I'm trying to fetch data from PostgreSQL with Erlang.
Here's my code that gets data from DB. However i have cyrrilic data in 'status' column. This cyrrilic data is not being fetched correctly.
I tried using UserInfo = io_lib:format("~tp ~n",[UserInfoQuery]), however this doesn't seem to work, because it crashes the app.
UserInfoQuery = odbc_queries:get_user_info(LServer,LUser),
UserInfo = io_lib:format("~p",[UserInfoQuery]),
?DEBUG("UserInfo: ~p",[UserInfo]),
StringForUserInfo = lists:flatten(UserInfo),
get_user_info(LServer, Id) ->
ejabberd_odbc:sql_query(
LServer,
[<<"select * from users "
"where email_hash='">>, Id, "';"]).
Here's the data that is fetched from DB
{selected,[<<"username">>,<<"password">>,<<"created_at">>,
<<"id">>,<<"email_hash">>,<<"status">>],
[{<<"admin">>,<<"admin">>,<<"2014-05-13 12:40:30.757433">>,
<<"1">>,<<"adminhash">>,
<<209,139,209,132,208,178,208,176,209,139,209,132,208,
178,208,176>>}]}
Question:
How can i extract data from column? For example only data from
'status' column?
How can i extract data in unicode from DB? Should i fetch the data from DB then use
io_lib:format("~tp~n") on it? Is there any better way to do it?
Additional question: is there any way to get string in human readable format, so that StringForUserInfo = 'ыфваыфва' from RowUnicode?
I tried this:
{selected, _, [Row]} = UserInfoQuery,
RowUnicode = io_lib:format("~tp~n", [Row]),
?DEBUG("RowUnicode: ~p",[RowUnicode]),
StringForUserInfo = lists:flatten(RowUnicode),
Error:
bad argument in call to erlang:iolist_size([123,60,60,34,97,100,109,105,110,34,
62,62,44,60,60,34,97,100,109,105,110,34,62,62,44,60,60,34,50,...])
Erlang ODBC driver perfectly fetched the status column from your database. Indeed, PostgreSQL encodes your data is UTF-8, and the value you get is UTF-8 encoded.
Status = <<209,139,209,132,208,178,208,176,209,139,209,132,208,178,208,176>>.
This is a binary representing the string ыфваыфва in UTF-8.
You can directly use UTF-8 encoded binaries in your code. If you want to use unicode character points instead of UTF-8 bytes, you can convert this to a list of integers (a string in Erlang parlance). Just use unicode:characters_to_list/1, which in your case will yield list [1099,1092,1074,1072,1099,1092,1074,1072]. This is a list representation of the same string. Unicode character 1099 (16#044B in hex) is ы (CYRILLIC SMALL LETTER YERU, cf Cyrillic excerpt unicode chart).
Erlang can handle unicode texts in the two representations above: lists of unicode characters as integers and binaries of UTF-8 encoded characters.
Let's examine a smaller example, string "ы". This string is composed of unicode character 044B CYRILLIC SMALL LETTER YERU, and it can be encoded as a binary as <<209,139>> or as a list as [16#044B] (= [1099]).
Historically, lists of integers as well as binaries were Latin-1 (ISO-8859-1) encoded. Unicode and ISO-8859-1 have the same values from 0 to 255, but UTF-8 transformation only matches ISO-8859-1 for characters in the 0-127 range. For this reason, Erlang's ~s format argument has a unicode translation modifier, ~ts. The following line will not work as expected:
io:format("~s", [<<209,139>>]).
It will output two characters, 00D1 (LATIN CAPITAL LETTER N WITH TILDE) and 008B (PARTIAL LINE FORWARD). This is because <<209,139>> is interpreted as a Latin-1 string and not as a UTF-8 encoded string.
The following line will fail:
io:format("~s", [[1099]]).
This is because [1099] is not a valid Latin-1 string.
Instead, you should write:
io:format("~ts", [<<209,139>>]),
io:format("~ts", [[1099]]).
