which makes it seem like Firefox (or Safari) is doing this.
urllib.quote_plus(x.encode("latin-1"))
'%E2%99%A5'
which makes sense, except for things that can't be encoded in Latin-1, like the triple dot character.
…
If I type the URL
http://www.google.com/search?q=…
into my browser then copy and paste, I get
http://www.google.com/search?q=%E2%80%A6
back. Which seems to be the result of doing
urllib.quote_plus(x.encode("utf-8"))
which makes sense since … can't be encoded with Latin-1.
But then its not clear to me how the browser knows whether to decode with UTF-8 or Latin-1.
Since this seems to be ambiguous:
In [67]: u"…".encode('utf-8').decode('latin-1')
Out[67]: u'\xc3\xa2\xc2\x80\xc2\xa6'
works, so I don't know how the browser figures out whether to decode that with UTF-8 or Latin-1.
What's the right thing to be doing with the special characters I need to deal with?
I would always encode in UTF-8. From the Wikipedia page on percent encoding:
The generic URI syntax mandates that new URI schemes that provide for the representation of character data in a URI must, in effect, represent characters from the unreserved set without translation, and should convert all other characters to bytes according to UTF-8, and then percent-encode those values. This requirement was introduced in January 2005 with the publication of RFC 3986. URI schemes introduced before this date are not affected.
It seems like because there were other accepted ways of doing URL encoding in the past, browsers attempt several methods of decoding a URI, but if you're the one doing the encoding you should use UTF-8.
The general rule seems to be that browsers encode form responses according to the content-type of the page the form was served from. This is a guess that if the server sends us "text/xml; charset=iso-8859-1", then they expect responses back in the same format.
If you're just entering a URL in the URL bar, then the browser doesn't have a base page to work on and therefore just has to guess. So in this case it seems to be doing utf-8 all the time (since both your inputs produced three-octet form values).
The sad truth is that AFAIK there's no standard for what character set the values in a query string, or indeed any characters in the URL, should be interpreted as. At least in the case of values in the query string, there's no reason to suppose that they necessarily do correspond to characters.
It's a known problem that you have to tell your server framework which character set you expect the query string to be encoded as--- for instance, in Tomcat, you have to call request.setEncoding() (or some similar method) before you call any of the request.getParameter() methods. The dearth of documentation on this subject probably reflects the lack of awareness of the problem amongst many developers. (I regularly ask Java interviewees what the difference between a Reader and an InputStream is, and regularly get blank looks)
IRI (RFC 3987) is the latest standard that replaces the URI/URL (RFC 3986 and older) standards. URI/URL do not natively support Unicode (well, RFC 3986 adds provisions for future URI/URL-based protocols to support it, but does not update past RFCs). The "%uXXXX" scheme is a non-standard extension to allow Unicode in some situations, but is not universally implemented by everyone. IRI, on the other hand, fully supports Unicode, and requires that text be encoded as UTF-8 before then being percent-encoded.
IRIs do not replace URIs, because only URIs (effectively, ASCII) are permissible in some contexts -- including HTTP.
Instead, you specify an IRI and it gets transformed into a URI when going out on the wire.
The first question is what are your needs? UTF-8 encoding is a pretty good compromise between taking text created with a cheap editor and support for a wide variety of languages. In regards to the browser identifying the encoding, the response (from the web server) should tell the browser the encoding. Still most browsers will attempt to guess, because this is either missing or wrong in so many cases. They guess by reading some amount of the result stream to see if there is a character that does not fit in the default encoding. Currently all browser(? I did not check this, but it is pretty close to true) use utf-8 as the default.
So use utf-8 unless you have a compelling reason to use one of the many other encoding schemes.
Related
So I don't really want this question to be language specific, however I suspect Go (my language choice) is playing a part here.
I'm trying to find a string within the body of a raw email. To do so, I am getting the encoding, and the marjority of cases are quoted-printable.
Ok so thats fine, I am encoding my search query quoted printable and then doing a search for it. That works.
However. In one specific case the raw email I see in gmail looks fine, however when I retrieve the raw email from the gmail API the although the encoding and everything is identical, its encoding the " as =22
Research shows me thats because the charset is utf-8.
I haven't quite got my head around whether thats encoded utf-8 then quoted-printable or the other way around, but thats not quite the question either....
If I look at the email where the " is =22 I see the char set is utf-8 and when I look at another where its not encoded, the charset is UTF-8 (notice the case). I can't believe that the case here is whats causing this to happen, but it doesn't seem a robust enough way to work out if =22 is actually =22 or is a " encoded utf-8.