Erlang's ~p format argument also has a unicode translation modifier, ~tp. However, ~tp will not do what you are looking for alone. Whether you use ~p or ~tp, by default, io_lib:format/2 will format the Status UTF-8 encoded binary above as:
<<209,139,209,132,208,178,208,176,209,139,209,132,208,178,208,176>>
Indeed, t modifier only means the argument shall accept unicode input. If you do use ~p, when formatting a string or a binary, Erlang will determine whether this could be represented as a Latin-1 string since input may be Latin-1 encoded. This heuristic allows Erlang to properly distinguish lists of integers and strings, most of the time. To see the heuristic at work, you can try something like:
io:format("~p\n~p\n", [[69,114,108,97,110,103], [1,2,3,4,5,6]]).
The heuristic detects that [69,114,108,97,110,103] actually is "Erlang", while [1,2,3,4,5,6] is just, well, a list of integers.
If you do use ~tp, Erlang will expect strings or binaries to be unicode-encoded, and then apply the default identification heuristic. And default heuristic happens to currently (R17) be latin-1 as well. Since your string cannot be represented with Latin-1, Erlang will display it as a list of integers. Fortunately, you can switch to Unicode heuristics by passing +pc unicode to Erlang on command line, and this will produce what you are looking for.
$ erl +pc unicode
So a solution to your problem is to pass +pc unicode and to use ~tp.
I don't understand why io:format("~tp") doesn't work, but you can extract the row and column you need and print that with io:format("~ts"):
> {selected, _, [Row]} = UserInfoQuery.
> io:format("~ts~n", [element(6, Row)]).
ыфваыфва
ok
Related
I'm currently working on something that requires me to pass a Base64 string to a PowerShell script. But while decoding the string back to the original I'm getting some unexpected results as I need to use UTF-7 during decoding and I don't understand why. Would someone know why?
The Mozilla documentation would suggest that it's insufficient to use Base64 if you have Unicode characters in your string. Thus you need to use a workaround that consists of using encodeURIComponent and a replace. I don't really get why the replace is needed and shortened it to btoa(escape('✓ à la mode')) to encode the string. The result of that operation would be JXUyNzEzJTIwJUUwJTIwbGElMjBtb2Rl.
Using PowerShell to decode the string back to the original, I need to first undo the Base64 encoding. In order to do System.Convert can be used (which results in a byte array) and its output can be converted to a UTF-8 string using System.Text.Encoding. Together this would look like the following:
$bytes = [System.Convert]::FromBase64String($inputstring)
$utf8string = [System.Text.Encoding]::UTF8.GetString($bytes)
What's left to do is URL decode the whole thing. As it is a UTF-8 string I'd expect only to need to run the URL decode without any further parameters. But if you do that you end up with a accented a that looks like � in a file or ? on the console. To get the actual original string it's necessary to tell the URL decode to use UTF-7 as the character set. It's nice that this works but I don't really get why it's necessary since the string should be UTF-8 and UTF-8 certainly supports an accented a. See the last two lines of the entire script for what I mean. With those two lines you will end up with one line that has the garbled text and one which has the original text in the same file encoded as UTF-8
Entire PowerShell script:
Add-Type -AssemblyName System.Web
$inputstring = "JXUyNzEzJTIwJUUwJTIwbGElMjBtb2Rl"
$bytes = [System.Convert]::FromBase64String($inputstring)
$utf8string = [System.Text.Encoding]::UTF8.GetString($bytes)
[System.Web.HttpUtility]::UrlDecode($utf8string) | Out-File -Encoding utf8 C:\temp\output.txt
[System.Web.HttpUtility]::UrlDecode($utf8string, [System.Text.UnicodeEncoding]::UTF7) | Out-File -Append -Encoding utf8 C:\temp\output.txt
Clarification:
The problem isn't the conversion of the Base64 to UTF-8. The problem is some inconsistent behavior of the UrlDecode of C#. If you run escape('✓ à la mode') in your browser you will end up with the following string %u2713%20%E0%20la%20mode. So we have a Unicode representation of the check mark and a HTML entity for the á. If we use this directly in UrlDecode we end up with the same error. My current assumption would be that it's an issue with the encoding of the PowerShell window and pasting characters into it.