My original thought was to always decode the quoted-printable and then re-encode it before doing the search but I don't think this is going to be a robust approach going forward and thought others might have a better suggestion?
Conclusion, I'm trying to find a string in a raw email but the encoding is causing me problems getting my search string to match the encoding of the body
The =22-type encoding actually has nothing to do with the charset (whether that is utf-8 lowercase or UTF-8 uppercase or any other charset).
It is the Content-Transfer-Encoding: quoted-printable encoding.
The quoted-printable encoding is just a way of hex-encoding octets, typically limited to octets that fall outside of the printable ascii range. It seems odd that the DQUOTE character would be encoded in this way, but it's perfectly legal to do so.
If you want to search for strings in the body of the message, you'll need to first decode the body of the message. Otherwise you will not be successful.
I would recommend reading rfc2045 at a minimum.
You may also need to end up reading rfc2047 if you end up wanting to search headers at some point, but that gets... tricky due to various bugs that sending clients have.
Now that I've been "triggered" into a rant about MIME, let me explain why decoding headers is so hard to get right. I'm sure just about every developer who has ever worked on an email client could tell you this, but I guess I'm going to be the one to do it.
Here's just a short list of the problems every developer faces when they go to implement a decoder for headers which have been (theoretically) encoded according to the rfc2047 specification:
First off, there are technically two variations of header encoding formats specified by rfc2047 - one for phrases and one for unstructured text fields. They are very similar but you can't use the same rules for tokenizing them. I mention this because it seems that most MIME parsers miss this very subtle distinction and so, as you might imagine, do most MIME generators. Hell, most MIME generators probably never even heard of specifications to begin with it seems.
This brings us to:
There are so many variations of how MIME headers fail to be tokenizable according to the rules of rfc2822 and rfc2047. You'll encounter fun stuff such as:
a. encoded-word tokens illegally being embedded in other word tokens
b. encoded-word tokens containing illegal characters in them (such as spaces, line breaks, and more) effectively making it so that a tokenizer can no longer, well, tokenize them (at least not easily)
c. multi-byte character sequences being split between multiple encoded-word tokens which means that it's not possible to decode said encoded-word tokens individually
d. the payloads of encoded-word tokens being split up into multiple encoded-word tokens, often splitting in a location which makes it impossible to decode the payload in isolation
You can see some examples here.
Something that many developers seem to miss is the fact that each encoded-word token is allowed to be in different character encodings (you might have one token in UTF-8, another in ISO-8859-1 and yet another in koi8-r). Normally, this would be no big deal because you'd just decode each payload, then convert from the specified charset into UTF-8 via iconv() or something. However, due to the fun brokenness that I mentioned above in (2c) and (2d), this becomes more complicated.
If that isn't enough to make you want to throw your hands up in the air and mutter some profanities, there's more...
Undeclared 8bit text in headers. Yep. Some mailers just didn't get the memo that they are supposed to encode non-ASCII text. So now you get to have the fun experience of mixing and matching undeclared 8bit text of God-only-knows what charset along with the content of (probably broken) encoded-words.
If you want to see how to deal with these issues, you can take a look at how I did it using C in my GMime library, here: https://github.com/jstedfast/gmime/blob/master/gmime/gmime-utils.c#L1894 (in case line offsets change in the future, look for _g_mime_utils_header_decode_text() and the various internal methods it uses in that source file - I have written comments explaining how it deals with the above issues).
Or you can see how I did it using C# in my MimeKit library, here: https://github.com/jstedfast/MimeKit/blob/master/MimeKit/Utils/Rfc2047.cs
For more infomation about why & how dealing with email is hard, check out Joshua Cramner's blog series: http://quetzalcoatal.blogspot.com/search/label/email-hard
If you have binary data that you need to encode, what encoding scheme do you use?
I know about:
Hex encoding. Very simple, but quite verbose, expands one byte to two.
Base 64. Most common, not so verbose, expands three bytes to four.
Base 85. Not common, less verbose again, expands four bytes to five.
Are there any other encoding schemes in common use? If so, what are there advantages and disadvantages?
Edit: This is useful, for example, when trying to store arbitrary data in a cookie. Cookies can only store text, not arbitrary data, so you need to convert it in some way, preferably with a way to convert it back. Further, assume that you are using a stateless server so that you cannot save the state on the server and just put an identifier into the cookie. Of course, if you do this you would also need some way of verifying that what the user is passing back to you is what you passed to the user, for example a signature.
Also, since the current consensus is that you should use base64 since it is widespread, I will also point out that this is what I use... I am just curious if anyone used anything else, and if so, why.
Edit: Just in case someone stumbles across this, if you do want to use Base64 to store data in a cookie, you need to use a modified Base64 implementation. See this answer for the reason why.
For encoding cookie values, you need to be careful. See this older answer:
With Version 0 cookies, values should
not contain white space, brackets,
parentheses, equals signs, commas,
double quotes, slashes, question
marks, at signs, colons, and
semicolons. Empty values may not
behave the same way on all browsers.
Base64 encoding can generate = symbols for certain inputs, and this technically is not permitted in cookies (version 0 cookies, anyway, which are the most widely supported). In practice, I suspect the = will actually work fine, but maybe not.
I would suggest that to be absolutely sure that your encoded binary is cookie-compatible, then basic hex encoding is safest (e.g. in java).
edit: As #Paul helpfully pointed out, there is a modified version of Base 64 that is "URL safe" (and, I assume, "cookie safe"). Using a modified version of a standard algorithm rather dilutes its charm, mind you.
edit: #shoosh pointed out that the = is only used to denote the end of the base64 string, so you could trim the =, set the cookie, then reattach the = again when you need to decode it.
Base64 wins because it's so common that I don't have to ever worry about rolling my own encoder/decoder. I haven't run into any applications where I've been worried about saving bandwidth or filespace in encoded binary data.
Once upon a time, there was UTF-7. It's officially deprecated, but it still works as an ACE (ASCII Compatible Encoding). Now there's IDN.
uuencode is popular is some circles
HTML and XML encode unicode using this syntax
Base64 is the de-facto standard. Using anything else is asking for trouble.
when we type in or paste it to a browser's address bar:
http://www.google.com/search?q=%E5%A4%A9
i think there is no way to tell whether the encoding is UTF-8 or any other encoding, so the application will usually assume it is UTF-8. So is it entirely up to the app to interpret it as whatever encoding it wants to or assumes to be?
(for all websites and even the platform i worked on, they seems to be almost always UTF-8)
Update: changed to the webapp instead.
RFC 3986 says:
"When a new URI scheme defines a
component that represents textual data
consisting of characters from the
Universal Character Set [UCS], the
data should first be encoded as octets
according to the UTF-8 character
encoding [STD63]; "
So UTF-8 is definitely the way to go for any new HTTP GET apis.
The servers don't care. They just pass it to PHP or Ruby or whatever.
When one creates web content in languages different than English the problem of search engine optimized and user friendly URLs emerge.
I'm wondering whether it is the best practice to use de-accented letters in URLs -- risking that some words have completely different meanings with and without certain accents -- or it is better to stick to the usage of non-english characters where appropriate sacrificing the readability of those URLs in less advanced environments (e.g. MSIE, view source).
"Exotic" letters could appear anywhere: in titles of documents, in tags, in user names, etc, so they're not always under the complete supervision of the maintainer of the website.
A possible approach of course would be setting up alternate -- unaccented -- URLs as well which would point to the original destination, but I would like to learn your opinions about using accented URLs as primary document identifiers.
There's no ambiguity here: RFC3986 says no, that is, URIs cannot contain unicode characters, only ASCII.
An entirely different matter is how browsers represent encoded characters when displaying a URI, for example some browsers will display a space in a URL instead of '%20'. This is how IDN works too: punycoded strings are encoded and decoded by browsers on the fly, so if you visit café.com, you're really visiting xn--caf-dma.com. What appears to be unicode chars in URLs is really only 'visual sugar' on the part of the browser: if you use a browser that doesn't support IDN or unicode, the encoded version won't work because the underlying definition of URLs simply doesn't support it, so for it to work consistently, you need to % encode.
When faced with a similar problem, I took advantage of URL rewriting to allow such pages to be accessible by either the accented or unaccented character. The actual URL would be something like
http://www.mysite.com/myresume.html
And a rewriting+character translating function allows this reference
http://www.mysite.com/myresumé.html
to load the same resource. So to answer your question, as the primary resource identifier, I confine myself to 0-9, A-Z, a-z and the occasional hyphen.
Considering URLs with accents often tend to end up looking like this :
http://fr.wikipedia.org/wiki/%C3%89l%C3%A9phant
...which is not that nice... I think we'll still be using de-accented URLs for some time.