Turns out it actually isn't all that strange. It's just for what I want to do it's advantages to use a newer function. I'm still not sure why it works if you use the UTF-7 encoding. But anyways, as an explanation:
... The hexadecimal form for characters, whose code unit value is 0xFF or less, is a two-digit escape sequence: %xx. For characters with a greater code unit, the four-digit format %uxxxx is used.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/escape
As TesselatingHecksler pointed out What is the proper way to URL encode Unicode characters? would indicate that the %u format wasn't formerly standardized. A newer version to escape characters exists though, which is encodeURIComponent.
The encodeURIComponent() function encodes a Uniform Resource Identifier (URI) component by replacing each instance of certain characters by one, two, three, or four escape sequences representing the UTF-8 encoding of the character (will only be four escape sequences for characters composed of two "surrogate" characters).
The output of this function actually works with the C# implementation of UrlDecode without supplying an additional encoding of UTF-7.
The original linked Mozilla article about a Base64 encode for an UTF-8 strings modifies the whole process in a way to allows you to just call the Base64 decode function in order to get the whole string. This is realized by converting the URL encode version of the string to bytes.
I am using regular Stream Reader to get response from Facebook graph API response
https://graph.facebook.com/XXXX?access_token=&fields=id,name,about,address,last_name
I am reading the response stream yet it returns me
{"id":"XXXXX","name":"K\u0131r\u0131nt\u0131 Reklam"...}
My code is below - I unsuccessfully tried using explicitly UTF-8 and "iso-8859-9" (Turkish) encodings and setting accept-charset headers. I read Joel's famous article about encodings. It looks like each of the chars '\' 'u' '1' '3' '1' are coming as characters from facebook - I thought this would have been 2 bytes for value 131 in UTF-8. I am confused. I expect this string to be "Kırıntı Reklam".
I could simply find/replace those strings - yet it would be far from elegant and maintainable. How should I properly process or convert the facebook graph api response for strings with accents?
using (WebResponse response = request.GetResponse())
{
using (Stream dataStream = response.GetResponseStream())
{
if (dataStream != null)
{
using (StreamReader reader = new StreamReader(dataStream))
{
responseFromServer = reader.ReadToEnd();
}
}
}
}
Thank you in advance
tldr; use a JSON library - I like Json.NET - and don't worry about it.
The JSON shown is valid JSON where \uABCD in a JSON string represents a UTF-16 encoded character1. The internal JSON character escaping format is useful to avoid having to deal with Unicode stream encoding issues - it allows JSON to be represented entirely in ASCII/7-bit-clean characters (which is a subset of UTF-8).
Using a conforming JSON library to parse the JSON with such escapes would restore the JSON into an appropriate object-graph, of which some values will be properly-decoded String values. The library is responsible for understanding JSON and converting/reading it as appropriate - this includes correctly handling any such \u escape sequences.
The stream itself (that of the JSON text) should use the encoding that the server says, is indicated by a BOM, or has been pre-negotiated: but really, just UTF-8 here. This is how the JSON text is encoded, but has no bearing on the escape sequences found in JSON strings.
1 Per RFC 4627, The application/json Media Type for JavaScript Object Notation (JSON):
Any character may be escaped. If the character is in the Basic
Multilingual Plane (U+0000 through U+FFFF), then it may be
represented as a six-character sequence: a reverse solidus, followed
by the lowercase letter u, followed by four hexadecimal digits that
encode the character's code point. The hexadecimal letters A though
F can be upper or lowercase. So, for example, a string containing
only a single reverse solidus character may be represented as
"\u005C".
Alternatively, there are two-character sequence escape
representations of some popular characters. So, for example, a
string containing only a single reverse solidus character may be
represented more compactly as "\\".
To escape an extended character that is not in the Basic Multilingual
Plane, the character is represented as a twelve-character sequence,
encoding the UTF-16 surrogate pair. So, for example, a string
containing only the G clef character (U+1D11E) may be represented as
"\uD834\uDD1E"
For the doubters, here is a LINQPad example. This uses JSON.Net and imports the Newtonsoft.Json.Linq namespace.
var json = #"{""name"":""K\u0131r\u0131nt\u0131 Reklam""}";
json.Dump(); // -> {"name":"K\u0131r\u0131nt\u0131 Reklam"}
var name = JObject.Parse(json)["name"].ToString();
(name == "Kırıntı Reklam").Dump(); // -> true
Is there any way to extract the first letter of a UTF-8 encoded string with Lua?
Lua does not properly support Unicode, so string.sub("ÆØÅ", 2, 2) will return "?" rather than "Ø".
Is there a relatively simple UTF-8 parsing algorithm I could use on the string byte per byte, for the sole purpose of getting the first letter of the string, be it a Chinese character or an A?
Or is this way too complex, requiring a huge library, etc.?
You can easily extract the first letter from a UTF-8 encoded string with the following code:
function firstLetter(str)
return str:match("[%z\1-\127\194-\244][\128-\191]*")
end
Because a UTF-8 code point either begins with a byte from 0 to 127, or with a byte from 194 to 244 followed by one or several bytes from 128 to 191.
You can even iterate over UTF-8 code points in a similar manner:
for code in str:gmatch("[%z\1-\127\194-\244][\128-\191]*") do
print(code)
end
Note that both examples return a string value for each letter, and not the Unicode code point numerical value.
Lua 5.3 provide a UTF-8 library.
You can use utf8.codes to get each code point, and then use utf8.char to get the character:
local str = "ÆØÅ"
for _, c in utf8.codes(str) do
print(utf8.char(c))
end
This also works:
local str = "ÆØÅ"
for w in str:gmatch(utf8.charpattern ) do
print(w)
end
where utf8.charpattern is just the string "[\0-\x7F\xC2-\xF4][\x80-\xBF]*" for the pattern to match one UTF-8 byte sequence.
Documentation all directs me to unicode support, yet I don't think my request has anything to do with Unicode. I want to work with raw bytes within the context of a single scalar; I need to be able to figure out its length (in bytes), take substrings of it (in bytes), write the bytes to disc, and over the network. Is there an easy way to do this, without treating the bytes as any sort of encoding in perl?
EDIT
More explicitly,
my $data = "Perl String, unsure of encoding and don't need to know";
my #data_chunked_into_1024_bytes_each = #???
Perl strings are, conceptually, strings of characters, which are positive 32-bit integers that (normally) represent Unicode code points. A byte string, in Perl, is just a string in which all the characters have values less than 256.
(That's the conceptual view. The internal representation is somewhat more complicated, as the perl interpreter tries to store byte strings — in the above sense — as actual byte strings, while using a generalized UTF-8 encoding for strings that contain character values of 256 or higher. But this is all supposed to be transparent to the user, and in fact mostly is, except for some ugly historical corner cases like the bitwise not (~) operator.)
As for how to turn a general string into a byte string, that really depends on what the string you have contains and what the byte string is supposed to contain:
If your string already is a string of bytes — e.g. if you read it from a file in binary mode — then you don't need to do anything. The string shouldn't contain any characters above 255 to being with, and if it does, that's an error and will probably be reported as such by the encryption code.
Similarly, if your string is supposed to encode text in the ASCII or ISO-8859-1 encodings (which encode the 7- and 8-bit subsets of Unicode respectively), then you don't need to do anything: any characters up to 255 are already correctly encoded, and any higher values are invalid for those encodings.
If your input string contains (Unicode) text that you want to encode in some other encoding, then you'll need to convert the string to that encoding. The usual way to do that is by using the Encode module, like this:
use Encode;
my $byte_string = encode( "name of encoding", $text_string );
Obviously, you can convert the byte string back to the corresponding character string with:
use Encode;
my $text_string = decode( "name of encoding", $byte_string );
For the special case of the UTF-8 encoding, it's also possible to use the built-in utf8::encode() function instead of Encode::encode():
utf8::encode( $string );
which does essentially the same thing as:
use Encode;
$string = encode( "utf8", $string );
Note that, unlike Encode::encode(), the utf8::encode() function modifies the input string directly. Also note that the "utf8" above refers to Perl's extended UTF-8 encoding, which allows values outside the official Unicode range; for strictly standards-compliant UTF-8 encoding, use "utf-8" with a hyphen (see Encode documentation for the gory details). And, yes, there's also a utf8::decode() function that does pretty much what you'd expect.