Though, things should get better, as accented URLs are now accepted by web browsers, it seems.
The firefox 3.5 I'm currently using displays the URL the nice way, and not with %stuff, btw ; this seems to be "new" since firefox 3.0 (see Firefox 3: UTF-8 support in location bar) ; so, not probably not supported in IE 6, at least -- and there are still quite too many people using this one :-(
Maybe URL with no accent are not looking the best that could be ; but, still, people are used to them, and seem to generally understand them quite well.
You should avoid non-ASCII characters in URLs that may be entered in browser manually by users. It's ok for embedded links pre-encoded by server.
We found out that browser can encode the URL in different ways and it's very hard to figure out what encoding it uses. See my question on this issue,
Handling Character Encoding in URI on Tomcat
There are several areas in a full URL, and each one might has different rules.
The protocol is plain ASCII.
The DNS entry is governed by IDN (International Domain Names) rules, and can contain (most) of the Unicode characters.
The path (after the first /), the user name and the password can again be everything. They are escaped (as %XX), but those are just bytes. What is the encoding of these bytes is difficult to know (is interpreted by the http server).
The parameters part (after the first ?) is passed "as is" (after %XX unescapeing) to some server-side application thing (php, asp, jsp, cgi), and how that interprets the bytes is another story).
It is recommended that the path/user/password/arguments are utf-8, but not mandatory, and not everyone respects that.
So you should definitely allow for non-ASCII (we are not in the 80s anymore), but exactly what you do with that might be tricky. Try to use Unicode and stay away from legacy code pages, tag your content with the proper encoding/charset if you can (using meta in html, language directives for asp/jsp, etc.)
There doesn't seem to be an accepted way of sending down a header parameter in non ascii format.
The header for file download usually looks like
Content-disposition: attachment; filename="theasciifilename.doc"
Except if you smash a utf8 encoded string in the filename parameter, Firefox will handle it fine, whereas IE will throw up.
There is a document on CodeProject that explains a method for encoding the filename.
This document encodes Bản Kiểm Kê.doc to B%e1%ba%a3n%20Ki%e1%bb%83m%20K%c3%aa.doc by hex encoding the bytes.
Problem #1: the first character in that string: ả has a value of ả -- encode that number in Hex and you get %a3%1e. How did this guy get %e1%ba%a3? (I'm obviously missing something simple here)
Problem #2: While IE acknowledges this encoding, Firefox doesn't! What to do?
The specs basically don't permit anything other than US-ASCII. HTTP headers are US-ASCII. HTTP's payload defaults to ISO 8859-1 but that refers to the content body, not the headers.
Arguably the Right Thing to do would be to use MIME's technique for encoding non-ASCII data in headers, as described in RFC 2047, but I have no idea whether browsers actually support that.
EDIT: Whoops, no, RFC 2047 section 5 explicitly says that the encoded form is not permitted in Content-Disposition. Looks like you're out of luck - there is no standard.
EDIT 2: There is a standard - RFC 2231 defines how this is now supposed to work. It has support from some browsers, but is not supported in IE. I found some test cases which demonstrate how it works and what browser support is available.
Answer to question #1: You are confusing Unicode and UTF-8. The hex value of 'ả' is 0xA31E however that is not a UTF-8 character. In UTF-8 that character requries three bytes, 0xE1 0xBA 0xA3. URL encoding is poorly defined for non-ascii encodings but %e1%ba%a3 is the valid UTF-8 encoding to use for that character.
For Problem #2 you need to URL encode the file name for both Internet Explorer and Firefox. The only difference is that you need to use the format of RFC 2231 in Firefox.
This applies to Firefox 3 and Internet Explorer 7.
In the link you've got above, e1 ba a3 is the UTF-8 encoding of the character mentioned, not the character code.
Answer (sort of) to problem #2:
Since you've discovered that the naming scheme in one browser does not work in the other, your only solution is to do it differently for each browser, similar to the example here.
In case the link goes away, the solution is basically:
1. If browser is IE URL encode filename
2. Generate Content-disposition header
Of course determining if the browser is IE by User-agent (which is about the only way you can do it) is fraught with all sorts of the usual peril.
As North American centric as this sounds, if it is important that this work in a large number of browsers you do not control which may have the User-agent blocked, or modified, then simply avoid UTF-8 encoded characters in the filename and always use "Download" or something.
Unfortunately, there currently is no single way that would work in all User Agents.
See http://greenbytes.de/tech/tc2231/ for test cases, then complain to Microsoft, Google and Apple.