If I understood your question correctly, what you want is the pack/unpack functions: http://perldoc.perl.org/functions/pack.html
As long as your string doesn't contain characters above codepoint 255, it will mostly work as plain byte string, with length and substr operating on bytes. Additionally, most output functions like print expect octets/bytes by default and will actually complain if you try to stuff anything else to them.
You may need to explicitly encode/decode your output if it is known to be in some encoding, but more details can only be added if you ask another specific question for each problematic part of your program.
I've tried everything Google and StackOverflow have recommended (that I could find) including using Encode. My code works but it just uses UTF8 and I get the wide character warnings. I know how to work around those warnings but I'm not using UTF8 for anything else so I'd like to just convert it and not have to adapt the rest of my code to deal with it. Here's my code:
my $xml = XMLin($content);
# Populate the #titles array with each item title.
my #titles;
for my $item (#{$xml->{channel}->{item}}) {
my $title = Encode::decode_utf8($item->{title});
#my $title = $item->{title};
#utf8::downgrade($title, 1);
Encode::from_to($title, 'utf8', 'iso-8859-1');
push #titles, $title;
}
return #titles;
Commented out you can see some of the other things I've tried. I'm well aware that I don't know what I'm doing here. I just want to end up with a plain old ASCII string though. Any ideas would be greatly appreciated. Thanks.
The answer depends on how you want to use the title. There are 3 basic ways to go:
Bytes that represent a UTF-8 encoded string.
This is the format that should be used if you want to store the UTF-8 encoded string outside your application, be it on disk or sending it over the network or anything outside the scope of your program.
A string of Unicode characters.
The concept of characters is internal to Perl. When you perform Encode::decode_utf8, then a bunch of bytes is attempted to be converted to a string of characters, as seen by Perl. The Perl VM (and the programmer writing Perl code) cannot externalize that concept except through decoding UTF-8 bytes on input and encoding them to UTF-8 bytes on output. For example, your program receives two bytes as input that you know they represent UTF-8 encoded character(s), let's say 0xC3 0xB6. In that case decode_utf8 returns a representation that instead of two bytes, sees one character: ö.
You can then proceed to manipulate that string in Perl. To illustrate the difference further, consider the following code:
my $bytes = "\xC3\xB6";
say length($bytes); # prints "2"
my $string = decode_utf8($bytes);
say length($string); # prints "1"
The special case of ASCII, a subset of UTF-8.
ASCII is a very small subset of Unicode, where characters in that range are represented by a single byte. Converting Unicode into ASCII is an inherently lossy operation, as most of the Unicode characters are not ASCII characters. You're either forced to drop every character in your string which is not in ASCII or try to map from a Unicode character to their closest ASCII equivalents (which isn't possible in the vast majority of cases), when trying to coerce a Unicode string to ASCII.
Since you have wide character warnings, it means that you're trying to manipulate (possibly output) Unicode characters that cannot be represented as ASCII or ISO-8859-1.
If you do not need to manipulate the title from your XML document as a string, I'd suggest you leave it as UTF-8 bytes (I'd mention that you should be careful not to mix bytes and characters in strings). If you do need to manipulate it, then decode, manipulate, and on output encode it in UTF-8.
For further reading, please use perldoc to study perlunitut, perlunifaq, perlunicode, perluniintro, and Encode.
Although this is an old question, I just spent several hours (!) trying to do more or less the same thing! That is: read data from a UTF-8 XML file, and convert that data into the Windows-1252 codepage (I could also have used Latin1, ISO-8859-1 etc.) in order to be able to create filenames with accented letters.
After much experimentation, and even more searching, I finally managed to get the conversion working. The "trick" is to use Encode::encode instead of Encode::decode.
For example, given the code in the original question, the correct (or at least one :-) way to convert from UTF-8 would be:
my $title = Encode::encode("Windows-1252", $item->{title});
or
my $title = Encode::encode("ISO-8859-1", $item->{title});
or
my $title = Encode::encode("<your-favourite-codepage-here>", $item->{title});
I hope this helps others having similar problems!
You can use the following line to simply get rid of the warning. This assumes that you want to use UTF8, which shouldn't normally be a problem.
binmode(STDOUT, ":encoding(utf8)");